Skull Study of Europasaurus Fossils Throws Up Jurassic Puzzle

A study of the skulls of a Late Jurassic dwarf Sauropod whose fossils have been found in Germany, has thrown up some intriguing questions about how Sauropods came to be small.  Sauropods were herbivorous, saurischian (lizard-hipped), dinosaurs with small heads, long necks, massive bodies and long tails.  As a group, they evolved sometime in the Late Triassic and survived until the very end of the Age of Reptiles.  Typical well known Sauropods are the likes of Diplodocus, Apatosaurus and Brachiosaurus, some genera of the Sauropoda represent the largest land living animals known to science.

However, with the Sauropoda, big is not always beautiful.  This new research, published in the “Journal of Systematic Palaeontology”, focuses on a dwarf, a dinosaur named Europasaurus (E. holgeri), which although related to the likes of Brachiosaurus was substantially smaller.  The study suggests there were actually two dwarf forms of Europasaurus.

An Illustration of the Late Jurassic Sauropod Europasaurus

Dwarf dinosaur from Germany.

Dwarf dinosaur from Germany.

Picture Credit: Everything Dinosaur

In 1998, the fossilised remains of a group of Sauropods was discovered in a limestone quarry in Lower Saxony (Germany).  At first, these fossils, thought at the time to represent at least eleven individuals, were considered to be a group of baby dinosaurs.  However, later studies proved that the largest of the dinosaurs found were adults and fully grown.  The fossils represented dinosaurs that ranged in size from Shetland pony size up to around six metres in length.  Europasaurus was classified as a dwarf member of the Brachiosauridae family, closely related to enormous dinosaurs such as Lusotitan from Portugal, but much smaller in stature, with even the very biggest specimens weighing no more than a tonne.

Recently, Bullyland of Germany produced a scale model of this remarkable dinosaur, to see Everything Dinosaur’s video review of the model: Europasaurus Model Review

How did these relatively small dinosaurs evolve?  The most widely accepted theory, one that is backed up with observations amongst living vertebrates today, goes like this.  Once upon a time, back in the Kimmeridgian faunal stage of the Late Jurassic (around 154 million years ago), much of Europe was underwater.  There was an archipelago of small islands off the coast, this land had been part of the mainland but rising sea levels had isolated it and left a string of islands as the only landmasses surrounded by a warm, tropical sea.  Dinosaurs cut off from the mainland adapted to their new island homes by becoming dwarf forms of their mainland cousins.  These islands had limited food resources and so the Sauropod population slowly evolved into miniaturised forms.

To view the range of Bullyland prehistoric animal models: Bullyland Prehistoric Animal Models

Skull fossils of Sauropods are exceptionally rare in the fossil record.  Those small heads tend to fall off the long necks when the animal dies and the body begins to rot.  Very few skull fossils of Sauropods are known, so the bone bed of Europasaurus fossils with perhaps as many as fourteen skulls of various sizes to study would be an ideal place to start when looking into how the heads of dinosaurs changed shape as they grew and matured.  This is exactly what a the team of scientists based in the University of Bonn set out to do in collaboration with colleagues from Argentina.

A Drawing of the Skull of an Adult Europasaurus

Looking at how skull shape of Sauropods change as they grew.

Looking at how skull shape of Sauropods change as they grew.

Picture Credit: Jean Sebastian Marpmann et al

The diagram above shows the skull of an adult Europasaurus drawn in (A) lateral view, (B) viewed from the back and (C) in dorsal view, that is, seen from above.  The research team identified that the skull morphology (shape) was most unusual.  It seems that fully grown adults retained skull characteristics of juveniles.  They had proportionately larger eye sockets and some parts of the skull bones were not fully fused.  Intriguingly, this analysis confirmed the findings of an earlier study that looked at the collection of vertebrae (back bones) found in the quarry.  The vertebrae study suggested that the Europasaurus fossils could be split into two, distinct groups – a small dwarf and a larger dwarf.  The larger dwarves were up to 35% bigger than the smaller forms.

One of the authors of the scientific paper, Professor Martin Sander at the Steinmann-Institute of Geology, Mineralogy and Palaeontology (University of Bonn), explained how the skull study was conducted:

“Bone microstructure tells us that the largest of the two kinds of Europasaurus was fully grown.  To find this out, we had to grind samples of Europasaurus bones into thin slices, about one-twentieth of a millimetre in thickness.”

Such small, thin samples allow researchers to examine the bones’ microstructure as the bone becomes translucent and can be studied under a microscope.  Given the number of skulls fossils available to study, the team were able to plot changes in skull shape as the animal grew and developed.  In total 123 skull bones were examined.

However, the mystery of why there are two sorts of dwarf dinosaur remains.

A number of theories have been proposed and team members at Everything Dinosaur have summarised them below, what do you think?

  • We have two types of Europasaurus preserved in the quarry because one set of fossils represent males, whilst the other group are females.
  • We have two types of Europasaurus preserved in the quarry because the fossils, all of which were washed out to sea, represent two distinct populations from nearby islands whose remains got caught in the same currents and deposited in the same location.
  • We have two types of Europasaurus because the quarry has preserved two different populations, they both died in flood events and were washed out to sea but these events were separated by thousands of years.
  • The bones in the quarry represent a range of individuals of different ages from youngsters to fully grown adults, with the medium sized dinosaurs (the teenagers and young adults) not present.  Perhaps immature and young ,adult Europasaurus lived outside the herd in their own groups, as seen with young African elephant males today.  Young male, African elephants tend to form their own herds away from the larger female dominated herd.
  • Perhaps the bone bed represents two distinct species of Europasaurus (E. holgeri major and E. holgeri minor)?

There could be other explanations of course, but this is a case of one palaeontology study raising more questions than it answers.  The research team included Professor Martin Sander, the scientist who perhaps more than anyone knows most about this strange enigmatic German dinosaur.  For it was Martin, who as a young researcher at the University of Bonn, who first recognised that the limestone quarry Sauropod fossils were not babies but represented a dwarf form and indeed, it was Martin and his colleagues who were responsible for formally naming and describing this genus back in 2006.

Two Dwarf Forms of Europasaurus

Two types of Europasaurus?

Two types of Europasaurus?

Picture Credit: Everything Dinosaur

This new research has contributed significantly to our understanding of how Europasaurus grew and developed.  In addition, it is part of a bigger research project that sets out to explore how dwarfism can occur in the Dinosauria.  It is likely that the fossils of Europasaurus will be involved in many more studies and the researchers are hopeful that further Sauropod remains will be found in the quarry and nearby sites in the future.

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