Extinct genus of turtles
Caninemys
is an
extinct
genus
of large freshwater
side-necked turtle
, belonging to the family
Podocnemididae
. Its
fossils
have been found in
Brazil
[2]
and
Colombia
,
[3]
in rocks dating back from the middle to late
Miocene
.
Discovery and naming
[
edit
]
The type specimen of
Caninemys
, a well preserved skull (DNPM-MCT 1496-R), was found in 1962 in
Acre State
,
Brazil
by
Llewellyn Ivor Price
. Originally mentioned by Lapparent de Broin (1993) alongside several shell fragments similar to
Stupendemys
, it was concluded that the data was not sufficient enough to refer the skull to the massive podocnemid, especially in the light of other similarly sized turtle remains from Miocene South America. In 2009 Meylan, Gaffney and De Almeida Campos described
Caninemys
on the basis of the skull alone, not including the shell fragments mentioned by de Broin due to the possibility of a chimeric combination. They do however consider it very probable that LACM 141498, a lower jaw, belongs to the same taxon. Both the holotype skull and the aforementioned lower jaw were used as a basis for the skull of the restored
Stupendemys
skeleton exhibited at the
American Museum of Natural History
. However, for the remains of the enormous
Stupendemys
to match the skull material of
Caninemys
, the later had to be scaled up to twice its original size.
[2]
In 2020 Cadena and colleagues described new specimens of
Stupendemys geographica
, in the process synonymizing both
S. souzai
and
Caninemys
with this genus on the basis of lower jaws found in the same area as
Stupendemys
fossils.
[4]
Later finds of additional
Caninemys
material (shells and skulls) as well as new undisputed
Stupendemys
skull material helped re-establish
Caninemys
as a valid genus. The new material was discovered in the
Colombian
La Victoria Formation
in the
Tatacoa Desert
.
[3]
Caninemys
is named for its
bulldog
-like appearance, with the maxillary processes found in the taxon mirroring the placement of the
canine (tooth)
in mammals. The species name derives from the tridentate ("three toothed") appearance of the skull, as most easily observed when viewed from the front.
[2]
Description
[
edit
]
The skull of
Caninemys
is robust and roughly triangular in shape with thick and massive premaxilla. The eyes are dorsally oriented, facing slightly upward. No
nasal bones
are present as in other members of
Pelomedusoides
. Instead the
prefrontals
make up most of the anterior portion of the skull, including the area just above the nares. The prefrontals extend past the maxilla, giving it a somewhat stub-nosed appearance. The paired prefrontals,
frontals
and
parietals
all contact their respective second bone at the midline. The frontals lack the groove that is characteristic for
Podocnemis
. Scales are preserved on the skull roof, especially over the parietals. Based on this
Caninemys
had triangular interparietal scales, similar to modern
Podocnemis
species. The
premaxilla
are paired, but only make up a small portion of the jaws just below the nares. The triturating (grinding) surface of
Caninemys
is notably more complex than in modern podocnemidids, with a sharp labial ridge that forms a small but distinct toothlike process at the midline contact of the premaxilla. The premaxilla also form a large recess to accommodate for a hooked lower jaw, as seen in the modern
Alligator Snapping Turtle
. The
maxilla
of
Caninemys
are noticeably enlarged and give the animal a superficially "bulldog-like" appearance. The maxilla also stands out for the large, tooth-like processes formed by the labial ridge and flanking the premaxilla on both sides. These processes, superficially resembling the canine teeth seen in mammals, are very noticeable when the skull is viewed head-on. These two processes, alongside the premaxillary process, account for the tridentate condition that gives
Caninemys tridentata
its species name. Even without these processes the labial ridge is very pronounced in
Caninemys
, being thick and extending downward 2 centimeters into a flattened edge. The ridge curves upwards close to the maxilla, creating a u-shaped notch. However,
Caninemys
does not possess a
secondary palate
like in
Bairdemys
,
Stereogenys
and
Shweboemys
.
[2]
The lower jaw LACM 141498 may represent the same taxon as the
Caninemys
holotype. The lower jaw possesses a pronounced symphyseal hook similar to those seen in modern alligator snapping and musk turtles. Although the jaw is slightly too large to belong to the exact same specimen as the holotype, the jaws line up well. While there is no direct link between the two fossils, they match closely enough to suggest they belong to at least closely related taxa, if not the same species. This would suggest that
Caninemys
, besides having pronounced maxilla, also had a robust and hooked lower jaw. This combination of features leads Meylan
et al.
to compare
Caninemys
to a "pleurodiran snapping turtle".
[2]
Based on the head:shell ratio of extant podocnemidid species (including
Podocnemis expansa
),
Caninemys
was likely much smaller than
Stupendemys
, reaching an estimated length of 1.2 to 1.5 meters.
[2]
Phylogeny
[
edit
]
Caninemys
shows multiple morphological characters that clearly identify it as a pelomedusoid pleurodire, specifically a podocnemidid. The phylogenetic tree below is based on the initial analysis conducted in 2009.
[2]
The following phylogenetic tree is a simplified version of the one recovered by Cadena
et al.
(2021), recovering
Stupendemys
and
Caninemys
as being quite distant from one another within Podocnemididae. The scoring of this tree was significantly improved through the discovery of additional remains for both taxa. While
Stupendemys
claded with the extant
Big-headed Amazon River turtle
,
Caninemys
was found to be much more basal, being recovered as the sister taxon to the clade that includes both the
Stupendemys
branch as well as the lineage that leads to the
Madagascan big-headed turtle
.
[3]
This was later reaffirmed in the description of
Peltocephalus maturin
, with the phylogenetic tree of said study being shown below.
[5]
Paleobiology
[
edit
]
The three tooth-like processes of
Caninemys
are similar to those seen in the living
Claudius angustatus
, the Narrow-bridged musk turtle, a member of a group known to utilize a specialised
hyoid
apparatus to capture highly mobile prey via vacuum feeding. Such a feeding style in combination with the massive jaws and tooth-like processes may suggests that it would have been a predatory animal with a lifestyle similar to snapping turtles, feeding on fish, crocodilians and snakes respectively.
[2]
This hypothesis was later contested by Cadena and colleagues in 2020, who instead proposed that
Caninemys
(by them treated as a synonym of
Stupendemys
) had a much broader diet not exclusive to vertebrate prey.
[4]
However, in their 2021 follow-up paper, Cadena and colleagues once again inferred a more carnivorous, vacuum-feeding strategy for
Caninemys
in opposition to a generalist/durophagous
Stupendemys
, arguing that these dietary differences might explain the co-occurrence of two large-bodied turtles within the same ecosystems.
[3]
References
[
edit
]
- ^
"†
Caninemys
Meylan et al. 2009 (sideneck turtle)"
.
Fossilworks
.
- ^
a
b
c
d
e
f
g
h
Meylan, P. A.; Gaffney, E. S.; Campos, J. D. (2009).
"Caninemys, A New Side-Necked Turtle (Pelomedusoides: Podocnemididae) from The Miocene of Brazil. (American Museum novitates, no. 3639)"
.
American Museum Novitates
(3639): 1?26.
doi
:
10.1206/608.1
.
S2CID
85801142
.
- ^
a
b
c
d
Cadena, E.A.; Link, A.; Cooke, S.B.; Stroik, L.K.; Vanegas, A.F.; Tallman, M. (2021).
"New insights on the anatomy and ontogeny of the largest extinct freshwater turtles"
.
Heliyon
.
7
(12): e08591.
Bibcode
:
2021Heliy...708591C
.
doi
:
10.1016/j.heliyon.2021.e08591
.
PMC
8717240
.
PMID
35005268
.
- ^
a
b
Cadena, E.-A.; Scheyer, T.M.; Carrillo-Briceno, J.D.; Sanchez, R.; Aguilera-Socorro, O.A.; Vanegas, A.; Pardo, M.; Hansen, D.M.; Sanchez-Villagra, M.R. (12 Feb 2020).
"The anatomy, paleobiology, and evolutionary relationships of the largest extinct side-necked turtle"
.
Science Advances
.
6
(7): eaay4593.
Bibcode
:
2020SciA....6.4593C
.
doi
:
10.1126/sciadv.aay4593
.
PMC
7015691
.
PMID
32095528
.
- ^
Ferreira, G. S.; Nascimento, E. R.; Cadena, E. A.; Cozzuol, M. A.; Farina, B. M.; Pacheco, M. L. A. F.; Rizzutto, M. A.; Langer, M. C. (2024).
"The latest freshwater giants: a new Peltocephalus (Pleurodira: Podocnemididae) turtle from the Late Pleistocene of the Brazilian Amazon"
.
Biology Letters
.
20
(3).
doi
:
10.1098/rsbl.2024.0010
.
PMC
10932709
.
PMID
38471564
.