Thursday, September 8, 2022

[Paleontology • 2022] Tuebingosaurus maierfritzorum • A New Massopodan Sauropodomorph from Trossingen Formation (Germany) hidden as ‘Plateosaurus’ for 100 years in the Historical Tübingen Collection

 Tuebingosaurus maierfritzorum
Omar Rafael Regalado Fernández and Ingmar Werneburg. 2022

A literature review showed that there is not a defined consensus on what specimens belong to Plateosaurus in current phylogenetic analyses, and after the assignation of SMNS 13200 as the neotype for Plateosaurus, the specimen composition of Plateosaurus as an operational taxonomic unit (OTU) needs to be addressed in further iterations of phylogenetic analyses. At least one of the specimens used to illustrate plateosaurian anatomy contains several characters identified in more derived sauropodomorphs commonly referred to as massopodans. This partial skeleton, traditionally known as specimen ‘GPIT IV’, was found in the lower dinosaur bone bed of the Obere Mühle, a Trossingen Formation outcrop, during an excavation in 1922 near the city of Tübingen, Germany. The holotype of Plateosaurus trossingensis and several other specimens referred to as this species were found in this level, which was initially interpreted as a synchronic deposit of animals. However, the current understanding of the Trossingen Formation indicates that this bed was probably a constant accumulation of carcasses through miring and transport down a river for hundreds of years. In this work, a framework to compare phylogenetic signals with morphological and histological data is provided to help in the species delineation of Plateosaurus, and support is found to refer the historic specimen ‘GPIT IV’ as a new genus and a new species.

Keywords: Comparative anatomy, Late Triassic, Massopoda, phylogenetics, Sauropodomorpha

Summary of the taxonomic history of Late Triassic sauropodomorphs.

Reconstruction of Tuebingosaurus maierfritzorum gen. et sp. nov. as a quadruped dinosaur, using the outline of Riojasaurus as a base ‒ next to the silhouette of Friedrich von Huene. The drawing of the bones is based on and modified from the original illustrations of specimen “GPIT IV” in von Huene (1932, pl. 38) that have been replicated in the literature. The right fibula is marked in grey as it was found nearby with similar measurements to the left fibula and has been assumed to be part of the same individual.
 Systematic palaeontology
 Dinosauria Owen, 1842
Sauropodomorpha von Huene, 1932
Massopoda Yates, 2007

Tuebingosaurus gen. nov.

Etymology: The genus name refers to the city of Tübingen, Germany. The holotype described here has been housed in the university's palaeontological collection since 1922, when it was discovered during an excavation of the nearby Trossingen Formation.

Tuebingosaurus maierfritzorum sp. nov.

Etymology: The species name refers to Uwe Fritz and Wolfgang Maier. The former is the editor-in-chief of the journal Vertebrate Zoology, and, in his journal, he facilitated the Festschrift edited by Ingmar Werneburg and Irina Ruf in honour of Wolfgang Maier. The latter was a professor of evolutionary zoology in Tübingen from 1987 to 2007, and the Festschrift was published on the occasion of his 80th birthday in 2022.

Holotype: GPIT-PV-30787, specimen historically referred to as ‘GPIT IV’, comprising a complete pelvis (three sacral vertebrae, two ilia, two pubes, two ischia), five anterior caudal vertebrae, four chevrons, left femur, left tibia, left and right fibulae, left astragalus, left calcaneum, metatarsal I, pedal fingers 3 and 4 (Fig. 5).

Diagnosis: Sauropodomorph with a unique combination of features: a fused pair of primordial sacrals; a robust and rugose expansion in the postacetabular process of the ilium; a pentagonal outline in the distal surface of the tibia, characterised by an additional posterior projection; a deep lateroventral fossa on the anterior margin of the astragalus; a ventrally directed heel with a lateral projection on the lateral articulation of the astragalus supporting the reduced calcaneum.

Reconstruction of the last moments in the life of Tuebingosaurus maierfritzorum (collection number of the painting: GPIT-PV-41827). The cortical bone on the left side of the fossil is fractured into flakes, which can be explained if the carcass was exposed over a long time on the mud, two to four years, before being buried – in the reconstruction, the animal will fall to its right body side. The reconstruction shows the animal sinking in a mud trap, attacked by a rauisuchian, Teratosaurus Meyer, 1861, which has also been found in the Trossingen Formation in Baden-Württemberg (Brusatte et al. 2009). In the background, a herd of Plateosaurus trossingensis runs away from the scene. The flora in the swamp is reconstructed based on fossils from the Germanic basin, with shoots of horsetails and ferns covering the swamp and a forest comprising cycads (Taeniopteris Brongniart, 1828), lycophytes (Lepacyclotes Emmons, 1856) and coniferous plants (Brachyphyllum Brongniart, 1828) (Kustatscher et al., 2018).

Based on our phylogenetic analysis, the new species Tuebingosaurus maierfritzorum is positioned as the earliest massopodan discovered in the Trossingen beds (Fig. 19). It displays some characters traditionally considered plateosaurian, like the heel-like projection in the posterior part of the ischiadic peduncle of the ilium and a straight lateral margin in metatarsal II. The fact that it has been illustrated since the early 20th century as part of Plateosaurus may suggest that some noise has been introduced into the phylogenetic analyses of the past decade by assuming all the medium to large-sized sauropodomorphs from Germany belonged to the same species. It is also clear that there is no consensus, in phylogenetic terms, on plateosaurian features and massopodan features since, through the literature, two incompatible overall topologies have been produced. Through comparative anatomy and the evidence from our phylogenetic analysis, Tuebingosaurus displays several derived features consistent with the position among massopodans and hints to an early diversification of Sauropodomorpha as they occupied the vacant niches in Pangaea left by rhynchosaurs and aetosaurs (Barrett et al. 2010). A rapid disparification event could explain the contradictory phylogenetic signals discussed in the literature. Many cranial characters that support one group could be a product of convergence as the animals adopted similar feeding strategies in different parts of Pangaea.

Furthermore, a thorough revision needs to be done to the material referred to as P. trossingensis or Plateosaurus that was not obtained from the Obere Mühle outcrop, and the hypothesis that these are different species needs to be tested with morphometric, specimen-level phylogenetic, and stratigraphic analyses. Nevertheless, restricting P. trossingensis to SMNS 13200, GPIT-PV-30784, AMNH FARB 6810, and all Seemann’s material stored in Stuttgart should remove any noise that may have been added by using the literature in which all specimens were considered Plateosaurus. SMNS 13200, GPIT-PV-30784, AMNH FARB 6810, and all Seemann’s material specimens come from the lower dinosaur bone bed in Obere Mühle and are likely to represent different individuals that died at different times, but that can be referred to as part of the same chronospecies.

Omar Rafael Regalado Fernández and Ingmar Werneburg. 2022. A New Massopodan Sauropodomorph from Trossingen Formation (Germany) hidden as ‘Plateosaurus’ for 100 years in the Historical Tübingen Collection. [Festschrift in Honour of Professor Dr. Wolfgang Maier; Edited by Ingmar Werneburg & Irina Ruf] Vertebrate Zoology. 72: 771-822. DOI: 10.3897/vz.72.e86348