Tetrapod Zoology

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On to our second day of talks (read part I first): things kicked off with Mike A. Taylor and Angela Milner’s talk on the history and collections of Street. Pinpointing the locations of original quarries is always difficult as exact records are often not kept, and of course the areas once used for quarrying change function and appearance over time. One interesting point is that the concept of ‘Street’ as a locality should perhaps be interpreted as broadly as possible, given that certain other, nearby Somerset sources might sometimes have provided specimens too [adjacent photo by Mo Hassan of Disillusioned Taxonomist].

Dave Martill looked at the taphonomy of Mesozoic marine reptiles, and hence at such things as the role of carcasses as ‘benthic islands’ and the orientation of carcasses in the substrate. While discussing decomposition and putrefaction, he even showed a photo of the Zuiyo-maru carcass (though misidentified it, alas). Mike Benton spoke again about trends in diversity across the PTB and beyond, this time in tetrapods as a whole. This included his work on the rise of dinosaurs (and on how they were effectively ‘victors by default’), and on the recent work by Brusatte et al. (2008) on the changing fortunes of crurotarsans and ornithodirans during the Triassic. Lez Noè discussed plesiosaur diversity and palaeobiology, noting that their rarity in the Upper Triassic is most likely an artefact resulting from evolution in open waters that aren’t well represented by the sedimentological record. The few Triassic plesiosaur fossils we have (including those from Svalbard, Scotland and England) do suggest the presence of a ghost lineage for the clade that extends well back into the Triassic. Lez also focused on his proposal that long-necked plesiosaurs might have been benthic feeders that used the neck to reach down to the bottom. Lots to say on that, but I’ll wait until he’s published! [image below shows Kevin the temnodontosaur, as displayed at the Philpots Museum. Kevin was discovered by Paddy Howe (the museum's geologist) in 2005. Unfortunately, most of its skull is missing].

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Ryosuke Motani looked at ichthyosaur evolution across the Triassic-Jurassic boundary. Traditionally, it’s been thought that fish-shaped ichthyosaurs (known today as parvipelvians) were uniquely Jurassic and Cretaceous, and that Triassic ones were less modified. New specimens and new work have shown that things were far more complex, and that the suite of characters involved in the acquisition of the parvipelvian-style tail were assembled piecemeal among non-parvipelvian taxa, and that the transition to a fish-like body shape occurred during the Triassic. So, there was no clear morphological turnover at the Triassic-Jurassic boundary… but was there a taxonomic turnover? Jurassic ichthyosaur taxa have yet to be reported from the Triassic (previous records of such are now known to be incorrect: recall that Macgowania was originally described as a species of Ichthyosaurus), but stem members of several lineages do seem to be present, as indicated by Ichthyosaurus-like, Leptonectes-like and Temnodontosaurus-like animals from British Columbia. It now seems that non-parvipelvians made it into the Jurassic, as demonstrated by a very interesting new taxon. A great talk, and the copious new data discussed therein is due to be published soon [image below shows a Jurassic marine contingent photographed at Lyme Regis. From left to right: Jeff 'Leedsichthys' Liston, Ryosuke Motani, Richard Forrest, Adam Stuart Smith].

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Incidentally, a talk on marine crocodilians was conspicuous by its absence (though, admittedly, they don’t appear until the Toarcian and are hence somewhat younger than the strata at Street). This wasn’t an oversight: an effort had been made to include the group in the proceedings, but the two speakers who were approached were both unable to appear on the day.

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The indoor element of the meeting ended with an open-floor discussion led by Michael Benton. A lot of historical stuff was thrashed out (I asked an intelligent question about the origin of the weird ichthyosaur on the road sign, but have forgotten the answer… Mike Taylor tells me that they’d lifted the pic from one of Thomas Hawkins’s books). Ella Hoch asked if Mesozoic marine reptiles ever evolved suction feeding analogous to that practised by extant beaked whales. It’s an open secret that a new ichthyosaur specimen with suction-feeding adaptations has been written up, but the authors have lost momentum on their paper after having it rejected (for unsound and retarded reasons) several times; it’s currently in limbo. It shows that at least some Mesozoic marine reptiles were ziphiid-like in terms of ecomorphology. Placodonts, pachypleurosaurs and at least one nothosaur all had suction-feeding adaptations similar to those of extant turtles. I’ve been saying for ages that I’ll elaborate on this at some stage… and at some stage I will. Meanwhile, see Rieppel (2002) [adjacent photo courtesy of Stig Walsh, taken outside the venue. Wow, so I do look like an australopithecine...].

Incidentally, for the duration of the meeting we had access to excellent marine reptile fossils, so got to see more than our fair share of Street’s plesiosaurs and ichthyosaurs. Many are beautifully preserved and fully or partially articulated, and some pose really interesting questions about taphonomy and preservation. Chris Moore and Simon Carpenter were also good enough to bring specimens along to the meeting, as were the Lyme Museum people [another temnodontosaur from Lyme Regis shown below (well, a cast: the real thing is too heavy to be wall-mounted like this). This specimen was found by Henry Ellis, donated to the museum in 1927, and prepared by David Costin in 1985. You're looking at the underside of the incomplete skull].

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Things finished with a field trip or two. The original plan was to visit various quarries in the Street area, but this couldn’t happen due to rain (it is summer after all). Instead, we visited Charmouth and Lyme Regis, so we got to visit the Charmouth Local Heritage Centre, the Philpot Museum (see Taylor (1986) for a review of the Philpot collection’s history), Chris Moore’s workshop and house, and other places too. The Philpot Museum has various temnodontosaur and other ichthyosaur specimens on display, as well as a juvenile scelidosaur and some Dimorphodon material. Charmouth has – among many other things – a cast of the amazing new scelidosaur figured by Naish & Martill (2007) – shown below – and discussed here. We saw some brand-new stuff, including at least one new ichthyosaur species (I won’t say what it was).

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I’ve done the whole palaeo-tourist thing along the Dorset coastline many, many times (a consequence of going to a university on the southern coast of England), but it was brilliant to see all of these specimens, and to do so in the company of so many experts and specialists. Hey: if you worked on Jurassic marine vertebrates and didn’t come along… where were you?

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All in all, I feel that ‘Sea Dragons of Avalon’ was a great success. We had our themed Arthur Cruickshank day, hosted an outstanding public lecture, and saw an appropriate selection of technical talks that covered all aspects of Street’s geology and palaeontology [adjacent image shows Lias mural on display at Charmouth Local Heritage Centre]. We (by which I mean ‘I’) also had lots of beer and curry, and as usual I stayed up far too late, talking about Thundercats, La Roux, Duran Duran and Torchwood. Many thanks to Mike A. Taylor, Lez Noè and Adam Smith for assisting with the write-up you’ve just read, to Mike, Lez, Jeff, David Hill, Chris Moore, Paddy Howe, Simon Carpenter and others for organisation and access to fossils, to Jeff for driving me there and back, and to everyone else involved for making it what it was.

For previous articles relevant to some of the material discussed here see…

And here’s that cake again, thanks to Lez Noè…

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Refs – -

Brusatte, S., Benton, M. J., Ruta, M. & Lloyd, G. T. 2008. Superiority, competition, and opportunism in the evolutionary radiation of dinosaurs. Science 321, 1485-1488.

Naish, D. & Martill, D. M. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, London 164, 493-510.

Rieppel, O. 2002. Feeding mechanisms in Triassic stem-group sauropterygians: the anatomy of a successful invasion of Mesozoic seas. Zoological Journal of the Linnean Society 135, 33-63.

Taylor, M. A. 1986. The Lyme Regis (Philpot) Museum: the history, problems and prospects of a small museum and its geological collection. The Geological Curator 4, 309-317.

Comments

  1. #1 Nathan Myers
    August 5, 2009

    That’s a very nice patina on that plaque on the cake. The bones are OK too. Who actually did the bones, Mike or the baker?

  2. #2 Laura Tamara henson
    August 5, 2009

    Have they actually classified the marine reptiles yet? Last I heard plesiosaurs were Lepidosaurs “related to turtles” but then came several studies placing turtles in the Archosauriformes close to crocodiles and aetosaurs. On a related note if turtles are aetosaur decedents then is Reptilia a valid clade or is it a synonym for Diapsida? After all it is defined as the last common ancestor of Turtles, Crocodiles, Lizards and Snakes. In addition the earliest member of Ichthyopterygia the platypus-like Hupehsuchus was a “thecodont”. Needless to say all my books on this subject are old and all the new ones I’ve seen only give a vague family tree with the sea reptiles branching off Reptilia and no cladogram at all.

    P.S. I think it’s funny that so many people identify perfectly identifiable pictures of dead whales (and raccoons) as sea serpents. My mom made an even more hilarious misidentification when I was a child. Driving by a local turkey farm (which also contained such exotics as peacocks and kangaroos) she sighted what she excitingly informed her family was a “giant turkey”. Everyone piled into the car to see only to find out that the giant turkey was an ostrich! She never lived it down and we made sure to bring it up every thanksgiving.

  3. #3 Zach Miller
    August 5, 2009

    Ichthyosaurs are still tenuously placed between lepidosaurs and archosaurs, last I checked. As for plesiosaurs, they are united with thalattosaurs (maybe), placodonts, pliosaurs, pachypleurosaurs, “pistosaurs,” “nothosaurs,” and currently turtles in a monophyletic Sauropterygia, which are also close to lepidosaurs (I think).

    Hupehsuchus is an ichthyopterygian, but it’s so derived as to not be informative about its immediate ancestry.

  4. #4 Vasha
    August 5, 2009

    So, it seems that the idea that turtles are non-diapsids is very much in the minority these days… who’da thunk it. Sometimes, the redrawing of the tree of life that’s taken place during my lifetime is still able to surprise me.

  5. #5 David Marjanović
    August 6, 2009

    Hypotheses on the relationships of turtles that occur in the current literature:
    1) Morphological:
    a) Inside the pareiasaurs (outside Diapsida).
    b) Next to the procolophonoids (outside Diapsida).
    c) Next to the euryapsids (inside Lepidosauromorpha).
    d) Next to the lepidosaurs (inside Lepidosauromorpha, duh).
    2) Molecular:
    a) Inside Archosauromorpha, but outside Archosauria.
    b) Inside Crurotarsi, but outside Crocodylia.
    c) Inside Sauropsida, but outside Diapsida.

    Funny, eh? The only molecular hypothesis that is compatible with any of the morphological ones is 2c.

    1a would make a lot of sense, except it runs into problems with Odontochelys. 2b is almost ridiculous; employing the aëtosaurs as stem-turtles is a valiant attempt, but still utterly unconvincing. 2c (which might be the same as 1a or 1b) has only been found in a single analysis so far (Frost et al. 2006), which used a questionable method (POY) and focussed on something different (lissamphibian phylogeny — the turtles were just there as part of the amniote outgroup).

    1c and 1d are almost the same: they come from the same team, and the position of the turtles differs only by one node between them. However, by putting the euryapsids into Lepidosauromorpha, they contradict AFAIK unpublished results that find them in Archosauromorpha…

    Currently, my money is on 1b (…as in “surprisingly, my thesis supervisor appears to be right after all”). Odontochelys looks vaguely like a procolophonoid in some respects, it has no trace of temporal fenestration, and the procolophonid Sclerosaurus has one row of osteoderms above each rib, fitting a scenario that was so far only considered possible under 1a. But my thesis hasn’t progressed to the point where I could say anything defensible on this topic.

    ————-

    The plesiosaurs (including pliosaurs and “pistosaurs”) are the sister-group of the notho- and/or pachypleurosaurs. All together form Sauropterygia (called Eosauropterygia* by Rieppel and his students). The sister-group of Sauropterygia is Placodontia; both together form Euryapsida (called Sauropterygia** by Rieppel and his students). And this clade probably sits inside the diapsid crown-group somewhere; either in Lepidosauromorpha or in Archosauromorpha. That’s where the disagreements begin.

    Ichthyopterygia + Hupehsuchia and Thalattosauria are probably close to each other and could sit either just outside the diapsid crown-group or close to Sauropterygia***. (Or maybe even both.)

    In what sense are Hupehsuchus and Nanchangosaurus “platypus-like”??? Is that just an allusion to the fact that they’re toothless? And who ever called them “thecodont”?

    * Frankly, this name is stupid.
    ** Rieppel & friends are right that this is the original use of that name — but it’s far, far less common in the literature than the other usage.
    *** If Ichthyopterygia and Sauropterygia form a clade, it gets the name Enaliosauria****… or Euryapsida according to some, which would go against a lot of historical usage.
    **** “In-the-sea lizards”. Or, more literally, “in-the-salt lizards”. Compare the stem-pinniped Enaliarctos.

    —————

    Finally, the name Reptilia should simply be abandoned. We don’t need it, we have Amniota, and we have Sauropsida… Reptilia only comes with historical baggage.

    —————

    So, it seems that the idea that turtles are non-diapsids is very much in the minority these days… who’da thunk it.

    Talking about minorities doesn’t have much sense in this small field. Basically, 1a is Lee, 1b is Laurin, 1c is Rieppel, 1d is Müller… and 2c, despite its 19 authors, is a single paper.

  6. #6 David Marjanović
    August 6, 2009

    I forgot to mention I can’t remember anyone grouping sauropterygians and thalattosaurs, at least to the exclusion of ichthyosaurs.

    Also…

    Frankly, this name is stupid.

    More importantly, it contradicts Recommendation 11G (more precisely Note 11G.1) of the PhyloCode.

  7. #7 Mike Taylor
    August 6, 2009

    To revert to the original topic of Arthur’s cake (also discussed in the comments to the previous posting!), it was made by Ms Samantha Butt the cake designer of Bridgwater – see http://www.cakesbysamantha.co.uk/index.html where Arthur’s cake already features (under ‘Corporate’, logically enough). If I recall rightly, we used the appropriate engraving from Hawkins’s monster books as the model …

  8. #8 Darren Naish
    August 6, 2009

    Thanks David for thoughts. Inclusion of placodonts within Sauropterygia is ‘consensus’ I would say (though it’s true that most of the articles I have in mind are by Rieppel, or Rieppel and colleagues). In fact I can’t recall seeing this contested since Sues 1987: which authors do you have in mind? Analyses (like Müller’s) that find a placodont + Eosauropterygia clade aren’t using ‘Eosauropterygia’ as a synonym for Sauropterygia, but rather are using it for the pachypleurosaur + nothosauroid + plesiosaur clade… or that was my impression anyway.

    Hupehsuchians have been suggested on occasion to be ‘thecodonts’. This is in the original description (Young & Dong 1973), in the popular literature (e.g., Long & Welles All New Dinosaurs and Their Friends), and I think also in Olshevsky’s publications. It’s all because of their dorsal scutes, plus an inability to put them anywhere else. It’s tempting to regard them as close to ichthyopterygians and thalattosaurs/thalattosauriforms (and within archosauromorphs?), and there’s some support for this, but more work is needed.

    Finally – - when, David, will you publish a paper arguing that we should abandon that most loaded of terms, Reptilia?

  9. #9 Zach Miller
    August 6, 2009

    I still like the term Reptilia and it can be a useful term, but its use needs to be restricted, perhaps to become more or less synonymous with Diapsida. Though, depending on where they end up, it may exclude turtles.

  10. #10 Nick Gardner
    August 6, 2009

    “I forgot to mention I can’t remember anyone grouping sauropterygians and thalattosaurs, at least to the exclusion of ichthyosaurs.”

    Nosotti and Rieppel (2003) placed sauropterygians and thalattosaurs together to the exclusion of ichthyosaurs, I believe. :)

    Cheers,
    -Nick

  11. #11 windy
    August 7, 2009

    That first pic brings to mind an old classic…

    fetch me the woman. The Anning woman

  12. #12 neil
    August 7, 2009

    “I forgot to mention I can’t remember anyone grouping sauropterygians and thalattosaurs, at least to the exclusion of ichthyosaurs.”

    Nosotti and Rieppel (2003) placed sauropterygians and thalattosaurs together to the exclusion of ichthyosaurs, I believe. :)

    Assuming that you are talking about the Eusaurosphargis paper, ichthyopterygians were not included in that analysis nor were they in Rieppel’s 1998 paper on Hanosaurus that found a similar sister group relationship between thalattosaurs and sauropterygians. In both cases, the node is fairly weakly supported so I think the jury is still out. Someone should really write something up about thalattosaurs, interesting critters….

  13. #13 Zach Miller
    August 7, 2009

    Aren’t they, though? In fact, if I recall correctly (the mind is hazy, it’s been so long), I sent a bunch of thalattosaur restoration to somebody with the hope that they’d be featured in a…series…

    “Triassic Heckasaurs?” Something like that…

  14. #14 David Marjanović
    August 8, 2009

    Finally – - when, David, will you publish a paper arguing that we should abandon that most loaded of terms, Reptilia?

    As procrastination during my postdoc, maybe… :-(

    Like you, I always have about 5 projects running at the same time.

    Hupehsuchians have been suggested on occasion to be ‘thecodonts’. [...]

    Oopsie.

    Analyses (like Müller’s) that find a placodont + Eosauropterygia clade aren’t using ‘Eosauropterygia’ as a synonym for Sauropterygia, but rather are using it for the pachypleurosaur + nothosauroid + plesiosaur clade… or that was my impression anyway.

    That’s what I mean, I think.

    Most of 20th century :: Rieppel
    Sauropterygia :: Eosauropterygia
    Euryapsida :: Sauropterygia

  15. #15 Nick Gardner
    August 9, 2009

    “Assuming that you are talking about the Eusaurosphargis paper, ichthyopterygians were not included in that analysis nor were they in Rieppel’s 1998 paper on Hanosaurus that found a similar sister group relationship between thalattosaurs and sauropterygians.”

    My mistake, I thought they were included. I double-checked and it seems you are right. :-(

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