Alligator and Deinosuchus enter the LRT

One is a large extant icon of Florida, famous for crossing golf courses. The other is a Cretaceous giant of coastal North America. Today Alligator (Fig. 1) and Deinosuchus (Fig. 2) enter the large reptile tree (LRT, 1936+ taxa; subset Fig. 3).

This started with an online NPR story (link below):
“There’s this concept out there that crocodylians are unchanging forms,” Brochu said. “That they appear way back in the distant past and haven’t changed since the days of the dinosaurs. That is simply not true.” Dr. Chris Brochu was a co-author on the paper: Cosette AP and Brochu CA 2020, a systematic review of Deinosuchus, which prompted the NPR story.

Figure 1. Alligator skull colorized here.

Alligator mississippiensis (Holbrook 1842; originally Crocodilius mississippiensis, Daudin 1802; up to 4.6m) is the American alligator. Derived (through a long chain of transitional taxa) from a sister to Middle Cretaceous Isisfordia (Fig. 4), these aquatic archosaurs have shifted the internal nares to the rear of the pterygoid enabling breathing while eating, like mammals.

Figure 2. Deinosuchus riograndensis assembled and colorized from Cosette and Brochu 2020. Lateral view of 3D model from the Langston lab. It doesn’t quite match the fossil. Note the lack of deep pterygoids in the model.

Deinosuchus riograndensis
(Colbert and Bird 1954, originally Phobosuchus riograndensis, TMM 43620-1), original genus: (Deinosuchus hatcheri (Holland 1909 CM963; Late Cretaceous; approaching 10m in length) is a coastal giant of North America. Premaxillary fenestrae are found on the anterior dorsally expanded premaxilla, as in Crocodylus niloticus, but not Alligator. The confluent nares open dorsoposteriorly along the parasagittal plane. Note the model lateral view does not quite match the fossil dorsal view with regard to the anterior extent of the quadratojugal.

Figure 3. Subset of the LRT focusing on Crocodylomorpha with the addition of Alligator and Sebecus. Many scores were rescored with this addition. This is part of the LRT process: review.

The cladogram by Cosette and Brochu 2020
focused solely only the species surrounding Deinosuchus and do not extend to the base of the Crocodylomorpha and beyond. When you deal at the species level, like that, you may need more characters or you may not, but you will need more pertinent characters to separate taxa at the specimen and species level, while eliminating irrelevant characters and states.

Figure 4. Isisfordia was a Middle Cretaceous precursor to later alligator and crocodiles in the LRT.
Figure 4. Isisfordia was a Middle Cretaceous precursor to later alligator and crocodiles in the LRT.

In the LRT,
working at the generic level, 238 multi-state characters have, so far, done the job of separating one fish from another, one croc from another, etc. Calls for more characters in the LRT are not based on experience and fact, but on out-of-date hypotheses still found in university textbooks and lectures. Not sure why academics are adamant about adding traits and equally adamant about not adding taxa. That’s why the LRT experiment exists.

Figure 5. Sebecus with a new premaxilla based on Deinosuchus (Fig. 2).

Sebecus icaeorhinus
(Simpson 1937, Pol et al. 2012, Eocene; Fig. 5) is a land croc from South America. Like a theropod dinosaur, the teeth were laterally compressed and serrated. Sebecus was earlier nested with Baurusuchus, but now nests more closely to living crocs with conical teeth.

This hypothesis of interrelationships appears to be novel.
If there is a prior citation, please let me know so I can promote it here.

Cosette AP and Brochu CA 2020. A systematic review of the giant alligatoroid Deinosuchus from the Campanian of North America and its implications for the relationships at the root of Crocodylia. Journal of Vertebrate Paleontology 40(1):e1767638
Daudin FM 1801-2. Histoire Naturelle, Générale et Particulière des Reptiles; ouvrage faisant suit à l’Histoire naturell générale et particulière, composée par Leclerc de Buffon; et rédigee par C.S. Sonnini, membre de plusieurs sociétés savantes. Vol. 2. F. Dufart, Paris, 432 pp.
Hollbrook JE 1842. North American Herpetology; or, A description of the reptiles inhabiting the United States. Vol II (2nd ed.). J. Dobson, Philadelphia, 142 pp.
Simpson GG 1937. An ancient eusuchian crocodile from Patagonia. American Museum Noviates 965: 19–20.


2 thoughts on “Alligator and Deinosuchus enter the LRT

  1. OK, so…..having seen crocodyliform skulls from time to time, what is an “accessory naris?”

    I have to assume you’re referring to the holes on the premaxilla anterolateral to the naris. In living crocodylians, these are modified occlusal pits for the first dentary tooth. The dorsal surface frequently wears away, turning the pit into a hole. Sometimes, the anterior margin wear away as well, converting it into a a notch. These are variable in nature – they’re absent from hatchlings, and not all individuals have them. Indeed, they can be bilaterally asymmetrical in some skulls, present on one side but not the other. They occur in most crocodylian species. (They never occur in extant Alligator, and they start off as notches in tubulirostrine forms like Gavialis and Tomistoma.)

    These openings have no relationship whatsoever to the respiratory system, and they are not homologous with the openings seen in Deinosuchus. If these are the openings you refer to, please stop calling them “accessory nares.

    The openings in Deinosuchus are likewise not directly connected with the nares. They instead appear to be related to one of the paranasal sinuses in the snout. They may thus be pneumatic in nature, but they would not have been extensions of the nasal passages. Again, “accessory naris” is an inappropriate term for these openings.

    Your sutural reconstruction of the Deinosuchus skull is inaccurate on many points. Please use the reconstructions presented in the paper, which were based on direct observation of the specimens. The D. riograndensis skull used in your reconstruction is damaged, and you are being misled by cracks.

    “Calls for more characters in the LRT are not based on experience and fact, but on out-of-date hypotheses still found in university textbooks and lectures. Not sure why academics are adamant about adding traits and equally adamant about not adding taxa.”

    A couple of things here –

    First- when we ask that you add characters, it’s not because we’re closed-minded traditionalists. It’s because we know that (a) adding characters can make a profound difference in the resulting trees and (b) some of the stranger conclusions on your trees result from a failure to include characters that would link taxa that we know, based on loads of information, are closely related. THere’s a lot of character evidence showing that Gavialis is related to Alligator and Crocodylus and not to thalattosuchians or tethysuchians. Unless you’ve included it, your contention that Gavialis is related to thalattosuchians and/or tethysuchians can and should be disregarded as an artifact of insufficient character sampling.

    Second – can you point me to an academic who is “adamant about not adding taxa?” I can think of cases where we might advocate not adding a specific taxon (e.g. because it’s fragmentary), but every one of us believes taxon sampling and character sampling are equally important. The only one being doctrinaire here is you by being adamant about adding taxa and equally adamant about not adding traits.

    • “accessory naris” – you are correct, of course. I ignored these landmarks earlier. It’s been several weeks. Now, after looking up my sources, I’m not sure where I got the term. Googling does not bring it up. I will make the change to your ‘premaxillary fenestrae’.

      “adding characters” – these are needed, as noted, getting down to separating species. So far, adding characters has not been needed to lump and separate tested genera. That’s just a fact.

      “adamant about not adding taxa” – Anyone and everyone dealing with the origin of whales, turtles, snakes, pterosaurs, pterodactyloid-grade pterosaurs, bony fish, placoderms, sharks, cephalopods, Vancleavea, caseasauria, reptilia, birds (no one includes as many Solnhofen birds), placentals, bats, the two convergent diapsid clades, you know, the usual list.

      Thank you for your input.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.