Murusraptor

By Gemma Tarlach

Sexy Beast of the Week: Murusraptor barrosaensis, the newest member of the megaraptor gang. The Patagonian predator of 80 million years ago was larger but had a more fine-boned build than other megaraptorids. Credit: Jan Sovak. Want to find some awesome dinosaur species new to science? Head south. South America is clearly the place to be these days, with Patagonian predator Murusraptor barrosaensis the latest intriguingly odd animal to stomp onto the paleoscene. Like fellow Argentine Gualicho shinyae, announced last week, Murusraptor is known from the partial skeleton of a single specimen. And while Gualicho made headlines for its shorty-short forelimbs, Murusraptor is like those models in perfume ads: a leggy mystery that's got people intrigued.

Murusraptor is a large, slender megaraptorid. You may read "raptor" and think oh, velociraptor*, bitey bitey, clever girl, but, while megaraptorids did have big ol' claws, they're not closely related to the stars of the Jurassic Park movies. (*Yes, I know Hollywood's idea of a velociraptor is, shall we say, just a bit outsized when compared with the fossil record, but let's not have that discussion right here and right now, 'k?) Megaraptorids were a group of carnivorous dinosaurs from the Cretaceous that, in addition to those claws, had some sweet pneumatization action going on. A number of their bones were essentially hollow, or at least partly so, full of air pockets. Murusaptor is notably, shall we say, aerated. It's a trait also seen in most modern birds and some other dinosaurs, particularly those most closely related to birds. (Don't feel too left out, puny human: those sinus cavities of yours, currently all stuffed up from summer allergies, are another example of pneumatization.) Airy bones are one reason paleontologists have found it challenging to determine where megaraptorids sit in the family tree of theropods, a diverse bunch of mostly carnivorous, bipedal dinosaurs spanning more than 230 million years, from the earliest dinos to that chicken you're eating for dinner. Within Theropoda, the megaraptorids have variously been classified as allosaurid, coelurosaurid and, more specifically within the coelurosaurs, as tyrannosaurids. Without getting too deep into the -id of it all, megaraptors are all over the map in terms of how they might be related to other dinosaurs. More on that in a bit. Murusraptor presented additional opportunities for head-scratching. Even the authors of the first paper on the animal, published today in the open-access journal PLOS One, weren't sure what they'd dug up.

Co-author Philip Currie of the University of Alberta, one of the world's leading paleontologists, admits Murusraptor initially had him stumped. Sending a quick email as he headed back into the field, Currie shared the team's process of figuring out what they had on their hands: "The animal completely puzzled us when we found it because it is an animal as large as a tyrannosaur like Albertosaurus [about 30 feet long], but was as pneumatic as an oviraptorosaur [a very bird-like bunch of dinos]...." Currie went on to explain that the dinosaur had other traits that might have placed it as a primitive, or basal, maniraptor (the line which eventually led to birds) or even a spinosaurid, a particularly whacky group of crocodilian-skulled dinosaurs that includes the largest predatory dinosaur ever known.

The fossilized bones of Murusraptor found by the team and shown here in white include much of the rear cranium. The braincase in particular is well-preserved and allowed researchers to determine the animal was not fully mature at time of death. Credit: Coria et al (2016) Only after all the fossils of the specimen — unearthed more than a decade ago — were prepped and analyzed did the team feel comfortable assigning Murusraptor to the megaraptor group. Currie and lead author Rodolfo Coria, another megafigure in paleontology, used the new data gleaned from analyzing Murusraptor to see if it would help them answer, once and for all, where on the family tree megaraptorids belonged. Spoiler alert: it didn't. When they compared specific traits of megaraptorids, including Murusraptor, with those of other dinosaurs, slight tweaks to the modeling process yielded two very different results. In other words, the jury is still out on whether these animals are allosaurids or tyrannosaurids.

While we're still not sure where Murusraptor and the other megaraptorids fit in the dinosaur evolution story, this specimen is exciting because it includes a fair chunk of the cranium. In particular, the braincase is beautifully preserved. In fact, it was in such great shape that the team was able to see signs of infection on the left side of the skull — no word on whether the boo-boo was responsible for the animal's death, however. Believed to be just over 21 feet long, the Murusraptor specimen was a juvenile — researchers were able to determine that because the bones of the rear skull, while knitted together as in adults, still showed their seams. That's a tip-off that the animal had not yet reached full maturity. Look for more news about that gorgeous braincase soon. For now, initial analysis of the cranium suggests Murusraptor may have had a crest on the top of its head. Show-off.

Murusraptor and last week's dino-breakout Gualicho were found in the same large basin in west-central Argentina, an area centered around the small city of Plaza Huincul. The animals were separated by millions of years, however: Murusraptor is about 80 million years old, while Gualicho is 10-14 million years older. The animals also represent different branches of the theropod family tree. They're just the latest pair of predators to emerge from the neighborhood, in addition to a number of other dinosaurs and other extinct animals discovered there. "Off the top of my head I would guess that the sites are within a hundred kilometers of each other," notes Currie. "This area (about 200 km radius around Plaza Huincul) is definitely the hot spot for dinosaurs in South America."

New dinosaur fossil pushes evolution of gigantism in sauropods back 30 million years

A new dinosaur called Ingentia prima appeared to have a air sacs in its neck, shown in this artist's impression in green, and walked on flexed feet. (Supplied: Jorge A. González)

ABC Science By science reporter Belinda Smith

Think of a plant-eating dinosaur, and chances are you picture something along the lines of a brachiosaurus.

These iconic giants belonged to a group of dinosaurs called sauropods — massive creatures with thick, column-like legs and a long neck and tail.

Now, the discovery of a new dinosaur species suggests gigantism in sauropods evolved about 30 million years earlier than previously thought.

The newly uncovered bones, belonging to a plant-eater dubbed Ingentia prima, also suggest that there were a couple of different ways these giant dinosaurs evolved.

The fossil find was unveiled in Nature Ecology and Evolution today by an Argentinian crew led by National University of San Juan palaeontologist Cecilia Apaldetti.

"Now we are rethinking the evolution of giant size in dinosaurs," Dr Apaldetti said.

Most palaeontologists think sauropod dinosaurs first appeared on the scene in the early Jurassic period, starting with the 11-metre Vulcanodon about 180 million years ago.

The discovery of the Ingentia prima — a dinosaur that existed about 205 million years ago and was about 8-10 metres long — has challenged this idea.

But whether the new dinosaur walked on two legs or four, and was a sauropod at all, is up for debate.

The story of Ingentia prima starts with a cattle farmer in northern Argentina.

"He [told the local museum], 'I have seen bones inside rocks but they don't seem to be from cows'," Dr Apaldetti said.

When she and her colleagues went to check them out, they found a rich trove of fossils dating back to the Triassic and Jurassic periods, or 190 million to 210 million years ago.

Today, the region is dry and scrubby. But back when the fossilised specimens were living, breathing animals, it was part of the supercontinent Pangaea.

Being near the equator, the climate was warm with periodic rains, Dr Apaldetti said: "Something similar to a current savannah, probably with a large amount of shrubs to satisfy the great herbivores of that time."

Among the fossilised remains, in 2015 they found a new dinosaur species — Ingentia prima — alongside other, previously known relatives called Lessemsaurus sauropoides.

Weighing in at an estimated 7–10 tonnes, both dinosaurs sported a long neck and tail, as well as air sacs in their body, like later sauropods did.

 Ingentia prima, a new dinosaur species discovered in Argentina, was about 8 to 10 metres long.(Supplied: Jorge A González)

Air sacs are thought to help keep the massive beasts cool.

But unlike their more recent four-legged counterparts, which stood on straight tree-trunk-like legs, Ingentia prima seemed to stand on flexed feet.

Their bones also showed signs of seasonal growth, also different to how palaeontologists think later sauropods grew.

Dinosaurs like brachiosaurus, Dr Apaldetti said, probably grew at a fairly rapid but consistent rate.

Ingentia prima's bones show it grew even faster at times, but slowed at others.

"With this discovery we can see that the first steps toward gigantism occurred 30 million years before the giants dominated practically the entire planet," Dr Apaldetti said.

"It [also] shows that there were other ways to be giant, and not necessarily implied the same anatomical changes that all other giants such as the titanosaurs required."

Four legs or two?

But Steve Salisbury, a palaeontologist at the University of Queensland who was not involved with the study, isn't convinced that Ingentia prima was a sauropod.

Rather than walking on four legs, he suspects they probably walked on two.

Scientists are hopeful the discovery of a fossilised dinosaur skeleton in outback Queensland will shed light on what was on the menu around 95 million years ago.

"Dinosaurs similar to Ingentia prima are typically referred to as 'basal sauropodomorphs', meaning they are on the side of the dinosaurian family tree that includes sauropods, but they are not there quite yet," he said.

"Most basal sauropodomorphs are thought to have walked on their hind legs like their meat-eating cousins, the theropods, but had a long neck and ate plants, like their descendants, the sauropods."

The new fossil haul was missing a few vital bones, such as Ingentia prima's hip, thigh bone and most of the lower leg.

Without them, Dr Salisbury said, it's hard to gauge the animal's posture.

And based on the few bones reported in the paper, "Ingentia prima's hand doesn't look ideal for putting on the ground," he added.

"They don't have a lot of the skeleton and, overall, the bits that are there don't look all that different from other basal sauropodomorphs."

So Ingentia might have been able to get on all fours, but probably spent most of its time on two legs — a little like another basal sauropodomorph that lived about 210 million years ago called Plateosaurus engelhardti, which is known from much more complete material.

"Although Ingentia prima looks like it was large for a basal sauropodomorph, unfortunately, they just don't have enough in this paper to make it appear too different to something like Plateosaurus engelhardti, and it's pretty much agreed that it was bipedal," he said.

"If that's the case, the transition to four-legged locomotion must have happened later."