Dimacrodon hottoni was a synapsid that lived during the mid-Permian, about 272 million years ago, in what is now Texas, USA.
Known only from incomplete skull material, it had a thin bony crest on its forehead and a long snout with unusually toothless jaw tips — which had a rough bone texture suggesting there was a small keratinous beak there.
Its full body proportions aren’t known, but since its skull measured around 50cm (~1’8″) it was probably at least 2.5-3m long (~8-10′).
When its fossil remains were first discovered in the mid-20th century it was thought to be a dicynodont-like anomodont, but later examination in the 1990s suggested it was actually a more basal “pelycosaur-grade” synapsid, possibly a sphenacodont close to early therapsids. There hasn’t been any further study on Dimacrodon since then, though, so its exact evolutionary relationships remain very murky.
Its ecology is equally unclear, but its beak-like jaws suggest it may have been somewhat herbivorous. It would have lived around a coastal river delta in a semi-arid climate, alongside herbivorous caseids like Cotylorhynchus and Angelosaurus, predatory sphenacodontids like Dimetrodon, small lizard-like parareptiles and captorhinids, and aquatic temnospondyl amphibians.
References:
- Laurin, Michel, and Robert W. Hook. “The age of North America’s youngest Paleozoic continental vertebrates: a review of data from the Middle Permian Pease River (Texas) and El Reno (Oklahoma) Groups.” Bulletin de la Société Géologique de France 193.1 (2022). https://doi.org/10.1051/bsgf/2022007
- Olson, Everett C., and James R. Beerbower. “The San Angelo formation, Permian of Texas, and its vertebrates.” The Journal of Geology 61.5 (1953): 389-423. https://doi.org/10.1086/626109
- Olson, Everett C. “Late Permian terrestrial vertebrates, USA and USSR.” Transactions of the American Philosophical Society 52.2 (1962): 1-224. https://doi.org/10.2307/1005904
- Sidor, C. A., and J. A. Hopson. “The taxonomic status of the Upper Permian eotheriodont therapsids of the San Angelo Formation (Guadalupian), Texas.” Journal of Vertebrate Paleontology. Vol. 15 suppl.3 (1995): 53A. https://doi.org/10.1080/02724634.1995.10011277
- Wikipedia contributors. “Dimacrodon” Wikipedia, 18 Nov. 2024, https://en.wikipedia.org/wiki/Dimacrodon