Bryan Gee

News from the dawn of the dinosaurs

Paper link: https://www.tandfonline.com/doi/full/10.1080/14772019.2019.1602855

Metoposaurids are a globally distributed clade of large (2-3 m adult body length) freshwater temnospondyl amphibians that lived during the Late Triassic, the so called "dawn of the dinosaurs." They're the only large temnospondyls in North America at the time, and thus are a critical component for understanding freshwater ecosystems. 

Although metoposaurids were some of the first extinct tetrapods to be described (1842), a lot of gaps remain in our understanding of their basic taxonomy, anatomy, and biogeography because flat-headed amphibians with toilet-seat jaw-opening mechanics aren't as attractive as dinosaurs for some reason. 

For this study, my coauthors from the National Park Service and I re-examined historic metoposaurid specimens that were collected from Wyoming and described over a century ago in 1905. Previously, these specimens were first described as two separate species of the genus Anaschisma and were subsequently considered to be undiagnostic, leading them to be mostly ignored. 

       However, after many hours of sticking our faces very close to the fossils, we were able to prove that they in fact belong to a genus (Koskinonodon aka my Twitter handle) that is much better known from the American southwest and often thought to be restricted to only this region. This validates a largely overlooked hypothesis that was first proposed by my academic great-grandfather (the famous American paleontologist Alfred S. Romer) that various metoposaurid populations across North America are not taxonomically distinct, and because Anaschisma pre-dates Koskinonodon, the former now becomes the valid name for arguably the best-known metoposaurid taxon.

We also attempted a phylogenetic analysis of metoposaurids (only the second to date), which produced an extreme lack of resolution that reflects a high degree of morphological conservatism and polymorphism in this clade. This gives us more unresolved questions than answers, but this study already provides cautionary tales about the effects of intraspecific variation on phylogenetic reconstruction in extinct taxa and provides compelling evidence that geographic occurrence is not always a reliable data point for informing alpha taxonomy.

dwn

 

 

Summary from Bryan’s blog: Temno Talk

Read this paper »