Browsing by Subject "Paleopathology"

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Evaluation of Plateosaurus trossingensis from the Upper Triassic (upper Norian) of Central Europe
(2024) Schaeffer, Joep; Schoch, Rainer
Plateosaurus is the fifth described dinosaur species that is still considered valid today. It is one of the best known non-sauropod sauropodomorphs and arguably the best known European dinosaur. Since its naming in 1837, partial and complete skeletons from over 250 individuals have been excavated in Germany, France and Switzerland. The majority of the specimens comes from three major localities along with several smaller sites. The largest of the three main localities is the Obere Mühle in Trossingen in Baden-Württemberg, Southwestern Germany, where over 100 individuals have been excavated. The second significant locality is the Gruhalde quarry in Frick in Aargau, Northern Switzerland, where around 80 individuals have been found. The Last locality, which was discovered the earliest, is the Baerecke-Limpricht clay-pit in Halberstadt in Saxony-Anhalt, Central Germany yielding over 40 specimens. Despite the discovery of numerous specimens over the past 190 years, significant controversy still surrounds the taxonomy of Plateosaurus. Over the past 187 years at least 30 taxa has been named within the genus of Plateosaurus or referred to it at some point. The type specimen of Plateosaurus engelhardti was deemed undiagnostic in 2019, after which it was replaced by a new type, SMNS 13200, using the name Plateosaurus trossingensis. SMNS 13200 was excavated in 1912 by Eberhard Fraas, and described by Friedrich von Huene in 1926. This was the most comprehensive description of a complete, adult specimen of Plateosaurus for 98 years. Chapter 1 of this dissertation offers a detailed redescription of this same specimen, SMNS 13200, the holotype of Plateosaurus trossingensis. I identified a unique combination of characters, making up a revised diagnosis for the species; six premaxillary teeth; nasal length greater than half the length of the skull roof; dorsal end of the lacrimal with a broad, weakly rugose, lateral sheet covering the posterodorsal corner of the antorbital fenestra; anterolateral notch in prefrontal; palatine with a ventrally located, ventral, peg-like process; the cultriform process of the parabasisphenoid is positioned ventrally to the level of the occipital condyle; posteromedially directed median process at the base of the basipterygoid processes; deep median recess on the ventral surface of the basioccipital, directly anterior to the basal tubera; anterior end of the dentary is downturned; sacrum consisting of two fused primordial vertebrae and an unfused caudosacral vertebra; anterior three caudal neural spines have an anteroposterior length greater than 40% of their height; stout metacarpal V with a convex proximal articular surface; laterally compressed, sub-oval, distal ischial expansions. An new phylogenetic analysis places Plateosaurus trossingensis within the Plateosauridae, accompanied by Sellosaurus and Unaysaurus, just outside of Massopoda. This redescription establishes an updated reference point for comparing new and existing specimens, representing a crucial first step toward resolving the taxonomic difficulties within the genusPlateosaurus. During the redescription of SMNS 13200, several pathologies in the chevrons of this specimen were observed. Palaeopathologies have been identified in nearly all groups of fossil vertebrates with dinosaurs being a significant group of which many pathologies have been documented. However, despite the discovery of over 250 specimens, no pathologies has previously been described for Plateosaurus. A more detailed investigation of several collections around the world revealed additional Plateosaurus specimens with pathologies in their chevrons. In Chapter 2, we studied two specimens in detail, SMNS 13200 and SMNS 92196, both exhibiting three consecutive pathological chevrons. In SMNS 13200 there was significant growth of periosteal new bone and SMNS 91296 showed distinct breaks. Using µCT scans, we identified potential causes for the pathologies in these specimens. First of all, in both specimens the pathologies could have been caused by a predator attack where the bite did not pierce the thick muscle covering of the tail, but left considerable damage to the periosteum in SMNS 13200 and broke three chevrons in SMNS 91296. Other possibilities would be tendon avulsions on all three chevrons of SMNS 13200, and ordinary trauma such as a fall or accidental self-trauma for SMNS 91296. From other collections we identified an additional two specimens of Plateosaurus with pathologies in the chevrons. In total 14.8% of the specimens of Plateosaurus with at least 10 preserved chevrons has some form of a pathology in the chevrons of the anterior to mid-section of the tail. This indicates pathologies in the chevrons were relatively common and could often besurvived, as long as there is no severe functional damage inflicted, the chevrons would still be able to perform their primary functions. Over the past 40 years, numerous attempts employing various methods have been made to resolve the taxonomy of Plateosaurus, yet no consensus has been reached. In chapter 3, we utilize three-dimensional geometric morphometrics to analyse 268 bones across 16 skeletal elements attributed to Plateosaurus trossingensis, collected from eight different localities. By examining the constructed morphospaces we can identify which specimens, grouped by locality, share a similar morphospace occupation, and which specimen plot in entirely different areas of the morphospace. Our results show that the specimen from the lower beds of the type locality of Plateosaurus trossingensis do not exhibit any clustering, suggesting that they likely represent a single taxon. In contrast, the specimens from Bebenhausen, Wüstenroth and Stuttgart-Erlenberg plot far away from the main cluster of specimens, indicating substantial morphological differences that may signify their classification under one or more different taxa than Plateosaurus trossingensis. The specimens from Halberstadt, Stuttgart-Degerloch, Trossingen Upper Beds, Frick and the Ruehleia bedheimensis specimens from Römhild present a more ambiguous morphospace occupation. While there are notable morphological differences between these specimens and those from the type locality, an equal number of similarities also exist. Based on these results, a detailed redescription of several specimens currently attributed to Plateosaurus trossingensis is warranted. This reassessment will involve comparing them with the holotype of Plateosaurus trossingensis to determine whether they truly belong to this species or represent a different taxon.