Sunday, April 18, 2010

Prestosuchus

Meaning: "Presto's Crocodile"
Species: P. chiniquensis and P. loricatus
Nominal Author: Huene 1942
Age: Ladinian - Carnian (Middle/Late Triassic)
Location: Santa Maria Formation, Brazil
Physical Characteristics: Large (~5 meters) quadrupedal predator with an erect posture


Taxonomy
Prestosuchus was originally described by Friedrich von Huene in 1942 as two different species: P. chiniquensis and P. loricatus. However, because of the amount of material and Huene's failure to designate holotype specimens, Prestosuchus taxonomy has been problematic. Krebs (1976) has suggested that the two Prestosuchus species are in fact synonymous and Barberena (1978) presented a specimen as being the skull of Prestosuchus. Brusatte et al (2010) have recently concluded that if the Barberena skull and the Huene material do indeed represent different taxa, then they are at least very closely related. A detailed revision of Prestosuchus taxonomy is currently being performed by Julia B. Desojo.

Phylogeny
Prestosuchan (and Rauisuchan, for that matter) phylogenetics has been extremely problematic. Fortunately, a recent study by Brusatte et al (2010) seems to have sorted things out. Prestosuchus and Batrachotomus have been shown to compose a sister taxon pair with an 81% bootstrap value. Prestosuchidae Romer 1966 is described the most inclusive clade containing Prestosuchus chiniquensis Huene 1942 but not Rauisuchus tiradentes Huene 1942. By the Brusatte phylogeny, Prestosuchidae therefore consists of Prestosuchus, Batrachotomus, and Saurosuchus. Moving out further in the phylogeny, we get Rauisuchoidea which includes Prestosuchidae plus Rauisuchidae and a basal cluster which includes Ticinosaurus. Finally, we see a monophyletic Rauisuchia made up of Rauisuchoidea and Poposauroidea.



This is the first in a series of weekly posts I will be making. Every Sunday, I will feature an overview of a Crurotarsan species (or genus for that matter). I will mostly choose at random but requests are welcome.

17 comments:

  1. Very interesting... Regarding the suggestions, i'd like to see, along with "taxonomy" and "Phylogeny", a brief chapter about "paleobiology" included in every description of these beasts.

    Oh, and a post about the mighty Postosuchus is something i'm really waiting for ;)

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  2. Very interesting!
    I'm looking for the next posts!

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  3. Alessio,

    Thanks! You are right. I definitely need to include info on paleobiology (and even paleoecology). For whatever reason, finding such information on Prestosuchus proved to be a bit of a challenge, but I will try harder for future posts.

    And don't worry, Postosuchus is on its way. I'll try to feature him sometime in May. = )

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  4. Thanks for the post! Rauisuchians are amazing, seriously
    Too bad rauisuchia showed to be very unstable...

    I wanna contribute to this blog: you could put a list of references at the bottom of the article, so your readers will have the possibility of reading even more about taxa you talk about

    By the way, can't wait for the next post! ^^

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  5. I love the prestosuchids. In the alternate timeline I had thought up where the T-J extinction never happened, I was originally going to have the rauisuchids (as in the family) end up as some of the dominant predators, until I realized that a lot of rauisuchids were big, easily killable apex carnivores, while prestosuchids seemed to be much more variable in niche and size range (see Yarasuchus and Ticinosuchus), and could easily grow to Postosuchus size (Saurosuchus). At least, that's the impression I got from the sources I read on prestosuchids, the literature may have changed since then.

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  6. Fabrizio,

    If you check ou the resources page, I've been trying to list all the papers reference, as well as books and other such things related to the topics of this site. And if you have anything you want to contribute, I am open to suggestions (no guarantees that anything will be posted tho).

    Metalraptor,

    Yeah, prestosuchids aresome of my favorites, but as I talked about in the post, they have been problematic in regards to phylogeny. Definitely check out the new paper "The higher-level phylogeny of Archosauria" by Brusatte et al in the most recent publication of the Journal of Systematic Palaeontology if you can.

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  7. Thanks for the answers, Susan :)

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  8. What was the consistency index for the MPTs in Brusatte et al's paper? It's somewhat important to know in evaluating the reliability of other values (bootstraps, tree lengths, etc).

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  9. True. The consistency index was 0.31. Also, the retention index was 0.68 and each tree (70 MPTs) was 747 steps, in case you wanted to know.

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  10. OK, I'll take low CI as a positive sign if the bootstrap value is high..

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  11. Given the available material, support values aren't exactly going to be great for rauisuchians, but the ones from Brusatte et al are decent considering. And hopefully the new Prestosuchus material from Brazil will help improve things.

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  12. Maybe we will found out, after the taxonomical revision currently undertaken by Julia B. Desojo is finalized, if Karamuru, the genus erected by Kischlat from material previously assigned to Prestosuchus (including the skull described by Barbarena), is a valid taxon or should it be P. vorax or even P. chiniquensis as originally proposed by Barberena.
    And now a few questions:
    Did the remains recovered by von Huene contain any cranial material? And if they do, how complete was it?
    Was Prestosuchus capable of bipedal movement as proposed in the case of Postosuchus?
    Is the 5 m value suggested for the length of Prestosuchus based on the almost 1 m long skull described by Barbarena or other skulls that are similar in length? If that is the case, my impression is that this estimate is rather conservative considering that the saltwater crocodile, the largest still living crurotarsan, can manage to obtain lengths close to the 7 m mark by having skulls only of about 80 cm in length. Of course, this obviously assumes that they had somewhat similar skull/ body length ratios.
    And finally is the reconstruction from ANMH accurate? Maybe it's just me or it's due to the optical perspective but the skull from the reconstruction doesn't seem too similar to the one from the previous diagram, for example the form and the placement of the fenestrae or the length and the positioning of the teeth.

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  13. I'll have to look up the info on the von Huene material and the bipedality of Prestosuchus (although, considering the limb proportions of Prestosuchus and Postosuchus, I would assume at least a small amount of bipedal movement was possible).

    I don't remeber where I got the 5 meter estimate, but I think it's old and I think Prestosuchus was more likely 7+ meters.

    If you look at the AMNH reconstrustion from less of an angle (there's a better picture on the "Pictures" page of this blog) it compares a lot better to the diagram, except maybe for the antorbital fenestra (which I'm having some difficulty interpreting from that diagram). I know that the AMNH skeleton is a composite, but it is indeed labeled as P. chiniquensis, so there could be some discrepencies with a complete Prestosuchus. It also seems a little short to me (4 - 5 meters), but that could just be the composite cast nature of the display.

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  14. Wow, that was quick. Thanks.
    I'm not sure if sufficient post-cranial material was retrieved to do this, but there is any study about the forelimb/hindlimb ratio of Prestosuchus? It would be interesting if we could compare it to other rauisuchians or even theropods. But if there wasn't enough material before, perhaps the new nearly complete skeleton discovered will shed some light on the locomotion of prestosuchids.
    So, when you said that Prestosuchus could achieve a length of 7 meters plus, was your estimate based on the original remains or it also includes the ones that are sometimes ascribed to Karamuru, do you personally consider Karamuru to be a valid genus?
    Indeed, some aspects can be attributed to the angle of the photo but even so there still are some discrepancies in the morphology of the skull, specially when it comes to teeth length ratios. You can compare it to the skull found on this page (it's the most similar angle I could find): http://www6.ufrgs.br/paleovert/ and the diagram resembles quite closely this one: http://www.coladaweb.com/img/gallery/geografia/fosseis5.jpg.

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  15. I forgot to mention it, although I'm not sure if it's proper to address it here, but perhaps can you add other sebecosuchians besides Baurusuchus to your LifeList, at least Sebecus if nothing else and even a dryosaurid like Phosphatosaurus or some one of those weird suspension feeders like Stomatosuchus or Mourasuchus.

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  16. Pete, sorry it took me so long to get back to you. Life is very busy. I am doing my best to update the Life List to include post-Triassic species like thalattosuchians.

    I will definitely have to do some research into the locomotion of Prestosuchus. Personally, I'm still a little skeptical about Karamuru, but hopefully we'll get better descriptions of both Prestosuchus and "Karamuru" soon.

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  17. Getting really close to some of my favorite crurotarsans (Saurosuchus in particular)

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