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Trematosauroids, those gharial-snouted, marine temnospondyls

The views expressed are those of the author and are not necessarily those of Scientific American.


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Long-time Tet Zoo readers will know of my various efforts to get through all the temnospondyl lineages. Alas, I just haven’t been able to finish this grand project due to my getting stuck somewhere round about dissorophoids (see below for links to previous Tet Zoo temnospondyl articles). In frustration, here’s a section from late in the series: it’s a very brief bit of text on the (often?/sometimes?) marine trematosauroids.

Life reconstruction of the trematosaurine trematosaurid trematosauroid Trematosaurus brauni from the Early Triassic of Germany; image by Dmitry Bogdanov, licensed under Creative Commons Attribution 3.0 Unported license.

Trematosauroids are long-skulled (even gharial-like), Triassic temnospondyls known from India, Pakistan, Africa, Germany, Svalbard, Greenland, Nova Scotia, the USA and elsewhere. Long thought restricted to the Early Triassic, it was discovered during the 1980s that they survived into the Late Triassic: Hyperokynodon, the animal in question, is the largest trematosauroid currently known, with a skull estimated at 80 cm in length (Schoch et al. 2002). [Life reconstruction of Trematosaurus above by the excellent Dmitry Bogdanov.]

More recently, a single ilium from the Toutunhe Formation of the Junggar Basin, China, has been identified as that of a trematosauroid: this unit is Middle Jurassic in age. If the bone is correctly identified, it shows that “trematosaurs were probably not an extremely short-lived family, but were in fact one of the most remarkably long-lived families of temnospondyls” (Maisch et al. 2004, p. 582).

The trematosaurid trematosauroid phylogeny published by Steyer (2002). Note the especially long snouts of the lonchorhynchines.

Early trematosauroids had a narrow, wedge-shaped and blunt-snouted skull, rather small orbits located near the edges of the skull margins, and an elongate skull table. While retaining most of these features, the particularly long-snouted lonchorhynchines were unusual in that some taxa lack the anterior palatal vacuities that are otherwise so typical of temnospondyls. The cladogram shown here (from Steyer 2002) shows the trematosauroid clade Trematosauridae consisting of a monophyletic Trematosaurinae and Lonchorhynchinae; a more recent analysis (Schoch 2006) failed to support monophyly of the former.

Aphaneramma, a trematosauroid sometimes illustrated in those books that feature prehistoric ‘amphibians’, is a member of the lonchorhynchine clade, as are Cosgriffius, Erythrobatrachus and Wantzosaurus. Juvenile and adults specimens of Wantzosaurus from Madagascar indicate that the snout grew under strong positive allometry in these animals, though even juveniles were proportionally long-snouted compared to other trematosauroids and other temnospondyls (Steyer 2002). Changes of this sort seem to have been usual for long-snouted trematosauroids.

Particularly big palatal tusks are present in some basal trematosauroids, and in the South African form Microposaurus the teardrop-shaped nostrils accommodated the big tusks of the lower jaw’s tip: a unique configuration (Damiani 2004). Lateral line canals show that trematosauroids were aquatic predators, but beyond that little is known of their biology. The long, shallow body shape and elongate snout of some lonchorhynchines indicates that these animals were laterally undulating, pelagic or semi-pelagic predators that caught small, fast-moving prey with rapid lateral swipes of their jaws.

Trematolestes hagdorni, a close relative of the lonchorhynchines. Image by Ghedoghedo, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

However, Trematolestes from the Middle Triassic of Germany is relatively deep-bodied. [Adjacent photo of holotype by Ghedoghedo.] A preserved patch of skin indicates that Trematolestes had naked skin, but some other trematosauroids had osteoderms covering their neck regions at least. Trematolestes is further interesting in that the palate (including the palatal vacuities) is covered with polygonal ossicles that were themselves covered with irregularly spaced denticles. This is a feature of pre-Mesozoic temnospondyls and its presence in a trematosauroid is surprising: Schoch (2006) suggested that the ossicles “probably formed a ‘flexible palate’ that may have assisted in swallowing large prey items” (p. 40).

For previous Tet Zoo articles on temnospondyls, see…

Refs – -

Damani, R. 2004. Cranial anatomy and relationships of Microposaurus casei, a temnospondyl from the Middle Triassic of South Africa. Journal of Vertebrate Paleontology 24, 533-541.

Maisch, M. W., Matzke, A. T., & Sun, G. 2004. A relict trematosauroid (Amphibia: Temnospondyli) from the Middle Jurassic of the Junggar Basin (NW China). Naturwissenschaften 91, 589-593.

Schoch, R. R. 2006. A complete trematosaurid amphibian from the Middle Triassic of Germany. Journal of Vertebrate Paleontology 26, 29-43.

- ., Milner, A. R. & Hellrung, H. 2002. The last trematosaurid amphibian Hyperokynodon keuperinus revisited. Stuttgarter Beiträge zur Naturkunde Serie B (Geologie und Paläontologie) 321, 1-9.

Steyer, S. J. 2002. The first articulated trematosaur ‘amphibian’ from the Lower Triassic of Madagascar: implications for the phylogeny of the group. Palaeontology 14, 771-793.

Darren Naish About the Author: Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at darrennaish.wordpress.com. He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at tetzoo.com! Follow on Twitter @TetZoo.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. Dallas Krentzel 12:57 pm 04/4/2013

    What did the mandibular symphyses look like in the long snouted forms?

    Link to this
  2. 2. David Marjanović 2:32 pm 04/4/2013

    Yay, temnospondyls! ^_^

    Link to this
  3. 3. anzha 3:21 pm 04/4/2013

    You should have put more in about their marine habits!

    We have them in the XenoPermian too:

    http://thedragonstales.blogspot.com/2013/01/xenopermian-gift-teaser-for-weekend.html

    Link to this
  4. 4. HSUES 6:59 pm 04/4/2013

    Watch for a forthcoming article in JVP by Rainer Schoch and me on another huge Late Triassic trematosaur. The alleged record of a Mid-Jurassic trematosaur from the Junggar basin is not based on any derived features; the ilium may be attributable to a brachyopoid.

    Link to this
  5. 5. AlHazen 8:16 pm 04/4/2013

    “Trematolestes”– this week’s winner of the coveted Basilosaurus Prize! (“Lestes” — I think the Greek means something like robber or thief — tends to be an ending used on generic names of small(-ish), predatory (well, not obviously non-predatory) mammals. There’s no official rule about what endings to use for what kinds of animal, but it seems to me that communication is facilitated by conventions that restrict certain endings to certain taxa.)

    Link to this
  6. 6. Gigantala 8:17 pm 04/4/2013

    Thank you for posting this! Trematosaurs have always been my favourite extinct “amphibians”.

    Just out of curiousity, is there any particular hypothesis as to why sauropsids and not trematosaurs have taken over Triassic marine niches?

    Link to this
  7. 7. Andreas Johansson 3:28 am 04/5/2013

    For a lateral undulator, wouldn’t it make more sense to have a deep (and narrow) body than a shallow one?

    Link to this
  8. 8. Mark Evans 6:45 am 04/5/2013

    @5 How about Simolestes (snub-nosed robber) the Mid Jurassic pliosaurid. Of course there is also the mammal Cimolestes which I’ve always assumed is pronounced the same (at least I pronounce it the same way – I suppose it could be “Keemolestes”), and has the same meaning, Wikipedia not withstanding.

    Link to this
  9. 9. AlHazen 5:59 pm 04/5/2013

    Mark Evans– I had actually heard of Simolestes… but only because of a Tetzoo post. Darren is gradually educating the world! (Even, at a glacial pace, educating me!)
    On the other side, there is Libycosaurus.

    Link to this
  10. 10. David Marjanović 7:58 am 04/6/2013

    another huge Late Triassic trematosaur

    Awesome!!!

    Link to this
  11. 11. Hai~Ren 11:05 am 04/6/2013

    There are also the theropods Saurornitholestes and Ornitholestes.

    I’m finding it interesting that the Triassic trematosauroids appear quite similar to the Permian archegosauroids like Prionosuchus and Archegosaurus – another instance of convergence?

    Link to this
  12. 12. Esker 11:27 am 04/6/2013

    What kind of integument and what kind of eggs did these ‘amphibians’ have? Was the skin waterproof? Is there any evidence of a heterocercal tail and a fluke, like you see on so many secondarily marine amniotes? Were the eggs shelled? Were they laid at sea, in the rivers, or could trematosauroids walk reasonably well? Could they have been oviviparous instead? Could that even work for a critter with no amnion? We have to know!

    Link to this
  13. 13. souhjiro 2:22 pm 04/6/2013

    Temnospondyls (perhaps!) were metabolically like fishes, trematosaurids could not be so different in the sense of saltwater tolerancy to the freshwater fish clades colonizing the seas(like ariid catfish), also many “fishes”have fully working ovovivipary and true vivipary also. Don’t know if the younger or larval trematosaurids are found on brackish or freshwater environments…

    Link to this
  14. 14. David Marjanović 3:26 pm 04/8/2013

    Oh, so the SciAm blogs are accessible again. Good. Till a few hours ago, any attempt to access any of them was redirected to the SciAm main page.

    another instance of convergence?

    Of course.

    What kind of integument and what kind of eggs did these ‘amphibians’ have?

    Skin: fishy. Eggs: no evidence.

    Could that even work for a critter with no amnion?

    It works for a lot of extant amphibians, and so does viviparity…

    Don’t know if the younger or larval trematosaurids are found on brackish or freshwater environments…

    Larval ones, at least, are unknown.

    Link to this
  15. 15. Therizinosaurus 12:42 am 04/12/2013

    “How about Simolestes (snub-nosed robber) the Mid Jurassic pliosaurid. Of course there is also the mammal Cimolestes which I’ve always assumed is pronounced the same”

    I wonder if the one named more recently had 19th century attempts to rename it, ala Kentrurosaurus, since people back then oddly thought this needed to be done.

    “On the other side, there is Libycosaurus.”

    Well, that was thought to be a dinosaur when named, so made sense at the time.

    Link to this

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