Bipedal crocodyliforms of the Cretaceous

[Newt]

Many of you will be aware that there were (at least facultatively) bipedal basal crocodylomorphs ("sphenosuchians") and crocodyliforms (Protosuchidae) roaming about in the Late Triassic and Early Jurassic. Most were small (>1.5 m TL), but some of the Triassic "sphenosuchians", such as Carnufex and Redondavenator, reached 3 m plus in length and were larger than most contemporary theropods. A recent paper by Kim et al. describes bipedal crocodylomorph trackways from the medial Cretaceous (?Aptian/Albian) of South Korea. Track size indicates animals 3 to nearly 6 m in length. Open access below:


https://www.nature.com/articles/s41598-020-66008-7.pdf


This is intriguing to me because I had sort of assumed that those large predatory bipedal loricates - not only the aforementioned "sphenosuchians" and protosuchids but rauisuchids, poposauroids, and the like as well - had been completely replaced by theropods by the Late Jurassic. Whether the Korean animal was a late-surviving protosuchid or a newly bipedal crocodylomorph evolved from quadrupedal ancestors, it indicates that crocs were still able to compete in the bipedal predator space in the Cretaceous. Also perhaps relevant, Edentosuchus from the Lower Cretaceous of Xinjiang has been interpreted as a late-surviving protosuchid:


doi:10.1016/j.cretres.2004.05.002 (mef.org.ar)

[Loon]

Not really a group I was too familiar with, at least by name, but I knew what these types of animals looked like. It's interesting that they, or something like them, survives that long, especially in the creataceous when you think they couldn't even compete with Theropods.

[Newt]

Yeah. Crocs were more diverse than they get credit for. The only ones I see get mentioned are the supergiants Deinosuchus, Purussaurus, and occasionally Sarcosuchus (there are several other crocs in the 10-12 m range, but only these three seem to get much press), plus Kaprosuchus. There's so much more to the wonderful world of extinct crocodylomorphs. Fish-tailed sea-goers! Carnosaur-headed Cenozoic terrestrial predators! Miniature omnivores! Filter-feeders! Shell-crackers! Duck snouts! Horns! 

[Halichoeres]

Interesting! I also thought of this as a strictly Triassic phenomenon.

[andrewsaurus rex]

interesting indeed.  I'm still having trouble wrapping my head around the fact the Postosuchus was bipedal.   It looks so front heavy.  Like it would do a face plant every time it stood up.

[Thialfi]

Very fascinating, thanks for sharing! I never realized they were around post-Triassic.

interesting indeed.  I'm still having trouble wrapping my head around the fact the Postosuchus was bipedal.   It looks so front heavy.  Like it would do a face plant every time it stood up.

I hear you, I am warming up to the idea though. Recently saw a short video of a pangolin walking on its hind legs comfortably, which helped in shaping the image for these crocodyloforms and -morphs as well:



https://www.youtube.com/watch?v=B95NdS77fZM&ab_channel=NoelleAlcorn

[Newt]

Pangolins are amazing.

I have seen references to Postosuchus being bipedal, but not the research. Anyone have a link?

[Smilodon P.]

I have seen references to Postosuchus being bipedal, but not the research. Anyone have a link?

@Newt I believe this is the paper you are looking for (paywall):

https://sp.lyellcollection.org/content/379/1/525.abstract

Spoiler

(Off topic: what the #### is that thing on the pangolin's back? a tracker? A baby pangolin? A dead rat?)

[close]

[Newt]

Cheers S @Smilodon P. !


*EDIT* I've actually read that paper, but it apparently didn't stick. IIRC there are quadrupedal cheirotheriid tracks from the strata that have produced both Postosuchus kirkpatricki and P. alisonae, and they are considered the most likely trackmakers. So either they were at least facultatively quadrupedal or there was another, yet unknown, big quadrupedal loricate in Carnian/Norian North America.

[andrewsaurus rex]

I thought it had been proven that Postosuchus' arms/front legs were too weak to bear the weight of walking.  Unless that conclusion has changed in the past few months..

its front limbs are pretty small for a quadruped.....I haven't seen the tracks in question but they should at least reflect the small size and low load bearing capability of the front limbs, if made by Postosuchus.

However, I still have trouble with a bipedal Postosuchus because, as I said above it looks so front heavy with it's big body and big head.  Even if it could somehow balance on 2 legs, as a predator it is going to have to subdue prey, which means biting, wrestling with and to a degree lifting a struggling prey animal.  All of which will serve to make it even more front heavy and make it more difficult to stand on 2 legs without falling flat on its face.

[Thialfi]

A @andrewsaurus I can imagine their front limbs would do fine to provide temporary support, for example in case of struggle or uneven terrain etc., but not as permanent walking pose.

In Planet Dinosaur there is a pretty interesting scene in which you see ouranosaurs grazing, drinking and using their front legs as support while doing this, but rearing up and running on solely their hind legs. A heavy tail helps a lot as well in their balancing act.

[Newt]

From Weinbaum 2013:


"The manus is so reduced as to make it unlikely that it was used for any type of full-time locomotion. Each digit is also reduced towards the distal end and terminates in a tiny, nub-like ungual with the exception of digit 1, which does have a large, recurved ungual, which perhaps Postosuchus may have used to help rip open carcasses. The paratype specimen shows this same configuration. Interestingly, the first digit is semi-opposable to the rest of the manus, which would have afforded a limited grasping ability."

"Although most workers consider nonpoposauroid paracrocodylomorphs ('rauisuchids') to have been quadrupedal (e.g. Long & Murry 1995; Peyeret al. 2008; Gower & Schoch 2009; Nesbitt 2011), evidence presented herein and by Weinbaum (2007) suggests at least that Postosuchus may have been habitually bipedal, although more testing is needed to further support that hypothesis. I disagree with the interpretation of the UNC Postosuchus specimen by Peyer et al. (2008, p. 380), who state that 'The massive pectoral girdle, extended arms, the tightly joined metacarpus indicate that the forelimbs were actively involved in locomotion'. Many theropods possess relatively massive shoulder girdles and clearly do not use their forelimbs for locomotion."


So Weinbaum's argument for bipedalism seems to rest entirely on the size of the manus.


I'll see if I can find pics of the cheirotheriid tracks in question.

*EDIT* It appears the tracks I was thinking of (Brachychirotherium spp.) are now thought to be made by aetosaurs, and so have no bearing on the Postosuchus question.

[Halichoeres]

Apparently sauroid posted about this some months ago, but the lone comment on the post suggests that someone didn't read the article. http://dinotoyblog.com/forum/index.php?topic=8730.0

[Newt]

Well spotted!

[andrewsaurus rex]

ok, well we definitely now need Safari to make a bipedal Postosuchus figure, the same size as their exiting quadrupedal one.  Would make for a great side by side display