Tetrapod Zoology

Giants and sirens: caudates part I

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Did I mention that 2008 is Year of the Frog? Just kidding. In actuality, the conservation effort so many of us are now involved in doesn’t just concern anurans (frogs and toads), but all the living amphibian groups: as you’ll know, there are, besides anurans, two other such groups. We looked previously at the bizarre caecilians. This time round we get through the last group of the three: the caudates, or salamanders, of which there are about 560 living species. Again, these animals are anything but boring. Yes, this is that group that, believe it or don’t, includes species that have evolved beaks, are partially herbivorous, can be extremely tolerant to cold, and – in the big species – can easily bite open a human hand…

Most salamanders are small, but some species have approached or exceeded lengths of 2 m. Beaks, crushing teeth, claws, prehensile tails, reduced-limbed, eel-like body shapes, and ribs that literally protrude through the skin have all been evolved by caudates. Intra-uterine cannibalism, neoteny, the defensive shedding of tails and limbs, weird developmental shifts in digital development, bizarre warning displays, lekking and nuptial dancing, facultative herbivory and fungivory, dedicated cave-dwelling… it’s all here. The term caudate means ‘possessing a tail’ and, in contrast to anurans and caecilians, salamanders retain the body shape that seems to have been plesiomorphic for lissamphibians. Having said that, even salamanders exhibit a list of anatomical specialisations that make them unusual compared to other tetrapods: they’ve lost a long list of skull bones that are present in other amphibians (including the postorbitals, jugals, tabular, supraoccipital and ectopterygoids), and also lack a middle ear (though they’re not deaf). Bizarrely, salamanders have disproportionately large amounts of DNA [image at top shows a mole salamander in characteristic head-butting posture. More on all that later].

Salamanders are generally Laurasian and the groups that occur on the southern continents (there are plethodontids in South America and some salamandrids in northern Africa) have only gotten there comparatively recently. An important theme which has cropped up several times independently within different salamander clades is neoteny: the retention of juvenile characters into sexual maturity. It’s been widely suspected that neoteny results in the retention of confusing plesiomorphic characters, and in extensive convergence, so working out the relationships of neotenous salamander clades has been difficult (Wiens et al. 2005). Phylogenetic studies on salamanders have in fact differed pretty radically in the relationships they infer, though a rough consensus has started to emerge.

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The oldest salamanders we know of are Middle Jurassic forms from central Asia (Kokartus honorarius) and England (two species of Marmorerpeton). What we know indicates that these basal forms looked superficially like stout-bodied living forms, but they lacked various bony and muscular characters present in the crown-group. The best known basal salamander – Karaurus sharovi from the Upper Jurassic of Kazakhstan [shown in adjacent image] – has been compared to living mole salamanders (ambystomatids) and probably lived in a similar manner (Estes 1981). Whether the name Urodela is restricted to the crown-group, with Caudata used for the total-group, or whether the name Caudata is restricted to the crown-group, with Urodela used for the total-group, depends on which authors you pay attention to. Evans & Milner (1996) argued that it made better sense to use Caudata for the total-group for several reasons, and this seems to have been mostly followed and is used here. So Marmorerpeton and the karaurids Kokartus and Karaurus are stem-caudates but not urodeles, and a few other Mesozoic taxa, like Pangerpeton and Jeholotriton from the Jurassic or Cretaceous of Liaoning Province in China, are too (Wang & Evans 2006).

It has been argued that, even by the Middle Jurassic, crown-group salamanders had appeared and started to diversity: this would be so if one recently named taxon, Chunerpeton tianyiensis, has been correctly interpreted (Gao & Shubin 2003), and if the sediments it comes from are Middle Jurassic in age and not younger as has been argued (Marjanovi? & Laurin 2007). Chunerpeton was described as a cryptobranchoid (explanation on that term below), in which case members of both of the youngest major salamander clades, Cryptobranchoidea and Salamandroidea (aka Salamandriformes, or Diadectosalamandroidei), had both appeared by this time (given that both are sister-taxa). Fossil members of Salamandroidea (or at least of its stem) are known from the Upper Jurassic: the best preserved being little Iridotriton hechti from the Morrison Formation (Evans et al. 2005). By the Upper Cretaceous, members of most or all of the living salamander ‘families’ had probably appeared.

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In an effort to do the same thing I did with anurans (and have yet to complete!), here is a quick run-through of all the salamander clades (though not all the ones known only as fossils). You should see this as A Beginner’s Guide to Salamander Diversity, though a fairly advanced beginner’s guide if you get my meaning. I’ve tried desperately not to get distracted too much, nor to get into the minutiae like taxonomy, phylogeny or fossil history. Here we go.

Cryptobranchoids: giant salamanders and Asiatic salamanders

Two particularly primitive groups of salamanders are still around today: the hynobiids and the cryptobranchids. Hynobiids, generally just called Asiatic salamanders, are a poorly known group of about 50 species that occur from Afghanistan and Iran eastwards to Japan, though from the Miocene and into the Pleistocene they also occurred in Europe (Venczel 1999). Some hynobiids occur in cold parts of northern Asia and are particularly cold-tolerant, being able to withstand freezing at temperatures below -50°; C for months at a time (that is, they literally get frozen alive and stay dormant in a block of ice). Some species employ aquatic suction feeding while others have a projectile tongue, and some (like Onychodactylus) have evolved claw-like structures on their digit tips [in the adjacent image, the animal at the bottom is O. japonicus. You can just see its claws. The species at the top is Hynobius nigrescens]. A recent study of hynobiid phylogeny and biogeography indicated that, following its origin in China, the history and distribution of the group was mostly controlled by local geological effects like the desertification of Mongolia and the uplift of the Tibetan plateau (Zhang et al. 2006).

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Grouped with hynobiids in the clade Cryptobranchoidea (or Cryptobranchiformes), are the giant salamanders, or cryptobranchids. There are only three extant species (the North American Hellbender Cryptobranchus alleganiensis, the Chinese giant salamander Andrias davidianus and Japanese giant salamander A. japonicus); all are salamanders of fast-flowing, well-oxygenated water (but this wasn’t the case for all fossil species). All possess dorsoventrally flattened bodies. Gills are absent in the adults and their lungs apparently don’t function in respiration, so all gas exchange occurs across the extensively folded, wrinkled skin. Eyelids are absent (a sure sign of aquatic habits in a caudate).

Giant salamanders are famous for, well, being giant, with record-holding specimens of the Chinese giant salamander reaching 1.8 m and 65 kg (some fossil species were bigger, with A. matthewi from Miocene North America reaching 2.3 m). Little known is that they have particularly vicious teeth, exude a foul smell which has been partially likened to ‘the rankest public urinal crossed with that of stale sweat’ (Brazil 1997, p. 64), and that the males brood the eggs. Giant salamanders can inflict massive wounds with their teeth: during territorial fights males frequently sever digits, limbs, and bits of tails of rivals, and massive fatal slices across the neck – sometimes resulting in decapitation – are apparently not uncommon. We’ll be coming back to giant salamanders in a later article.

Chunerpeton from the Jurassic of China (mentioned above) has been identified as a cryptobranchid, in which case both this group and its sister-taxon Hynobiidae have been around for a long time. Chunerpeton seems to have been reasonably large – about 200 mm long – but of course not ‘large’ by comparison with the Cenozoic species.

The amazing sirens

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Several features support the view that cryptobranchoids are primitive relative to the other crown-group salamanders, the salamandroids. Unlike more derived salamanders, cryptobranchoids still possess an angular bone in the lower jaw, and they also practise external fertilization. Some studies indicate that cryptobranchoids are not alone in being outside of Salamandroidea (or Salamandriformes, or Diadectosalamandroidei), but that the bizarre sirens belong here too (Wiens et al. 2005). Sirens (Sirenidae) are perhaps the strangest salamanders: indeed, at times they’ve even been excluded from Caudata and put on their own as the Trachystomata, or Meantes. Superficially eel-like, neotenic animals that lack a pelvis and hindlimbs, they possess external gills, lack eyelids, are adept at burrowing in mud, and reach 95 cm in the largest species (Siren lacertina, the Greater siren: shown in adjacent pic, borrowed from USGS). The Cretaceous siren Habrosaurus reached 1.6 m.

The big surprise for many people is that sirens have a horny beak and pavements of teeth on the palate. The beak forms a broad platform inside the jaws, and the jaw joint is ventrally displaced relative to the rest of the skull. All of these features are adaptations for crushing, and field studies show that sirens specialize in feeding on gastropods and bivalves. Sirens also appear to be partially herbivorous, ingesting vascular plants and algae. They have enlarged hindguts that may house symbiotic microbes (Pryor et al. 2006). If this is correct it’s a big deal and would make them unique among caudates. They are also unusual in that they can survive desiccation by forming a sort of mucus cocoon in the mud, a habit very similar to that better known for lungfishes. Oh yeah, and they emit a yelping noise when grabbed (Halliday & Verrell 1986). Sirens have a fossil record extending back to the Upper Cretaceous, and while the extant species are all North American, fossil representatives have been described from Sudan, Germany, India and Bolivia. However, the identification of all of these fossils as sirenids has recently been challenged (Gardner 2003) [image below shows the Lesser siren S. intermedia].

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Ok, gotta stop there. I have a horrible feeling this is all going to take longer than planned, but I next need to get through amphiumas, proteids, mole salamanders, salamandrids and plethodontids. Surely that can’t be difficult…

Refs – -

Brazil, M. 1997. Mission massive. BBC Wildlife 15 (4), 62-67.

Estes, R. 1981. Handbuch der Paläoherpetologie. Teil 2. Gymnophiona, Caudata. Gustav Fischer Verlag, Stuttgart.

Evans, S. E., Lally, C., Chure, D. C., Elder, A. & Maisano, J. A. 2005. A Late Jurassic salamander (Amphibia: Caudata) from the Morrison Formation of North America. Zoological Journal of the Linnean Society 143, 599-616.

- . & Milner, A. R. 1996. A metamorphosed salamander from the early Cretaceous of Las Hoyas, Spain. Philosophical Transactions of the Royal Society of London B 351, 627-646.

Gao, K. & Shubin, N. H. 2003. Earliest known crown-group salamanders. Nature 422, 424-428.

Gardner, J. D. 2003. Revision of Habrosaurus Gilmore (Caudata; Sirenidae) and relationships among sirenid salamanders. Palaeontology 46, 1089-1122.

Halliday, T. R. & Verrell, P. 1986. Salamanders and newts. In Halliday, T. & Adler, A. (eds) Animals of the World: Reptiles and Amphibians. The Leisure Circle (Wembley, UK), pp. 18-29.

Marjanovi?, D. & Laurin, M. 2007. Fossils, molecules, divergence times, and the origin of lissamphibians. Systematic Biology 56, 369-388.

Pryor, G. S., German, D. P. & Bjorndal, K. A. 2006. Gastrointestinal fermentation in greater sirens (Siren lacertina). Journal of Herpetology 40, 112-117.

Venczel, M. 1999. Land salamanders of the family Hynobiidae from the Neogene and Quaternary of Europe. Amphibia-Reptilia 20, 401-412.

Wang, U. & Evans, S. E. 2006. A new short-bodied salamander from the Upper Jurassic/Lower Cretaceous of China. Acta Palaeontologica Polonica 51, 127-130.

Wiens, J. J., Bonett, R. M. & Chippindale, P. T. 2005. Ontogeny discombobulates phylogeny: paedomorphosis and higher-level salamander relationships. Systematic Biology 54, 91-110.

Zhang, P., Chen, Y.-Q., Zhou, H., Liu, Y.-F., Wang, X.-L., Papenfuss, T. J., Wake, D. B. & Qu, L.-H. 2006. Phylogeny, evolution, and biogeography of Asiatic salamanders (Hynobiidae). Proceedings of the National Academy of Sciences 103, 7360-7365.

Comments

  1. #1 budak
    January 12, 2008

    Giant salamanders that rose against their human owners and conquered the world were the ‘protagonists’ of the dystopian satire ‘War with the Newts’ by Karel Capek.

    http://ebooks.adelaide.edu.au/c/capek/karel/newts/

  2. #2 Luna_the_cat
    January 12, 2008

    Very cool, indeed. I should have guessed that these would be amphibians…!

  3. #3 David Marjanovi?
    January 12, 2008

    and also lack a middle ear, so they’re deaf.

    Oh no. While there’s no air-filled middle ear, the stapes works in low-frequency sound conduction in aquatic species, and terrestrial individuals have a so-called operculum, a bone near the stapes footplate that, via a muscle, transmits low-frequency vibrations from the forelimb and shoulder girdle to the inner ear.

    The operculum (os operculare auris; not homologous to any gill lid) is shared with terrestrial frogs and with Eocaecilia.

    Most of the skull bone losses are shared with one or more of the other lissamphibian groups.

    and a few other Mesozoic taxa, like Pangerpeton and Jeholotriton from the Jurassic or Cretaceous of Liaoning Province in China, are too (Wang & Evans 2006).

    According to that same paper, though, they have one or two cryptobranchoid autapomorphies, so we put them in that clade in our paper. No good cladistic analysis of fossil salamanders exists, however.

    Chunerpeton tianyiensis from the Jiulongshan Formation

    No, contrary to the initial description (and several papers who relied on it for calibrating molecular dating analyses… sigh), it’s not from the Jiulongshan Fm, which is the point.

    (Besides, herpeton is neuter, so C. tianyiense.)

    and if the sediments it comes from are Middle Jurassic in age and not younger as is possible (Marjanovi? & Laurin 2007).

    Why do you cite us and not our source? Also, it’s not merely possible — the sediments overlie rather than underlie the volcanic layer that dates to the Middle-Late Jurassic boundary.

    We missed the Indian noterpetontid. Could you give me a citation? Also, Gardner (2003) is not in your ref list.

  4. #4 Mike Keesey
    January 12, 2008

    Evans & Milner (1996) argued that it made better sense to use Caudata for the total-group for several reasons, and this seems to have been mostly followed and is used here. So Marmorerpeton and the karaurids Kokartus and Karaurus are stem-caudates but not urodeles

    I think “stem-X” is better used where “X” is a crown group, e.g. stem-mammal, stem-avian, stem-cetacean, etc. So they’re stem-urodeles (i.e., non-urodele pan-urodeles). (Or you could just say “stem-salamander”, of course….)

  5. #5 Mike Keesey
    January 12, 2008

    We’ll be coming back to giant salamanders in a later article.

    Yay!

    My interest is also sparked by these sirens (the yelping ones, not the singing ones).

  6. #6 Sven DiMilo
    January 12, 2008

    dessication

    Ah, the most misspelled word in environmental biology.
    One ‘s’, two ‘c’s.

    So I forgot about siren beaks. Partially herbivorous? I’m dubious.
    Hurry up and get to the poison-spitting, huh?

  7. #7 Luna_the_cat
    January 12, 2008

    particularly viscous teeth

    Oh well, if we’re going to pick out “the most misspelled word in environmental biology”, could I please nominate vicious?

    I’ve become amazed at how many vicious things are apparently semi-liquid and sticky.

  8. #8 Mokele
    January 12, 2008

    I’m a bit skeptical of the herbivory and durophagy of sirens, in part because the Siren lacertina I kept for several years never made a move on any of snails or plants in its tank, but would devour fish voraciously.

    Still, that should be easy to test with stomach content studies, since it’s not like sirens are exactly rare.

  9. #9 David Marjanovi?
    January 12, 2008

    I think “stem-X” is better used where “X” is a crown group, e.g. stem-mammal, stem-avian, stem-cetacean, etc. So they’re stem-urodeles (i.e., non-urodele pan-urodeles). (Or you could just say “stem-salamander”, of course….)

    That would mean that stem-urodeles are not urodeles. I’d rather use “stem-caudates” instead.

    Oh well, if we’re going to pick out “the most misspelled word in environmental biology”, could I please nominate vicious?

    Oh. That explains how “particularly viscous teeth” can make all those injuries. I was wondering if maybe the pedicel was particularly elastic or something and managed to drag the otherwise severed teeth along…

    English spelling does have rules, over 80 % of the time. That’s still the lowest value of any language that uses an alphabet or syllabary, but…

  10. #10 Darren Naish
    January 12, 2008

    Many thanks for comments and corrections, especially for pointers to dumbass spelling mistakes and stupid technical errors. Even I’m not perfect, apparently. What I’ve done is change the text according to your comments, so you can all count yourself as reviewers. Out of interest, does anyone object to me just outright making changes like this, or would you rather see me admit to my stupidity and leave old mistakes left in (perhaps with a strike-through? Carl Zimmer does this). Anyway…

    – The stuff on stapes, opercula and middle ears. Well, yeah. My bad. Me stupid. Derived loss of skull bones: yeah, some lissamphibians other than caudates also lack postorbitals, jugals, tabular, supraoccipital and ectopterygoids. I know this, but was lazy and opted to follow Larson et al. at Tree of Life (here).
    Chunerpeton: I had more or less naively assumed that Gao & Shubin were correct in attributing this taxon to the Jiulongshan Formation, though I was aware that there was question about this. I’ve sort of changed the text, though I can’t be bothered to go into the details.
    – David, you’re the only person I know who seems to object every time I cite your paper. Your paper with Laurin includes discussion of this area (particularly the note added in proof, p. 388) so is an appropriate citation, and a good place to point others to.
    – Indian noterpetontid: you know that Evans et al. (1996) sunk Noterpetontidae into Sirenidae? However, this might be wrong if Gardner (2003) was right in excluding noterpetontids from Sirenidae. Anyway, the alleged Indian sirenid was described by Yadigiri (1986): Evans et al. (1996), and others authors, argued that the material was not diagnostically sirenid, nor even definitely from Urodela.
    – When the crown-group is Caudata and the total-group Urodela, is a non-caudate a stem-caudate or a stem-urodele? I’m particularly bad at remembering things like this; the taxon would be on the stem of Caudata, making it a stem-caudate. This seems to be more usual usage, though expect to see me getting this sort of thing wrong in the future. I screwed up on the same issue when discussing stem-lagomorphs a while back.
    – Herbivory and durophagy in sirens: herbivory is now well-established and in fact sirens are hindgut fermenters, probably with microbial symbionts. See Pryor et al. (2006), a paper I forgot to cite in the article and am now going to insert and cite. The assertions about durophagy are mostly inspired by comments and citations in Gardner (2003): there are a string of papers showing that sirens feed heavily on gastropods and bivalves (Burch & Wood 1955, Altig 1967, Hanlin 1978, Moler 1994).

    That does it. Phew – on any other blog this would count as an article :)

    Refs – -

    Altig, R. 1967. Food of Siren intermedia nettingi in a spring-fed swamp in souther Illinois. The American Midland Naturalist 77, 239-241.

    Burch, P. R. & Wood, J. T. 1955. The salamander Siren lacertina feeding on clams and snails. Copeia 1955, 255-256.

    Evans, S. E., Milner, A. R. & Werner, C. 1996. Sirenid salamanders and a gymnophionan amphibian from the Cretaceous of the Sudan. Palaeontology 39, 77-95.

    Gardner, J. D. 2003. Revision of Habrosaurus Gilmore (Caudata; Sirenidae) and relationships among sirenid salamanders. Palaeontology 46, 1089-1122.

    Hanlin, H. G. 1978. Food habits of the greater siren, Siren lacertina, in an Alabama coastal plain pond. Copeia 1978, 358-360.

    Moler, P. E. 1994. Siren lacertina (greater siren). Diet. Herpetological Review 25, 62.

    Pryor, G. S., German, D. P. & Bjorndal, K. A. 2006. Gastrointestinal fermentation in greater sirens (Siren lacertina). Journal of Herpetology 40, 112-117.

    Yadagiri, P. 1986. Lower Jurassic lower vertebrates from Kota Formation, Pranhita-Godavari Valley, India. Journal of the Palaeontological Society of India 31, 89-96.

  11. #11 Neil
    January 12, 2008

    So by saying aminotes I infact left one remaining tetrapod group, that was the answer. woops.
    As for giant salamanders, they have been a long time fav, Im looking forward to the article. I got quite exciting when dave mentioned there was a live one in the stuttgart? museum we were visiting on the 3rd year trip. Is that where the photo was taken?

  12. #12 Luna_the_cat
    January 12, 2008

    David Marjanovi? — English also has its origin in three different languages, thus three different grammars and systems for modifying nouns and verbs for number and tense. It ended up with one of the sloppiest and most flexible system for sentence construction on the planet….but you can say such wonderful things in it. Got to admit, it’s done pretty well!

    Darren — I have absolutely no objection to your correcting things, although if you change the text substantially on anything it would probably be a good idea to note it. And, for the record, I used to work as a copyeditor, but now (in the interests of civilised discourse) I try to suppress all my Grammar Nazi instincts. I’ll unleash them if you want, but I advise against inviting me to do so.

  13. #13 Mike from Ottawa
    January 12, 2008

    That does it. Phew – on any other blog this would count as an article :)

    It is the Glory of TetZoo that it includes such ‘comments’, both your own and those of some of your readers.

    I find Carl’s marking up his posts annoying (laudable as the motivation is), as it is just confusing as one reads the post without having read the comments first (yeah, I’m funny that way) so the striking out makes no sense and just distracts. I think the way you do things here is fine; making changes and either inserting a note in the commenter’s comment or making a comment of your own to acknowledge the correction. You certainly take correction with better grace than I likely would should I ever err.

  14. #14 Mike Habib
    January 12, 2008

    I am quite pleased to say that I live within an hour of two hellbender-bearing streams. They are pretty awesome animals. One thing that I find quite interesting about cryptobranchids is their rather slow life history, which seems to relate (in part) to their preference for cold water. I’d be interested to see what their vascular anatomy looks like, especially with regards to the pulmonary vasculature, given the lung’s reduced importance for respiration (but continued use in controlling buoyancy). Any idea if that’s been illustrated somewhere?

    Cheers,

    –Mike

  15. #15 Nathan Myers
    January 12, 2008

    Regular readers would do better to send spelling corrections by e-mail. When Darren does corrections, then, latecomers will be none the wiser. Technical disagreements, though, make for a more lively comment section. Strikethroughs help to keep the comments making sense.

    Darren’s only habitual spelling error is writing “compliment” when he means “complement”. I’ve caught him at it twice.

  16. #16 David Marjanovi?
    January 13, 2008

    Chunerpeton: I had more or less naively assumed that Gao & Shubin were correct in attributing this taxon to the Jiulongshan Formation, though I was aware that there was question about this. I’ve sort of changed the text, though I can’t be bothered to go into the details.

    Now the text says “Jurassic”. But there’s no way to tell if it’s Late Jurassic or Early Cretaceous. It does underlie the Yixian Fm, so it can’t be Aptian or younger in age, but all other possibilities remain open, with vague stratigraphic and biostratigraphic arguments (same sedimentary cycle as the Yixian Fm, similar fauna) favouring the younger end of the range.

    David, you’re the only person I know who seems to object every time I cite your paper. Your paper with Laurin includes discussion of this area (particularly the note added in proof, p. 388) so is an appropriate citation, and a good place to point others to.

    :-)

    Fine, but our note added in proof is merely a short summary of W?ng et al. (2005) (abstract), which is available online in its full glory in a secret undisclosed location (pdf). (If it weren’t, I’d never have seen it — I don’t go around burrowing for obscure geology journals.) We merely parrot the conclusions, we haven’t done any research on the topic.

    You can still cite us, though, using a phrase like “as pointed out by”. :o)

    Actually, I should cite myself for a little more discussion of this topic. :-)

    you know that Evans et al. (1996) sunk Noterpetontidae into Sirenidae?

    Yes, but that was merely an extension of Sirenidae to cover the total group, wasn’t it?

    However, this might be wrong if Gardner (2003) was right in excluding noterpetontids from Sirenidae.

    Oh yeah, the Habrosaurus paper… Gardner didn’t argue (or offer evidence) that Sirenidae and Noterpetontidae could not be sister-groups, so it’s possible his view differs from that of Evans et al. only in nomenclature, isn’t it? (That’s how we interpreted the situation in our paper. I think we even mentioned this somewhere deep in an appendix, but I can’t check that now.)

    Anyway, the alleged Indian sirenid was described by Yadigiri (1986): Evans et al. (1996), and others authors, argued that the material was not diagnostically sirenid, nor even definitely from Urodela.

    Ah, thanks.

    herbivory is now well-established and in fact sirens are hindgut fermenters, probably with microbial symbionts.

    :-o

    Convergence between Sirenidae and Sirenia. :-o

    David Marjanovi? — English also has its origin in three different languages, thus three different grammars and systems for modifying nouns and verbs for number and tense. It ended up with one of the sloppiest and most flexible system for sentence construction on the planet….but you can say such wonderful things in it. Got to admit, it’s done pretty well!

    Yes, but that has nothing to do with the spelling. I only talked about the spelling.

    (Incidentally, for a language that really had three grammars, as opposed to small parts of three grammars, check out Ottoman Turkish.)

  17. #17 Mark Lees
    January 13, 2008

    Well if Darren ever decides to turn these articles into a book it looks like he has no shortage of proof readers.

  18. #18 Mike Keesey
    January 13, 2008

    That would mean that stem-urodeles are not urodeles. I’d rather use “stem-caudates” instead.

    So what? Stem-mammals are not mammals. Stem-whales are not whales. Stem-humans are not humans.

    I think it’s much preferable to use the crown group as the basis for the formula for the simple reason that there are far more named crown groups than named total groups (especially outside of this little field called vertebrate paleontology, one of the few places where total groups are named at all).

    Also consider the PhyloCode‘s Pan-/pan- prefix and how this would play out. It’s quite possible that, under the PhyloCode, the crown group would be Urodela and the total group would be Pan-Urodela (or at least an informal pan-Urodela coexisting with a formal Caudata). What would be the point of saying “stem-pan-urodele”?

  19. #19 Mike Keesey
    January 13, 2008

    Oh well, if we’re going to pick out “the most misspelled word in environmental biology”, could I please nominate vicious?

    And here I was anticipating the explanation of how, exactly, teeth could be viscous….

  20. #20 Alan Kellogg
    January 14, 2008

    I find it interesting that among reptiles and amphibians you have two legless groups, but in mammals none. In what lies the difference? How far back did the mammals split off from the basal reptile/amphibian line?

  21. #21 John Scanlon, FCD
    January 14, 2008

    Alan K – among squamate reptiles alone there is a plethora, a multitude, a cornucopia of limb-reduced (only occasionally fully limbless) ‘serpentiform’ groups. An explanation for the contrast with mammals was suggested by (iirc) F.H. Pough in about 1983 or even earlier, i.e. that a limbless (and necessarily elongate) body form would have an excessive surface-to-volume ratio for mammalian physiology. I’m not totally convinced intuitively, and I’m not sure what has been written on this more recently. The closest thing to serpentiform small mammals would be weasels, which are astoundingly voracious but also (contrary to what the Pough idea would predict?) cope well with cold conditions. Among large mammals, there are Basilosaurus and some other mid-Tertiary whales which were rather mosasaur-like or perhaps even more serpentiform; in water, the thermal disadvantage of the elongate body shape is even greater so only possible at large size. But consider a beast like a Marsupial Mole, Golden Mole, or Mole-rat living underground in the tropics: any reason why such an animal couldn’t benefit from a more elongate and limb-reduced form? A kind of mammalian amphisbaenian-analogue (wasn’t there a giant one in After Man?).

  22. #22 Darren Naish
    January 14, 2008

    Believe it or don’t, there is a hypothesis positing the evolution of mammals (from mole-like ancestral forms) from amphisbaenians. I have yet to track down the reference…

  23. #23 Nick
    January 14, 2008
    Oh well, if we’re going to pick out “the most misspelled word in environmental biology”, could I please nominate vicious?

    And here I was anticipating the explanation of how, exactly, teeth could be viscous….

    It’s one of the early warning signs of spontaneous dental hydroplosion.

  24. #24 Nick
    January 14, 2008

    Luna_the_cat wrote:

    English also has its origin in three different languages, thus three different grammars and systems for modifying nouns and verbs for number and tense. It ended up with one of the sloppiest and most flexible system for sentence construction on the planet….but you can say such wonderful things in it. Got to admit, it’s done pretty well!

    Um, which three are you thinking of?

    Sure, English has borrowed a lot of words from French and Latin (and Old Norse, and Greek, and…), but for the most part they’re shoehorned into a fairly ordinary modern Germanic morphosyntactic system. Apart from the lack of grammatical gender, that is, and even that is shared with Afrikaans (though independently developed in the two languages).

  25. #25 Sven DiMilo
    January 14, 2008

    in sirens: herbivory is now well-established and in fact sirens are hindgut fermenters, probably with microbial symbionts. See Pryor et al. (2006)

    Ok, that’s the coolest thing I’ve learned this month. Thanks for the reference.
    That means hindgut fermentation has evolved convergently in sirens, tortoises, sea turtles, freshwater turtles, iguanines, Uromastyx, geese, various ungulates, wombats, various fishes…

  26. #26 David Marjanovi?
    January 14, 2008

    The closest thing to serpentiform small mammals would be weasels, which are astoundingly voracious but also (contrary to what the Pough idea would predict?) cope well with cold conditions.

    I’ve read that they have a metabolism twice as high as usual for mammals their size, so probably they cope with the cold by cranking up the heating, an approach that has obvious limits.

    This would, however, not apply to Basilosaurus which lived in very warm water.

    But it could be that mammalian thoracic and lumbar vertebrae cannot multiply as they please. Even slight abnormities in the number of cervical vertebrae in humans (by “slight” I mean things like a rudimentary cervical rib on the 7th vertebra) are correlated with other development abnormities and a very high risk for cancer developping very early in life; sloths and sea cows get away with different numbers of neck vertebrae by having a lower metabolism and therefore a lower cancer risk; and (for, presumably, some reason) birds basically don’t get cancer. Sure, mammalian thoracics and lumbars are obviously not as limited as the cervicals, but maybe a mammal with 40 thoracics is still impossible.

  27. #27 Dave Godfrey
    January 14, 2008

    It might have something to do with the bellows mechanism mammals use to breathe, and the constraints that places on the chest morphology. As noted here most serpentiform animals have elongated the body and reduced the tail.

  28. #28 Luna_the_cat
    January 17, 2008

    Nick:
    1. Middle Germanic (yep, good old Anglo-Saxon)
    2. Norse (sometimes referred to as “Northern Germanic”; seriously, don’t discount the Norse contribution, a lot of the Northern Germanic systems for basic verb tense, like “take/took” or “give/gave” for example, were introduced in the 11th C. when the Danes had colonised…well, almost everywhere in the UK)
    3. Norman French (we borrowed grammatical constructions, too, not just words — and not just the introduction of previously unknown continuous verb tenses, ultimately the Norman influx was also responsible for the solidification of the standard subject-verb-object word order).

  29. #29 Jerzy
    January 17, 2008

    I would guess something related to limb mobility. Burrowing reptiles dig with their nose, mammals with forearms.

    Casually, weasels and ferrets are close to some snakes in lifestyle. They hunt rodents in their holes and spend up to 90% of time underground.

  30. #30 David Marjanovi?
    January 17, 2008

    a lot of the Northern Germanic systems for basic verb tense, like “take/took” or “give/gave” for example, were introduced in the 11th C. when the Danes had colonised…well, almost everywhere in the UK)

    Are you sure about give/gave? Because that’s gibt/gab (3rd person singular) in German just as well.

    Also, where is the French connection to the continuous aspect? French has nothing remotely similar.

    The word order had no choice but to consolidate when the inflection was gone — German has two different forms of “the”, analogous to he/him, to distinguish “the dog bites the man” from “the man bites the dog” regardless of word order; in fact, the word order of modern English is on average quite a bit stricter than that of modern French.

    Burrowing reptiles dig with their nose, mammals with forearms.

    Except for those mammalimorphs that dig at least partially with their noses: golden moles, Haldanodon… Lots of rodents dig with their teeth, naked mole rats most famously.

  31. #31 David Marjanovi?
    January 17, 2008

    (Not that it matters, but I’ve never seen “Middle Germanic” before, only “West Germanic”.)

    I should also have mentioned that the word order of Chinese, which lacks any trace of inflection, is even stricter than that of English for the obvious reason.

  32. #32 Luna_the_cat
    January 17, 2008

    Bear in mind that my last linguistics class was in 1988. However, having said that, I’m fairly sure of my facts here. The official etymology for “give” is the Old Norse gefa, and the “given” and “gave” forms specifically would appear to be either directly from or closely related to the Old Danish givæ. It’s hard to tell which version of Germanic words came from, though, considered free of grammatical context, because Middle Germanic (and I’ve heard it called that quite commonly, as well as West Germanic, this probably reflects educational convention as much as anything) and North Germanic were more dissimilar in grammatical construct than in actual vocabulary.

    And all the continuous forms of verbs ending in “-ing” are credited to the Norman influence, even though there is no direct Norman French “ancestor” to this construct; certainly in pre-Norman Old English, the only available tenses of verbs were past and present, with indicative, imperative and subjunctive moods. Under the Norman influence, inflectional endings were largely dropped, and people started doing things like using the preposition “of” instead of the genitive inflection, and the use of a wider range of tenses (past and present continuous and future) developed in a way that, ultimately, turned out to be rather unique. You can see it happen in the literature of the period between 1066 and the early 16th C.

    …sorry to hijack the thread away from the weird cool salamanders….

  33. #33 David Marjanovi?
    January 18, 2008

    Under the Norman influence, inflectional endings were largely dropped

    That, like the loss of gender, was credited to the other Norman influence last time I checked: the Norse settlements in e. g. York. Makes sense, as far as I can tell, because today’s Scandinavian languages lack even the am-is-are distinction.

  34. #34 Brian
    January 18, 2008

    Concerning limbless animals, I believe there is a fossil species of hedgehog (from the Miocene of North America, I think) that IS thought to be limbless, which would make it unique among mammals and probably even synapsids.

    I could be wrong, but I don’t think I am.

  35. #35 David Marjanovi?
    January 18, 2008

    IIRC this hedgehog species was once thought to be possibly limbless and is now known to have retained limbs… but I could be wrong, too…

  36. #36 Abby
    July 5, 2009

    HOW BIG IS Andrias-davidianus brain man how big

  37. #37 Nick Gardner
    July 5, 2009

    “or would you rather see me admit to my stupidity and leave old mistakes left in (perhaps with a strike-through? Carl Zimmer does this).”

    I actually have no problem with this. Since there is no version history (AFAIK) for your blog posts, it’s difficult to know what the misunderstandings mentioned in the blogging comments were.

    Often, it’s better to learn from the mistakes of others so you don’t repeat them yourself. :-)

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