Sebecus

Abstract: We describe postcranial remains of new specimens referred to Sebecus icaeorhinus found in the lower section of the Sarmiento Formation at Canadon Hondo (central Patagonia, Argentina), commonly regarded as part of the Casamayoran South American Land Mammal Age (middle Eocene). The new specimens include a partially articulated postcranium associated with teeth and fragmentary remains of the mandible that allows their identification as S. icaeorhinus. This taxon was almost exclusively known from skull remains from the same stratigraphic unit and was characterized by unique cranial features such as a long, high, and narrow rostrum bearing serrated teeth. The new material reveals numerous details on the postcranial anatomy of this crocodyliform, including the presence of proportionately long limbs and 10 autapomorphies in the vertebrae, forelimb, and pelvic girdle (some of which are interpreted as adaptations to terrestriality and an erect limb posture). These features depict a highly modified postcra...

Abstract: A new family, genus and species of a sebecosuchian crocodile from the late Paleocene of northwestern Argentina is described. This new taxon shows several apomorphic conditions such as the bent premaxillae, very high posterior part of the jugal, bent pterygoids, 3 pairs of procumbent teeth and a broad retroarticular process. The cladistic analysis carried out places this taxon as the sister group of Sebecus. The sebecosuchians are defined as a natural group restricted to South America. The baurusuchids come from several upper Cretaceous localities of southeastern Brazil, and northwest of Patagonia. The bretesuchids were found in the middle Paleocene of Brazil, late Paleocene and late Eocene of Argentina. The wider geographical and chronological distribution corresponds to the sebecids. They are registered from the early Paleocene in Patagonia and Bolivia to the middle Miocene in Colombia. The sebecosuchians were strong predators and probably more terrestrial in habits than other crocodilians. The lateral c...

Abstract: A new crocodyliform, Sahitisuchus fluminensis gen. et sp. nov., is described based on a complete skull, lower jaw and anterior cervical vertebrae collected in the Sao Jose de Itaborai Basin of Rio de Janeiro, Brazil. The specimen is one of the best preserved crocodyliforms from Paleocene deposits recovered so far and represents a sebecosuchian, one of the few clades that survived the Cretaceous-Paleogene biotic crisis. The new taxon is found in the same deposit as an alligatoroid, a group that experienced large diversification in the Paleogene. The sebecosuchian record suggests that after the Cretaceous-Paleogene biotic crisis, the less specialized members of this clade characterized by a higher number of teeth compared to the baurusuchid sebecosuchians survived, some having terrestrial habits while others developed a semi-aquatic life style (e.g., Lorosuchus). Starting in the Eocene, sebecid sebecosuchians became specialized with a more accentuated oreinirostry as observed in Sebecus and in Langstonia, but not showing the typical reduced dentition developed by the Cretaceous baurusuchid sebecosuchians. The basal position of Barinasuchus arveloi, a high-snouted Miocene sebecid, indicates the occurrence of an independent lineage sometime after the K-Pg biotic crisis that developed accentuated oreinirostry, suggesting a more complex history of the post-K-Pg crocodyliform radiation.

Abstract: A new sebecid from the early Eocene of Jujuy, with more generalized characteristics than Sebecus, is described. A tooth from the same formation (Lumbrera Formation, Salta Group) and age, in the province of Salta, is assigned to ?Sebecus sp. Another sebecosuchian comes from the late Eocene of Mendoza. A sebecid from the early Oligocene in Patagonia (Chubut) is the most recent record of sebecosuchians in Argentina. Certain local environments in the Tertiary of South America are inferred on the basis of presence of sebecosuchians and associated herpetofauna. Hypotheses of origin and geographical distribution of the Sebecosuchia s.l. (Langston, 1956; Sill, 1969; Steel, 1973; Buffetaut, 1980; Molnar, 1981) are analyzed. Finally, it is confirmed that ziphodonty arose several times during crocodilian history, and that in order to understand the origin and evolution of the Sebecosuchia it will be necessary to have more and better material.