| Abdalodon | |
|---|---|
| |
| A reconstruction of Abdalodon diastematicus | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Order: | Therapsida |
| Suborder: | Cynodontia |
| Family: | †Charassognathidae |
| Subfamily: | †Abdalodontinae |
| Genus: | †Abdalodon |
| Type species | |
| †'Abdalodon diastematicus Kammerer, 2016 | |
Abdalodon is an extinct genus of late Permian cynodonts, known by its only species A. diastematicus. Abdalodon together with the genus Charassognathus, form the clade Charassognathidae. This clade represents the earliest known cynodonts, and is the first known radiation of Permian cynodonts.
Abdalodon diastematicus is known from one crushed fossil skull from the Karoo Basin of South Africa. Of all Permian Therapsids, cynodonts are among the most rare (Biarmosuchians being the only therapsids being of comparable rarity). The fossil record of Permian cynodonts is characterized by a long ghost lineage. Abdalodon has been important for discerning the early evolution of cynodonts. Abdalodon, and its sister taxa Charassognathus are both small bodied animals, Abdalodon having a skull around six centimeters in length and the Charassognathus skull being slightly smaller. This suggests that early cynodont evolution occurred at small body size, which could explain the rarity of Permian cynodont fossils, because there is an inherent taphonomic bias against the fossilization of small bodied animals.
Description[]
Skull
The only existing specimen for Abdalodon is an incomplete, dorsoventrally crushed skull, In which the lower jaws are tightly occluded to the palate.
Abdalodon diastematicus is characterized by the presence of diastema between the canines and postcanines of the dentary, and on the maxilla, an even longer diastema between the canines and postcanines. The maxilla has an indentation behind the canine root, and in the same area possess several large foramina. These suggest that Abdalodon may have had whiskers. The posterior end of the maxilla bends medially, insetting the postcanines from the labial border of the snout. The dentary of Abdalodon diastematicus has a well defined masseteric fossa (a synapomorphy of cynodonts). It sits high on the coronoid process, and is where the masseter muscle would have attached to the dentary. The postdentary bones, which are of particular importance since they form the ear bones in mammals, are absent or severely damaged. The nasal bone is relatively flat, and is separated from the maxilla at the anterior end of the snout by the septomaxilla (a therapsid synapomorphy). The lacrimal bone is smaller and narrower than is typical for early cynodonts. Additionally the skull has a significantly broader interorbital region, a shorter temporal region, and a broader snout than either of its closest known relatives: Charassognathus gracilis and Procynosuchus delaharpe. This gives the skull stout appearance comparatively. The dorsal side of the orbital margin is formed entirely by the prefrontal and postorbital bones. The zygomatic arch is nearly entirely formed from the jugal bone, which also makes up part of the postorbital bar.
The anterior region palatal surface of the skull is obscured by the lower jaw, which tightly fixed to the palate. The transverse processes of the pterygoid sweep laterally and posteriorly. When first described the skull was considered to have a triangular interpterygoing vacuity, however upon later examination, the status of a pterygoid vacuity was left ambiguous. The dentary symphysis is covered with foramina, suggesting there may have been whiskers there. The dentary symphysis is tall and sharply angled forming a distinct chin.