Plateosaurus: A dinosaur that laid foundations

Image result for plateosaurus
Two Plateosaurus greeting each other, whether its friendly or not is debateable!
Image Credit: Nobu Tamara, http://spinops.blogspot.com/

The Triassic period was a time when the age of dinosaurs was just starting. The Permian/Triassic Extinction event of 250 million years ago (mya) had killed off almost 90% of all life, making it the biggest mass extinction event of all time. In the millions of years after this, the world was recovering. Life that survived this catastrophe expanded to fill in the many niches that had been left behind. This resulted in a weird menagerie of animals, dominated mostly by the reptiles. One group of reptiles known as the dinosaurs (you may have heard of them!) first evolved roughly 240 million years ago, and for the first 30 million years of their existence they competed with other reptile groups (e.g. rauisuchians, dicynodonts and cynodonts to name a few) for the inheritance of the earth. However by the Later Triassic, roughly 210 mya, dinosaurs were starting to gain the upper hand, and with the extinction of competing reptile groups were able to diversify into a variety of different shapes and sizes. This included their first evolutionary exploration into becoming giants. Whilst the true giants of the dinosaur world, the sauropods, had yet to appear on the scene their distant ancestors (and fellow members of the Sauropodomorpha sub-order) were already taking these first steps. These were the prosauropods. This group of dinosaurs were iconic members of the Late Triassic ecosystem and group members included some of the oldest dinosaurs yet discovered. The most famous member of this family would have been a common sight across the European edge of Pangea (a massive landmass consisting of all of the continents put together) 214-204 mya. Its name was Plateosaurus; meaning “flat lizard” (not because it was shaped like a pancake but because its fossils were noted to be much flatter than others discovered).

The first Plateosaurus fossils were discovered in 1834 by German Palaeontologist Johann Friedrich Engelhardt, and one Plateosaurus species (Plateosaurus engelhardti) was even named after him. This means that it was discovered just before Richard Owen coined the term “dinosaur”. However Plateosaurus wasn’t included as one of Richard Owen’s examples of dinosaurs because it was known only from fragmentary remains, which meant that it was poorly understood at the time. However this has changed, with multiple fossils of this animal having since been discovered (mostly in Germany but with some in Greenland and Norway too). One area which has produced multiple Plateosaurus fossils is a site near the village of Trossingen in the Black Forest, Germany. Here multiple Plateosaurus individuals have been unearthed, buried here over a period of time. One theory as to why this is the case is that the area contained thick sticky mud, in which the dinosaurs got stuck, before eventually collapsing and dying from exhaustion as they desperately tried to wiggle free (which is not a way to go!). However the large number of fossils means that Plateosaurus is now one of the best understood dinosaurs, with multiple papers being published about it, something I noticed when researching for this blog! These papers detail its anatomy and lifestyle, from studies of its skull, locomotion, its vertebrae and even its growth. As such Plateosaurus is one of the best known Triassic dinosaurs.

A reconstructed skeleton (known as “Skelett 2”) of Plateosaurus engelhardti in the Institute of Geosciences of the Eberhard-Karls University in Tübingen, Germany. This reconstruction is based on two individuals found at Trossingen.
Image Credit: FunkMonk, https://commons.m.wikimedia.org/wiki/File:Plateosaurus_Skelett_2.jpg

Due to the large concentration of fossils it is thought that Plateosaurus travelled in large herds. These herds would have stripped the landscape of almost any vegetation that they came across, the leaves of ferns and cycads being their favourite meal (though an estimated faster jaw closure speed than later sauropods, and different types of teeth, suggest that they might have eaten meat occasionally). To access this vegetation they would have used their long necks to reach leaves that were too high up for other herbivores. They also had claws to hook around and pull down plants and sharp crushing teeth to rip off leaves before swallowing them whole. Plateosaurus could also reach these heights because they walked around on two legs, with their long tail balancing out their long neck. This is a new discovery; previously it was thought they walked on all fours like their sauropod descendants. This theory is based on two main observations; firstly their front arms couldn’t pronate, meaning that they couldn’t lie their hands flat on the ground to support their weight; and secondly their centre of gravity was located over the hips, meaning that the hind limbs supported all of the weight. Further studies have also revealed another side to Plateosaurus. Deep depressions found in its dorsal vertebrae suggest that it possessed a bird like respiratory system with air sacs. This is surprising, as birds evolved from small, nimble theropod dinosaurs; not large long necked sauropods! One possible explanation is that bird like characteristics evolved much earlier in dinosaurs than previously thought, before they had diversified into their key groups. The other is that this system evolved convergently (i.e. it evolved separately in two different groups). These air sacs would have allowed Plateosaurus to carry around their large bulk more efficiently, and would have enabled them to process enough oxygen to have a more active, almost warm-blooded lifestyle. Plateosaurus is best envisaged as the Elephant of its day, approaching 10 metres long and 4 tons in weight. However not all adults would have reached this size. This is because Plateosaurus is one of only a few dinosaurs that is known to show “developmental plasticity”. In simple terms this is variation in growth between different Plateosaurus individuals, resulting in different adult sizes (in this case an adult range of 5-10 metres long and 0.6-4 tons). This is seen on a smaller scale in humans, with adults ranging from approximately 5”0 to as tall as 6”8. Being relatively large, a fully grown Plateosaurus would have been a tough proposition for most predators. Two exceptions however were the simply named Smok (meaning dragon in Polish), a 6 metre long archosaur reptile related to dinosaurs, and Liliensternus, a 5.2 metre long theropod dinosaur belonging to a family known as the Coelophysidae. Like the pro-sauropods this group were also dinosaurs that were characteristic of the Triassic, and fights between Liliensternus and Plateosaurus would be a subject for a segment in any nature documentary about life in the Triassic.

Plateosaurus has even appeared on the stage! This is from the Walking with Dinosaurs live show
Image Credit: Dark Dwarf, https://www.flickr.com/photos/darkdwarf/42887589745

Plateosaurus is undoubtedly one of the most famous dinosaurs of their earliest days. Its large size, plentiful fossils and connection to the later sauropods makes it a talisman among dinosaur enthusiasts. I think Walking with Dinosaurs summed up Plateosaurus the best, stating “This is the shape of things to come”.

EDIT: Based on studies of related pro-sauropods such as Massospondylus and Mussaurus (e.g. Otero et. al. 2019) it is thought that while Plateosaurus was a biped when fully grown, they were actually quadrupeds when they were juveniles. This theory is based on evidence such as observed changes in the centre of mass from the mid-thorax (in juveniles) to the pelvis (in adults), and in changes in body mass over time (e.g. Mussaurus grew from 60g when hatched, to 7kg at 1 years old, to over 1000kg when adults).

References/Extra Reading

Hofmann & Sander 2014 paper on the study of juvenile Plateosaurus fossils and developmental plasticity in Plateosaurus

Hofmann, Rebecca, and P Martin Sander. “The first juvenile specimens of Plateosaurus engelhardti from Frick, Switzerland: isolated neural arches and their implications for developmental plasticity in a basal sauropodomorph.” PeerJ vol. 2 e458. 3 Jul. 2014, doi:10.7717/peerj.458

Gunga et al 2007 paper estimating body mass and volume in Plateosaurus

Gunga, H., Suthau, T., Bellmann, A. et al. Body mass estimations for Plateosaurus engelhardti using laser scanning and 3D reconstruction methods. Naturwissenschaften 94, 623–630 (2007). https://doi.org/10.1007/s00114-007-0234-2

Mallison 2010 paper accessing range of motion of Plateosaurus legs and vertebrae, proving, among other results, that Plateosaurus walked on two legs only

Mallison, H. (2010). “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(3): 433-458, 426.

Button, Barrett & Rayfield 2016 paper comparing the jaws of Plateosaurus with the Late Jurassic sauropod Camarasaurus

Button, D, Barrett, P, Rayfield, E. Comparative cranial myology and biomechanics of Plateosaurus and Camarasaurus and evolution of the sauropod feeding apparatus. Palaeontology, Vol 59, Iss 6, 887-913 (2016), https://doi.org/10.1111/pala.12266

Otero 2019 paper on the grow changes in Mussaurus, a close relative, that show a shift in locomotion from a quadruped to a biped

Otero, A., Cuff, A.R., Allen, V. et al. Ontogenetic changes in the body plan of the sauropodomorph dinosaur Mussaurus patagonicus reveal shifts of locomotor stance during growth. Sci Rep 9, 7614 (2019). https://doi.org/10.1038/s41598-019-44037-1

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