Raptorex – A Tiny Dinosaur with a Big Future (Upsets the Tyrannosaur Applecart)

A largely accepted theory concerning the peculiar body shape of tyrannosaurs with their massive skulls, immense jaws yet puny arms is that something had to give at the front of the animal to counterbalance the weight of that near six-foot-long skull.  So heavy was the head of a T. rex that gradually the arms got smaller and smaller as natural selection solved the problem of the need to lighten the rest of the front end of the animal to compensate for that increasingly massive, heavy head with its huge jaws.

However, the discovery of a 3-metre-long ancient ancestor of T. rex with the same body proportions has upset the scientist’s applecart.  If tyrannosauroids gradually evolved smaller arms to counterbalance the weight of the increasingly massive skulls, then how come a 1 metre tall, 1/100th scale replica of Tyrannosaurus rex has the same tiny arms and body proportions as its descendant the fearsome T. rex?

The evolution of the tyrannosaur family is unclear, the fossil record being so poor, but the announcement of the discovery of Raptorex kriegsteini in the magazine “Science” and the papers written about this near complete fossilised skeleton shed new light on the origins of T. rex.

Raptorex

Raptorex has the same big jaws, “D-shaped” teeth, and powerful legs but weighed no more than about 10 stone (65kgs), compared to the 6,500kgs of an adult Tyrannosaurus rex.  This Early Cretaceous specimen, believed to have been excavated in north-eastern China has been dated to approximately 125 million years ago (Barremian faunal stage).  The fossil indicates that the tyrannosaur body type and proportions changed little over millions of years except in overall size.

An Illustration of a Typical Large Tyrannosaurus

Picture credit: Everything Dinosaur

Tyrannosaurs

Over the last decade or so, a number of early tyrannosaur fossils have come to light.  Most palaeontologists now believe that the later, larger tyrannosaurids migrated from northern Asia to the Americas in the Late Cretaceous at some time when land bridges existed between these two landmasses.  Where tyrannosaurs originate from remains a mystery, with early tyrannosaur remains being found in places as far apart as China and the Isle of Wight.

Earlier discoveries such as the Isle of Wight Eotyrannus show that primitive tyrannosaurs were relatively small-bodied, fast running, long-armed dinosaurs.  In fact Eotyrannus has one of the largest hands of any bipedal dinosaur in relation to the size of the rest of its body.  These previous discoveries seemed to indicate that the big tyrannosaurs were descended from small-bodied, long-armed ancestors.

However, Raptorex kriegsteini looks identical to a big T. rex except that it is the best part of 100 times smaller.  The research team led by the American, Professor Paul Sereno of the University of Chicago have studied the skull of this new meat-eating dinosaur and determined that the shape of the skull with its enlarged olfactory bulbs and big eyes indicate that Raptorex has an acute sense of smell and superb eyesight just like its giant descendant.

A Drawing of Eotyrannus lengi

Eotyrannus illustrated.

Picture credit: Everything Dinosaur

Commentating on the new discovery, lead researcher Dr Paul Sereno, from the University of Chicago, stated:

 “It’s as close to the proverbial missing link on a lineage as we might ever get for T. rex.”

He went onto add:

“From the teeth to the enlarged jaw muscles, the enlarged head, the small forelimbs, the lanky, running, long hind-limbs with the compressed foot for hunting prey: we see this all, to our great surprise, in an animal that is basically the body weight of a human or 1/90th the size that ultimately this lineage would reach in T. rex at the end of the Cretaceous”.

A New Dinosaur Discovery

The researchers believe that this new dinosaur discovery overturns accepted opinion on the evolution of tyrannosaurs.  Until now it had been thought that their strange body shape evolved as a consequence of their large size.   The fossil record bears out the previous theory that as tyrannosaurs developed truly giant size over time, they needed to modify their entire skeletons so they could continue to function as a predators as they grew.

Co-author Stephen Brusatte of the American Museum of Natural History (New York) is confident that Raptorex is going to overturn the evolutionary applecart when it comes to understanding the evolution of Tyrannosauroidae.

He stated:

“Here we have an animal that’s 1/90th or 1/100th of the size of T. rex, about my size, but with all the signature features – the big head, the strong muscles, the tiny little arms – that were thought to be necessary adaptations for a large body predator.  So really we can say that these features did not evolve as a consequence of large body size but rather that they evolved as an efficient set of predatory weapons in an animal that was just 1/100th of the size of T. rex and that lived 60 million years before T. rex”.

Photographs show Dr. Paul Sereno adding the final pedal ungual to the reconstructed skeleton of R. kriegsteini.  The pedal ungual is the hoof or claw bearing bone at the end of each toe.

The known fossil record indicates that tyrannosaurs only grew to huge sizes during the last twenty million years or so of the Cretaceous.

Dr Brusatte stated:

“So that means that for most of their evolutionary history, about 80% of the time that they were on Earth, tyrannosaurs were small animals that lived in the shadow of other types of very large dinosaur predators.  In short, much of what we thought we knew about tyrannosaur evolution turns out to be either simplistic or out-and-out wrong”.

It is fascinating to speculate how the tyrannosaurs were able to become the apex predators in so many environments, gradually usurping other large theropods.  The fossilised bones of Raptorex are believed to be from a young adult, perhaps no more than six or seven years old when it died.  Although the fossils are associated with sandstone sediments laid down in a watercourse (lake bed), perhaps this early tyrannosaur hunted smaller dinosaurs, lizards and birds in wooded areas whilst trying to avoid the larger allosaur type predators such as the Sinraptoridae.

The researchers say that fragments of sand and sediment on the skeleton indicate that it came from an area of north-eastern China rich in fossils.  It was dug up illicitly and spirited out of the country and ultimately sold.

The species name is named after Henry Kriegstein, a private collector, who bought it from a dealer.  He contacted Dr Sereno in 2006 and asked him to analyse the specimen, and agreed to give it back to science.  Mr Henry Kriegstein, has helped write the research paper and has generously agreed to return the fossil to China.

Update

Debate continues as to whether this is a new genus of primitive tyrannosaur from approximately 125 million years ago, or indeed a representative of a juvenile Tarbosaurus bataar dating from approximately 70 million years ago.  The problem with this specimen is that there is not a lot of information concerning the location or indeed the geological formation from which the fossil was extracted.  In June 2011, in the peer reviewed publication PLoS One, a team of scientists after reviewing the fossil evidence suggested that this was a specimen of a very young Tarbosaurus, perhaps only 36 months old.

If the fossil is proved to be from the Early Cretaceous Yixian Formation then this specimen would date from 125 million years ago and challenge the accepted view on tyrannosaur morphology.  However, if after pollen analysis and other such tests to establish biostratigraphical relationships between this fossil matrix and other sediments then this fossil could represent a much more recent tyrannosaur, such as a juvenile Tarbosaurus.

Everything Dinosaur stocks a large range of model tyrannosaurs including the Papo model range.  To view Papo prehistoric animal models: Papo Dinosaur Models.

The Discovery of a New Spiky Tailed Primitive Sauropod Announced

The discovery of a new type of sauropod dinosaur armed with spikes on its tail like a Stegosaurus has been announced after research by a joint German and Spanish team.  The fossils of this particular dinosaur were found in Niger (Africa). The dinosaur is to be named Spinophosaurus nigeris (the name means spiny lizard from Niger).  Niger has proved a successful hunting ground for dinosaur discoveries in recent years, famous palaeontologists such as the American Paul Sereno, from the University of Chicago, have led several expeditions to the country and recovered some amazing fossils of new types of dinosaur.

Spinophosaurus nigeris

Perhaps the most famous long-necked dinosaur associated with this particular African country is Nigersaurus, nick-named the Mesozoic vacuum cleaner because of the broad shape of this dinosaur’s muzzle.  Spinophosaurus dates from much earlier in the fossil record when compared to Nigersaurus.  It is a much more primitive sauropod, perhaps it is a type of cetiosaur rather than the diplodocid type of sauropod that Nigersaurus is believed to be.  Fossils of Nigersaurus have been dated to the Early Cretaceous, around 110 million years ago, whilst the strata from which the fossils of Spinophosaurus were extracted are much older.  Scientists estimate that this dinosaur dates from the Early to Middle Jurassic 170 million years ago (Bajocian faunal stage).

A Model of a Nigersaurus

The “Lawn Mower” sauropod.  A model of Nigersaurus.

During the time of Spinophosaurus, this part of Africa was a vast river delta system in what was the huge, super-continent of Gondwanaland.  Commenting on the discovery of this new dinosaur, and in reference to the primitive skeletal features and strange, spines on the tail, which looked out of place on a sauropod, Professor Ulrich Joger of the State Natural History Museum in Braunschweig (Brunswick) stated:

“At the time we thought we had found another dinosaur of the Jobaria variety”.

Jobaria

Jobaria is another type of long-necked sauropod, a titanosaur that was discovered in Tanzania by a much earlier German expedition.   However, it was formerly named and described by Paul Sereno after much more fossil material was discovered in the Sahara desert in the mid 1990s.  Despite dating from the Cretaceous, roughly the same time period as Nigersaurus, Jobaria retained many features of early, primitive members of the sauropod clade.

It was a detailed study of the leg bones that led the German team to conclude that they had discovered a previously unknown type of dinosaur.  Jobaria is distinguished by having lighter forelimbs compared to its back legs, but this new dinosaur’s leg bones were very different indicating that this was indeed a new species.

Sauropod

The most remarkable feature of this mid-sized sauropod is the tail with its spikes sticking out at the end.  Such a tail would have made a very formidable weapon, although such defences on sauropods are known to science, this is still a very remarkable discovery.  The spikes on the tail resemble those on a stegosaur.  Palaeontologists refer to the spiked tails of stegosaurs as “Thagomizers”.  This is not a scientific name but the moniker has stuck after a Stegosaurus tail was described using this word in a Gary Larson cartoon “The Far Side”.

To read more about how this type of dinosaur tail got named: Thagomizer – How the Spikes on the Tail of a Stegosaurus got Named.

As more and more sauropod material is recovered and increasing numbers of caudal bones are found, it seems that several of these long-necked giants were armoured and had defensive weapons.  Although, dermal armour and spines along the body is more closely associated with later titanosaurids such as Agustinia from South America, at least one other primitive Jurassic sauropod had an armoured tail.  Fossils of Shunosaurus from the famous Dashanpu Quarry sites near Zigong in Sichuan Province, China, show that these 9-metre-long giants had a bony club on the end of the tails.

To view a models of Agustinia, Shunosaurus and other strange sauropods: Dinosaur and Prehistoric Animal Models.

Professor Joger and his team are particularly excited about the discovery of this very early type of sauropod, hoping that further examination of the skeleton will help the team to piece together the Sauropodomorpha family tree.

He commented

“The discovery is of particular importance as this dinosaur sits at the top of the sauropod genealogical tree.  With this find, Africa moves to the centre of dinosaur research.  But Africa is a politically unstable continent, often making digs there particularly difficult.  There was a far reaching river complex in the area, so the animals we found there were surrounded by an overwhelming presence of life”.

Excavation Project

The excavation project was undertaken between 2005 and 2008, mostly in the Republic of Niger. Local nomadic people showed the German scientists where the leg bones could be found, lying exposed as they were. The dig site initially revealed two skeletons, to be taken back to Germany for preparation, before the site was shut down.

Unfortunately for the Germans, it was a Spanish led group that first got hold of one of the skeletons of this newly discovered long-necked dinosaur after hearing about the exposed leg bones weathering out on the rock surface.  Since then, researchers from the two countries have been working together on the specimen in Bonn and Brunswick.

Sauropod Dinosaur

However, Professor Joger revealed that his team had discovered a third fossil specimen, not a sauropod but a meat-eating dinosaur described as a “raptor”.  This specimen was found in same area just a few hundred metres from Spinophosaurus, and it too, is probably a new genus.  If this new carnivorous dinosaur does turn out to be a raptor (dromaeosaurid type dinosaur), then this would be a very significant discovery indeed. To date such dinosaurs are associated with the Northern Hemisphere and not known from this part of Africa.

As a thank you for helping with the discovery of Spinophosaurus and the subsequent excavation work, the German scientists have worked with a charity to establish a school for the local tribe and provided many thousands of school books.  Indeed, representatives from Niger are going to be present when the restored fossils are put on display in the State Natural History Museum of Braunschweig next month.