After a long time of inactivity, here’s what I’ve been up to.
My first ever full-body skeletal shows a (currently) unpublished juvenile specimen of Plateosaurus engelhardti
from Frick, Switzerland, MSF 15.8. "Fabian", whose postcranium I have been describing for my bachelor’s thesis. At approximately 2.3m total length, and an estimated 40kg in body mass, this is the smallest Plateosaurus
individual currently known (and by a wide margin, the next-smallest individuals approaching 5m). The suspicious lack of juvenile material of this taxon has been attributed to a taphonomic filter (miring in soft mud) in the most important localities for this taxon (Frick, Trossingen and Halberstadt), which favoured the preservation of large individuals (Sander 1992).Plateosaurus
is also very interesting for its seemingly random growth pattern (developmental plasticity sensu Sander & Klein 2005), which results in a poor correlation between age and body size. "Fabian" is the first instance of an early-stage juvenile being discovered, as supported by its unfused sutures, small size and histology (the latter currently under study by one of my colleagues). Conspicuously, its morphology is fairly similar to adults, especially in the vertebral collumn, despite the massive size and age difference. This is paralleled by the only previously described juveniles, a number of isolated neural arches from Frick (Hofmann & Sander 2014), which are also anatomically identical to those of adults, with the difference being that those remains are also similar in size to adult specimens.
There are some differences in the body proportions, notably the neck is proportionately longer. Furthermore, the forelimbs appear to be proportionately shorter than in adults, except for the manus, which is disproportionately large. However, this is complicated by the strong grade of compaction experienced by some of the bones. Just as in adults (Reiss & Mallison 2014) the limb morphology and ratios of antebrachial and manual shaft cross-sections do not support a quadrupedal mode of locomotion, which contrasts with the embryos and early-stage juveniles of Massospondylus
(Reisz et al. 2005) and Mussaurus
(Bonaparte & Vince 1979).
The skeleton was reconstructed on the basis of a partial skeleton encompassing large parts of the presacral and some parts of the sacral and caudal vertebral collumn, a large number of ribs and an almost complete appendicular skeleton, with the missing portions filled in by material of SMNS 13200 (von Huene 1926) and GPIT 1 (Mallison 2010ab).
This is a work in progress, any suggestions and feedback are welcome!
Bonaparte, J. F., and Vince, Martin. 1979: El hallazgo del primer nido de dinosaurios triasicos,(Saurischia, Prosauropoda), Triásico superior de Patagonia, Argentina. Ameghiniana 16:173–182.
Hofmann, R., and P. M. Sander. 2014: The first juvenile specimens of Plateosaurus engelhardti from Frick, Switzerland: isolated neural arches and their implications for developmental plasticity in a basal sauropodomorph. PeerJ 2:e458.
von Huene, F. R. F. 1926: Vollständige Osteologie eines Plateosauriden aus dem schwäbischen Keuper. Geologische und Paläontologische Abhandlungen 15:1–43.
Mallison, H. 2010a: The digital Plateosaurus I: body mass, mass distribution, and posture assessed using CAD and CAE on a digitally mounted complete skeleton. Palaeontologia Electronica 13.
———. 2010b: The digital Plateosaurus II: an assessment of the range of motion of the limbs and vertebral column and of previous reconstructions using a digital skeletal mount. Acta Palaeontologica Polonica 55:433–458.
Reiss, S., and H. Mallison. 2014: Motion range of the manus of Plateosaurus engelhardti von Meyer, 1837. Palaeontologia Electronica 17:1–19.
Reisz, R. R., T. D. Huang, E. M. Roberts, S. Peng, C. Sullivan, K. Stein, A. R. LeBlanc, D. Shieh, R. Chang, and C. Chiang. 2013: Embryology of Early Jurassic dinosaur from China with evidence of preserved organic remains. Nature 496:210.
Sander, P. M. 1992: The Norian Plateosaurus bonebeds of central Europe and their taphonomy. Palaeogeography, Palaeoclimatology, Palaeoecology 93:255–299.
Sander, P. M., and N. Klein. 2005: Developmental plasticity in the life history of a prosauropod dinosaur. Science 310:1800–1802.