Luisa C. Pusch, Christian F. Kammerer & JÃrg FrÃbisch (2019)
Cranial anatomy of the early cynodont Galesaurus planiceps and the origin of mammalian endocranial characters
Journal of Anatomy (advance online publication)
The cranial anatomy of the early nonâmammalian cynodont Galesaurus planiceps from the South African Karoo Basin is redescribed on the basis of a computed tomographic reconstruction of the skull. Previously, little was known about internal skull morphology and the nervous and sensory system of this taxon. The endocranial anatomy of various cynodonts has been intensively studied in recent years to understand the origin of mammalian characters in the nasal capsule, brain and ear. However, these studies have focused on only a few taxa, the earliest of which is another Early Triassic cynodont, Thrinaxodon liorhinus. Galesaurus is phylogenetically stemward of Thrinaxodon and thus provides a useful test of whether the mammalâlike features observed in Thrinaxodon were present even more basally in cynodont evolution. The cranial anatomy of G. planiceps is characterized by an intriguing mosaic of primitive and derived features within cynodonts. In contrast to the very similar internal nasal and braincase morphology of Galesaurus and Thrinaxodon, parts of the skull that seem to be fairly conservative in nonâprozostrodont cynodonts, the morphology of the maxillary canal differs markedly between these taxa. Unusually, the maxillary canal of Galesaurus has relatively few ramifications, more similar to those of probainognathian cynodonts than that of Thrinaxodon. However, its caudal section is very short, a primitive feature shared with gorgonopsians and therocephalians. The otic labyrinth of Galesaurus is generally similar to that of Thrinaxodon, but differs in some notable features (e.g. proportional size of the anterior semicircular canal). An extremely large, protruding paraflocculus of the brain and a distinct medioventrally located notch on the anterior surface of the tabular, which forms the dorsal border of the large parafloccular lobe, are unique to Galesaurus among therapsids with reconstructed endocasts. These features may represent autapomorphies of Galesaurus, but additional sampling is needed at the base of Cynodontia to test this.
Clemens, William A. (2019)
Puercolestes and Betonnia (Cimolestidae, Mammalia) from the early Paleocene (Puercan 3 Interval Zone) of northeastern Montana, U.S.A.
PaleoBios 36 ucmp_paleobios_42705.: 1â17ÂÂ
In northeastern Montana, fossil localities in the Garbani Channel Complex and other early Paleocene (Puercan 3 Interval Zone) localities are preserved in the Tullock Member of the Fort Union Formation. They document an early phase in the recovery of the terrestrial fauna of the North American Western Interior after the mass extinction marking the Cretaceous-Paleogene (K-Pg) boundary. The cimolestids Puercolestes simpsoni and Betonnia tsosia were typified on fragmentary jaws and isolated teeth found in Puercan 2 and 3 Interval Zones (Pu2, Pu3) in the Nacimiento Formation, San Juan Basin, New Mexico. The available samples of these genera from both New Mexico and Montana are small and dominantly consist of isolated teeth. Characters of upper cheek teeth, P4 and M1âM3, justify provisional recognition of Puercolestes sp. cf. Pu. simpsoni and the somewhat smaller Betonnia sp. cf. Be. tsosia in Pu3 local faunas in the Tullock Member. In contrast, discovery of characters distinguishing the isolated lower cheek teeth, p4s and m1âm3s, of these species must await recovery of dentulous dentaries documenting the patterns of morphological variation of their lower dentitions. Fossils from the Tullock Member add support to the current interpretation that cimolestids were taxonomically diverse and geographically widespread but relatively rare members of the faunas of the North American Western Interior during approximately the first million years of the Paleocene.