Amargasaurus – A Bizarre Late Diplodocid

As an increasing number of bizarre forms of sauropod have been unearthed for example Amargasaurus. The family tree of these huge long-necked dinosaurs is becoming more complicated.  Although, thanks to recent discoveries of more basal sauropods and prosauropods the evolution of these saurischians has become a little clearer, there is still a lot of confusion over the taxonomic relationships between the various families.

To read further about this: Changing Views on Sauropods.

The Argentine Amargasaurus for instance, is an example of a strange looking, long-necked dinosaur and the strata from which the single fossil skeleton so far known was discovered adds to the mystery of the sauropods.  The global fossil record indicates that the diplodocid type of sauropod was beginning to become rare during the Early Cretaceous. Their heyday appears to have been the Late Jurassic when behemoths such as Diplodocus, Barosaurus and Apatosaurus roamed.  However, the fossils of Amargasaurus date from the early Cretaceous (Hauterivian faunal stage – approximately 135-130 million years ago).  This indicates that this particular group of long-necked dinosaurs were still present, at least in the southern hemisphere during the Early Cretaceous.

Amargasaurus also had a very strange appearance, being relatively small compared to the diplodocids known from the Upper Jurassic deposits of the Morrison Formation of the western United States.  For a start, it was only about 12 metres in length, considerably smaller than Diplodocus and Apatosaurus and it had a much shorter neck, compared to other diplodocids.

The most distinguishing feature though was that along the neck and back of the animal was an array of long, spines extending up from the back bone.  These spines consisted of two rows of long spines over the neck and shoulders, gradually reducing to a set of single spines running along the back to the hind quarters.

An Illustration of Amargasaurus

Picture credit: Everything Dinosaur

To view a model of Amargasaurus and other long-necked dinosaurs: Dinosaur and Prehistoric Animal Models.

The exact purpose of these spines is hotly debated by scientists.  Some believe that they supported a brightly coloured sail that could have been used as signalling device amongst members of the herd, whilst others suggest that the spines were for defence against attack from large meat-eaters that shared the same environment.  Those spines on the neck which are paired, may not have supported a sail, but been covered in horn helping to protect a vulnerable part of this animal’s body.  Certainly, with the likes of members of the Allosaur family wandering around it would pay to have some form of protection, but the precise purpose of these spines remains unclear.

Amargasaurus may be a member of the Dicraeosauridae, a group of sauropods that all possessed long neural spines.  Amargasaurus may have been a descendant of the genus Dicraeosaurus, a diplodocid from the Late Jurassic of East Africa.

Close up of Amargasaurus Head

Picture credit: Everything Dinosaur

As can be seen in this illustration of Amargasaurus, the presence of skin stretched between the large neural spines is played down, instead they are depicted as having more of a defensive purpose.  What ever they were for, this is certainly a very peculiar looking sauropod, with its large neural spines, so of which were over 5 feet tall.