Portuguese dinosaurs give clue to formation of Atlantic

news: Portuguese dinosaurs give clue to formation of Atlantic

DURING A second phase of excavations at the village of Andrés, near Pombal (central Portugal), palaeontologists have unearthed more dinosaur bones believed to have belonged to the fearsome carnivore “Allosaurus”, a giant reptile that lived between 148 and 155 million years ago.

The team of investigators, led by Dr. Pedro Dantas of the University of Lisbon’s National Museum of Natural History and Spanish dinosaur expert Dr. Francisco Ortega of Astúrias Jurassic Museum, are now sure that they have discovered the remains of, at least, two of the animals. They have recovered a substantial amount of well preserved fossilised bone specimens, some up to 30 centimetres in length, and a large quantity of skull fragments.

Excavation sheds light

Formerly, following the first phase of excavations some 17 years ago, experts had believed that they were only dealing with the remains of one dinosaur.

The site was first excavated in 1988, after land owner José Amorim discovered large pieces of petrified bone while digging the foundations for a storage shed. He promptly reported the find to the National Museum of Natural History, which ordered an emergency excavation, retrieving parts of a skull, ribs, pelvis, hind members and vertebrae.

The remains were then subject to a lengthy and painstaking analysis in collaboration with experts from Spain and the US. It was not until May of 1999 that the first results of the study were published, appearing in the British Journal of the Geological Society, when it was announced that the bones were those of an Allosaurus fragilis, one of the largest dinosaur predators to be discovered in Portugal.

Allosaurus first found in

North America

Much more important, however, was the fact that until the discovery of the site at Andrés, Allosaurus had only been found in North America. Experts now believe that this crucial detail may shed light on how and when the continents of Euro-Asia and North America split from each other, forming the Northern Atlantic Ocean, a process that was underway during the late Jurassic period (160-140 million years ago), the time when Allosaurus roamed the prehistoric swamps and forests.

The degree of separation of the continents and the depth of the sea between the continental land masses of Euro-Asia and North America, during the late Jurassic period, have long been a subject of debate in scientific circles. At that time, North America and the Iberian Peninsula were very much closer together and the Atlantic Ocean was in its infancy and much narrower.

Atlantic’s terrestrial crossing

The discovery of Allosaurus in Portugal now raises the possibility that, even as late as the end of the Jurassic period, animals were able to cross the “Proto-Atlantic Ocean” by means of a terrestrial passage perhaps consisting of reefs, strings of islands or a natural causeway. If this was indeed the case, according to experts, this link between the continents was still in existence “only yesterday” on the geological time-scale.

Expert comments

Geologist Fernando Barriga, Director of the National Museum of Natural History, explained to The Resident: “So far, we know of three Allosaurus in Portugal, at least two at Andrés and another at a site in Cambelas near Torres Verdes.” He continued that these were the only known examples in Europe to date.

He added that, although there was no doubt that the animals were of the Allosaurus genus, there was now some doubt as to the exact sub-species. “When the first set of bones was discovered during the first phase of excavations, all the critical bones conformed to the fragilis species type, however, following this second operation, we now have so much more material to analyse that, at this point, it is too early to say for certain that we are dealing with the fragilis species type, another known species type or possibly even a hitherto undiscovered species type.”

Most important collection at

Portugal’s museum

The Allosaurus remains found at Andrés show that the Portuguese dinosaurs would have been between seven and eight metres long, up to two metres high (from the ground to the pelvic girdle) and would have weighed around one tonne.

Additionally, the quantity and quality of the skull fragments retrieved means that the National Museum of Natural History now has one of the most important collections of dinosaur cranial bones in Europe.

The Andrés site has also yielded a substantial amount of other important prehistoric organic material including fossilised remains of crocodiles, rare invertebrates, an abundance of molluscs and a substantial amount of petrified vegetation.

• To learn more about the Allosaurus fragilis, you can visit the University of Lisbon’s National Museum of Natural History website, www.mnhn.ul.pt. The site is in Portuguese, but an English version is currently under construction.

The first Allosaurus fossil was discovered in 1869 in the US, near Granby, Colorado, and was described as a “petrified horse hoof”. It was not until 1877 that renowned American palaeontologist, Othniel Charles Marsh, identified it as a vertebrae (tail bone) belonging to a hitherto unknown dinosaur genus, to which he gave the name Allosaurus, meaning “different lizard” or “strange lizard”, so christened because Marsh found that the vertebrae of the Allosaurus were substantially different from those of other dinosaurs.

Growing up to 12m (38ft) long and weighing as much as 1.4 tonnes, Allosaurus is known to have been the biggest meat-eating dinosaur in North America during the late Jurassic period. It was a ferocious predator that walked on two powerful hind legs. It had short arms, with three-fingered hands with 15cm long claws, while its head would have been some 90cm (3ft) long, with strong bone crushing jaws and serrated teeth, between two and four inches long, designed exclusively for tearing flesh.

Allosaurus is thought to have fed on large plant-eating dinosaurs like Stegosaurus and Diplodocus. By measuring its brain to body weight, experts believe that Allosaurus possessed a high intelligence relative to other dinosaurs.