What A Bone Can Tell

Due to their excellent preservation, the plateosaur finds from Frick, Switzerland have provided some interesting insight in the evolutionary biology of dinosaurs.

Until some twenty or thirty years ago, there was a general consensus that dinosaurs, a group descended from reptiles, were cold blooded just as present day reptiles are. This view changed drastically in the last couple of decades and it was stipulated that at least the farthest evolved dinosaurs could have been warm blooded.

> Were plateosaurs cold blooded? Copyright painting by Raúl Martín.

In the last ten years or so, the osteology (bone structure) of many dinosaurs has therefore been studied in order to find out more about the physiology of dinosaurs (dinosaur bones preserved well enough to display microscopic structures are still rather rare). The microscopic bone structure of cold blooded and warm blooded animals differs in that cold blooded animals have a lamellar bone structure mirroring the seasonally different growing rates due to changing ambient temperatures. Warm blooded animals on the other hand have a more uniform bone structure, mirroring steady growth rates throughout the year.

It turned out that dinosaurs have a bone structure that ressembles the one of present warm blooded animals such as birds or mammals rather than that of cold blooded reptiles. The interesting point is that judging from their bone structure, apparently even some of the oldest dinosaurs already displayed a warm blooded physiology.

In the last years, the new paradigm therefore was that dinosaurs probably descended from reptiles which (like the predescessors of mammals) had already evolved a warm blooded physiology.

A study by Dr. Martin Sander on the bone structure of the plateosaurs from Frick which was published in the december 2005 issue of “Science“ for the first time revealed apparently cold blooded bone structures in dinosaurs.

> Microscopic cross section through a plateosaur bone. Copyright photo: Dr. M. Sander.

So the Frick plateosaurs could proove that a warm blooded physiology was actually developed independently several times in evolution; in mammal-like reptiles and mammals but also in different groups of early dinosaurs. It seems that some of the earliest dinosaurs such as plateosaurus were rather cold blooded after all.

On a related note it is interesting that the importance of these bones was only discovered recently. When the bone structure of the Frick plateosaurs was first fotographed some ten years ago (at the time I also took some photos from the bones I found at “my“ site), it was not surprising to see an apparently cold blooded structure in these ancient dinosaurs. At the time the bone structures of dinosaurs was largely unknown and many questions on bone structures had yet to be answered in present animals. So then, we were rather disappointed in what we saw. Only after some ten years of studying bone structures and discovering that any other preserved dinosaur bones (including triassic forms) looked warm blooded did we actually understand that our original find was interesting after all...

2006 Theropod Find In Frick, Switzerland

In 2006, for the first time in Frick, Switzerland, the remains of a small theropod were unearthed. Apart from the missing hind legs and skull, the find is relatively complete and well preserved. The find was excavated and prepared by Dr. Ben Papst. The complete specimen would measure approximately 2.5 metres (8 feet).

> Reconstruction of a Liliensternus liliensterni, one of the members of the coelophysoid theropods.

The 2006 specimen is currently in the Paleontological Institute and Museum of the University of Zurich for further investigation. The scientific determination is pending. It surely belongs into the group of coelophysoid theropods; thus it could be a Coelophysis, a Liliensternus, an other known species or even a new species from that group. The specimen is later to be on display in the Frick Dinosaur Museum.

> Fotos from the 2006 coelophysoid find. Note the small 4th finger of the specimen. You can also watch the fotos as slideshow here.

This find is relatively important since it is one of only 4 or 5 finds of it's kind in Europe and the only one from Switzerland. One important feature of the 2006 find is that it has three fully formed fingers and one smaller one. It could thus mark a missing link in the evolution of theropods who reduced their fingers from 5 to 3 early in their lineage.

Learn more about the Frick, Switzerland site here

History Of The Frick, Switzerland Site

In the town of Frick, which is situated in the Jura Mountains of northwestern Switzerland, a clay pit has been exploited for the production of brick since the early 1900s. The sediments the factory exploits are from the Late Triassic and Early Jurassic, and span about 27 million years, from 217-190 million years (get stratigraphic timetable here). In 1961, the factory lab chief found what later turned out to be the first dinosaur bones.

> Zoomable satellite map of the Frick clay pit. View Larger Map

The bones were from strata deposited in the Norian Stage of the Late Triassic, about 205 to 210 million years ago. More bones turned up in the following years and in 1976 and 1977, first excavations began. It became obvious that the excavated dinosaur bones belonged to Plateosaurus engelhardti, a prosauropod of about 6-10 metres (18-30 feet).

> Plateosaurs. Copyright painting by Raúl Martín.

In 1979 and 1984/1985, more excavations were organized. The latter excavation yielded an almost complete skeleton which is now on display in it's finding position in the Frick Dinosaur Museum (website in German only).

> Almost complete Plateosaur specimen unearthed in 1985 on display in the Frick Dinosaur Museum. See more photos from the Frick Dinosaur Museum in this post.

Further excavations took place in 1988, 1995, 2006 and 2007. The different successive excavations yielded about a dozen more or less (in)complete plateosaur skeletons, as well as a number of theropod theeth.

> Foto from the 2007 dig. See more photos from this dig here.

The 2006 dig for the first time revealed a theropod find which is currently studied at the University of Zurich (read more about the 2006 theropod find here). The skeleton is a small, yet to be determined coelophysoid (Coelophysis, Liliensternus,...?).

> The 2006 coelophysoid theropod remains. Copyright photo: Dr. Ben Pabst.

Associated finds include small scattered remains such as lung fish teeth, crocodile dermal denticles, as well as remians from fish and even freshwater sharks. The sedimentologic and taphonomic study revealed that the region was once a broad, arid coastal mud flat which was episodically affected by mud flows from flash floods in nearby wadis (see late triassic paleogeography in this post). The excavated Plateosaurs most certainly got stuck in mud traps.

> Plateosaurs stuck in a mud trap. Copyright painting by Raúl Martín.

This is evidenced by the fact that most Plateosaur finds are embedded in the same position; lying on their belly, with their spread out hind legs below the body. Also, many finds only consist of the lower half of the body. Aparently, small predators were eating away the upper body of many of the trapped Plateosaurs. Accordingly, many shattered bones from the upper bodies as well as predator theet have been found all around.

> Note the height differences in the 1985 specimen's body parts, pointing to a deposition in a mud trap.

Considered all the finds, Frick is one of the most important Plateosaur finding sites in the world and (unlike the German Trossingen) the only major European site that currently delivers fossils.

> Section of the Frick clay pit by Dr. H. Furrer. Measurments are in metres, time is indicated in million years.

Other interesting findings include the fact that the bones have been preserved in the form of the iron phosphate mineral vivianite. Vivianite has also been found in many archeologic sites where bodies have been deposited in dysoxic conditions and it is known to form within few years. The preservation of the bones is indeed exceptional and even microscopic bone structures have been preserved. The bones have also been found to be enriched in rare earth elements.