Escalona52
ANARTIA
Publicación del Museo de Biología de la Universidad del Zulia
ISSN 1315-642X (impresa) / ISSN 2665-0347 (digital)
https://doi.org/10.5281/zenodo.13755882 / Anartia, 38 (junio 2024): 52-63
New and unusual field records of Chelus spp. in Venezuela
(Testudines: Chelidae)
Registros nuevos e inusuales de Chelus spp. en Venezuela (Testudines: Chelidae)
Tibisay Escalona
Centro Interdisciplinar de Investigação Marinha e Ambiental (CIIMAR)-University of Porto, Faculty of Science, Porto, Portugal.
Correspondencia: tiby.escalona@gmail.com
(Received: 06-05-2024 / Accepted: 06-06-2024 / On line: 12-09-2024)
These researchers, relying on morphological evidence such
as shell shape, plastron pigmentation and neck coloration
patterns, suggested geographic variation between the
Amazon and Orinoco Basin populations of C. fimbriata.
Specifically, Amazonian matamatas were described as
having a rectangular carapace shape (Fig. 1), a dark
pigmented plastron, and bold black bands on the ventral
side of the neck. In contrast, Orinoco matamatas were
characterized by an oval carapace shape (Fig. 1), a light
yellow-unpigmented plastron, and light coloration (often
bright red-pink) on the underside of the neck. Given the
new taxonomic resolution of Chelus, it is currently assumed
that historical records from the Orinoco hydrographic
system are presumed to be of C. orinocensis. Nonetheless, a
call has been made to take caution on this hypothesis and
instead advises to confirm current records (e.g., museum
specimen, survey, citizen science observation) and to map
new sites to help distinguish more precisely the geographic
distribution of matamata lineages (see Cunha et al.
2021). Furthermore, the potential presence of hybrids or
intergrades, with anatomical intermediate morphotypes
(Sánchez-Villagra et al. 1995, Pritchard 2008), also
highlights the necessity for a more comprehensive
understanding and precise delineation of Chelus species
boundaries. Although challenging, accurate species
delimitation is crucial for precise taxonomy, managing
species diversity, and formulating effective conservation
strategies (Zachos 2016).
Taking all together, and to aid with Chelus sp. scientific
knowledge and conservation, I present information, new
records of occurrence from matamata turtles, including
some from the Lower Caura watershed (Bolivar State,
The genus Chelus, matamata turtles, is native to northern
South America, being widely distributed throughout the
Amazon and Orinoco Basins. It reaches the largest adult
body size among the extant Chelidae, and with straight-
line carapace length (SCL) ranging from 31.1-40.4 cm
(Pritchard & Trebbau 1984). However, larger individuals
do exist (i.e., > 50 cm SCL Barrio-Amorós & Manrique
2006). Matamatas are very charismatic and easy to
recognize by their unique morphological appearance (i.e.,
extremely flat and triangular head, long and thick neck,
wide mouth, long pointy snout, and a carapace with three
dorsal keels). They are classified as “Least Concern” by the
IUCN (2021), yet their natural history is largely unknown
despite the great interest shown by the herpetological
community. Likewise, the distribution range of Chelus
species remains only partially verified, and the taxonomic
revision of the genus suggesting the recognition of two
extant species leaves (see below) the geographic coverage of
each of them undocumented. This lack of comprehensive
distribution data hampers efforts to accurately understand
the biogeography and ecological niches of each species,
requiring further research to delineate their ranges more
precisely.
Recent genomic and morphological analyses have
delineated the genus Chelus into two distinct lineages:
C. orinocensis Vargas-Ramírez et al. 2020, inhabiting the
Orinoco Basin, including the Rio Negro and Essequibo
drainages, and C. fimbriata Schneider, 1783, found in
the Amazon and Mahury Basins (Vargas-Ramírez et al.
2020). These findings corroborate earlier hypotheses
proposed by Medem (1960), Pritchard & Trebbau (1984),
Sánchez-Villagra et al. (1995), and Pritchard (2008).
ANARTIA
Publicación del Museo de Biología de la Universidad del Zulia
ISSN 1315-642X (impresa) / ISSN 2665-0347 (digital)
https://doi.org/10.5281/zenodo.13755882 / Anartia, 38 (junio 2024): 52-63
New and unusual field records of Chelus spp. in Venezuela
(Testudines: Chelidae)
Registros nuevos e inusuales de Chelus spp. en Venezuela (Testudines: Chelidae)
Tibisay Escalona
Centro Interdisciplinar de Investigação Marinha e Ambiental (CIIMAR)-University of Porto, Faculty of Science, Porto, Portugal.
Correspondencia: tiby.escalona@gmail.com
(Received: 06-05-2024 / Accepted: 06-06-2024 / On line: 12-09-2024)
These researchers, relying on morphological evidence such
as shell shape, plastron pigmentation and neck coloration
patterns, suggested geographic variation between the
Amazon and Orinoco Basin populations of C. fimbriata.
Specifically, Amazonian matamatas were described as
having a rectangular carapace shape (Fig. 1), a dark
pigmented plastron, and bold black bands on the ventral
side of the neck. In contrast, Orinoco matamatas were
characterized by an oval carapace shape (Fig. 1), a light
yellow-unpigmented plastron, and light coloration (often
bright red-pink) on the underside of the neck. Given the
new taxonomic resolution of Chelus, it is currently assumed
that historical records from the Orinoco hydrographic
system are presumed to be of C. orinocensis. Nonetheless, a
call has been made to take caution on this hypothesis and
instead advises to confirm current records (e.g., museum
specimen, survey, citizen science observation) and to map
new sites to help distinguish more precisely the geographic
distribution of matamata lineages (see Cunha et al.
2021). Furthermore, the potential presence of hybrids or
intergrades, with anatomical intermediate morphotypes
(Sánchez-Villagra et al. 1995, Pritchard 2008), also
highlights the necessity for a more comprehensive
understanding and precise delineation of Chelus species
boundaries. Although challenging, accurate species
delimitation is crucial for precise taxonomy, managing
species diversity, and formulating effective conservation
strategies (Zachos 2016).
Taking all together, and to aid with Chelus sp. scientific
knowledge and conservation, I present information, new
records of occurrence from matamata turtles, including
some from the Lower Caura watershed (Bolivar State,
The genus Chelus, matamata turtles, is native to northern
South America, being widely distributed throughout the
Amazon and Orinoco Basins. It reaches the largest adult
body size among the extant Chelidae, and with straight-
line carapace length (SCL) ranging from 31.1-40.4 cm
(Pritchard & Trebbau 1984). However, larger individuals
do exist (i.e., > 50 cm SCL Barrio-Amorós & Manrique
2006). Matamatas are very charismatic and easy to
recognize by their unique morphological appearance (i.e.,
extremely flat and triangular head, long and thick neck,
wide mouth, long pointy snout, and a carapace with three
dorsal keels). They are classified as “Least Concern” by the
IUCN (2021), yet their natural history is largely unknown
despite the great interest shown by the herpetological
community. Likewise, the distribution range of Chelus
species remains only partially verified, and the taxonomic
revision of the genus suggesting the recognition of two
extant species leaves (see below) the geographic coverage of
each of them undocumented. This lack of comprehensive
distribution data hampers efforts to accurately understand
the biogeography and ecological niches of each species,
requiring further research to delineate their ranges more
precisely.
Recent genomic and morphological analyses have
delineated the genus Chelus into two distinct lineages:
C. orinocensis Vargas-Ramírez et al. 2020, inhabiting the
Orinoco Basin, including the Rio Negro and Essequibo
drainages, and C. fimbriata Schneider, 1783, found in
the Amazon and Mahury Basins (Vargas-Ramírez et al.
2020). These findings corroborate earlier hypotheses
proposed by Medem (1960), Pritchard & Trebbau (1984),
Sánchez-Villagra et al. (1995), and Pritchard (2008).
Chelus spp. in Venezuela53
Venezuela), a tributary of the middle Orinoco drainage
(Fig. 2). I also comment on the specimen’s habitat and
provide original data on size (carapace length, width,
and weight), while comparing with other published size
records from the Orinoco basin.
I discuss three museum catalogued records of the
matamata, two of which are from outside the Orinoco
Basin, and one from the Casiquiare River Canal, which
connects the Upper Orinoco and Upper Rio Negro Basins.
From the former two records, one is new from the Lake
Maracaibo Basin (Zulia State), and the other validates
previously cited record by Pritchard & Trebbau (1984)
from the Santa Rosa-Putucual region (Sucre State). The
specimen from the Casiquiare River (Amazonas State)
represents a new site record from this hydrographic
system.
CAURA RIVER BASIN (BOLÍVAR STATE)
RECORDS
New locality of occurrence
Two adult living matamatas, a female and a male, were
captured and measured in the remote Nichare River, an
affluent of the Lower Caura River Basin (LCR) and part
of The Caura National Park (Fig. 2). These individuals
were sampled by chance during the dry season of 2000
(February-April) while conducting a three-year research
study (1999-2001) on the nesting ecology of another
native aquatic turtle (Podocnemis unifilis Troschel 1848)
(Escalona 2003, Escalona et al. 2009a). The female was
caught directly by hand from a boat after being spotted
moving on the surface across a narrow section of the river.
Although it tried to dive, it did so very slowly, allowing it
to be approached and captured rapidly. The male, on the
other hand, was caught with a fishing net used in a shallow
flooded lagoon to catch P. unifilis (Fig. 3). Location
details are shown in figure 2. On the map, the Nichare
River locality is indicated by black circle 6. Within this
locality, the specific site for the female was recorded at
(06°20’7” N, 64°57’31” W), and the male at (06°19’16” N,
64°57’12” W).
Habitat and Nichare River
It is well recognized that matamatas are highly aquatic
bottom-walkers that rarely swim or float and are never
seen basking. Habitats of preference are rivers and streams,
mainly in areas of slower water flow or still waters such
as lagoons, wells, oxbow lakes and temporary overflow
pools. It inhabits all types of water: white, clear, and black
(Pritchard & Trebbau 1984, Barrio-Amorós & Narbaiza
2008, Morales-Betancourt et al. 2020, Cunha et al. 2021).
The Nichare is a black water meandrous river about 5 to 20
meters wide that sustains habitats of similar characteristics
and conditions to those described above. It contains lateral
Figure 1. Shell shapes representing each of the two matamata lineages. Left: Amazonian morphotype (Chelus fimbriata) having a
rectangular carapace shape (PCHP 39–from the vicinity of Leticia, Colombia). Right: Orinoco morphotype (Chelus orinocensis)
having an oval carapace shape (MCNUSB 427–from the Llanos, Venezuela) (images taken and modified from Sánchez-Villagra et
al. 1995).
Venezuela), a tributary of the middle Orinoco drainage
(Fig. 2). I also comment on the specimen’s habitat and
provide original data on size (carapace length, width,
and weight), while comparing with other published size
records from the Orinoco basin.
I discuss three museum catalogued records of the
matamata, two of which are from outside the Orinoco
Basin, and one from the Casiquiare River Canal, which
connects the Upper Orinoco and Upper Rio Negro Basins.
From the former two records, one is new from the Lake
Maracaibo Basin (Zulia State), and the other validates
previously cited record by Pritchard & Trebbau (1984)
from the Santa Rosa-Putucual region (Sucre State). The
specimen from the Casiquiare River (Amazonas State)
represents a new site record from this hydrographic
system.
CAURA RIVER BASIN (BOLÍVAR STATE)
RECORDS
New locality of occurrence
Two adult living matamatas, a female and a male, were
captured and measured in the remote Nichare River, an
affluent of the Lower Caura River Basin (LCR) and part
of The Caura National Park (Fig. 2). These individuals
were sampled by chance during the dry season of 2000
(February-April) while conducting a three-year research
study (1999-2001) on the nesting ecology of another
native aquatic turtle (Podocnemis unifilis Troschel 1848)
(Escalona 2003, Escalona et al. 2009a). The female was
caught directly by hand from a boat after being spotted
moving on the surface across a narrow section of the river.
Although it tried to dive, it did so very slowly, allowing it
to be approached and captured rapidly. The male, on the
other hand, was caught with a fishing net used in a shallow
flooded lagoon to catch P. unifilis (Fig. 3). Location
details are shown in figure 2. On the map, the Nichare
River locality is indicated by black circle 6. Within this
locality, the specific site for the female was recorded at
(06°20’7” N, 64°57’31” W), and the male at (06°19’16” N,
64°57’12” W).
Habitat and Nichare River
It is well recognized that matamatas are highly aquatic
bottom-walkers that rarely swim or float and are never
seen basking. Habitats of preference are rivers and streams,
mainly in areas of slower water flow or still waters such
as lagoons, wells, oxbow lakes and temporary overflow
pools. It inhabits all types of water: white, clear, and black
(Pritchard & Trebbau 1984, Barrio-Amorós & Narbaiza
2008, Morales-Betancourt et al. 2020, Cunha et al. 2021).
The Nichare is a black water meandrous river about 5 to 20
meters wide that sustains habitats of similar characteristics
and conditions to those described above. It contains lateral
Figure 1. Shell shapes representing each of the two matamata lineages. Left: Amazonian morphotype (Chelus fimbriata) having a
rectangular carapace shape (PCHP 39–from the vicinity of Leticia, Colombia). Right: Orinoco morphotype (Chelus orinocensis)
having an oval carapace shape (MCNUSB 427–from the Llanos, Venezuela) (images taken and modified from Sánchez-Villagra et
al. 1995).
Escalona54
Figure 2. Hydrographic map of Venezuela showing Chelus record sites referenced in this study. The map highlights key local-
ities from left to right and south. Triangles represent sites within the Lake Maracaibo Basin in Zulia state. Triangle 1 marks
the location of a recently discovered museum specimen (MBUCV 7096) at coordinates (10°13’30” N, 71°47’45” W). Tri-
angle 2 indicates the site observed by José L. Lira in 1974 (09°31’17” N, 71°57’25” W). Star marks the location of museum
specimen KU 117344 from the Santa Rosa-Putucual Lagoon Swamp (10°22’12” N, 63°16’48” W), Gulf of Paria Basin,
Sucre state. Circles denote localities in the Lower Caura River Basin, Bolívar state. Circle 4 represents the site along the
Mato River (07°08’08” N, 65°12’43” W), while circles 5 and 6 indicate record sites along the Caura River (06°48’04” N,
64°49’40” W) and Nichare River (06°21’08” N, 64°58’17” W), respectively. Black square shows the locality for museum
specimen MBUCV 7278, from the Casiquiare River Canal, Amazonas state. This specimen was found in the community
of San Carlos de Rio Negro (01°55’12’’ N, 67°03’40’’ W).
and meandric sand bars, shore complexes of pools, flooded
lagoons, and oxbow lakes. It is considered a “Seasonally
Flooded Riparian Ecosystem” in an “Evergreen Lowland
Forest” (Rosales & Huber 1996, Rosales et al. 2003).
Morphological characteristics (shell shape, plastron
pigmentation, neck coloration, size)
Shell shape (rectangular vs oval), plastron pigmentation
(dark vs light) and neck underside coloration (bold black
bands vs light or red-pink color) were used as features for
species diagnostic. Shell characters were measured linearly
using a 50 cm caliper. This included the maximum straight
carapace length (SCLmax) and straight-line carapace
width (SCW), as shown in figure 4. Body mass was weighed
using a 20 kg Pesola spring scale. No abnormalities were
detected during measurements. After taking photographs
and measurements, the matamatas were released into the
same location of capture.
Sex determination
Although sexual dimorphism is not very marked in
matamatas, the sex can be easily determined because
females can reach larger sizes than males, and males have
longer and thicker tails (Figs. 5 and 6) and seem to have
a more concave plastron (Fig. 7) compared to females
(Figs. 5 and 8). Differences, were also confirmed by the few
available studies on matamata size, which have indicated
that individuals over 40 cm in SCL tend to be females (see
Pritchard & Trebbau 1984, Sánchez-Villagra et al. 1995,
and see Figs. 3 and 4 of Morales-Betancourt et al. 2020).
Female: This individual is characterized by an oval shell
outline, such as in the Orinoco morphotype (see Sánchez-
Figure 2. Hydrographic map of Venezuela showing Chelus record sites referenced in this study. The map highlights key local-
ities from left to right and south. Triangles represent sites within the Lake Maracaibo Basin in Zulia state. Triangle 1 marks
the location of a recently discovered museum specimen (MBUCV 7096) at coordinates (10°13’30” N, 71°47’45” W). Tri-
angle 2 indicates the site observed by José L. Lira in 1974 (09°31’17” N, 71°57’25” W). Star marks the location of museum
specimen KU 117344 from the Santa Rosa-Putucual Lagoon Swamp (10°22’12” N, 63°16’48” W), Gulf of Paria Basin,
Sucre state. Circles denote localities in the Lower Caura River Basin, Bolívar state. Circle 4 represents the site along the
Mato River (07°08’08” N, 65°12’43” W), while circles 5 and 6 indicate record sites along the Caura River (06°48’04” N,
64°49’40” W) and Nichare River (06°21’08” N, 64°58’17” W), respectively. Black square shows the locality for museum
specimen MBUCV 7278, from the Casiquiare River Canal, Amazonas state. This specimen was found in the community
of San Carlos de Rio Negro (01°55’12’’ N, 67°03’40’’ W).
and meandric sand bars, shore complexes of pools, flooded
lagoons, and oxbow lakes. It is considered a “Seasonally
Flooded Riparian Ecosystem” in an “Evergreen Lowland
Forest” (Rosales & Huber 1996, Rosales et al. 2003).
Morphological characteristics (shell shape, plastron
pigmentation, neck coloration, size)
Shell shape (rectangular vs oval), plastron pigmentation
(dark vs light) and neck underside coloration (bold black
bands vs light or red-pink color) were used as features for
species diagnostic. Shell characters were measured linearly
using a 50 cm caliper. This included the maximum straight
carapace length (SCLmax) and straight-line carapace
width (SCW), as shown in figure 4. Body mass was weighed
using a 20 kg Pesola spring scale. No abnormalities were
detected during measurements. After taking photographs
and measurements, the matamatas were released into the
same location of capture.
Sex determination
Although sexual dimorphism is not very marked in
matamatas, the sex can be easily determined because
females can reach larger sizes than males, and males have
longer and thicker tails (Figs. 5 and 6) and seem to have
a more concave plastron (Fig. 7) compared to females
(Figs. 5 and 8). Differences, were also confirmed by the few
available studies on matamata size, which have indicated
that individuals over 40 cm in SCL tend to be females (see
Pritchard & Trebbau 1984, Sánchez-Villagra et al. 1995,
and see Figs. 3 and 4 of Morales-Betancourt et al. 2020).
Female: This individual is characterized by an oval shell
outline, such as in the Orinoco morphotype (see Sánchez-
Chelus spp. in Venezuela55
Figure 3. Fishing net technique in curiaras (bote) from the Lower Caura River Basin. Top left and right: Capturing Podocnemis unifilis
in the Nichare River. Bottom left: Fisherman fishing in the Caura River and who caught two male matamata turtles. Photo: Tibisay
Escalona.
Figure 4. Shell of Matamata turtle. Measurements indicated are based on a specimen of unknown provenance deposited in the Pale-
ontological Collection of the Instituto Venezolano de Investigaciones Científicas (IVIC), Venezuela. Maximum straight-line carapace
length (SCLmax; left) and width (SCW; right). Photo: Gilson Rivas.
Figure 3. Fishing net technique in curiaras (bote) from the Lower Caura River Basin. Top left and right: Capturing Podocnemis unifilis
in the Nichare River. Bottom left: Fisherman fishing in the Caura River and who caught two male matamata turtles. Photo: Tibisay
Escalona.
Figure 4. Shell of Matamata turtle. Measurements indicated are based on a specimen of unknown provenance deposited in the Pale-
ontological Collection of the Instituto Venezolano de Investigaciones Científicas (IVIC), Venezuela. Maximum straight-line carapace
length (SCLmax; left) and width (SCW; right). Photo: Gilson Rivas.
Escalona56
Figure 6. Male matamata from the Nichare River (SCLmax 37.7 cm). Left: Dorsal view: Oval-carapace shape, neck and head; Middle:
Ventral side: Stained plastron and thick tail, and red-pink underside neck color; and Right: Dorsal view: Head and neck (features a nar-
row, continuous dark line along the midline, flanked by two thin dark lines on either side). Based on shell shape, this male may be a rep-
resentative from the Orinoco morphotype (Chelus orinocensis). Photo (left): Ivonne Monge; photo (middle, right): Tibisay Escalona.
Figure 5. Female matamata from the Nichare River (SCLmax 48.8 cm). Left: Dorsal view: Oval-carapace outline, neck, head; Middle:
Ventral view: Stained plastron and thin tail; Right: Head. Based on shell shape, this female may be a representative from the Orinoco
morphotype (Chelus orinocensis). Photo: Andres Rosenchein.
Figure 6. Male matamata from the Nichare River (SCLmax 37.7 cm). Left: Dorsal view: Oval-carapace shape, neck and head; Middle:
Ventral side: Stained plastron and thick tail, and red-pink underside neck color; and Right: Dorsal view: Head and neck (features a nar-
row, continuous dark line along the midline, flanked by two thin dark lines on either side). Based on shell shape, this male may be a rep-
resentative from the Orinoco morphotype (Chelus orinocensis). Photo (left): Ivonne Monge; photo (middle, right): Tibisay Escalona.
Figure 5. Female matamata from the Nichare River (SCLmax 48.8 cm). Left: Dorsal view: Oval-carapace outline, neck, head; Middle:
Ventral view: Stained plastron and thin tail; Right: Head. Based on shell shape, this female may be a representative from the Orinoco
morphotype (Chelus orinocensis). Photo: Andres Rosenchein.
Chelus spp. in Venezuela57
Figure 7. Ventral view (plastron) of an adult male matamata. Compare to females (see Fig. 9, ventral view), males have a thicker tail and
a greater degree of concavity in the plastron, which is noticeable towards the abdominal, femoral, and anal scutes, with the concavity
being most prominent in the femoral scute area. This pattern requires further investigation. Photo: Tibisay Escalona.
Villagra et al. 1995, Cadena et al. 2023). The plastron
seems heavily stained rather than naturally pigmented,
most likely due to the tannin-rich black waters typical of
the Nichare ecosystem. However, further investigation
is needed to confirm this observation. The underside
neck coloration pattern was not possible to describe, due
to lack of images (Fig. 5). This large female matamata
turtle, measuring 48.8 cm in SCLmax (37.4 cm in SCW)
and weighing 12.7 kg, is, to the best of my knowledge,
the second-largest live matamata ever recorded in the
Venezuelan Orinoquia. The largest so far was caught in
Apure River and measured 52.6 cm in SCLmax with a
weight of 17.7 kg (Barrio-Amorós & Manrique 2006). For
Colombian Orinoquia (Bojonawi Natural Reserve - BNR),
the maximum size reported is 47 cm SCLmax (37 cm in
SCW) and a weight of 13.42 kg (Morales-Betancourt et
al. 2020). Additional records of large female specimens
are available in museum collections. For instance, a female
with an oval shell shape from Raudales de Atures, Puerto
Ayacucho (Amazonas State, Venezuela) was originally
documented by Barrio-Amorós & Narbaiza (1999). This
specimen, recently re-measured by T. Escalona, has an
Figure 8. Validated record of occurrence for matamata turtle from Santa Rosa region, likely from Putucual lagoon swamp (Sucre State,
Venezuela) deposited at Kansas Univeristy (KU) Biodiversity Institute and Natural History Museum (KU 117344). This adult female
(CCL: 35.5 cm) catalogued as Chelus fimbriata is characterized by having from left to right: Dorsal view (oval carapace shape), ventral
view (unpigmented plastron and light color on the underside of the neck). The specimen should be re-identified as C. orinocensis given
its morphological similarities to the Orinoco morphotype. Photo: Ana Motta.
Figure 7. Ventral view (plastron) of an adult male matamata. Compare to females (see Fig. 9, ventral view), males have a thicker tail and
a greater degree of concavity in the plastron, which is noticeable towards the abdominal, femoral, and anal scutes, with the concavity
being most prominent in the femoral scute area. This pattern requires further investigation. Photo: Tibisay Escalona.
Villagra et al. 1995, Cadena et al. 2023). The plastron
seems heavily stained rather than naturally pigmented,
most likely due to the tannin-rich black waters typical of
the Nichare ecosystem. However, further investigation
is needed to confirm this observation. The underside
neck coloration pattern was not possible to describe, due
to lack of images (Fig. 5). This large female matamata
turtle, measuring 48.8 cm in SCLmax (37.4 cm in SCW)
and weighing 12.7 kg, is, to the best of my knowledge,
the second-largest live matamata ever recorded in the
Venezuelan Orinoquia. The largest so far was caught in
Apure River and measured 52.6 cm in SCLmax with a
weight of 17.7 kg (Barrio-Amorós & Manrique 2006). For
Colombian Orinoquia (Bojonawi Natural Reserve - BNR),
the maximum size reported is 47 cm SCLmax (37 cm in
SCW) and a weight of 13.42 kg (Morales-Betancourt et
al. 2020). Additional records of large female specimens
are available in museum collections. For instance, a female
with an oval shell shape from Raudales de Atures, Puerto
Ayacucho (Amazonas State, Venezuela) was originally
documented by Barrio-Amorós & Narbaiza (1999). This
specimen, recently re-measured by T. Escalona, has an
Figure 8. Validated record of occurrence for matamata turtle from Santa Rosa region, likely from Putucual lagoon swamp (Sucre State,
Venezuela) deposited at Kansas Univeristy (KU) Biodiversity Institute and Natural History Museum (KU 117344). This adult female
(CCL: 35.5 cm) catalogued as Chelus fimbriata is characterized by having from left to right: Dorsal view (oval carapace shape), ventral
view (unpigmented plastron and light color on the underside of the neck). The specimen should be re-identified as C. orinocensis given
its morphological similarities to the Orinoco morphotype. Photo: Ana Motta.
Escalona58
SCLmax of 48.7 cm and an SCW of 39 cm. It is deposited
at the Estación Biológica Rancho Grande in Maracay,
Venezuela, under the catalog number EBRG 3596. Other
museum records indicating CL larger than 40 cm are
described in Pritchard & Trebbau (1984) (Deposited in
Peter CH Pritchard, personal collection, Oviedo, Florida,
USA as PCHP 1209) and Sánchez-Villagra et al. (1995)
(Deposited at Colección Estación Biológica Hato Piñero,
Cojedes, Venezuela as CEBHP unnumbered).
Male: This individual has an oval-shaped carapace
similar to the Orinoco morphotype and a heavily stained
plastron akin to that of the female described above. The
ventral side of the neck is reddish-pink, while the dorsal
side features a narrow, continuous dark line running along
the midline, flanked by two thin dark lines on either side
(Fig. 6). The size of this male, ranks among the largest
ever reported. The SCLmax, SCW and weight are:
37.7 cm, 28.6 cm, and 5.7 kg. A similar maximum size
but much heavier was registered by Morales-Betancourt
et al. (2020) for Colombian Orinoquia (i.e., 37.7 cm in
SCLmax, 30.3 cm in SCW, and 7.6 kg). During a seven-
year mark and recapture matamata population study, the
latter authors found that most males examined (about
86%) had a SCLmax less than 33.1 cm, and the few larger
ones (interval 36.1-39 cm) represented only 3%. The
largest males ever reported in the literature include one
individual living in captivity in Venezuela, measuring 39.7
cm in SCLmax (Pritchard & Trebbau 1984), and another
specimen from Guyana reaching an SCLmax of 41.9 cm
(Pritchard 2008).
OTHER OCCURRENCES WITHIN
THE LOWER CAURA BASIN
Chelus was confirmed to inhabit the Mato (black
circle 4) and Caura Rivers (black circle 5) (Fig. 2). It is
important to point out that matamatas have previously
been observed in both rivers, though they were referred to
as C. fimbriata (Pritchard & Trebbau 1984, Rojas-Runjac
et al. 2011).
Mato River
The observation was made at the locality known as
Morrocoy (07°08’08” N, 65°12’43” W), where a male was
captured for consumption by local hunters using an arrow
and a long spear. Hunters were observed on top of trees
near the river shoreline, waiting for any turtle to surface
(Fig. 9). This live male, measured 36.6 cm in SCLmax,
28.6 cm in SCW, and weighted about 5 kg. Based on its
oval shell shape, reddish-pink ventral neck coloration and
probably stained plastron, this male appears to exhibit
morphological characteristics typical of the Orinoco
morphotype rather than Amazonian.
Caura River
Two males were caught with fishing nets by local
fisherman near La Fortuna (06°48’04”N, 64°49’40”W)
and were freed back into the river (Fig. 3). Sizes were as
follows: 1) SCLmax: 32.1 cm, SCW: 23.9 cm, weight:
3.5 kg, and 2) SCLmax: 33.6 cm, SCW: 23.4 cm, weight:
3.5 kg (see Fig. 3 for fishing technique). Although no
Figure 9. Turtles collected by local hunters on the Mato River. From left to right: Hunter on top of tree (see white arrow); Hunter
with spear; Turtle (Podocnemis unifilis) captured with spear; Collected turtles are kept inside a boat (curiara) either tied or in a bag.
Male matamata can be observed in front and various P. unifilis behind. This individual was characterized by having an oval shell shape,
stained plastron, and red-pink color pattern on the ventral side of the neck, and measuring SCLmax of 36.6 cm. Photo: Tibisay Es-
calona.
SCLmax of 48.7 cm and an SCW of 39 cm. It is deposited
at the Estación Biológica Rancho Grande in Maracay,
Venezuela, under the catalog number EBRG 3596. Other
museum records indicating CL larger than 40 cm are
described in Pritchard & Trebbau (1984) (Deposited in
Peter CH Pritchard, personal collection, Oviedo, Florida,
USA as PCHP 1209) and Sánchez-Villagra et al. (1995)
(Deposited at Colección Estación Biológica Hato Piñero,
Cojedes, Venezuela as CEBHP unnumbered).
Male: This individual has an oval-shaped carapace
similar to the Orinoco morphotype and a heavily stained
plastron akin to that of the female described above. The
ventral side of the neck is reddish-pink, while the dorsal
side features a narrow, continuous dark line running along
the midline, flanked by two thin dark lines on either side
(Fig. 6). The size of this male, ranks among the largest
ever reported. The SCLmax, SCW and weight are:
37.7 cm, 28.6 cm, and 5.7 kg. A similar maximum size
but much heavier was registered by Morales-Betancourt
et al. (2020) for Colombian Orinoquia (i.e., 37.7 cm in
SCLmax, 30.3 cm in SCW, and 7.6 kg). During a seven-
year mark and recapture matamata population study, the
latter authors found that most males examined (about
86%) had a SCLmax less than 33.1 cm, and the few larger
ones (interval 36.1-39 cm) represented only 3%. The
largest males ever reported in the literature include one
individual living in captivity in Venezuela, measuring 39.7
cm in SCLmax (Pritchard & Trebbau 1984), and another
specimen from Guyana reaching an SCLmax of 41.9 cm
(Pritchard 2008).
OTHER OCCURRENCES WITHIN
THE LOWER CAURA BASIN
Chelus was confirmed to inhabit the Mato (black
circle 4) and Caura Rivers (black circle 5) (Fig. 2). It is
important to point out that matamatas have previously
been observed in both rivers, though they were referred to
as C. fimbriata (Pritchard & Trebbau 1984, Rojas-Runjac
et al. 2011).
Mato River
The observation was made at the locality known as
Morrocoy (07°08’08” N, 65°12’43” W), where a male was
captured for consumption by local hunters using an arrow
and a long spear. Hunters were observed on top of trees
near the river shoreline, waiting for any turtle to surface
(Fig. 9). This live male, measured 36.6 cm in SCLmax,
28.6 cm in SCW, and weighted about 5 kg. Based on its
oval shell shape, reddish-pink ventral neck coloration and
probably stained plastron, this male appears to exhibit
morphological characteristics typical of the Orinoco
morphotype rather than Amazonian.
Caura River
Two males were caught with fishing nets by local
fisherman near La Fortuna (06°48’04”N, 64°49’40”W)
and were freed back into the river (Fig. 3). Sizes were as
follows: 1) SCLmax: 32.1 cm, SCW: 23.9 cm, weight:
3.5 kg, and 2) SCLmax: 33.6 cm, SCW: 23.4 cm, weight:
3.5 kg (see Fig. 3 for fishing technique). Although no
Figure 9. Turtles collected by local hunters on the Mato River. From left to right: Hunter on top of tree (see white arrow); Hunter
with spear; Turtle (Podocnemis unifilis) captured with spear; Collected turtles are kept inside a boat (curiara) either tied or in a bag.
Male matamata can be observed in front and various P. unifilis behind. This individual was characterized by having an oval shell shape,
stained plastron, and red-pink color pattern on the ventral side of the neck, and measuring SCLmax of 36.6 cm. Photo: Tibisay Es-
calona.
Chelus spp. in Venezuela59
images were taken from these individuals, they both are
described as having an oval-shell outline.
Collectively, the data confirm the presence of Chelus in
at least three river localities (Nichare, Mato, and Caura)
within the Lower Caura River Basin. Additionally, the
morphological characteristics of the observed individuals
suggest that they are representatives of the Orinoco
morphotype (C. orinocensis). Nonetheless, further genetic
and morphological research is needed to substantiate
these findings throughout the Caura drainage, especially
since previous work on the Podocnemis unifilis turtle
documented a complex geographical pattern of genetic
variation heavily influenced by landscape features
(Escalona et al. 2009b).
The data also reinforces the notion by Pritchard &
Trebbau (1984), Pritchard (2008), and studies by Morales-
Betancourt et al. (2020) that matamata females can grow
very large and attain larger sizes than males. Although there
are exceptions to this pattern (see Pritchard 2008), most
males are smaller than 40cm in SCLmax, indicating sexual
size dimorphism. In matamatas, tail size differs between
mature males and females of equal length, it remains to be
explored whether there is variation in shell shape or other
morphological traits (e.g., skull size)between individuals
shorter than 40 cm. Plastron concavity as a reliable trait
for sex determination requires further research, as some
females show concavity and some males have a rather flat
plastron (see Sánchez-Villagra et al. 1995, T. Escalona
pers. obs.).
Since shell shape is a key trait distinguishing the
two Chelus lineages –C. orinocensis with its oval shape
and C. fimbriata with its rectangular outline (Fig. 1)–
future research utilizing geometric morphometrics
is essential to enhance the identification of shape
differences across various river systems. This work should
also be complemented by genetic studies that prioritize
comprehensive geographic sampling, especially in under-
sampled regions such as Venezuela. Such sampling will
facilitate the testing of genetic distinctiveness within
specific watersheds and the assessment of gene flow
between peripheral and central localities within the
species’ distributional range.
It is important to note that field records should not be
forgotten, as they can still yield valuable insights despite
the time since the observation. They can provide useful
new knowledge, validate, and improve previous and recent
records. This is particularly significant for elusive species
with limited observations and remain poorly known, such
as the matamata turtles.
LAKE MARACAIBO BASIN (ZULIA STATE)
RECORDS
The occurrence of Chelus in the Lake Maracaibo
Basin has remained uncertain. Previously, in this region,
matamata turtle occurrences were only known from two
observations dated more than 40 years ago (see Pritchard
& Trebbau 1984). One of these observations has recently
been validated by Gilson Rivas (Museo de Biología,
Universidad del Zulia) after interviewing Professor Jose L.
Lira from University of Zulia on April 18, 2024. Professor
Lira recalls seeing on 1974, a live matamata (Chelus sp.)
caught by a local fisherman in the Santa Ana River (Fig. 2;
black triangle 2), a tributary on the west side of the lake
(G. Rivas, pers. comm.). Furthermore, until recently
(9 April 2024), museum specimens of matamata turtles
from this region were not known. However, a matamata,
preserved in alcohol, was discovered in the herpetological
collection of Museo de Biología of Universidad Central
de Venezuela (MBUCV), Caracas (deposited as MBUCV
7096, T. Escalona, pers. obs.) (Fig. 10). It is important to
acknowledge, that although the hand-written catalogue
provides the exact location of the specimen (i.e.,
northwestern side of the lake; Fig. 2; black triangle 1), there
is no mention of who brought it to the museum or even the
date it was collected. It is only noted that it was found by
local fisherman and identified by Oswaldo Fuentes in the
mid-late 1990s as Chelus fimbriata. However, determining
whether the specimen is truly a C. fimbriata or possibly
a C. orinocensis or even a different species or subspecies
remains uncertain, as it is a small juvenile (SCLmax: 6
cm) with an incompletely ossified shell that lacks a well-
defined shape (Fig. 10). The true identity of this juvenile
will require further morphological and genetic analysis.
Recent museum records and the validated observation
by Professor Lira, it suggests that Chelus sp. may inhabit
Lake Maracaibo, warranting further investigation. If
confirmed, matamata turtles in this area could represent
an isolated breeding population that deserves attention.
This is particularly significant because the Lake Maracaibo
Basin is situated in a secluded geomorphological region,
surrounded by substantial physical barriers (i.e., to the
east, is separated from the Orinoco-Amazon system by
the Andean mountain range, and to the west, from the
Magdalena system by the Sierra de Perijá, and to the south
by the union of these). Biogeographic evidence from
freshwater fishes indicates that this relative isolation of
the Lake acted as a Refugia, allowing the differentiation of
fish populations into distinct biotas. This differentiation
images were taken from these individuals, they both are
described as having an oval-shell outline.
Collectively, the data confirm the presence of Chelus in
at least three river localities (Nichare, Mato, and Caura)
within the Lower Caura River Basin. Additionally, the
morphological characteristics of the observed individuals
suggest that they are representatives of the Orinoco
morphotype (C. orinocensis). Nonetheless, further genetic
and morphological research is needed to substantiate
these findings throughout the Caura drainage, especially
since previous work on the Podocnemis unifilis turtle
documented a complex geographical pattern of genetic
variation heavily influenced by landscape features
(Escalona et al. 2009b).
The data also reinforces the notion by Pritchard &
Trebbau (1984), Pritchard (2008), and studies by Morales-
Betancourt et al. (2020) that matamata females can grow
very large and attain larger sizes than males. Although there
are exceptions to this pattern (see Pritchard 2008), most
males are smaller than 40cm in SCLmax, indicating sexual
size dimorphism. In matamatas, tail size differs between
mature males and females of equal length, it remains to be
explored whether there is variation in shell shape or other
morphological traits (e.g., skull size)between individuals
shorter than 40 cm. Plastron concavity as a reliable trait
for sex determination requires further research, as some
females show concavity and some males have a rather flat
plastron (see Sánchez-Villagra et al. 1995, T. Escalona
pers. obs.).
Since shell shape is a key trait distinguishing the
two Chelus lineages –C. orinocensis with its oval shape
and C. fimbriata with its rectangular outline (Fig. 1)–
future research utilizing geometric morphometrics
is essential to enhance the identification of shape
differences across various river systems. This work should
also be complemented by genetic studies that prioritize
comprehensive geographic sampling, especially in under-
sampled regions such as Venezuela. Such sampling will
facilitate the testing of genetic distinctiveness within
specific watersheds and the assessment of gene flow
between peripheral and central localities within the
species’ distributional range.
It is important to note that field records should not be
forgotten, as they can still yield valuable insights despite
the time since the observation. They can provide useful
new knowledge, validate, and improve previous and recent
records. This is particularly significant for elusive species
with limited observations and remain poorly known, such
as the matamata turtles.
LAKE MARACAIBO BASIN (ZULIA STATE)
RECORDS
The occurrence of Chelus in the Lake Maracaibo
Basin has remained uncertain. Previously, in this region,
matamata turtle occurrences were only known from two
observations dated more than 40 years ago (see Pritchard
& Trebbau 1984). One of these observations has recently
been validated by Gilson Rivas (Museo de Biología,
Universidad del Zulia) after interviewing Professor Jose L.
Lira from University of Zulia on April 18, 2024. Professor
Lira recalls seeing on 1974, a live matamata (Chelus sp.)
caught by a local fisherman in the Santa Ana River (Fig. 2;
black triangle 2), a tributary on the west side of the lake
(G. Rivas, pers. comm.). Furthermore, until recently
(9 April 2024), museum specimens of matamata turtles
from this region were not known. However, a matamata,
preserved in alcohol, was discovered in the herpetological
collection of Museo de Biología of Universidad Central
de Venezuela (MBUCV), Caracas (deposited as MBUCV
7096, T. Escalona, pers. obs.) (Fig. 10). It is important to
acknowledge, that although the hand-written catalogue
provides the exact location of the specimen (i.e.,
northwestern side of the lake; Fig. 2; black triangle 1), there
is no mention of who brought it to the museum or even the
date it was collected. It is only noted that it was found by
local fisherman and identified by Oswaldo Fuentes in the
mid-late 1990s as Chelus fimbriata. However, determining
whether the specimen is truly a C. fimbriata or possibly
a C. orinocensis or even a different species or subspecies
remains uncertain, as it is a small juvenile (SCLmax: 6
cm) with an incompletely ossified shell that lacks a well-
defined shape (Fig. 10). The true identity of this juvenile
will require further morphological and genetic analysis.
Recent museum records and the validated observation
by Professor Lira, it suggests that Chelus sp. may inhabit
Lake Maracaibo, warranting further investigation. If
confirmed, matamata turtles in this area could represent
an isolated breeding population that deserves attention.
This is particularly significant because the Lake Maracaibo
Basin is situated in a secluded geomorphological region,
surrounded by substantial physical barriers (i.e., to the
east, is separated from the Orinoco-Amazon system by
the Andean mountain range, and to the west, from the
Magdalena system by the Sierra de Perijá, and to the south
by the union of these). Biogeographic evidence from
freshwater fishes indicates that this relative isolation of
the Lake acted as a Refugia, allowing the differentiation of
fish populations into distinct biotas. This differentiation
Escalona60
is notable when compared to neighboring hydrological
systems like the Orinoco, Amazon, and Magdalena. The
lake, today harbors ancient relictual lineages, new species
that arrived via coastal dispersal, and species that evolved in
seclusion, leading to high levels of endemism (Rodrigues-
Olarte et al. 2011).
SANTA ROSA RIVER–PUTUCUAL LAGOON
SWAMP, GULF OF PARIA BASIN (SUCRE STATE)
RECORD
To date, there is only one known record of the matamata
turtle from Sucre State. This specimen is catalogued at the
KU Biodiversity Institute and Natural History Museum
(Lawrence, KS) under the accession number KU 117344
(see Pritchard & Trebbau 1984). To validate this record,
Ana Motta, the Herpetology Collection Manager at
KU, confirmed the physical existence of the specimen.
She also provided information from the hand-written
catalogue, and took the carapace measurement (Curved
Carapace Length - CCL: 35.5 cm), and photographs
from both the dorsal and ventral views (Fig. 8). According
to the catalogue, this specimen, identified as Chelus
fimbriata, was collected by James D. Smith on February
26, 1967, in the vicinity of Santa Rosa River (10°24’55” N,
63°23’29” W), located by road 20 km southeast of
Casanay Village (10°30’13” N, 63°25’03” W), likely
from the Putucual Lagoon Swamp (Fig. 2; black star 3).
However, after analyzing the photographs, it is apparent
that this individual has an oval-shaped carapace with an
unpigmented yellow plastron, and having two dark fine
bands running along the light color of the underside of
the neck, features diagnostic of the Orinoco morphotype.
Consequently, based on these characteristics the specimen
appears to be instead a C. orinocensis, pending further
investigation (T. Escalona, pers. obs.). Interestingly, the
Santa Rosa River is in the lowlands and flows southeast
where it merges into Putucual. This swamp drains its
water eastward into the San Juan River, which eventually
flows into the Gulf of Paria (Melfran Herrera, pers.
comm.). This hydrographic system is part of the Gulf of
Paria Basin, where some tributaries can connect with those
of the Orinoco Delta during flooding. These connections
may facilitate the exchange of water and aquatic species
between the Orinoco and the Gulf of Paria, influencing
the biodiversity and ecological dynamics of the entire
region. Given this context, the presence of matamata
turtles in Sucre State is plausible. Nevertheless, our current
understanding of the chelonian fauna in this region
remains largely unknown, highlighting the necessity for
further research to explore turtle diversity in this area.
CASIQUIARE RIVER CANAL
(AMAZONAS STATE) RECORD
Morphological shell shape data from museum records
indicate the occurrence of both matamata lineages in
the Upper Orinoco and Upper Rio Negro Basins within
the Amazonas State in southern Venezuela. However, it
remains unclear where along this hydrographic gradient
the two lineages coexist (Pritchard & Trebbau 1984,
Sánchez-Villagra et al. 1995, Barrio-Amorós & Narbaiza
1999, Pritchard 2008). Here, I report about one record
from the Casiquiare drainage, the only contact zone
between the Orinoco and Rio Negro Basins. A large-sized
specimen, with burned carapace and missing plastron is
documented, measuring 48.4 cm in SCLmax and 36.9 cm
in SCW (Fig. 11). This incomplete shell was discovered in
Figure 10. Newly discovered catalogued museum record of matamata turtle from the northwestern side of Lake Maracaibo, Venezuela.
This new record is deposited in the Herpetological Collection of the Museum of Biology of the Universidad Central de Venezuela
(MBUCV 7096). Left: Tag validating the locality and catalogue record. Middle: Dorsal view (carapace). Right: Ventral view (plas-
tron). This very small juvenile specimen measured 6 cm in SCLmax. Photo: Tibisay Escalona.
is notable when compared to neighboring hydrological
systems like the Orinoco, Amazon, and Magdalena. The
lake, today harbors ancient relictual lineages, new species
that arrived via coastal dispersal, and species that evolved in
seclusion, leading to high levels of endemism (Rodrigues-
Olarte et al. 2011).
SANTA ROSA RIVER–PUTUCUAL LAGOON
SWAMP, GULF OF PARIA BASIN (SUCRE STATE)
RECORD
To date, there is only one known record of the matamata
turtle from Sucre State. This specimen is catalogued at the
KU Biodiversity Institute and Natural History Museum
(Lawrence, KS) under the accession number KU 117344
(see Pritchard & Trebbau 1984). To validate this record,
Ana Motta, the Herpetology Collection Manager at
KU, confirmed the physical existence of the specimen.
She also provided information from the hand-written
catalogue, and took the carapace measurement (Curved
Carapace Length - CCL: 35.5 cm), and photographs
from both the dorsal and ventral views (Fig. 8). According
to the catalogue, this specimen, identified as Chelus
fimbriata, was collected by James D. Smith on February
26, 1967, in the vicinity of Santa Rosa River (10°24’55” N,
63°23’29” W), located by road 20 km southeast of
Casanay Village (10°30’13” N, 63°25’03” W), likely
from the Putucual Lagoon Swamp (Fig. 2; black star 3).
However, after analyzing the photographs, it is apparent
that this individual has an oval-shaped carapace with an
unpigmented yellow plastron, and having two dark fine
bands running along the light color of the underside of
the neck, features diagnostic of the Orinoco morphotype.
Consequently, based on these characteristics the specimen
appears to be instead a C. orinocensis, pending further
investigation (T. Escalona, pers. obs.). Interestingly, the
Santa Rosa River is in the lowlands and flows southeast
where it merges into Putucual. This swamp drains its
water eastward into the San Juan River, which eventually
flows into the Gulf of Paria (Melfran Herrera, pers.
comm.). This hydrographic system is part of the Gulf of
Paria Basin, where some tributaries can connect with those
of the Orinoco Delta during flooding. These connections
may facilitate the exchange of water and aquatic species
between the Orinoco and the Gulf of Paria, influencing
the biodiversity and ecological dynamics of the entire
region. Given this context, the presence of matamata
turtles in Sucre State is plausible. Nevertheless, our current
understanding of the chelonian fauna in this region
remains largely unknown, highlighting the necessity for
further research to explore turtle diversity in this area.
CASIQUIARE RIVER CANAL
(AMAZONAS STATE) RECORD
Morphological shell shape data from museum records
indicate the occurrence of both matamata lineages in
the Upper Orinoco and Upper Rio Negro Basins within
the Amazonas State in southern Venezuela. However, it
remains unclear where along this hydrographic gradient
the two lineages coexist (Pritchard & Trebbau 1984,
Sánchez-Villagra et al. 1995, Barrio-Amorós & Narbaiza
1999, Pritchard 2008). Here, I report about one record
from the Casiquiare drainage, the only contact zone
between the Orinoco and Rio Negro Basins. A large-sized
specimen, with burned carapace and missing plastron is
documented, measuring 48.4 cm in SCLmax and 36.9 cm
in SCW (Fig. 11). This incomplete shell was discovered in
Figure 10. Newly discovered catalogued museum record of matamata turtle from the northwestern side of Lake Maracaibo, Venezuela.
This new record is deposited in the Herpetological Collection of the Museum of Biology of the Universidad Central de Venezuela
(MBUCV 7096). Left: Tag validating the locality and catalogue record. Middle: Dorsal view (carapace). Right: Ventral view (plas-
tron). This very small juvenile specimen measured 6 cm in SCLmax. Photo: Tibisay Escalona.
Chelus spp. in Venezuela61
Figure 11. Dorsal view of the carapace shape from two different Amazonian Chelus morphotypes depicting a rectangular shell shape
with parallel-sides. Left: Burned carapace of an adult female matamata turtle from the Casiquiare River (Amazonas state), southern
Venezuela (catalogued originally as C. orinocensis, and modify tentatively to C. fimbriata, pending investigation, MBUCV 7278) (Pho-
to: Tibisay Escalona). Right: from the vicinity of Leticia, Colombia (catalogued as C. fimbriata PCHP 39) (modified from Sánchez-
Villagra et al. 1995).
the community of San Carlos de Rio Negro (Fig. 2; black
square 7) after being consumed by locals. The locals reported
capturing the turtle along the Casiquiare River, though
no specific collection site was provided (C. Alvarado.
pers. comm.). This matamata is housed at MBUCV with
catalogue number 7278 and identified as C. orinocensis.
A closer examination and using shell shape outline as a
diagnostic character for taxon identification, indicates
that the specimen has a more rectangular shape rather
than oval (Fig. 10). Based on this feature, the specimen
is identified tentatively as an Amazonian morphotype
(C. fimbriata) (A. Rhodin and T. Escalona, pers. obs.)
until further morphological investigation (Fig. 10). This
finding is particularly intriguing, as current genetic studies
restrict C. fimbriata to the Amazon River Basin and
eastern Guianas (Vargas-Ramirez et al. 2020). However,
before making any conclusion, caution is warranted as
this specimen may also represent an interspecific hybrid
or intergrade, considering it originates from a locality
where both matamata lineages are suggested to co-occur.
Indeed, previous investigations have mentioned that
some specimens from this region exhibit a blend of traits
from the two Chelus morphotypes, making them difficult
to identify, and implying a subspecific relationship or
intermediate morphotype between C. orinocensis and C.
fimbriata (Sánchez-Villagra et al. 1995, Pritchard 2008).
Considering all these factors, it is reasonable to suggest
that the Casiquiare River Canal may serve as a dispersal
corridor for matamata turtles between the Orinoco
and Rio Negro Basins and vice versa, facilitating habitat
sharing and coexistence among Chelus lineages along this
contact zone. The Casiquiare River’s role as an important
biogeographic corridor in shaping species distribution,
genetic flow, and speciation processes is well-documented
for diverse aquatic fauna, such as in Amazon river dolphins,
Podocnemididae turtles (Emmons & Feer 1999, Pearse
et al. 2006, Escalona et al. 2009b), particularly for fish
species of the genus Cichla (Winemiller & Willis 2011).
Additionally, evidence of interspecific hybridization, as
seen in various fish studies (Crampton et al. 2003, Willis
et al. 2010, 2012, Thomaz et al. 2017), underscore the
river’s function in facilitating genetic mixing between
the Amazon and Orinoco Basins. However, the extent
to which this hybridization or intergrade has occurred
in other aquatic organisms, such as matamata turtles,
remains understudied. It is important to emphasize,
that hybridization among chelonian species have been
previously reported in other hydrographic regions (e.g.,
Figure 11. Dorsal view of the carapace shape from two different Amazonian Chelus morphotypes depicting a rectangular shell shape
with parallel-sides. Left: Burned carapace of an adult female matamata turtle from the Casiquiare River (Amazonas state), southern
Venezuela (catalogued originally as C. orinocensis, and modify tentatively to C. fimbriata, pending investigation, MBUCV 7278) (Pho-
to: Tibisay Escalona). Right: from the vicinity of Leticia, Colombia (catalogued as C. fimbriata PCHP 39) (modified from Sánchez-
Villagra et al. 1995).
the community of San Carlos de Rio Negro (Fig. 2; black
square 7) after being consumed by locals. The locals reported
capturing the turtle along the Casiquiare River, though
no specific collection site was provided (C. Alvarado.
pers. comm.). This matamata is housed at MBUCV with
catalogue number 7278 and identified as C. orinocensis.
A closer examination and using shell shape outline as a
diagnostic character for taxon identification, indicates
that the specimen has a more rectangular shape rather
than oval (Fig. 10). Based on this feature, the specimen
is identified tentatively as an Amazonian morphotype
(C. fimbriata) (A. Rhodin and T. Escalona, pers. obs.)
until further morphological investigation (Fig. 10). This
finding is particularly intriguing, as current genetic studies
restrict C. fimbriata to the Amazon River Basin and
eastern Guianas (Vargas-Ramirez et al. 2020). However,
before making any conclusion, caution is warranted as
this specimen may also represent an interspecific hybrid
or intergrade, considering it originates from a locality
where both matamata lineages are suggested to co-occur.
Indeed, previous investigations have mentioned that
some specimens from this region exhibit a blend of traits
from the two Chelus morphotypes, making them difficult
to identify, and implying a subspecific relationship or
intermediate morphotype between C. orinocensis and C.
fimbriata (Sánchez-Villagra et al. 1995, Pritchard 2008).
Considering all these factors, it is reasonable to suggest
that the Casiquiare River Canal may serve as a dispersal
corridor for matamata turtles between the Orinoco
and Rio Negro Basins and vice versa, facilitating habitat
sharing and coexistence among Chelus lineages along this
contact zone. The Casiquiare River’s role as an important
biogeographic corridor in shaping species distribution,
genetic flow, and speciation processes is well-documented
for diverse aquatic fauna, such as in Amazon river dolphins,
Podocnemididae turtles (Emmons & Feer 1999, Pearse
et al. 2006, Escalona et al. 2009b), particularly for fish
species of the genus Cichla (Winemiller & Willis 2011).
Additionally, evidence of interspecific hybridization, as
seen in various fish studies (Crampton et al. 2003, Willis
et al. 2010, 2012, Thomaz et al. 2017), underscore the
river’s function in facilitating genetic mixing between
the Amazon and Orinoco Basins. However, the extent
to which this hybridization or intergrade has occurred
in other aquatic organisms, such as matamata turtles,
remains understudied. It is important to emphasize,
that hybridization among chelonian species have been
previously reported in other hydrographic regions (e.g.,
Escalona62
Lovich et al. 1990, Arantes et al. 2020). If this is the case
of Chelus sp., it demands rigorous investigation in order
to help mitigate taxonomic ambiguity, as evidenced by
similar issues documented in Australian chelids (Cann &
Legler 1994, Spinks et al. 2015).
Lastly, expanding the discovery of new matamata
specimens is crucial for comprehensively understanding the
distribution, genetic diversity, and morphological variation
of Chelus lineages within and among these river basins.
ACKNOWLEDGEMENTS
Vivian P. Páez (Universidad de Antioquia, Medellín,
Colombia) and Marcelo Sánchez-Villagra (Palaeobiology
Institute, University of Zurich, Switzerland) provided
valuable comments and editing to the text. Anders
Rhodin (Chelonian Research Foundation) assisted
in the identification of several specimens described in
this note, including those from the Lake Maracaibo
Basin and the Casiquiare River Canal museum records.
Mónica Morales-Betancourt (Instituto de Investigación
de Recursos Biológicos Alexander von Humboldt)
shared detailed information on matamata size data from
Colombian Orinoquia (Bojonawi Natural Reserve).
Gilson Rivas (Museo de Biología, Universidad del Zulia)
facilitated exchange of information between John E.
Simmons, José L. Lira and Oswaldo Oliveros. José R. Lira
(retired Professor from Universidad del Zulia) provided
valuable information by ratifying his observations of a
matamata that he saw in Lake Maracaibo in 1974. John
E. Simmons (Museum Consultant) clarified information
and facilitated the communication with KU. Ana Motta
(KU Herpetology Collection Manager) validated the
matamata turtle record at KU museum (KU 117344),
took pictures and measurements. Jocelyn Colella
(KU Mammology Curator Manager) facilitated the
communication with James D. Smith who collected the
specimen (KU 117344) in Sucre State. Melfran Herrera
(Mosquito vector control Supervisor at Doctors Without
Borders (MSF) in the Sucre State) provided information
on the hydrogeographyc system of the lowlands of Gulf
of Paria Basin. Hedelvy Guada (Museo de Biología de
la Universidad Central de Venezuela, Caracas) allowed
examination of specimens under her care.
REFERENCES
Arantes, L. S., S. T. Vilaca, C. J. Mazzoni & F. R. Santos. 2020.
New genetic insights about hybridization and population
structure of hawksbill and loggerhead turtles from Brazil.
Journal of Heredity 111(5): 444–456.
Barrio-Amorós, C. & I. Narbaiza. 1999. Chelus fimbriatus
(Matamata). Maximum size. Herpetological Review 30: 164–
165.
Barrio-Amorós, C. & R. Manrique. 2006. Record de taille por
une Matamata (Chelus fimbriata) au Venezuela. Manouria
9(32): 23–26.
Cadena, E., A. Link, A.Vanegas, C. Avellaneda-Otero, C. Perdo-
mo, D. Urueña-Carrillo, R. Sánchez, R. Vanegas, T. Scheyer
& J. Carrillo-Briceño. 2023. New insights into the fossil re-
cord of the turtle genus Chelus Duméril, 1806 including new
specimens with information on cervicals and limb bones.
Comptes Rendus Palevol 22(34): 689–709.
Cann, J. & J. M. Legler. 1994. The Mary River Tortoise: A new
genus and species of short-necked Chelid from Queensland,
Australia (Testudines: Pleurodira). Chelonian Conservation
and Biology 1(2): 81–96.
Crampton, W. G., N. R. Lovejoy & J. C. Waddell. 2003. Mo-
lecular phylogenetics and evolution of the electric fish genus
Gymnotus (Teleostei: Gymnotiformes) using cytochrome b
and 16S rRNA sequences. Molecular Phylogenetics and Evo-
lution 26(3): 329–344.
Cunha, F., C. Fagundes, E. Brito et al. 2021. Distribution of
Chelus fimbriata and Chelus orinocensis (Testudines: Cheli-
dae). Chelonian Conservation and Biology 20(1): 109–115.
Emmons, L. H. & F. Feer. 1999. Neotropical rainforest mammals,
a field guide. 2 nd ed. Chicago: University of Chicago Press,
396 pp., 29 pls.
Escalona, T. 2003. Maternal effects on reproductive success in a
river turtle (Podocnemis unifilis) in southern Venezuela. St
Louis, Missouri: University of Missouri at St Louis, 84 pp.
[PhD thesis].
Escalona, T., N. Valenzuela & D. C. Adams. 2009a. Nesting
ecology in the freshwater turtle Podocnemis unifilis: spatio
temporal patterns and inferred explanations. Functional
Ecology 23(4): 826–835.
Escalona, T., T. Engstrom, O. Hernández, B. Bock, R. Vogt &
N. Valenzuela. 2009b. Population genetics of the endangered
South American freshwater turtle, Podocnemis unifilis, in-
ferred from microsatellite DNA data. Conservation Genetics
10: 1683–1696.
Ferreira, G., A. Rincón, A. Solórzano & M. Langer. 2016. Re-
view of the fossil matamata turtles: earliest well-dated record
and hypotheses on the origin of their present geographical
distribution. The Science of Nature 103 (28): 1–12.
González, N., G. Echevarría, F. Daza & F. Mass. 2012. Illustrat-
ed list of additions to the ichthyofauna of the Caura River,
Venezuela. CheckList 8: 43–52.
Medem, F. 1960. Datos zoo-geográficos y ecológicos sobre los
Crocodylia y Testudinata de los ríos Amazonas, Putumayo y
Caquetá. Caldasia 8 (38): 341–351.
Morales-Betancourt, M., C. Lasso, S. Bernal-Sierra, A. Sepúlve-
da-Seguro, K. Parra-Henao, M. Gómez-Rincón, V. Páez, B.
Castañeda & B. Marín. 2020. Historia natural de las tortugas
acuáticas de la Reserva Natural Bojonawi (Escudo Guayanés),
Orinoquia, Vichada, Colombia. pp. 431–45. In: Lasso C. A.,
Lovich et al. 1990, Arantes et al. 2020). If this is the case
of Chelus sp., it demands rigorous investigation in order
to help mitigate taxonomic ambiguity, as evidenced by
similar issues documented in Australian chelids (Cann &
Legler 1994, Spinks et al. 2015).
Lastly, expanding the discovery of new matamata
specimens is crucial for comprehensively understanding the
distribution, genetic diversity, and morphological variation
of Chelus lineages within and among these river basins.
ACKNOWLEDGEMENTS
Vivian P. Páez (Universidad de Antioquia, Medellín,
Colombia) and Marcelo Sánchez-Villagra (Palaeobiology
Institute, University of Zurich, Switzerland) provided
valuable comments and editing to the text. Anders
Rhodin (Chelonian Research Foundation) assisted
in the identification of several specimens described in
this note, including those from the Lake Maracaibo
Basin and the Casiquiare River Canal museum records.
Mónica Morales-Betancourt (Instituto de Investigación
de Recursos Biológicos Alexander von Humboldt)
shared detailed information on matamata size data from
Colombian Orinoquia (Bojonawi Natural Reserve).
Gilson Rivas (Museo de Biología, Universidad del Zulia)
facilitated exchange of information between John E.
Simmons, José L. Lira and Oswaldo Oliveros. José R. Lira
(retired Professor from Universidad del Zulia) provided
valuable information by ratifying his observations of a
matamata that he saw in Lake Maracaibo in 1974. John
E. Simmons (Museum Consultant) clarified information
and facilitated the communication with KU. Ana Motta
(KU Herpetology Collection Manager) validated the
matamata turtle record at KU museum (KU 117344),
took pictures and measurements. Jocelyn Colella
(KU Mammology Curator Manager) facilitated the
communication with James D. Smith who collected the
specimen (KU 117344) in Sucre State. Melfran Herrera
(Mosquito vector control Supervisor at Doctors Without
Borders (MSF) in the Sucre State) provided information
on the hydrogeographyc system of the lowlands of Gulf
of Paria Basin. Hedelvy Guada (Museo de Biología de
la Universidad Central de Venezuela, Caracas) allowed
examination of specimens under her care.
REFERENCES
Arantes, L. S., S. T. Vilaca, C. J. Mazzoni & F. R. Santos. 2020.
New genetic insights about hybridization and population
structure of hawksbill and loggerhead turtles from Brazil.
Journal of Heredity 111(5): 444–456.
Barrio-Amorós, C. & I. Narbaiza. 1999. Chelus fimbriatus
(Matamata). Maximum size. Herpetological Review 30: 164–
165.
Barrio-Amorós, C. & R. Manrique. 2006. Record de taille por
une Matamata (Chelus fimbriata) au Venezuela. Manouria
9(32): 23–26.
Cadena, E., A. Link, A.Vanegas, C. Avellaneda-Otero, C. Perdo-
mo, D. Urueña-Carrillo, R. Sánchez, R. Vanegas, T. Scheyer
& J. Carrillo-Briceño. 2023. New insights into the fossil re-
cord of the turtle genus Chelus Duméril, 1806 including new
specimens with information on cervicals and limb bones.
Comptes Rendus Palevol 22(34): 689–709.
Cann, J. & J. M. Legler. 1994. The Mary River Tortoise: A new
genus and species of short-necked Chelid from Queensland,
Australia (Testudines: Pleurodira). Chelonian Conservation
and Biology 1(2): 81–96.
Crampton, W. G., N. R. Lovejoy & J. C. Waddell. 2003. Mo-
lecular phylogenetics and evolution of the electric fish genus
Gymnotus (Teleostei: Gymnotiformes) using cytochrome b
and 16S rRNA sequences. Molecular Phylogenetics and Evo-
lution 26(3): 329–344.
Cunha, F., C. Fagundes, E. Brito et al. 2021. Distribution of
Chelus fimbriata and Chelus orinocensis (Testudines: Cheli-
dae). Chelonian Conservation and Biology 20(1): 109–115.
Emmons, L. H. & F. Feer. 1999. Neotropical rainforest mammals,
a field guide. 2 nd ed. Chicago: University of Chicago Press,
396 pp., 29 pls.
Escalona, T. 2003. Maternal effects on reproductive success in a
river turtle (Podocnemis unifilis) in southern Venezuela. St
Louis, Missouri: University of Missouri at St Louis, 84 pp.
[PhD thesis].
Escalona, T., N. Valenzuela & D. C. Adams. 2009a. Nesting
ecology in the freshwater turtle Podocnemis unifilis: spatio
temporal patterns and inferred explanations. Functional
Ecology 23(4): 826–835.
Escalona, T., T. Engstrom, O. Hernández, B. Bock, R. Vogt &
N. Valenzuela. 2009b. Population genetics of the endangered
South American freshwater turtle, Podocnemis unifilis, in-
ferred from microsatellite DNA data. Conservation Genetics
10: 1683–1696.
Ferreira, G., A. Rincón, A. Solórzano & M. Langer. 2016. Re-
view of the fossil matamata turtles: earliest well-dated record
and hypotheses on the origin of their present geographical
distribution. The Science of Nature 103 (28): 1–12.
González, N., G. Echevarría, F. Daza & F. Mass. 2012. Illustrat-
ed list of additions to the ichthyofauna of the Caura River,
Venezuela. CheckList 8: 43–52.
Medem, F. 1960. Datos zoo-geográficos y ecológicos sobre los
Crocodylia y Testudinata de los ríos Amazonas, Putumayo y
Caquetá. Caldasia 8 (38): 341–351.
Morales-Betancourt, M., C. Lasso, S. Bernal-Sierra, A. Sepúlve-
da-Seguro, K. Parra-Henao, M. Gómez-Rincón, V. Páez, B.
Castañeda & B. Marín. 2020. Historia natural de las tortugas
acuáticas de la Reserva Natural Bojonawi (Escudo Guayanés),
Orinoquia, Vichada, Colombia. pp. 431–45. In: Lasso C. A.,
Chelus spp. in Venezuela63
F. Trujillo, M. A. Morales-Betancourt (eds.). VIII. Biodiver-
sidad de la Reserva Natural Bojonawi, Vichada, Colombia: río
Orinoco y planicie de inundación. Serie Editorial Fauna Silves-
tre Neotropical. Bogotá, D. C.: Instituto de Investigación de
Recursos Biológicos Alexander von Humboldt.
Pearse, D. E., A. A. Arndt, N. Valenzuela, B. A. Miller, V. Can-
tarelli & J. W. Sites, Jr. 2006. Estimating population structure
under nonequilibrium conditions in a conservation context:
Continent-wide population genetics of the giant Amazon
river turtle, Podocnemis expansa (Chelonia; Podocnemidi-
dae). Molecular Ecology 15: 985–1006.
Pritchard, P. 2008. Chelus fimbriatus (Schneider, 1783) – Mata-
mata turtle. Chelonian Research Monographs 5: 020.1-020.10
Pritchard, P. & P. Trebbau. 1984. The turtles of Venezuela. Ithaca,
NY: Society for the Study of Amphibians and Reptiles, 403
pp.
Rodriguez-Olarte, D., J. I. Mojica & D. C. Taphorn. 2011.
Northern South America: Magdalena and Maracaibo Ba-
sins. January 2011. pp. 243-257. In: Albert S. J. & R. E. Reis
(eds.): Historical biogeography of Neotropical freshwater fish-
es. Berkeley and Los Angeles: University of California Press,
369 pp.
Rojas-Runjaic, F., A. Ferrer & C. Señaris. 2011. Tortugas conti-
nentales de la Orinoquía venezolana: situación actual e ini-
ciativas para su conservación y uso sustentable. pp. 174–207.
In: Lasso C. A., B. A. Rial, C. L. Matallana, W. Ramírez, J.
C. Señaris, A. Díaz-Pulido, G. Corzo & A. Machado-Allison
(eds.). Biodiversidad de la cuenca del Orinoco. II. Áreas prio-
ritarias para la conservación y uso sostenible. Bogotá, D. C.:
Instituto de Investigación de Recursos Biológicos Alexander
von Humboldt, Ministerio del Ambiente, Vivienda y De-
sarrollo Territorial, WWF Colombia, Fundación Omacha,
Fundación La Salle de Ciencias Naturales e Instituto de Estu-
dios de la Orinoquia (Universidad Nacional de Colombia),
304 pp.
Rosales, J., M. Bevilacqua, W. Díaz, R. Pérez, D. Rivas & S.
Caura. 2003. Riparian vegetation communities of the Caura
River Basin, Bolívar State, Venezuela. In: Chernoff B., A.
Machado-Allison, K. Riseng & J. R. Montambault (eds.). A
biological assessment of the aquatic ecosystems of the Caura Riv-
er Basin, Bolívar State, Venezuela. RAP Bulletin of Biological
Assessment 28. Washington, D. C.: Conservation Interna-
tional, Center for Applied Biodiversity Science, Department
of Conservation Biology, 284 pp.
Rosales, J. & O. Huber (eds.). 1996. Ecología de la cuenca del rio
Caura, Venezuela, I. Caracterización general. Scientia Guia-
nae 6: 1–152.
Sánchez-Villagra M., P. Pritchard, A. Paolillo & O. Linares.
1995. Geographic variation in the matamata turtle, Chelus
fimbriatus, with observations on its morphology and mor-
phometry. Chelonian Conservation and Biology 1(4): 293–
300.
Spinks, P., A. Georges & H. B. Shaffer. 2015. Phylogenetic un-
certainty and taxonomic re-revisions: an example from the
Australian short-necked turtles (Testudines: Chelidae). Co-
peia 2015: 536–540
Thomaz, A. T., L. R. Malabarba & L. L. Knowles. 2017. Genom-
ic signatures of paleogeographic history in the Neotropical
seasonal forest and savanna: the diversification of the an-
nual killifish genus Cynopoecilus. Molecular Ecology 26(10):
2716–2732.
TTWG-Turtle Taxonomy Working Group [Rhodin A., J. Iver-
son, R. Bour, U. Fritz, A. Georges, B. Shaffer & P. van Dijk].
2021. Turtles of the World: Annotated checklist and atlas of
taxonomy, synonymy, distribution, and conservation status
(9 th ed.). In: Rhodin A., J. Iverson, P. van Dijk, C. Stanford, E.
Goode, K. Buhlmann & R. Mittermeier (eds.): Conservation
biology of freshwater turtles and tortoises: A compilation proj-
ect of the IUCN/SSC Tortoise and Freshwater Turtle Specialist
Group. Chelonian Research Monographs 8:1–472.
Vargas-Ramírez, M., S. Caballero, M. Morales-Betancourt, C.
Lasso, L. Amaya, J. Martínez, M. Silva Viana, R. Vogt, I. Far-
ias, T. Hrbek, P. Campbell & U. Fritz. 2020. Genomic analy-
ses reveal two species of the matamata (Testudines: Cheli-
dae: Chelus spp.) and clarify their phylogeography. Molecular
Phylogenetics and Evolution 148: 106823.
Willis, S. C., M. Nunes, C. G. Montaña. I. P. Farias, G. Ortí &
N. R. Lovejoy. 2010. The Casiquiare River acts as a corridor
between the Amazonas and Orinoco river basins: Biogeo-
graphic analysis of the genus Cichla. Molecular Ecology 19:
1014–1030.
Willis, S. C., J. Macrander, I. P. Farias & G. Orti. 2012. Simul-
taneous delimitation of species and quantification of inter-
specific hybridization in Amazonian peacock cichlids (genus
Cichla) using multi-locus data. BMC Evolutionary Biology
12(96): 1–24.
Winemiller, K. O. & S. C. Willis. 2011. The Vaupes Arch and
Casiquiare Canal: Barriers and passages. pp. 225–242. In:
Albert S. J. &R. E. Reis. (eds.): Historical biogeography of
Neotropical freshwater fishes. Berkeley and Los Angeles: Uni-
versity of California Press, 369 pp.
Zachos, F. E. 2016. Species concepts in biology: Historical develop-
ment, theoretical foundations, and practical relevance. Cham:
Springer International Publishing, 215 pp.
F. Trujillo, M. A. Morales-Betancourt (eds.). VIII. Biodiver-
sidad de la Reserva Natural Bojonawi, Vichada, Colombia: río
Orinoco y planicie de inundación. Serie Editorial Fauna Silves-
tre Neotropical. Bogotá, D. C.: Instituto de Investigación de
Recursos Biológicos Alexander von Humboldt.
Pearse, D. E., A. A. Arndt, N. Valenzuela, B. A. Miller, V. Can-
tarelli & J. W. Sites, Jr. 2006. Estimating population structure
under nonequilibrium conditions in a conservation context:
Continent-wide population genetics of the giant Amazon
river turtle, Podocnemis expansa (Chelonia; Podocnemidi-
dae). Molecular Ecology 15: 985–1006.
Pritchard, P. 2008. Chelus fimbriatus (Schneider, 1783) – Mata-
mata turtle. Chelonian Research Monographs 5: 020.1-020.10
Pritchard, P. & P. Trebbau. 1984. The turtles of Venezuela. Ithaca,
NY: Society for the Study of Amphibians and Reptiles, 403
pp.
Rodriguez-Olarte, D., J. I. Mojica & D. C. Taphorn. 2011.
Northern South America: Magdalena and Maracaibo Ba-
sins. January 2011. pp. 243-257. In: Albert S. J. & R. E. Reis
(eds.): Historical biogeography of Neotropical freshwater fish-
es. Berkeley and Los Angeles: University of California Press,
369 pp.
Rojas-Runjaic, F., A. Ferrer & C. Señaris. 2011. Tortugas conti-
nentales de la Orinoquía venezolana: situación actual e ini-
ciativas para su conservación y uso sustentable. pp. 174–207.
In: Lasso C. A., B. A. Rial, C. L. Matallana, W. Ramírez, J.
C. Señaris, A. Díaz-Pulido, G. Corzo & A. Machado-Allison
(eds.). Biodiversidad de la cuenca del Orinoco. II. Áreas prio-
ritarias para la conservación y uso sostenible. Bogotá, D. C.:
Instituto de Investigación de Recursos Biológicos Alexander
von Humboldt, Ministerio del Ambiente, Vivienda y De-
sarrollo Territorial, WWF Colombia, Fundación Omacha,
Fundación La Salle de Ciencias Naturales e Instituto de Estu-
dios de la Orinoquia (Universidad Nacional de Colombia),
304 pp.
Rosales, J., M. Bevilacqua, W. Díaz, R. Pérez, D. Rivas & S.
Caura. 2003. Riparian vegetation communities of the Caura
River Basin, Bolívar State, Venezuela. In: Chernoff B., A.
Machado-Allison, K. Riseng & J. R. Montambault (eds.). A
biological assessment of the aquatic ecosystems of the Caura Riv-
er Basin, Bolívar State, Venezuela. RAP Bulletin of Biological
Assessment 28. Washington, D. C.: Conservation Interna-
tional, Center for Applied Biodiversity Science, Department
of Conservation Biology, 284 pp.
Rosales, J. & O. Huber (eds.). 1996. Ecología de la cuenca del rio
Caura, Venezuela, I. Caracterización general. Scientia Guia-
nae 6: 1–152.
Sánchez-Villagra M., P. Pritchard, A. Paolillo & O. Linares.
1995. Geographic variation in the matamata turtle, Chelus
fimbriatus, with observations on its morphology and mor-
phometry. Chelonian Conservation and Biology 1(4): 293–
300.
Spinks, P., A. Georges & H. B. Shaffer. 2015. Phylogenetic un-
certainty and taxonomic re-revisions: an example from the
Australian short-necked turtles (Testudines: Chelidae). Co-
peia 2015: 536–540
Thomaz, A. T., L. R. Malabarba & L. L. Knowles. 2017. Genom-
ic signatures of paleogeographic history in the Neotropical
seasonal forest and savanna: the diversification of the an-
nual killifish genus Cynopoecilus. Molecular Ecology 26(10):
2716–2732.
TTWG-Turtle Taxonomy Working Group [Rhodin A., J. Iver-
son, R. Bour, U. Fritz, A. Georges, B. Shaffer & P. van Dijk].
2021. Turtles of the World: Annotated checklist and atlas of
taxonomy, synonymy, distribution, and conservation status
(9 th ed.). In: Rhodin A., J. Iverson, P. van Dijk, C. Stanford, E.
Goode, K. Buhlmann & R. Mittermeier (eds.): Conservation
biology of freshwater turtles and tortoises: A compilation proj-
ect of the IUCN/SSC Tortoise and Freshwater Turtle Specialist
Group. Chelonian Research Monographs 8:1–472.
Vargas-Ramírez, M., S. Caballero, M. Morales-Betancourt, C.
Lasso, L. Amaya, J. Martínez, M. Silva Viana, R. Vogt, I. Far-
ias, T. Hrbek, P. Campbell & U. Fritz. 2020. Genomic analy-
ses reveal two species of the matamata (Testudines: Cheli-
dae: Chelus spp.) and clarify their phylogeography. Molecular
Phylogenetics and Evolution 148: 106823.
Willis, S. C., M. Nunes, C. G. Montaña. I. P. Farias, G. Ortí &
N. R. Lovejoy. 2010. The Casiquiare River acts as a corridor
between the Amazonas and Orinoco river basins: Biogeo-
graphic analysis of the genus Cichla. Molecular Ecology 19:
1014–1030.
Willis, S. C., J. Macrander, I. P. Farias & G. Orti. 2012. Simul-
taneous delimitation of species and quantification of inter-
specific hybridization in Amazonian peacock cichlids (genus
Cichla) using multi-locus data. BMC Evolutionary Biology
12(96): 1–24.
Winemiller, K. O. & S. C. Willis. 2011. The Vaupes Arch and
Casiquiare Canal: Barriers and passages. pp. 225–242. In:
Albert S. J. &R. E. Reis. (eds.): Historical biogeography of
Neotropical freshwater fishes. Berkeley and Los Angeles: Uni-
versity of California Press, 369 pp.
Zachos, F. E. 2016. Species concepts in biology: Historical develop-
ment, theoretical foundations, and practical relevance. Cham:
Springer International Publishing, 215 pp.