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 II: Flying and Slithering Reptiles

End-Times for Pterosaurs

Why aren’t any other pterosaur families found at the end of the Cretaceous? And what happened to all the small species? Were they on their way to extinction even before the asteroid struck? Were the small species out-competed by birds, as some scientists have suggested (and others have disagreed)?

Two presentations from this year’s SVPCA show that the problem isn’t the pterosaurs, but their fossils.

First, Nick Longrich and colleagues present some new pterosaur fossils from the late Maastrichtian (the very very end of the Cretaceous). Among these fossils are members of the azhardachid family, along with two other families – the nyctosaurs and the pteranodonts. Here we have evidence that numerous pterosaur families did in fact survive right up to the K-T extinction, we just haven’t been finding their fossils.

When certain organisms are preserved as fossils noticeably more or less than others, it is called preservation bias, and it isn’t all that surprising for pterosaurs, really. Pterosaur fossils are rare to begin with. Their bones are very thin-walled and often don’t survive the fossilization process. If we aren’t attentive, it’s easy to be fooled by an unbalanced fossil record.

Which brings us to the second study, by Mark Witton and colleagues. They also present a new pterosaur discovery from the Late Cretaceous, a single pterosaur related to the azhdarchid family. But it’s small, with a wingspan of only 1.5 meters. And the bones are at a mature developmental stage, indicating this is an adult, not just an young individual. So much for the disappearance of tiny pterosaurs!

Here again we have preservation bias. Large animals fossilize better than small ones. As the researchers of this study point out, not only are small pterosaur species practically unknown from the Late Cretaceous, but juveniles of large species are as well. This is a pretty good indication that the fossil record of this time period is simply biased against small-sized pterosaurs.

*The tiny pterosaur paper just came out yesterday! I also wrote about it at Earth Touch.

Together, these two reports indicate that pterosaurs may actually have been doing just fine up to the end of the Mesozoic, and that there a lot more fossils to find as paleontologists continue to put together the full picture.

Pterosaur Growth Rates

These days, paleontologists have quite a good understanding of growth rates in many dinosaurs, but pterosaurs remain much more mysterious. Part of the problem is that, as we’ve discussed, pterosaur fossils are rare, so it’s very unusual to find growth series (that is, fossils of every life stage of a species) like we get for some dinosaurs. On top of that, growth history in animals is often recorded in the bone tissue of limbs, but the thin-walled limb bones of pterosaurs preserve very little information.

In their talk, David Unwin and Charles Deeming examined two rare cases of pterosaur growth series, for the famous and tiny Rhamphorhynchus and for the bizarre flamingo-like Pterodaustro. For the various specimens, they estimated age and body mass, then calculated growth per day, and statistically compared the growth rate to modern-day reptiles (which grow slowly) and birds and bats (which grow quickly).

Their analysis found that pterosaur growth was very consistent with the slow growth of modern-day reptiles. This matches up with previous studies on Rhamphorhynchus and Pterodaustro which have found that, while the animals grew quickly at first, it ultimately took several years for them to reach adult size. Who knows how long it would have taken for the truly giant pterosaurs to grow up?

Microscopic Investigation of Pterosaur Diets

As with so many things pterosaur-related, their eating habits are a bit of a mystery. Interpretations of pterosaur diets, depending on the species, include fish, insects, small animals, shellfish, and even filter-feeding. But these conclusions are based mainly on the shape of the teeth, plus the rare discovery of gut contents. Another approach would really help solidify our understanding of what pterosaurs eat.

Jordan Bestwick and colleagues are working on analyzing something called microwear. When we eat, food scraping against our teeth (plus our teeth scraping against each other) leave behind microscopic abrasions. Different diets are known to leave different abrasion patterns on teeth, which can help us interpret the diets of ancient animals. This has been done for dinosaurs and extinct mammals, but never for pterosaurs.

It’s actually Bestwick’s PhD research study to examine pterosaur microwear, compare with modern-day animals, and test his results against other approaches. In this way, the hope is to establish a sure-fire test of pterosaur diet in a way that hasn’t been achieved before. The work is ongoing, and the SVPCA abstract doesn’t actually reveal what results he’s gleaned so far, which might still be preliminary. In any case, I’m excited to see the final product down the line.

Jonathan Rio and colleagues had the honor of being awarded Best Talk for the conference, I believe, and it was about a snake, so how could I pass it up!

The fossil record contains evidence for a prehistoric family of snakes unlike any alive today, the Madtsoiidae. These snakes persisted from the Cretaceous Period right up to the Ice Age before disappearing completely. They included some real behemoths such as the Australian Wonambi which rivaled the largest snakes today at up to 6 meters long.

The largest, and first described, madstoiid was Gigantophis, whose name literally means “giant snake,” discovered in Eocene rocks in Egypt. But the 20 vertebrae known from this original specimen weren’t described in detail, so the exact identification of this slithering giant has remained a bit elusive. Rio and colleagues re-examined the bones to determine exactly which characteristics identify the species.

In the end, they accomplished a few things: 1) they determined that one other fossil identified as Gigantophis was a mistake, meaning this big snake is so far only known from remains in Eocene North Africa; 2) they reinforced the understanding of exactly how this snake is related to other ancient madtsoiids; and 3) they used up-to-date models to estimate the full length of Gigantophis at a massive 7m, longer than just about any living snakes.

Wrapping up.

Scientific conferences are always a cacophony of exciting new research, and a great window into the cutting-edge of a field. Most of these abstracts will probably end up as full published papers before long. Something to look forward to!