Wednesday, August 12, 2015

Richard Delgado's Age of Reptiles: Ancient Egyptians

I have been a fan of Richard Delgado's Age of Reptiles series for a little while now. If you are unfamiliar with the series it is a comic that focuses on recreating the prehistoric world. Delgado has looked at the Morrison and Clovery Formations in the past with his previous volumes but it has been several years. Now he takes aim at the paleoecosystems of North Africa in the Late Cretaceous.
The cover of Issue 1. Copyright Dark Horse Comics.
 The story follows, so far, the exploits of a lone Spinosaurus as it cruises around the mangroves and deltas of what is now Egypt. The first thing that jumped out at me is that the animals in Ancient Egyptians are far more accurate than in some of his earlier works. For example:
What is happening here? Anatomy? Physiology? MAKE THEM FIGHT! Copyright Dark Horse Comics.
While the artwork has always been pleasant to downright gorgeous in previous installments of Age of Reptiles, I find the accuracy and beauty of this latest outing is commendable. I will state that I am not someone who works on Cretaceous vertebrates from North Africa, but looking at the animals and scenes presented in the first two issues of Ancient Egyptians I don't see anything that immediately jumps out at me as being horrendously wrong either paleontologically or behaviorally. I am impressed at the care that Delgado has put into portraying his animals and scenes.
Scene from Ancient Egyptians, copyright Dark Horse Comics. Holy cow, look at the difference between the earlier work and now! Blood, poop, backgrounds!
Ancient Egyptians does suffer one setback. This series doesn't fully take into account how recent work has changed our understanding of what Spinosaurus looked like. The sail is shown as one uninterrupted convex bulge. The forelimbs are long but the hind feet show three functional digits and no webbing. Both of these are contra Ibrahim et al. (2014). To his credit(?), Spinosaurus is shown on all fours multiple times...but that may not be reasonable considering it is a theropod. And Delgado does like to pronate his theropod hands.
The cover of Issue 2. Copyright Dark Horse Comics. The two back animals show pronated hands.
 Regardless, Delgado does a great job of making Spinosaurus seem alive and an actual animal, not like a monstrous killing machine (I'm looking at you Jurassic Park III). His Spinosaurus seems real. It poops. It fights. It sleeps. It fails at hunting. It hides. It tries to mate. It has the wounds to prove it.

The scarred protagonist Spinosaurus. Copyright Dark Horse Comics.
It isn't just the main character that seems real. Herbivores are violent and protective - not dumb domestic cows with scales. Mating and rearing rituals are brutal but also in line with what we know about modern animals. It may be hard to look at some of the illustrations later in Issue 2 but on the other side they are in line with what we know about how some modern adult males act in the presence of unrelated juveniles.

Issue 3 just came out at the end of last week and Issue 4 comes out in September. I am looking forward to picking them up and finishing the tale which Delgado likens to Samurai and Western classic films. The absence of narrative text might put some off but for myself I find it adds to the immersion. Where will the lone Spinosaurus find himself at the end of his journey?
The cover of Issue 3. Copyright Dark Horse Comics.
Delgado, Richard. "Age of Reptiles: Ancient Egyptians" Dark Horse Comics. (2015).

Ibrahim, Nizar, Paul C. Sereno, Cristiano Dal Sasso, Simone Maganuco, Matteo Fabbri, David M. Martill, Samir Zouhri, Nathan Myhrvold, and Dawid A. Iurino. "Semiaquatic adaptations in a giant predatory dinosaur." Science 345, no. 6204 (2014): 1613-1616.

Saturday, August 8, 2015

Brink et al. 2015 - What does it tell us about phytosaurs?

So new tooth news seems to be coming at a rapid pace this year! Several tooth-related papers have come out already and we're barely past the halfway mark. Most recently we have Brink et al. (2015) discussing funky features in meat-eating dinosaurs and, tangentially, other archosaurs. While I obviously love theropods and dinosaurs in general my interest at the moment is with non-dinosaurian archosaurs like our strange Chinle friends from Comb Ridge.

Duane Nash already did a good breakdown of what the article means in terms of theropod dinosaurs and how to relate the findings of Brink et al. to modern correlates as well as exploring what they could mean in terms of feeding and prey capture methods in various dinosaurs. If you haven't read his blog I'll wait.

Okay. Back? Good. As you can tell from both the article and the blog Brink et al. reject the stress-induced formation hypothesis for these interdental folds, as has been suggested previously. Instead they find that these structures are present even before stresses are placed on the teeth - while the unerupted teeth are still in the alveoli. So what does that have to do with Triassic teeth?

If you read the article you will see they sampled a few non-dinosaurian taxa (a phytosaur and an indeterminate Cretaceous croc) as well as the Triassic theropod Coelophysis. We have an abundance of phytosaur teeth at Comb Ridge and have picked up a few teeth we have tentatively IDed as theropod. So not only is Brink et al. a cool paper, it deals with some of our Triassic friends too!

Two views of phytosaur teeth in SEM and thin section, both from Brink et al. (2015), CC-BY
Image C shows mesial denticles under SEM and thin section. D shows a thin section with enamel, globular dentine, and primary dentine.
Brink et al. are looking mainly at the evolution and development of the structures with limited discussion on how the structures would have directly influenced prey capture and processing (though Nash, linked above, goes into that more). One of the more interesting things to me to come out of this is that phytosaurs have interdental fold structures like theropods and unlike crocs, Spinosaurus, ominivorous animals like Troodon and pure herbivores like ornithischian dinosaurs. Brink et al. further state that these adaptations are best interpreted as ways to capture large prey and crush bone. When we talk about phytosaurs, though, most people tend to interpret them as crocodile analogs. Sometimes this means perhaps ambushing large prey, other times preying on fish. This second option has been especially favored for the narrow-snouted forms, viewed by some as not robust enough to deal with large struggling prey.

A Redondasaurus attacks a decent sized prey item - a silesaurid. From Edyta Felcyn: go support her art!
There is some other evidence to suggest that phytosaurs were not just meekly eating fish and moderate-sized animals like dinosauromorphs (see image above). Coupled with their teeth that were perfectly adapted to ripping up large struggling prey items and mashing their bones, we have trace behavioral evidence to indicate this is exactly what happened. Last year Drumheller et al. documented a phytosaur attack on a living rauisuchian. You can read PastTime Podcast's take on the paper if you don't want to read through the paper itself. In short, though, they find evidence that a phytosaur tried to wreck shop on a rauisuchian, an animal that was basically a cross between a tyrannosaur and a crocodile. Wreck so much shop, in fact, that the phytosaur tooth went almost completely through the femur of the rauisuchian. This unfortunate fellow was then attacked by another rauisuchian and finally scavenged by a smaller phytosaur. Times were rough in the Triassic, even if you were the biggest, baddest fellow on the land.

Damaged psuedosuchian femur. The phytosaur attack is represented by the embedded tooth in Box A. Image from Drumheller et al. (2014).

If encounters like this were rare and the exception to the normal behavior of phytosaurs then the fossils described by Drumheller et al. are truly remarkable. Between the marked heterodonty found in adult phytosaurs described by Hungerbühler (2000) and the new evidence that they possessed dental adaptations that enabled them to capture, kill, and process prey larger than them it seems unlikely that this was a one-off chance encounter.

Ventral view of phytosaur snouts from Hungerbühler (2000). Note the different size and shapes of the teeth in this view.
 Instead our view of phytosaurs as fish-eaters occasionally attacking small-to-medium-sized land prey needs to be challenged. Phytosaurs were equipped with a dental battery that enabled them to routinely tackle large, dangerous, struggling prey as adults. This would include animals that were significantly larger than them. While juvenile phytosaurs seem to lack these dental adaptations (see, for example, my earlier post on this topic) and likely pursued prey smaller than themselves, adults would have been terrifying creatures to behold.

An interesting point to consider too: if phytosaurs were more like Nile Crocodiles than gharials, why don't we see ziphodont dentition in crocs? Certainly wildebeast and zebra don't give up after a fight. Brink et al. note that their Cretaceous croc also lacks ziphodont dentition, suggesting the behavior of crocs and their prey haven't changed much. Modern crocs are obviously capable of tackling large prey (though usually not larger than their own body). If they have gone hundreds of millions of years without the interdental folds and can eat large land prey, what were phytosaurs doing different?

Crocodiles and their prey in Africa - 2:57 from National Geographic

We don't have the fossils to answer that definitively but it would appear that modern crocodiles are not as good of an analogy for phytosaurs as has long been supposed. Hopefully future work at Comb Ridge and across Triassic collections will lead to new insights, clarifying what this unique clade was doing.

As an end note, Brink et al. suggest that ziphodont dentition with interdental folds is basal to all theropods, even thought phytosaurs possess the same tooth structure. It would have been nice to look at things like pseudosuchians from the Triassic to see if similar dental structure existed. If so, perhaps this sort of adaptation dates back to the rise of archosaurs in general. I guess that's another paper for another time.

Next up from me: a return to the lighter side. I'm going to be reviewing Richard Delgado's new Age of Reptiles comic series, Ancient Egyptians!


Brink, K. S., Reisz, R. R., LeBlanc, A. R. H., Chang, R. S., Lee, Y. C., Chiang, C. C., ... & Evans, D. C. (2015). Developmental and evolutionary novelty in the serrated teeth of theropod dinosaurs. Scientific reports, 5.

Drumheller, S. K., Stocker, M. R., & Nesbitt, S. J. (2014). Direct evidence of trophic interactions among apex predators in the Late Triassic of western North America. Naturwissenschaften, 101(11), 975-987.

Hungerbühler, A. (2000). Heterodonty in the European phytosaur Nicrosaurus kapffi and its implications for the taxonomic utility and functional morphology of phytosaur dentitions. Journal of Vertebrate Paleontology, 20(1), 31-48.