Dem Bones

Primordial Steps.

A 333-million year old broken bone is causing fossil scientists to reconsider the evolution of land-dwelling vertebrate animals, says a team of palaeontologists, including QUT evolutionary biologist Dr Matthew Phillips, and colleagues at Monash University and Queensland Museum.

Analysis of a fractured and partially healed radius (front-leg bone) from Ossinodus pueri, a large, primitive, four-legged (tetrapod), salamander-like animal, found in Queensland, pushes back the date for the origin of demonstrably terrestrial vertebrates by two million years, said Dr Phillips, a researcher in the Vertebrate Evolution Group in QUT’s School of Earth, Environmental and Biological Sciences.

“Previously described partial skeletons of Ossinodus suggest this species could grow to more than 2m long and perhaps to around 50kg,” Dr Phillips said.

“Its age raises the possibility that the first animals to emerge from the water to live on land were large tetrapods in Gondwana in the southern hemisphere, rather than smaller species in Europe.

“The evolution of land-dwelling tetrapods from fish is a pivotal phase in the history of vertebrates because it called for huge physical changes, such as weight bearing skeletons and dependence on air-breathing.”

Dr Phillips said the nature of the break in the radius bone was studied using high-resolution finite element analysis by Peter Bishop for his honours research at QUT.

“The nature of the fracture suggests the bone broke under high-force impact.

“The break was most plausibly caused by a fall on land because such force would be difficult to achieve with the cushioning effect of water.

Indeed, the fracture is somewhat reminiscent of people falling on an outstretched arm and the humerus crashing into and fracturing the radius.”

Dr Phillips said the researchers also found two other features that confirmed the tetrapod had spent substantial time on land.

“Firstly, the internal bone structure was consistent with re-modelling during life in accordance with forces generated by walking on land,” he said.

“We also found evidence of blood vessels that enter the bone at low angles, potentially reducing stress concentrations in bones supporting body weight on land.

“The three findings taken together suggest that Ossinodus spent a significant part of its life on land. This is augmented by its exceptional degree of ossification, which is also consistent with weight bearing away from the buoyancy of water.

“This specimen of Ossinodus is our oldest vertebrate relative shown biomechanically to have spent significant time on land. It is two million years older than the previous undoubtedly terrestrial specimens found in Scotland, which were less than 40cm long.”

Dr Phillips said the findings highlighted the value of combining studies on palaeontology, biomechanics and pathology to understand how extinct organisms lived.

 

 

Hell Boy.

About 10 years ago, Peter Hews stumbled across some bones sticking out of a cliff along the Oldman River in southeastern Alberta, Canada. Now, scientists describe in the Cell Press journal Current Biology, that those bones belonged to a nearly intact skull of a very unusual horned dinosaur, a close relative of the familiar Triceratops that had been unknown to science until now.

“The specimen comes from a geographic region of Alberta where we have not found horned dinosaurs before, so from the onset we knew it was important,” says Dr. Caleb Brown of the Royal Tyrrell Museum of Palaeontology in Alberta, Canada. “However, it was not until the specimen was being slowly prepared from the rocks in the laboratory that the full anatomy was uncovered, and the bizarre suite of characters revealed. Once it was prepared it was obviously a new species, and an unexpected one at that. Many horned-dinosaur researchers who visited the museum did a double take when they first saw it in the laboratory.”

Brown likes to say, only partly in jest, that the uniqueness of this specimen was so obvious that you could tell it was a new species from 100 meters away.

What made this new horned dinosaur distinctive was the size and shape of its facial horns and the shield-like frill at the back of the skull. This new species is similar in many respects to Triceratops, except that its nose horn is taller and the two horns over its eyes are “almost comically small.” But the new dinosaur’s most distinctive feature is that frill, including what Brown describes as a halo of large, pentagonal plates radiating outward, as well as a central spike. “The combined result looks like a crown,” he says.

Brown and study co-author Donald Henderson named the new dinosaur Regaliceratops peterhewsi, a reference to its crown-like frill and to the man who first found and reported it to the museum. Despite the formal name, the scientists say they’ve taken to calling this dinosaur by the nickname “Hellboy.”

While this new dinosaur is intriguing in its own right, Brown and Henderson say what’s most significant are the implications for the evolution of dinosaurs’ horned ornamentation. It’s long been known that horned dinosaurs fall into one of two groups: the Chasmosaurines, with a small horn over the nose, larger horns over the eyes, and a long frill, and the Centrosaurines, characterized by a large horn over the nose, small horns over the eyes, and a short frill.

“This new species is a Chasmosaurine, but it has ornamentation more similar to Centrosaurines,” Brown says. “It also comes from a time period following the extinction of the Centrosaurines.”

Taken together, he says, that makes this the first example of evolutionary convergence in horned dinosaurs, meaning that these two groups independently evolved similar features.

The researchers say they hope to uncover more Regaliceratops peterhewsi specimens. They’ll also be working on digital reconstructions of the skull, noting that, though intact, the fossil has been deformed after 70 million years in the Rocky Mountain foothills.

“This discovery also suggests that there are likely more horned dinosaurs out there that we just have not found yet, so we will also be looking for other new species,” Brown says.

 


Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s