November 13 , 2016:

by David

Last week, paleontologists gathered in Liverpool for the 64th Annual Symposium for Vertebrate Paleontology and Comparative Anatomy (SVPCA). I was unable to attend, mostly because of that big ocean sitting in the way (actually I’ve never been to SVPCA, I’d love to go) but I did get a hold of the abstract book. Lots of great talks and posters this year.

Here, I’ll go through some of my personal favorite highlights from this year’s meeting. I won’t have all the details, since I’m mostly going by the abstracts and not the full presentations, but I will be offering a glimpse into what’s currently happening in the field of paleontological research.

Part I: Dinosaurs

Floating Spinosaurus

Let's start with Donald Henderson throwing some big theropods in the water.

Spinosaurus is no stranger to controversy in paleontology or in the public eye (remember when it fought T. rex in Jurassic Park III? I know, lame, right?). But it’s had a resurgence lately ever since Nizar Ibrahim and colleagues published a study in 2014 with two really intriguing findings: 1) that Spinosaurus was specially adapted for semi-aquatic life, and 2) that this big predator, traditionally seen as a biped like all other meat-eating dinosaurs, may have been stuck on all fours. In general, most scientists and enthusiasts think the first finding is pretty neat, but there’s been a lot of arguing about the second one.

To gain some more insight into Spinosaurus locomotion, Henderson built a digital 3D model of the dinosaur and tossed it in the water (digitally). According to the model, Spinosaurus was perfectly capable of floating with its head above the water! At first, this seems like another great aquatic adaptation, but Henderson did the same thing for T. rex, and it floated just fine, too. Maybe theropods were just automatically good floaters? (Birds seem to do it pretty well).

One more thing: the model also indicated that the big dino’s center of mass was relatively close to the hips, supporting a two-legged stance. This is contrary to Ibrahim’s finding that the center of mass was too far forward for the Spinosaurus to walk on its back legs. And so the debate continues.

Speaking of large famous dinosaurs, let’s turn to Susie Maidment and colleagues’ talk on Stegosaurus, the iconic plated dinosaur found in fossil sites in Utah, Wyoming, and Colorado. Exactly how many species of Stegosaurus there are is a debate with a long history, but these researchers recognize two: the classic Stegosaurus stenops and the smaller Stegosaurus mjosi.

In this talk, Maidment presented a new fossil of S. mjosi recently discovered in Montana. When a fossil is found somewhere its species has never been found before, paleontologists call this a range extension. This find apparently got these scientists thinking about Stegosaurus distribution, so they gathered together data on the location of all the Stegosaurus fossils found from the same time period as this new fossil. It turns out the two species didn’t live together: the larger species lived in the south and the smaller ones lived in the north.

The coolest part about this is that the southern region, where the big stegos lived, was a more arid (dry) environment than the north at that time during the Late Jurassic Period. Scientists studying modern-day animals have suggested that big herbivorous mammals (like elephants and rhinos) may have evolved big body sizes as a survival strategy in dry conditions, so the fact that the larger Stegosaurus species lived in the more arid region implies that dinosaurs may have evolved similar traits as big mammals for similar reasons. Neat!

"How Big Did Barosaurus Get?"

Fans of dinosaur museums may be familiar with Barosaurus. One skeleton famously stands tall in the Teddy Roosevelt Rotunda at the AMNH in New York, dwarfing everything else in the room by far. Its neck alone is about 8.5 meters (28 feet) long. But this is apparently not particularly large for this dinosaur: far bigger bones have been discovered. So, how big did they get?

In this presentation, Mike Taylor and Matt Wedel (the two main guys behind the SV-POW blog) aimed to find out by taking a close look at some neck vertebrae from other Barosaurus fossils to see if they could calculate just how big was BIG.

Apparently, the length of neck vertebrae is pretty consistent with the full length of the neck, which means these two specimens would have had full neck lengths of at least 13 meters in the first, and a whopping 17 meters in the second specimen. Like I said, the "big" AMNH skeleton isn't all that big.

When I read this, I found myself wondering if a Barosaurus with a neck twice as long as the AMNH skeleton would also have a full body twice as long. But according to a paper by Melstrom et al., the neck of Barosaurus actually got proportionately longer as it grew older. I imagine it could only grow so much before the dinosaur toppled forward!

Tiny, Camouflaged Psittacosaurus

One of the most exciting recent developments in paleontology has been the discovery that we can detect the colors of fossil animals. Coloration can reveal all sorts of excellent information about an animal. In this case, Jakob Vinther and colleagues are using colors to interpret habitat.

The dinosaur in this case is little Psittacosaurus, and the fossil is so well-preserved that the researchers were able to identify patterns in its scales and colors, and duplicate them onto a life-sized (which is pretty small) model. They found that this dinosaur was darker on its back, lighter on the underside of its tail and belly, and had a dark face with some patterning along its back.

The pattern of dark-on-top-light-on-bottom is very common in modern animals. It’s called counter-shading, and it works like this: When light from the sun hits an object, like an animal, it illuminates the top and casts the bottom in shadow. In many animals, vision is tuned to pick up on this contrast to identify three-dimensional objects. If an critter's natural coloration is dark on top and light on bottom, it lessens the contrast between back and belly, reducing the effects of shading and making the animal appear more “flat” than 3D, and thus harder to see.

Animals' coloration is often reflective of their habitat. In a heavily forested environment an animal may have patterns of dark and light all across its body to “counter” the splotchy light that shines through leaves. Vinther and colleagues wondered if they could figure out Psittacosaurus’ habitat from its color.

Here's how they went about it: They made a second life-sized model, this one all gray. They put it in different lighting conditions (different weather, different habitats) and took pictures of the shadows cast on it. Then, digitally, they inversed the colors in the photos (switched darks for lights) and identified which “switched” pattern best fit the actual pattern of the dinosaur, to see which habitat’s lighting was best “countered” by the dinosaur’s natural coloration. Awesome.

What they found, as you might expect, is that the patterns on Psittacosaurus best matched a closed habitat with plenty of overhead tree cover,which fits well with the fact that the area where it is found also contains lots of evidence of ancient trees. This little dino would have been well-hidden among the patchy light filtering through the leaves.