| Typothorax Fossil range: Late Triassic | |
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Typothorax is a genus of extinct aetosaur that lived during the Late Triassic. Its remains have been found in North America.
Even though Typothorax was one of the first vertebrate fossils named from the Chinle Formation, most of the skull has not yet been described.
Description[]
Typothorax was an aetosaur, a pseudosuchian distantly related to modern crocodilians. Unlike modern crocodilians, aetosaurs were herbivorous. Typothorax and other aetosaurs possess small, leaf-shaped teeth that were unsuited for a diet consisting of meat. Unlike some aetosaurs such as Desmatosuchus, Typothorax does not have large shoulder spikes. It does, however, have a pair of enlarged spikes on the neck projecting from the third row of scutes. It has lateral scutes that bear horns that are posteriorly hooked along its back, while its sides and underbelly are covered with ornamented scutes. Although fossils of aetosaurs are not as common as other Triassic archosaurs, with their armor plates being the most common, Typothorax has been represented by fewer skeletal elements than other aetosaurs. The largest known specimen of T. coccinarum, described in 2023, would have been similar in size to Desmatosuchus, measuring over 5 metres (16 ft) long, though it has been identified as a skeletally immature individual (16 to 19 years old) based on the open neurocentral suture and the lines of arrested growth. However, the authors warn that, since smaller individuals have co-ossified neurocentral sutures, they may not be a reliable factor in determining maturity in aetosaurs. So this individual still may be an adult.
The vertebral column of Typothorax is shortened, with individual vertebrae being reduced in length. However, the osteodermsthat overly the vertebrae are not shortened. Instead, they are reduced in number so that each dorsal paramedian osteoderm (osteoderm that covers the back) overlies several dorsal vertebrae. In nearly all other crurotarsans, there is one row of osteoderms per vertebra. T. coccinarum has around 20 rows of presacral osteoderms and about 26 presacral vertebrae. If the cervical spikes of Typothorax are homologous to those of Desmatosuchus, it is likely that rows of osteoderms were removed from the front. This is because in Desmatosuchus the spikes are present in the fifth row, while in Typothorax they are present in the third.
In T. coccinarum, there are 10 thoraciccolumns and four caudal columns of ventral osteoderms on the underside. Unlike all other aetosaurs, Typothorax possesses spiked osteoderms on the underside of the tail, near the cloaca. This region is not covered by osteoderms to the extent that it is in other aetosaurs such as Aetosaurus and Coahomasuchus.
History[]
References[]
- King of the Crocodylians: The Paleobiology of Deinosuchus (Life of the Past) by David R. Schwimmer
- The Complete Dinosaur by James O. Farlow, M. K. Brett-Surman, and Robert F. Walters
External links[]
- Typothorax in the Paleobiology Database
