Cotylorhynchus romeri
- 演化之聲
- Mar 19
- 2 min read
Age
Permian（Kungurian）
283-272 Ma
Taxonomy
Kingdom: Animalia
Phylum: Chordata
Class: Synapsida
Family: Caseidae
Genus: Cotylorhynchus
Species: Cotylorhynchus romeri
Morphological description
Cotylorhynchus romeri is a caseid synapsid exhibiting an extremely specialized body plan. Its most striking feature is the combination of a massive body with an exceptionally small skull. The skull is remarkably reduced in size, a proportion that is rare among terrestrial vertebrates. The dorsal surface of the skull is flat, the snout is shortened, and the external nares are positioned close to the orbits.
The lower jaw is robust and curved, bearing small conical teeth, whereas the maxilla and premaxilla possess broad, leaf-shaped teeth adapted for processing plant material, often ornamented with longitudinal ridges. The overall dentition clearly indicates a herbivorous diet. The vertebrae and ribs are massive, supporting the large body; the ribs are strongly arched, giving the trunk a barrel-shaped appearance. The limbs are short and stout, with particularly well-developed hindlimbs. The humerus and femur are thick but relatively short, suggesting that Cotylorhynchus romeri was a slow-moving animal. The combination of a heavily built postcranial skeleton and a reduced skull reflects a highly specialized terrestrial herbivore.
The holotype specimen is catalogued as OMNH 00637.
Etymology
cotylo-: derived from Greek, meaning "cup" or "hollow."
-rhynchus: referring to "nose" or "snout."
romeri: named in honor of the paleontologist Alfred Sherwood Romer, who made significant contributions to the study of early synapsids and their evolutionary relationships.
Biological description
Cotylorhynchus romeri was a large herbivorous synapsid that lived during the middle to late Permian. It represents one of the earliest terrestrial vertebrates to achieve giant body size, reaching approximately 3 to 6 meters in length and up to 2 metric tons in mass. It is considered one of the dominant herbivores within terrestrial ecosystems of its time.
Despite its large size, it likely moved slowly and fed primarily on low-growing vegetation, using its specialized dentition to process large quantities of plant material.
Members of the genus Cotylorhynchus inhabited continental environments under hot, seasonally wet climates on landmasses such as Pangaea. Fossils are mainly found in Oklahoma and Texas in the United States. The fossil record of Cotylorhynchus provides important insight into how herbivorous vertebrates evolved large body sizes and into the evolutionary relationships between early synapsids and later mammals.
（Author: Shui-Ye You）
References
Olson EC and Beerbower JR. (1953). The San Angelo Formation, Permian of Texas and its Vertebrates. J. Geol.
Reisz RR et al. (2022). Cranial Anatomy of the Caseid Synapsid Cotylorhynchus romeri, a Large Terrestrial Herbivore From the Lower Permian of Oklahoma, U.S.A. Frontiers in Earth Science.
35.79, -97.56
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