Evolution of the side-necked turtles : the families Bothremydidae, Euraxemydidae, and Araripemydidae ; Bulletin of the American Museum of Natural History, no. 300

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New York, NY : American Museum of Natural History
Although pleurodires have been considered significantly less diverse than their sister group, the cryptodires, current discoveries show that pleurodires had a more complex and extensive evolutionary history than had been realized. Previously unknown radiations, particularly in the near-shore marine realm, are revealed by taxa with diverse cranial morphology, indicating many different feeding and sensory strategies. The pleurodire group that is changed the most by the new discoveries is its largest group, the hyperfamily Pelomedusoides. The hyperfamily Pelomedusoides now consists of the families Pelomedusidae, Podocnemididae, Bothremydidae, Araripemydidae, and Euraxemydidae, new family. The families Bothremydidae, Araripemydidae, and Euraxemydidae, new family, are documented with descriptions of skulls, lower jaws, and shells. The relationships of the family Podocnemididae to its sister taxa Hamadachelys and Brasilemys are recognized by placing them in the epifamily Podocnemidinura. The epifamily Podocnemidinura is the sister group to the family Bothremydidae, and together they form the superfamily Podocnemidoidea. The family Araripemydidae consists of one taxon, Araripemys barretoi, from the Aptian-Albian of Brazil. Description of new cranial material suggests that it is the sister group to all other Pelomedusoides or the sister group to the Pelomedusidae, but these relationships are only weakly supported. There is strong support for a multichotomy of Araripemys, Pelomedusidae, and remaining Pelomedusoides. Araripemys is characterized by very thin triturating surfaces and by a shell that lacks mesoplastra and has the first costals reaching the shell margin. The new family Euraxemydidae consists of two new genera: Euraxemys essweini, n. gen. et sp., from the Albian Santana Formation of Brazil, and Dirqadim schaefferi, n. gen. et sp., from the Cenomanian Kem Kem beds of Morocco. Members of the Euraxemydidae are united by the unique possession of a medial process of the quadrate partially covering the prootic and narrowly contacting a ventral process of the exoccipital, in contrast to all other pleurodires, which have either complete exposure or complete covering of the prootic ventrally. Furthermore, members have a ventral process of the exoccipital that is exposed at the lateral margin of the basioccipital in an elongate foot. The Euraxemydidae is hypothesized as the sister group to the superfamily Podocnemidoidea. The family Bothremydidae and the epifamily Podocnemidinura (consisting of the family Podocnemididae, Hamadachelys, and Brasilemys) are united as the superfamily Podocnemidoidea based on the possession of a quadrate-basioccipital contact, the complete or nearly complete ventral covering of the prootic, and the extension of the pectoral scales onto the entoplastron. The family Bothremydidae is a large and diverse group extending from the Albian to the Eocene in North and South America, Europe, Africa, and India. Its monophyly is supported by the presence of a wide exoccipital-quadrate contact, a eustachian tube separated from the incisura columellae auris usually by bone to form a bony canal for the stapes, absence of a fossa precolumellaris, a supraoccipital--quadrate contact (except in the tribe Taphrosphyini), and a posterior enlargement of the fossa orbitalis. Although there is a diversity of triturating surfaces within the family, primitively bothremydids have a posteriorly wide triturating surface with a significant palatine contribution in the upper jaw. The family Bothremydidae consists of four newly recognized, monophyletic groups: the tribes Kurmademydini, Cearachelyini, Bothremydini, and Taphrosphyini. The tribe Kurmademydini consists of two taxa: Kurmademys kallamedensis, from the Maastrichtian Kallamedu Formation of India, and Sankuchemys sethnai, from the Maastrichtian Intertrappean beds of India. The tribe Kurmademydini is characterized by extensive temporal and cheek emargination, a large fossa precolumellaris, and a small, anterior exposure of the prootic on the ventral surface. The tribe Kurmademydini is the sister group to the subfamily Bothremydinae (consisting of the tribes Cearachelyini, Bothremydini, and Taphrosphyini). Members of the subfamily Bothremydinae all possess a foramen stapedio-temporale that faces anteriorly. The tribe Cearachelyini consists of Cearachelys placidoi, from the Albian Santana Formation of Brazil, and Galianemys emringeri and Galianemys whitei, both from the Cenomanian Kem Kem beds of Morocco. The tribe Cearachelyini is characterized by a jugal retracted from the orbital margin and a fenestra postotica formed into a short slit. The tribe Cearachelyini is the sister group to the infrafamily Bothremydodda (consisting of the tribes Bothremydini and Taphrosphyini). The infrafamily Bothremydodda is characterized by a quadrate shelf formed below the cavum tympani, a foramen stapedio-temporale and foramen nervi trigemini that are very close together on the anterior face of the otic chamber, and a condylus occipitalis and occipital neck that are formed only by the exoccipitals. The tribe Bothremydini consists of Foxemys mechinorum, from the Campanian-Maastrichtian of France; Polysternon provinciale, from the Campanian of Europe; Zolhafah bella, from the Maastrichtian Dakla Formation of Egypt; Rosasia soutoi, from the Campanian-Maastrichtian of Portugal; Araiochelys hirayamai, n. gen. et sp., from the Danian phosphates of Ouled Abdoun Basin, Morocco; Bothremys cooki, from the Maastrichtian Navesink Formation of New Jersey; Bothremys maghrebiana, n. sp., from the Danian phosphates of Ouled Abdoun Basin, Morocco; Bothremys kellyi, n. sp., from the Ypresian phosphates of Ouled Abdoun Basin, Morocco; Bothremys arabicus, from the Santonian of Jordan; Chedighaii hutchisoni, n. gen. et sp., from the Campanian Kirtland Formation of New Mexico; and Chedighaii barberi, n. gen., from the Campanian of Arkansas, Alabama, Kansas, and New Jersey. The tribe Bothremydini is the sister group to the tribe Taphrosphyini. The tribe Taphrosphyini is characterized by the presence of a jugal-quadrate contact, the absence of a maxilla-quadratojugal contact, and the absence of a supraoccipital-quadrate contact. Members of the tribe Taphrosphyini have a considerable variety of triturating surfaces but they lack the wide, triangular surfaces typical of the other bothremydids. The tribe Taphrosphyini consists of Taphrosphys sulcatus, from the Danian Hornerstown Formation of New Jersey; Taphrosphys congolensis, from the Paleocene of Cabinda, west Africa; Taphrosphys ippolitoi, n. sp., from the Danian phosphates of the Ouled Abdoun Basin, Morocco; Labrostochelys galkini, n. gen. et sp., from the Danian phosphates of the Ouled Abdoun Basin, Morocco; Phosphatochelys tedfordi, from the Ypresian phosphates of the Ouled Abdoun Basin Morocco; Ummulisani rutgersensis, n. gen. et sp., from the Ypresian phosphates of the Ouled Abdoun Basin, Morocco; Rhothonemys brinkmani, n. gen. et sp., from the Paleogene phosphates of the Ouled Abdoun Basin, Morocco; Azabbaremys moragjonesi, from the Paleocene Teberemt Formation of Mali; Nigeremys gigantea, from the Maastrichtian of Niger; and Arenila krebsi, from the Maastrichtian Dakla Formation of Egypt. Among the Bothremydidae, the Taphrosphyini is the most diverse morphologically. The triturating surfaces show a wide range of variation. The long, narrow skull of Labrostochelys differs significantly from the very short skull of Phosphatochelys. Other genera, such as Azabbaremys and Arenila, have large and massive skulls, but without broadly expanded triturating surfaces, while Ummulisani has very narrow and deep labial ridges. The nasal regions of Taphrosphyini also show wide diversity. Rhothonemys has nasal openings and cavities more than twice the size of the orbits, but the nasal openings in Labrostochelys are smaller than the relatively small orbits. This diversity of Taphrosphyini skull morphology is mostly evident in the Paleogene of North Africa. A phylogenetic analysis of the core dataset of 41 taxa, 122 cranial characters, and 52 postcranial characters relies on comparative descriptions of these taxa. The analysis using PAUP results in one most parsimonious cladogram of 382 steps with a consistency index of 0.6. A Bremer decay analysis shows that the family Bothremydidae is strongly supported at five steps: the tribes Kurmademydini and Cearachelyini have an index of 2, and the tribe Taphrosphyini has an index of 3. The tribe Bothremydini becomes unresolved at one step and is the most weakly supported of these groups. The addition of selected shell-only taxa with low missing data values to the core dataset results in one equally parsimonious cladogram that is resolved as: (Proterochersis (Platychelyidae (Dortoka (Chelidae (Pelomedusidae + Araripemys) (Euraxemydidae (Teneremys (Podocnemididae + Hamadachelys + Brasilemys (Bothremydidae)))))))). A partitioned dataset consisting only of cranial characters (excluding all shell-only taxa) results in one equally parsimonious cladogram identical to the most parsimonious cladogram resulting from the whole dataset; however, a partitioned dataset consisting only of postcranial characters (excluding all skull-only taxa) resulted in 2704 trees, the consensus of which lacks resolution for nearly all Pelomedusoides, but which does resolve more basal pleurodires. When the skull morphology of the Bothremydidae is placed in the context of all other turtles, it becomes apparent that this family has the greatest range of skull forms of any turtle family yet known. In fact, the skull morphologies of many turtle families seem remarkably uniform in comparison (e.g., Testudinidae, Kinosternidae, Pelomedusidae, Trionychidae, Carettochelyidae)...
There are other turtle families with bizarre skull morphologies (e.g., Nanhsiungchelyidae; Meiolaniidae) but these are not taxonomically diverse, at least as they are now known. In no other family do we see the extremes exemplified by the skulls of forms like Cearachelys, Bothremys, Labrostochelys, Azzabaremys, Rhothonemys, and Phosphatochelys. It is this remarkable variation in skull morphology that has allowed us to formulate a strong hypothesis of bothremydid relationships in spite of the presence in Pelomedusoides of remarkably uniform shells"--P. 6-8.
698 p. : ill. (some col.), maps (1 col.) ; 26 cm.
Includes bibliographical references (p. 657-672).