University of Manchester Scientists “Slim down the Dinosaurs”

How big were the dinosaurs?  This is a question that has vexed palaeontologists ever since the first fossil bones of these prehistoric animals were studied in detail.  The size of extinct animals can be calculated by measuring the length of individual bones but the calculation of mass is much more difficult.  Scientists at the University of Manchester have developed a new technique that “slims down” the Dinosauria.  Some of the largest leviathans may not have weighed upwards of eighty metric tonnes as previously thought, around twenty-three tonnes may actually be nearer the mark.

How Big were the Dinosaurs?

Just how big were the dinosaurs has sparked lively debate for many years, to read an article on the possible size and weight of Brachiosaurus (published in 2009): Just how big was Brachiosaurus?

Palaeobiologists at the University have developed a new technique to accurately measure the weight and size of dinosaurs and discovered they are not as heavy as previously thought.  University of Manchester biologists used lasers to measure the minimum amount of skin required to wrap around the skeletons of modern-day mammals, including reindeer, polar bears, giraffes and elephants.  Using animals alive today, that can be weighed allows the researchers to test their calculations against the actual  recorded weight of the animal.

What the laser mapping technique shows, is that the dinosaurs may not have been as heavy as earlier estimates.  This has implications for the study of their behaviour and locomotion, even whether some of the biggest dinosaurs of all – the long-necked sauropods may have been capable of rearing up onto their hind legs.

Research from Manchester University

The Manchester based team discovered that the animals they measured had almost exactly 21% more body mass than the minimum skeletal “skin and bone” wrap volume.  They then applied this to a giant brachiosaur skeleton in Berlin’s Museum für Naturkunde, (Humboldt Museum).  This skeleton stands over forty feet tall, and is made up of the fossilised bones of several individuals.  It represents a brachiosaur from Africa and it is the largest mounted dinosaur skeleton on display in Europe.

Estimating the Weight of Brachiosaurus

Estimating the weight of dinosaurs.

Picture credit: Everything Dinosaur.

Estimating the Weight of Brachiosaurus

Previous estimates of this brachiosaur’s weight have varied, with estimates as high as 80 tonnes.  The Manchester team’s calculations – published in the journal Biology Letters – reduced that figure to just 23 tonnes.   Still a substantial weight, but intriguingly establishing the giant mammals known as the Indricotheres as potentially the heaviest land living animals known to science.  The team says the new technique will apply to all dinosaur weight measurements and thus the mass of all the known dinosaurs can be calculated.

Commenting on the research, lead author Dr Bill Sellers said:

“One of the most important things palaeobiologists need to know about fossilised animals is how much they weighed.  This is surprisingly difficult, so we have been testing a new approach.  We laser scanned various large mammal skeletons, including polar bear, giraffe and elephant, and calculated the minimum wrapping volume of the main skeletal sections”.

Arguments Put Forward

One of the arguments put forward against depicting the dinosaurs as more agile, active creatures was their great size and weight.  Despite a number of evolutionary adaptations to lighten their skeletons such as the evolution of pneumatised bones.  Many scientists had argued that predators such as Tyrannosaurus rex would have been just too heavy and slow to be effective hunters.  It has been proposed that these heavy carnivores probably scavenged carcases.

Dr Sellers went onto state:

“We showed that the actual volume is reliably 21% more than this value, so we then laser scanned the Berlin brachiosaur, Giraffatitan brancai, calculating the skin and bone wrapping volume and added 21%.  We found that the giant herbivore weighed 23 tonnes, supporting the view that these animals were much lighter than traditionally thought.”

Dr Sellers, based in Manchester’s Faculty of Life Sciences, explained that body mass was a critical parameter used to constrain biomechanical and physiological traits of organisms.

He added:

“Volumetric methods are becoming more common as techniques for estimating the body masses of fossil vertebrates but they are often accused of excessive subjective input when estimating the thickness of missing soft tissue. Here, we demonstrate an alternative approach where a minimum convex hull is derived mathematically from the point cloud generated by laser-scanning mounted skeletons.  This has the advantage of requiring minimal user intervention and is therefore more objective and far quicker.”

Brachiosaurus or Giraffatitan

Interestingly, as scientists debate the body weights of brachiosaurs, it is worth noting that until recently the brachiosaur in the Berlin museum was described as belonging to the genus Brachiosaurus.  However, studies of the fossil material ascribed to this genus that had been found in East Africa and the Western United States indicate that the African material is sufficient different to be put into its own, separate genus – Giraffatitan.

To read an article on the scientific debate between Brachiosaurus and Giraffatitan genera: Brachiosaurus versus Giraffatitan.

Explaining how the research team estimated the weight of the Berlin specimen, Dr Sellers stated:

“We tested this method on 14 large-bodied mammalian skeletons and demonstrated that it consistently underestimated body mass by 21%.  We suggest that this is a robust method of estimating body mass where a mounted skeletal reconstruction is available and demonstrate its usage to predict the body mass of one of the largest, relatively complete sauropod dinosaurs, Giraffatitan brancai, as 23,200 kilogrammes.”

Dinosaurs

When asked to put this new research into the context of earlier studies that had produced much higher weights for dinosaurs, Dr Sellers commented:

“The value we got for Giraffatitan is at the low range of previous estimates; although it is still huge, some of the enormous estimates of the past – 80 tonnes in 1962 – are exaggerated.  Our method provides a much more accurate measure and shows dinosaurs, while still huge, are not as big as previously thought.”

The Weight of the Dinosauria

The debate over the weight of the Dinosauria, especially the really big sauropods is likely to rumble on.  Still at twenty-three metric tonnes, this makes one particular Late Jurassic sauropod much heavier than any land living animal alive today.  This dinosaur would be many times the weight of the biggest elephants.

We are grateful to the University of Manchester for supplying information in a press release for use in this article.

For scale models of giant sauropods and other dinosaurs: Papo Sauropods and Prehistoric Animal Models.

Eoabelisaurus – Ancient Abelisaurid but with Advanced Anatomical Characteristics

A team of scientists from the Edigio Feruglio Museum of Palaeontology in Chubut (southern Argentina), have unveiled the near complete fossil skeleton of a Jurassic-aged abelisaurid theropod dinosaur.  A new abelisaurid dinosaur species has been described.  The fossils of this fearsome, meat-eating dinosaur were discovered in Middle Jurassic aged strata.

Basal abelisaurids are known from the Jurassic, but most of the fossils found of this type of predator in South America, are associated with much younger rocks laid down towards the end of the Cretaceous some ninety million years after this new dinosaur genus roamed what was to become Argentina.  The fossils reveal that this ancient creature, a dinosaur that lived before iconic dinosaurs of the Jurassic such as Brachiosaurus, Diplodocus and Allosaurus evolved, had a number of anatomical features associated with the last of the abelisaurs, creatures that roamed the Earth at the very end of the Cretaceous geological period.

New Abelisaurid Dinosaur Species

The abelisaurs are a very distinctive group of meat-eating dinosaurs, known almost exclusively  from fossils found in the Southern Hemisphere.  Palaeontologists believe that they evolved from a primitive line of theropod dinosaurs known as the ceratosaurids.  It seems that towards the end of the Cretaceous, whilst the tyrannosaurs became the dominant, apex predator in northern latitudes, in the south, the top predators were the abelisaurids.

An Illustration of a Typical Abelisaur (Rugops primus)

Fearsome predators of the Southern Hemisphere.

Picture credit: Everything Dinosaur

Abelisaurids are noted for their deep, blunt but narrow skulls, the top of which were often adorned with crests or horns.   These bipeds had large pelvises and very tiny, much reduced, stubby arms with four fingered hands.  A number of abelisaur fossils have been found mainly in India, Madagascar and South America.  Scientists have speculated that more primitive members of this group, earlier forms, referred to as basal abelisaurids, probably had longer arms, similar in proportion to their ceratosaur ancestors, but this new specimen, scientifically named as Eoabelisaurus mefi (Early Abel’s Lizard), although dating from 170-million-year-old strata, it too has the tiny arms of its relatives that lived much later in the Age of Dinosaurs.

Abelisaurs

As a group, the abelisaurs were virtually unknown until the mid-1980s when scientists exploring the geology of South America discovered the skull of a new type of huge, meat-eating dinosaur.  Argentinean palaeontologists Jose Bonaparte and Fernando Novas were responsible for the scientific study of this specimen and they named this new dinosaur Abelisaurus (A. comahuensis), the name honours Roberto Abel, the director of the Argentinean Museum of Natural Sciences at the time.

A paper describing this new dinosaur genus has been published in the leading London-based, scientific journal “the Proceedings of the Royal Society”.

The animal has been described as a scaled-down version of Tyrannosaurus rex, another dinosaur known for its tiny, stunted arms.  However, the tyrannosaurs and the abelisaurids were not closely related.   The forelimbs of these two types of predatory dinosaur may have been similar, but the resemblance was only superficial.

In tyrannosaurs, the bones of the lower arm (the ulna and radius), were smaller than the bone found in the upper arm (the humerus), but they were still substantial bones, the hand had two functional fingers (first and second digits), tyrannosaurs being descended from meat-eating dinosaurs that had three-fingered hands.  In later abelisaurids, the ulna and the radius were very much smaller than in similar sized tyrannosaurs, these bones in abelisaurs were little bigger than some of the bones that made up the wrist portion of the forelimb.

The Fossil Material Ascribed to the new Abelisaur Genus (Eoabelisaurus mefi)

New type of South American meat-eating dinosaur discovered.

Picture credit: AFP

Remarkable Fossil Discovery

This fossil discovery, is remarkable for two reasons.  Firstly, the fossils found make up an almost complete specimen, finding such a near complete specimen of a dinosaur, especially a theropod is exceptionally rare.  Secondly, this discovery helps confirm that primitive albelisaurs, albeit with some advanced anatomical features such as the reduced arms, were present in the Middle Jurassic.

This new species E. mefi, is one of the earliest known members of this group, and it predates most of the other Argentinean abelisaur material by tens of millions of years.  The only other basal abelisaurid known from this part of the Jurassic, is a species known as Berberosaurus liassicus, fossils of which were found in Morocco.

Scientists have estimated that this new South American dinosaur would have been at least six metres long, not the largest abelisaurid known to science; but a sizeable beast none the less, and probably the apex predator in the region during this part of the Jurassic geological period.  It is difficult to estimate the weight of such a creature, but the robust femur (thigh bone) and strong looking legs give an indication that this dinosaur could have weighed more than one tonne.

A spokes person for the scientists responsible for producing the academic paper on this creature stated that unlike other types of abelisaurid from the Early Cretaceous, Eoabelisaurus mefi had completely reduced arms and tiny claws.  The arm bones resemble those associated with much later types of abelisaurid, fearsome creatures such as Rajasaurus (India), Majungasaurus from Madagascar and Carnotaurus (also from Southern Argentina).  The fossils of these abelisaurids date from at least seventy million years ago, a time towards the end of the Age of Dinosaurs, at the very end of the Cretaceous.

An Illustration of Eoabelisaurus mefi

Fearsome Middle Jurassic predator.

Picture credit: AFP/Pol and Rauhut.

The reduced arms in this Middoe Jurassic dinosaur may be an example of convergent evolution, where two organisms evolve the same adaptations but are not necessarily that closely related.  For example, Eoabelisaurus could have evolved the same hunting technique and style of biting of its much later abelisaurid cousins such as Carnotaurus and Rajasaurus.  The arms being so small, would have been virtually vestigial and unable to grasp and hold prey.  It is likely that these types of dinosaurs evolved a technique of hunting that only required the use of their teeth.

The fossil evidence suggests that these dinosaurs had very powerful bites and strong, sharp teeth that would have made them very effective hunters of other large dinosaurs that shared their habitat.

The first fossilised remains of this dinosaur, consisting of part of the skull and backbone were found by a scientific expedition back in 2009, but as the weather closed in, the dig site, at a location known as Condor Hill, had to be abandoned until the following year.  Once the fossil material had been carefully excavated from the site, it was transported in large plaster-jacketed blocks for further preparation at the Edigio Feruglio Museum of Palaeontology in Chubut Province.  Palaeontologists hope that the near complete and articulated dinosaur fossils will form part of a new exhibition which will highlight the evolution of theropod dinosaurs in Argentina.

An Illustration of the Abelisaurid Majungatholus (Majungasaurus)

Fearsome abelisaurid predator.

Picture credit: Everything Dinosaur

To view replicas of abelisaurids and other theropod dinosaurs: Abelisaurids, Theropods and Other Dinosaur Models (CollectA Prehistoric Life Models).