Dr. Hungerbuehler Talks Phytosaurs

18 10 2009

Good tidings and well-wishes!

I apologize for the extreme tardiness which has accompanied this post, a fact largely due to recent restrictions on my schedule and that of the good doctor which have exposed themselves of late. So, without further ado, I present this long-awaited interview with my instructor and leading phytosaur expert, Dr. Axel Hungerbuehler of Mesalands Community College who has graciously agreed to ‘talk shop’ by answering a few questions about his favorite tetrapods .

(Below is a clip from a local news channel highlighting some of our recent aetosaur specimens which was filmed last January and features “Dr. H” and myself)

Q: Do Triassic researchers have any ideas regarding from what ancestors phytosaurs may have evolved?

A: Phytosaurs are widely regarded as the most basal group of the crurotarsans. Unfortunately, the earliest phytosaurs contain all of the major features that identify them as such, so it’s difficult to reconstruct what the ancestral forms looked like. And since there are no known ‘intermediates’, there’s very little to be said about where phytosaurs came from because the ones we know of are simply too derived.

A Redondasaurus skull on display at the New Mexico Museum of Natural History and Science in Albuquerque.

A Redondasaurus skull on display at the New Mexico Museum of Natural History and Science in Albuquerque.

Q: Phytosaurs are often directly compared with modern crocodilians. How apt is that comparison? Aside from the nostril position (it’s reasonably well known amongst Triassic enthusiasts that while modern crocodilians have nostrils at the tip of their snouts, phytosaurs sported theirs much closer to the eyes, and frequently just in front of them), what are some obvious differences between phytosaurs and modern crocodilians?

A: A modern crocodilian is the best living analogue, but I’d exercise some caution when invoking it because phytosaurs are certainly NOT identical to them. For instance, they have a much higher degree of heterodonty (‘they have multiple types of teeth in their mouths much more frequently’) than any living crocodilian. With regards to the overall shape of their skulls, all phytosaurs, even the robust ones, have comparatively narrow snouts. Thus, they can best be ecologically compared to the gharial (Gavialis gangeticus) and false gharial (Tomistoma schlegelii). Still, the overall similarity exists and its appropriate to compare them. However, it’s not an exact correspondence. As for other major differences between phytosaurs and modern crocs, all phytosaurs had a soft secondary palate (as opposed to the hard, bony secondary palates found in living crocodilians) which caused the reorganization in shape of all the area’s bones.

Rutiodon skeletal reconstruction.

Rutiodon skeletal reconstruction.

Q: How long did phytosaurs persist during the Triassic? Is there any chance that they may have survived into the Jurassic?

A: There’s no clear evidence of any phytosaur surviving into the Jurassic. Though three nicely-preserved teeth have been found in the Hettangian stage in France, they were most likely redeposited from older rocks. It’s recently been argued that the Triassic-Jurassic boundary is lower than it’s commonly considered to have been which, if true, could mean that some phytosaurs lived into the Jurassic after all, but we’ll have to await further evidence. As for the oldest phytosaurs, every phytosaur remain that’s been proven to have come from such an animal and has hailed from a clear locality is from the Upper Triassic. However, a basal phytosaur (Mesorhinosuchus) from Germany reportedly came from a Lower Triassic deposit, but the specimen was destroyed in 1944, so there’s no way to confirm this claim (though some rumors argue that the specimen survived, they cannot currently be substantiated and are of doubtful accuracy). We need either the actual specimen or a second one from the deposit to be sure.

Angistorhinus cranial reconstruction drawn by the Hairy Museum of Natural Historys Matt Celesky

Angistorhinus cranial reconstruction drawn by the Hairy Museum of Natural History's Matt Celesky

Q: What was the biggest phytosaur? What was the smallest?

A: Here we have to resort to skull length rather than total length — although phytosaur remains are the most abundant fossils in the majority of terrestrial Upper Triassic deposits in the northern hemisphere, complete skeletons are exceedingly rare (the total count here is 3). Also, there are some gigantic postcranial phytosaur elements known, but we have no means to assess the dimensions of their former bearer. The record-holder skull is that of Leptosuchus gregorii (AMNH 3060) with 1420 mm, on display in New York, followed by several specimens falling the size class between 1200 to 1300 mm (genera Angistorhinus, Leptosuchus, Pseudopalatus, and Redondasaurus). I assume the smallest means the smallest mature animal, rather than clear juveniles (the smallest complete skull of a juvenile is 275 mm). It’s hard to assess the individual age of smaller specimens (meaning smaller skulls), as most lack the axial skeleton that could potentially demonstrate whether the specimens were mature or not. The smallest skulls that ‘look’ mature are in the range of 600 to 650 mm (genera Paleorhinus, and Nicrosaurus).

A small but well-preserved phytosaur tooth I located in Petrified Forest National Park last summer. The shape is that of a posterior cutting tooth (away from the snout tip).

A small but well-preserved phytosaur tooth I located in Petrified Forest National Park last summer. The shape is that of a posterior cutting tooth ('away from the snout tip'). Mud from this site is still caked on my hiking boots.

Q: Do phytosaurs display interesting differences in ontogeny? Also, is there any speculated sexual dimorphism?

A: We don’t know about ontogeny differences as very few juveniles are known. Out of those we do have, standard features are observed (large orbits, etc.), but otherwise the traditional phytosaurian characteristics are present. As for the sexual dimorphism, the topic crops up every few generations with speculations frequently being made only to fade away. The problem is simple: to show sexual dimorphism, we need a population in a single quarry with several specimens to show that there were at least two morphs available. Sadly, such sites don’t exist and don’t produce specimens to the required degree. However, in sites with an array of around a half-dozen skulls, one can postulate that trends exist, which has been done with Pseudopalatus in the Canjilon quarry. Here, it’s been suggested that males had prenarial (‘in front of the nostrils’) crests and females didn’t. Personally, I think that the authors have a point here, but I’m afraid that some people will claim that because this distinction exists in Pseudopalatus, it exists in all phytosaurs, which isn’t the case. Also, there’s a wide variety of different crest types that have been described for many phytosaur species, some of which are ambiguously defined. I can live with the presence or absence of a crest in Pseudopalatus, but I’m not sold on this characteristic in other genera.

Parasuchus skull reconstruction in dorsal (aerial) view.

Parasuchus skull reconstruction in dorsal ('aerial') view.

Q: Were phytosaurs fairly uniform in their eating habits, or were different genera adapted to eating different things? What do you suspect they were eating? Do we have stomach contents for any phytosaurs?

A: We do have stomach contents: the two known Indian Parasuchus skeletons each have a prolacertiform in their stomachs (in fact, the holotype and paratype of Malerisaurus were the food items of these specimens). As for their eating habits, the old interpritation is that slender-snouted species were gharial-like piscivores whereas the massively-snouted ones were hunting terrestrial prey. However, the two aforementioned Parasuchus specimens each had slender snouts and meter-long Malerisaurus in their stomachs (they’re partially articulated and were likely swallowed whole). Thus, the only preserved phytosaur stomach contents contradict the standard theory, which I find amusing. My guess is that they were opportunistic predators like modern crocodilians and ate whatever they could fit into their snouts. I also have no problem with envisioning the massively-skulled phytosaurs (eg: Leptosuchus) bringing down essentially anything that moved since most had the dentition to tear these beasts into manageable chunks and almost certainly possessed the physical strength with which to kill these animals.

The Petrified Forest Musuems famed Leptosuchus skull.

The Petrified Forest Musuem's famed Leptosuchus skull.

I’d like to once again thank Dr. Hungerbuehler for agreeing to be interviewed and my readers for submitting such excellent questions.

May the fossil record continue to enchant us all!

Upcoming Posts: Prosqualodon, my new-found love of evolutionary psychology, and (less scientifically) a celebratory Godzilla post.




3 responses

18 10 2009
Zach Miller

A wonderfully informative interview! Thank you both! Now I know something about phytosaurs. I’ve really got to draw one of these suckers…

18 10 2009

I’m glad you liked it!

I’ve really got to do more of these interviews…

12 08 2010

Could you please clear up the Mesorhinosuchus/Mesorhinosaurus confusion? Some sources refer to one, but other sources give the other. Since none give both, it is impossible to determine which has priority.

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