Isopachys: worm-like skinks from Thailand and Myanmar

Limbless skinks are some of my favorite animal groups. Lerista, Aconita and Anomalopus all deserve their own Tet Zoo article (Lerista, maybe more than one.) How many times have limbs been lost in skinks? (let alone lizards?)

Perfectly camouflaged, these pests can wreak havoc in any shoelace factory!

Nice vestigials!
I take it the squamate phylogeny is not well enough established to permit an accurate count of independent limb-losing lineages. But I bet the minimum number is a lot.
Top of my head: snakes, amphisbaenians, dibamids, anniellids, anguids, pygopodids, skinks...and some of those multiple times.
a few more

Darren:

It's said that Isopachys skinks can reach lengths of about 300 mm, but most individuals are much smaller than this. Indeed, the largest known specimen of I. anguinoides is just 75 mm long (Pauwels et al. 2003).

Er, if the largest known specimen is 75 mm, where did 300 mm come from? Is there a (different) species in Isopachys for a which 300 mm specimen is known?

I think this falls into the category of: how many times have "snakes" evolved convergently from lizards? The answer appears to be "lots," and the fun part is that only the macrostomatans really underwent a true adaptive radiation.

I'm with the first commenter: I think limbless lizards are cool.

By my rather minimal Greek, "Isopachys" would mean something like "equal thickness": so the generic name is in honor of the lack of tapering at tail and neck? ... Lack of tapering would, I suppose, be adaptive in a burrowing animal: taper and you need a bigger-bore tunnel to fit the same total volume through. Cylindrophis is a burrower too, isn't it?
(Or: a little Greek can inspire big biomechanical speculations!)

Oh my goodness, that thing is just adorable, it's overbite jaw makes it look so dejected!

Yay Squamates

Not so much 'worm-like' as 'uropeltid-like'; many limbless skinks are more wormy than that. The skull isn't highly modified at all (near-complete postorbital bar, postorbital-squamosal contact, long epipterygoid, and there's nothing really remarkable about the length of that RAP), suggesting a relatively recent origin of fossoriality.

Skinks would include the majority of origins of (near-)limblessness in squamates, though none of the limb-reduced clades (of which there are quite a few independent ones within the large 'genus' Lerista) is as speciose or ecologically diverse as, say the Pygopodidae. Maybe it's juat not a long-run successful way to be a skink?

As for non-'macrostomatan' snakes (uh, did you know that Macrostomata isn't really the clade we thought it was a few years ago?) not having any 'true' adaptive radiations... OK I'd better not get started on madtsoiids (until a few more have been published)

Goodbye Reptiles

http://yglesias.thinkprogress.org/2010/11/goodbye-reptiles/

any opinion on this ?

Philippe--
Keeping to the Yglesias post itself, and not getting into the comments thereon (which quickly get far from science: more people seem to have opinions about Teddy Roosevelt and politics than do about cladistics)...

This is a big subject on which a lot of the regular contributors to Tetrapod Zoology discussions have strong opinions. If you are new to the field, maybe an "elementary" discussion will help you orient yourself. So...

This is old news. Reptiles, in the traditional sense (=lizards, snakes, turtles and crocodilians, + some selection of fossil types), do not form a CLADE: they are not all the descendants of a common ancestor. (Most recent common ancestor of lizards and alligators was also an ancestor of birds.) There are lots of zoologists who, at least in their official public statements, hold that we should only use terms for a "kind" of organism when the organisms of that kind form a clade.

(I remember Gareth Nelson, who was a paleoichthyologist at the American Museum of Natural History, giving a talk on ... this and related matters .., back in the late 1980s: one of his repeated slogans was "There is no such thing as a reptile.")

Some of us are a bit sceptical, and would like to argue that there IS sometimes a good reason to group organisms into non-clades, on the basis (e.g.) of general overall similarity. Alligators may be more closely related to birds than to lizards (reckoning "relatedness" in genealogical terms: more closely related = having a more recent common ancestor), but birds have evolved feathers and warmbloodedness, and in these respects alligators haven't changed as much. So, we might suggest, there might be useful biological generalizations we could make about "reptiles" which would justify continuing to use the concept REPTILE.

To which the cladists would answer (and Gary Nelson, for example, did answer in the talk I remember) that you are much more likely to be misled than helped by using a concept, REPTILE, based on a few superficial similarities. Alligators have been evolving just as long as birds have since their common ancestor lived roughly 250 million years ago, and have been changing all the time. It isn't a NECESSARY truth, any more than it is a necessary truth that if you toss a fair coin a hundred times it won't come up heads every time, but the ODDS are that they have changed about as much from what their common ancestor was like. Their common ancestor had a lot in common with the contemporary common ancestor of lizards (the common ancestor of alligators, birds and lizards probably lived not too many millions of years before the common ancestor of alligators and birds), but alligators have -- on the odds -- lost about as many "reptile" features as birds have.

And, in fact, there are LOTS of details of anatomy (e.g.: number of chambers in the heart) where alligators and lizards are different. So, if you were led by the idea that they are both "reptiles" to think that lizard-anatomy is a good guide to alligator-anatomy, you'd go wrong very often. So, the cladists plausibly argue, thinking in terms of the REPTILE concept will often be misleading. Often enough that we would be better off abandoning it.

Hope that is helpful.

Darren:

Axel Johann Einar Lönnberg

I noticed that the English-language Wikipedia article on Lönnberg says 'Johann', but according to the Swedish Wikipedia it should actually be 'Johan' - which would make sense as that is by far the more common way to spell that name in Swedish; 'Johann' is German. (In his publications the man usually only referred to himself as 'Einar Lönnberg'.)

could Lönnberg have named it for Nils Philip Gyldenstolpe (1734-1810), Marshal of the Royal Court of Sweden and member of the Swedish Academy?

Surely he could have, but he didn't; Lönnberg named the species after his colleague, the zoologist Nils Gyldenstolpe (1886-1961). And I strongly suspect that it was Gyldenstolpe who actually discovered the skink - he was in Thailand in 1911-1912 (Lönnberg, IIRC, was in Africa at the time).

Many thanks for comments. As seems widely recognised, yes, limb reduction and limblessness has definitely evolved independently on numerous separate occasions within Squamata; as Sven notes (comment 3), I'm not sure that phylogeny is well reconstructed enough for us to give a precise number across the whole clade, but it's gonna be something like 30 times or more. It might have evolved three times in Anguidae alone, as for skinks... yikes, I'm not on top of this yet, though some limbless and near-limbless taxa (the acontines Acontias and Typhlosaurus, and Typhlacontias, Melanoseps and Feylinia, for example) do group together in phylogenies. Note that reversal of digit loss has been suggested for Lerista. Remember that there are reduced-limbed cordylids.

Some select responses. llewely (comment 4) asked...

if the largest known specimen is 75 mm, where did 300 mm come from? Is there a (different) species in Isopachys for a which 300 mm specimen is known?

There are four species: the 75 mm max length applies to I. anguinoides while the 300 mm applies to I. gyldenstolpei.

And John (comment 9) is of course right about Isopachys not being particularly snake-like: I was only emphasising the fact that the claimed absence of limb girdles in I. borealis would be uncannily snake-like. I am compelled to cover Feylinia next - does anyone have any good photos? Photos are always a problem for these 'obscure herp' articles.

Thanks for the comments on the Macrostomatans. I'm not a herpetologist, and I wanted to be efficient rather than checking up. Madtsoiids are neat, though, I agree.

Re: Cladistics. When I was in grad school, I proposed this thought experiment to demonstrate the limits of cladistic thinking:

Let's assume that aliens come down and kidnap an entire classroom of cladistics students somewhere (feel free to nominate targets). They take this sample of humanity to an extremely Earth-like planet around another star, and use them to start another colony of humanity.

That colony then undergoes allopatric speciation, exactly as one would expect from a small group colonizing a novel environment.

The thing is, humans on Earth are no longer a unified clade, as there's another species that is not human that descended from humanity's common ancestor.

However, there's no way for us Earth humans to know this. It may have already happened, repeatedly.

That's the problem with strict cladistics. Allopatric speciation happens all the time (especially with the plants I'm more familiar with), and it almost never comes from a convenient edge of the cladogram where the new allo-species (or allo-genus) can be pinched off. Usually the new species appears right in the center of the parental tree.

Obviously, cladistics deals with this by developing hypotheses based on best available information. However, names and categories really should be useful. If a vagrant population has descended into an orgy of adaptation or adaptive radiation, it shouldn't negatively affect how we classify the ancestral group, especially when those ancestors are still around.

heteromeles, cladists do not (typically) insist that species be monophyletic, because of the kind of example you mention. Do note, however, that a species is (approximately, depending on what definition you are using on the day) the most inclusive group that can regain monophyly over time, whether it's established by plucking a sample from an existing species, introduction of a new geographic barrier, or hybridization of distant relatives. A 'genus' or 'order' that is para- or polyphyletic today will never become monophyletic through ordinary sexual reproduction, but a species can.

Ah, but what if I have a genus of skinks, all quite similar to one another. And what if I pluck a few skinks from some unassuming member in the center of this genus, and place them on a distant island. Wait a million years or so, and the island skinks have undergone massive radiation, becoming predators and herbivores, losing their legs several times! A passing naturalist would class the island skinks into several genera, while the stay at home skinks still plod along relatively unchanged.

So, how do you describe this situation, where a group too diverse to be a genus falls out phylogenetically right in the middle of an otherwise perfectly normal and conservative genus? How do you describe the true relationship AND the true character of the organisms involved?

How do you describe...?

With a map, a timeline, a phylogeny, and published data on morphology, ecology and behaviour.

The names are just handles.

What John Scanlon said.

As always, be careful not to confuse the science of phylogenetics with nomenclature. Cladistics reconstructs the tree; what labels we tie to the branches of the tree is a completely separate question, and it's one of convention, not of science.

Whether species have to be clades depends on your species concept. (Most concepts allow species to be paraphyletic.) Whether phylogenetics is at all relevant to what is and is not a species depends on your species concept.

Finally, do we really need to refer every organism to a species? The codes of rank-based nomenclature say so (at least implicitly), but under many species concepts there's no scientific reason for this. Accordingly, the PhyloCode will allow us to use specimens that do not (as we may claim) belong to a named species as specifiers for naming clades, and it will not require that we name a species in the process.