The problem with Spinosaurs
Palaeontologists debate how all the meat-eating dinosaurs are related to each other. There is little consensus when it comes to organising a family tree, especially with the large Theropods. The reasons for this are quite simple, big meat-eaters tend to be at the top of the food chain and as a result are not as common as other animals lower down the pecking order, as it were. For example, palaeontologists have hundreds of well preserved Maastrichtian Hadrosaur fossils, many of them found in association or articulation. However, in comparison very few Tyrannosaurus rex fossils have been recovered. There is plenty of evidence to indicate that plant-eaters moved around in large herds, just as many species of herbivores do today. So if a disaster occurs such as the herd panicking and floundering when crossing a swollen river, many animals may be killed. The corpses can drift downstream and slowly and surely as sediments cover them a vast bone bed of fossils can form.
The evidence of meat-eaters moving around in anything bigger than a small family group is patchy to say the least. Although there is evidence of group behaviour in fossils of certain Theropods such as Albertosaurs, many large meat-eaters may have lived solitary existences, so the chances of finding lots and lots of fossils of a particular genus is quite small.
The Spinosaurid family illustrate some of the difficulties that palaeontologists face. Firstly, there is still argument in scientific circles as to whether animals such as Baryonyx (a Baryonychid) is actually distinct enough from Spinosaurs to be regarded as a separate (but closely related) family. Some palaeontologists believe that the Baryonychidae are merely a sub-family of the Spinosaurs.
Baryonyx was first described from a specimen found in a clay pit in Smokejacks Brickworks, at Wallis Wood, near the village of Ockley, Surrey in England. About 30% of the remains of a sub-adult animal were recovered from this site. Since then Baryonyx fossils have been found on the Isle of Wight and in Spain. There is also evidence to suggest that Baryonychids were present in Africa during the early Cretaceous.
Although Baryonyx has a lot of features in common with animals such as Spinosaurus aegyptiacus, it is believed to more primitive. Baryonyx teeth are slightly recurved and are finely serrated, in true Spinosaurs these features have been lost. Spinosaur teeth tend to be straight, conicle shaped and have no serrations, possibly an adaptation for eating a much more fish dominated diet.
A Museum model Interpretation of Baryonyx
Picture courtesy of Everything Dinosaur
The model in the picture above is a 1:40 scale model of Baryonyx designed under the supervision of Dr Paul Barrett of the Natural History museum – London. Sales of this product help support the palaeontologists and fund their research.
To view the model: Dinosaur Models for Boys and Girls – Dinosaur Toys
Fossil bone material of large carnivores is extremely rare, but lots of teeth have been found, particularly in places such as the Isle of Wight. It seems that dinosaurs were able to shed teeth, replacing them with new ones erupting from the jaws. This is why when you look at the jaws of a meat-eating dinosaur in a museum exhibit, the teeth are different sizes. Some teeth did vary in size depending on which part of the jaw they came from, but the different sized teeth show younger teeth just emerging from the teeth sockets. Before Baryonyx was known, palaeontologists assigned many of the teeth fossils to extinct crocodile genera. Now much of this material has been reviewed by the likes of Dr Angela Milner of the Natural History museum (one of the scientists responsible for naming and describing Baryonyx from the Ockley specimen) and some of the teeth have been re-classified as belonging to Baryonyx.
Spinosaurs are known from Africa and South America. Once again the fossil record is fragmentary. Our knowledge of these bizarre Theropods has been hampered by the lack of fossil finds and as a result of mankind’s own stupidity and greed. The best known specimen of S. aegyptiacus was found by the German palaeontologist/geologist Ernst Stromer von Reichenbach on his expeditions to North Africa between 1911 and 1914. This species was named and described by him in 1915. The fossils recovered were never really studied to their full extent, perhaps as a result of the wealth of material brought back to Germany from Africa. Drawings were made and there were some descriptions and anatomical comparisons provided, but the Spinosaur fossils were destroyed by an American bombing raid on Germany during World War II.
Confusion also surrounds the South American Spinosaur, Irritator. This dinosaur was named and described in 1996 by a joint palaeontological team headed up by David Martill of the University of Portsmouth. The only known fossil of this animal is a partial skull recovered from eastern Brazil. The amateur fossil collector who first found the skull attempted to restore it and make it a more complete and valuable specimen using plaster and superglue. The scientists given the job of studying this fossil had to dismantle it again, this is how Irritator got its name, as it irritated the palaeontologists! The actual species is I. challengeri, named in honour of the fictional Professor Challenger, who led an exhibition to the plateau in Guyana (South America) and discovered prehistoric animals in the book “The Lost World” written by Sir Arthur Conan Doyle in 1912.
In the late 1990s another partial skull of a Spinosaur was recovered from the same sediments as Irritator (Santana Formation of Brazil). This animal was named as Angaturama but the remains could actually belong to the same skull as Irritator so the term Angaturama is not valid at present. It is classified as Nomen dubium.
The dispersion of Baryonychid and Spinosauridae fossils across South America, Europe and Africa provide an important piece of evidence as to the land bridge links in Gondwanaland during the early Cretaceous. During this time Africa, Europe and South America were linked (part of the southern land mass Gondwanaland), the various Spinosauridae and Baryonychid fossils found so far provide conclusive biogeographical evidence of the land bridges between these regions that existed prior to the formation of the Atlantic ocean.
Gondwanaland in the Cretaceous (90 mya)
Picture Credit: A. T. White
The picture shows Gondwanaland approximately 90 million years ago. During the Cretaceous this super continent began to break up and the Atlantic ocean started to form. Prior to the continent’s break up prehistoric animals could migrate between Africa, Europe and South America. This helps to explain the fossil distribution of Spinosaurs and Baryonychids.