Mbiresaurus and Tuebingosaurus

Things have picked up since late June. In the past couple of weeks, two new "prosauropods" have been published that cover both ends of the prosauropod spectrum. One, Mbiresaurus raathi, represents the early part of sauropodomorph evolution, while the other, Tuebingosaurus maierfritzorum, is close to the transition from clear-cut "prosauropods" to clear-cut "sauropods". Long-time readers will be familiar with the author's inexplicable fondness for prosauropods, so let's invite them in.

Mbiresaurus raachi

First up is Mbiresaurus raathi, from the early Late Triassic of Zimbabwe.

M. raathi was not published in an open-access journal, but I *do* happen to have a photo of an Eoraptor mount, and it's a reasonably similar dinosaur.

Genus and species: Mbiresaurus raathi. "Mbire" is a twofold reference to a Shona empire and the district containing the study area, and "raathi" honors paleontologist Michael Raath, who was one of the people who first reported fossils from the Dande area and in general is noted for his paleontological work in southern Africa (e.g., the naming of Syntarsus, which turned out to be preoccupied but these things happen) (Griffin et al. 2022). The combination gives us something like "Michael Raath's Mibre lizard".

Citation: Griffin, C. T., B. M. Wynd, D. Munyikwa, T. J. Broderick, M. Zondo, S. Tolan, M. C. Langer, S. J. Nesbitt, and H. R. Taruvinga. 2022. Africa's oldest dinosaurs reveal early suppression of dinosaur distribution. Nature 609:313–319. doi:10.1038/s41586-022-05133-x.

Stratigraphy and geography: M. raathi comes from the Carnian Pebbly Arkose Formation, which has also produced a cynodont, rhynchosaur, aetosaur, and herrerasaurid, currently undescribed. The discovery locality is in Dande Communal Land of the Mbire District, Mashonaland Central Province, Zimbabwe (Griffin et al. 2022).

Holotype: NHMZ 2222 (Natural History Museum of Zimbabwe, Bulawayo), a mostly complete, associated, and partially articulated skeleton of an individual mostly but not completely grown. Bits and pieces are missing, including some vertebrae and the more delicate parts of the skull, but there's certainly enough there to get a pretty good picture of its anatomy (Griffin et al. 2022). (In fact, this seemed like the first new dinosaur in a while that wasn't based on just a few bones.)

M. raathi, as you might have guessed from the substitute image of Eoraptor, is a more basal sauropodomorph than your typical Anchisaurus–Plateosaurus-type prosauropod, being a small gracile biped akin to taxa like Saturnalia, Panphagia, Guaibasaurus, and, yes, Eoraptor. These Carnian sauropodomorphs are pretty similar anatomically, which is part of a larger point the authors made: the Pebbly Arkose fauna is comparable to those of similar age in southern Pangaea (Argentina and India). The authors hypothesize that early dinosaurs were delayed from spreading across Pangaea by climatic barriers, most significantly latitude-spanning arid zones (Griffin et al. 2022).

Tuebingosaurus maierfritzorum

Meanwhile, in Germany, Plateosaurus continues to provide fodder for restudy.

Genus and species: Tuebingosaurus maierfritzorum. The genus name refers to Tübingen, with "ue" substituted for "ü". The species name honors Wolfgang Maier, professor of evolutionary zoology and the recipient of the Festchrift containing the description of this taxon, and Uwe Fritz, editor of the journal Vertebrate Zoology (Regalado Fernández and Werneburg 2022). This gives us something like "Wolfgang Maier's and Uwe Fritz's Tübingen lizard".

Citation: Regalado Fernández, O. R., and I. Werneburg. 2022. A new massopodan sauropodomorph from Trossingen Formation (Germany) hidden as 'Plateosaurus' for 100 years in the historical Tübingen collection. Vertebrate Zoology 72:771–822. doi:10.3897/vz.72.e86348.

Stratigraphy and geography: The type and only known specimen comes from the lower dinosaur bone bed of the Obere Mühle outcrop of the Trossingen Formation in Tübingen, Baden-Württemberg, Germany (Regalado Fernández and Werneburg 2022).

Holotype: GPIT-PV-30787 (Geologisch-Pälaontologishes Institut Tübingen, now housed in the Palaeontological Collection of the University of Tübingen), an articulated partial skeleton comprising most of the hindquarters. Specifically, it includes a pelvis with sacrum, five anterior caudal vertebrae with four chevrons, most of the left hind leg except for some toes (metatarsals I–III and the phalanges of I and IV have gone missing over the years), and probably a right fibula. The specimen was formerly known as GPIT IV and also included a partial forelimb, cervical, and mandible, but these specimens were not found articulated with the hindquarters and are excluded from the holotype at this time (Regalado Fernández and Werneburg 2022).

GPIT-PV-30787 restored, with Friedrich von Huene for scale. Figure 5 in Regalado Fernández and Werneburg (2022). CC BY 4.0.

The Obere Mühle outcrop is noted as the source of numerous prosauropod type specimens now generally attributed to Plateosaurus, most notably the type specimen of Plateosaurus trossingensis (type species of Plateosaurus following the 2019 ICZN audit of P. engelhardti). This is not especially surprising from a historical perspective, given the wild extremes of splitting and lumping in sauropodomorph research. Regalado Fernández and Werneburg (2022) include a substantial discussion on the twists and turns of Plateosaurus and Plateosaurus-adjacent specimens and species from Europe. Our particular point of interest, GPIT-PV-30787, was first attributed to Plateosaurus plieningeri, a species that itself started as Gresslyosaurus plieningeri. (If you're interested, the type specimen of the latter largely overlaps GPIT-PV-30787 but is not as complete.) Galton (2001) considered GPIT-PV-30787 to be a large female P. engelhardti. When analyzed by Regalado Fernández and Werneburg (2022), GPIT-PV-30787 turned out to be distinct from the rest of the Plateosaurus complex of specimens. In fact, in their phylogeny, it comes out as a true sauropod (under the definition that everything closer to Saltasaurus than Melanorosaurus is a sauropod). It also tends to be in the vicinity of another ex-Plateosaurus, the Swiss genus Schleitheimia (which, since there is always the temptation to lump basal sauropodomorphs, is intriguing and was addressed by the authors). (As a tag to Mbiresaurus, note also that in their phylogeny Eoraptor and Guaibasaurus are not sauropodomorphs but basal saurischians or basal theropods, respectively.) Aside from illustrating another phase in the transition to sauropods, the report also shows the value of running a thorough spring cleaning of Plateosaurus.

References

Galton, P. M. 2001. Prosauropod dinosaurs from the Upper Triassic of Germany. Pages 25–92 in Colectivo Arqueológico-Paleontológico de Salas, editors. Actas de las I Jornadas Internacionales sobre Paleontología de Dinosaurios y su Entorno. Junta de Castilla y León, Salas de los Infantes, Burgos, Spain.

Griffin, C. T., B. M. Wynd, D. Munyikwa, T. J. Broderick, M. Zondo, S. Tolan, M. C. Langer, S. J. Nesbitt, and H. R. Taruvinga. 2022. Africa's oldest dinosaurs reveal early suppression of dinosaur distribution. Nature 609:313–319. doi:10.1038/s41586-022-05133-x.

Regalado Fernández, O. R., and I. Werneburg. 2022. A new massopodan sauropodomorph from Trossingen Formation (Germany) hidden as 'Plateosaurus' for 100 years in the historical Tübingen collection. Vertebrate Zoology 72:771–822. doi:10.3897/vz.72.e86348.