Yet again I am going to have to go quiet-ish on Tet Zoo for a little while as I just cannot put the time into completing the many planned articles. Sigh. One thing approaching on the near horizon is eating up lots of my research time: the third Big Cats in Britain conference, happening in early March, and at which I'm speaking. I'll post details on it over the next few days. For now, I thought I'd enthuse a bit about lizards: like (I'm sure) everyone in the UK interested in zoology, I am watching David Attenborough's Life in Cold Blood series at the moment, and last night's episode (number 3, 'Dragons of the dry') was about lizards. I'm hoping to talk more about the series later on, as it has included some amazing stuff that hasn't been shown on TV before. For no particular reason (although they were featured in one episode of Life in Cold Blood I think), here are random thoughts on girdled lizards, the cordylids...
Girdled lizards are endemic to Africa and include about 50 species in four genera: flat-bodied flat lizards Platysaurus, the flattish crag lizards Pseudocordylus, the deeper-bodied, often spiny girdled lizards, zonures or sungazers Cordylus and the serpentiform grass lizards or ground lizards Chamaesaura. Molecular work indicates that Pseudocordylus is not monophyletic, with different species being nested in among the Cordylus assemblage (Frost et al. 2001). Furthermore, Cordylus seems to be paraphyletic to not only Pseudocordylus, but also to Chamaesaura. Frost et al. (2001) proposed that, as a result, both Pseudocordylus and Chamaesaura should be sunk into Cordylus, but this idea doesn't yet seem to have caught on (or, maybe it has: see du Toit et al. 2004) and I'll continue to use the old names for convenience.
Cordylids are closely related to another armoured scincomorph clade, the Afro-Madagascan gerrhosaurids or plated lizards, and the two were formerly grouped together. Some workers think that they should be united again in an inclusive Cordylidae. Gerrhosaurids + cordylids = Cordyliformes. The cordylid fossil record is poor (that of gerrhosaurids is better, with good records from the Miocene of Africa and possible records from the Eocene or Oligocene of Europe), but an Upper Cretaceous lizard from Madagascar, Konkasaurus mahalana, was cautiously interpreted as a cordylid by Krause et al. (2003).
Chamaesaura is weird: very long-tailed (the tail might be three or four times the body length), snake-like in movement, and superficially like reduced-limbed or limbless anguids but with an altogether more cordylid-look to the integument (the body scales are sharply keeled). They differ from most other cordylids in that osteoderms are restricted to the head (a condition which has convergently arisen in 'Pseudocordylus' species). They're viviparous, giving birth to 5-9 babies. 'Pseudocordylus' and Cordylus sensu lato are viviparous too, with females giving birth to one or two surprisingly large babies [image above shows Armadillo girdled lizard giving birth, her mouth open in a silent scream. Image borrowed from Gary Fogel's excellent page here]. Platysaurus (indicated by phylogenies to be the most basal cordylid) is oviparous, with females producing two elongate eggs. The remarkable flat bodies of these lizards have apparently resulted in the evolution of low clutch size and unusual egg shape (Pianka & Vitt 2003)
The three Chamaesaura species (Transvaal grass lizard C. aenea, Cape grass lizard C. anguina and Large-scaled grass lizard C. macrolepis), usually called grass lizards (a dumb name: it's used around the world for various entirely different types of lizard), recall other reduced-limbed, serpentiform lizards (like certain skinks for example) in that they represent a continuum, with one species (C. aenea) having five clawed digits on all four limbs, another (C. anguina) having only one or two clawed digits on its very much reduced limbs, and a third (C. macrolepis) lacking forelimbs, and only have a single clawed digit on its tiny, spike-like hindlimbs (Branch 1988) [adjacent image shows C. macrolepis, with arrow pointing to tiny hindlimb. C. macrolepis is also the species shown at the very top of the article: image from Herpetology in South Africa]. Broadley & Branch (2002) noted that the Ukinga girdled lizard Cordylus ukingensis appears to approach the Chamaesaura species in having a very reduced osteoderm compliment and in lacking the lateral groove that Cordylus species normally have along the side of the body.
While most cordylids are apparently solitary animals, the Armadillo girdled lizard Cordylus cataphractus is gregarious, with groups of up to 30 sharing the same refuge site. Lone individuals tend to be adult males; these differ from females in reaching larger sizes and in having proportionally larger heads and longer tails (Mouton et al. 1999). As a defensive measure, members of this species form a spiky ring by grabbing their tails in their mouths [see adjacent image]. Much recent work has been done on sorting out the many Cordylus species: there are terrestrial species, arboreal ones (like Co. tropidosternum), and melanistic ones that inhabit the cool Atlantic coast of South Africa (Broadley & Branch 2002, Mouton et al. 2002). I was originally planning to write more about these species, but got distracted by the grass lizards. And that's it - time's up, back to work...
Refs - -
Branch, B. 1988. Field Guide to the Snakes and Other Reptiles of Southern Africa. New Holland, London.
Broadley, D. G. & Branch, W. R. 2002. A review of the small east African Cordylus (Sauria: Cordylidae), with the description of a new species. African Journal of Herpetology 51, 9-34.
du Toit, A., Mouton, P. le F. N. & Flemming, A. F. 2004. Aseasonal reproduction and high fecundity in the Cape grass lizard, Cordylus anguinus, in a fire-prone habitat. Amphiphia-Reptilia 24, 471-482.
Frost, D., Janies, D., Mouton, P. le F. N. & Titus, T. 2001. A molecular perspective on the phylogeny of the girdled lizards (Cordylidae, Squamata). American Museum Novitates 3310, 1-10.
Krause, D. W., Evans, S. E. & Gao, K.-Q. 2003. First definitive record of Mesozoic lizards from Madagascar. Journal of Vertebrate Paleontology 23, 842-856.
Mouton, P. le F. N., Nieuwoudt, C. J., Badenhorst, N. C. & Flemming, A. F. 2002. Melanistic Cordylus polyzonus (Sauria: Cordylidae) populations in the Western Cape, South Africa: relics or ecotypes? Journal of Herpetology 36, 526-531.
Pianka, E. R. & Vitt, L. J. 2003. Lizards: Windows to the Evolution of Diversity. University of California Press, Berkeley.
It's interesting how leglessness has evolved so many times amongst the squamates.
I'm now wondering if there have any legless non-squamate lepidosaurs, or archosaurs. And if so, whether there is something about squamates that makes it easy for them to evolve leglessness.
I'm now wondering if there have any legless non-squamate lepidosaurs, or archosaurs.
None are known so far.
But to be fair, squamate diversity is much larger than the diversity of rhynchocephalians or that of archosaurs other than birds...
Armadillo lizards are among my favorite squamates. If I only catch one lizard in my lifetime, I want it to be Moloch horridus (thorny devil). If I catch TWO lizards, the second one can be an armadillo lizard.
Im loving life in cold blood, but then I cant think of anaff Attenborough program, so thats no suprise. And its nice to have an unofficial supplement to go with it :)
Don't forget Beelzebufo!!!! The giant toad from Hell deserves a Naishian post, doesn't it?
I've always thought it a pity that there are no mammalian "snakes". I guess it's that durned parasagittal gait ...
I guess it's that durned parasagittal gait ...
No, it's the endothermy. Weasels with their elongate bodies already have a metabolism twice as high as expected of a mammal their size because such a shape is just wrong for insulation.
(For anything smaller than Basilosaurus
...anyway. And even that one lived in very warm seas.)
Stupid treatment of HTML errors.
What about Lissodelphis? And does this mean that "sea serpent" type cryptids in colder waters can't be endotherms?
Has it ever been known for a limbless creature to re-evolve limbs? (I know there have been reports of pythons with small, presumably atavistic, hind limbs - i'm now thinking of, if selective pressures happened to work the right way, some sort of bipedal python-like snake that could move in a normal snakey way with its limbs flat against its sides, but could also "stand up" in order to reach prey in trees, or something...)
According to Wikipedia, Lissodelphis (the right-whale dolphin) has no dorsal fin and "small, pointed flippers". What's your point? It's still too big and too compact to fall under the constraint, I suppose.
Uh, Shiva, pythons and some other extant snakes have limbs comprising the femur and one claw on each side, only the claw projecting beyond the body wall between scales. However, there is no evidence that this is 'atavistic' in the sense of having reversed to an ancestral state from an even further reduced condition. All the sufficiently well preserved Cretaceous snakes do actually retain hindlimbs at least as far as the tarsals; very few Caenozoic fossil examples are known, but the evidence is consistent with unreversed reduction and loss in several parallel lineages.
External limbs do occasionally appear in cetaceans, so I would not be very surprised if truly atavistic individual pythons occurred with additional limb segments (tibia-fibula, maybe tarsals, maybe even separate metatarsals and phalanges of one or more digits), and in fact I have been a bit surprised that no such cases appear to be recorded. However, that such limbs would be useful for 'standing' or climbing is very implausible; snake tails are short relative to the body so that a hindlimbs+tail tripod would never be plausible, and pythons (with prehensile tails and, as constrictors, the ability to grip branches with any part of the body) are already fully equipped for tree-climbing.
One squamate where the possibility of reversal of limb-loss is worth thinking about is the amphisbaenian Bipes, although most phylogenies put it at the base of the clade where it could simply retain limbs lost once in the common ancestor of the rest. In contrast to snake-legs, its mole-like arms are highly functional and clearly modified in position and morphology, so it's a reasonavle candidate for having rebuilt its arms from a considerably more reduced condition.
And Darren, that Chamaesaura looks quite a lot like some pygopodine diplodactylid geckoes* (Aclys or Pletholax) that coincidentally live in south-western Australia, floristically quite similar to South Africa's Cape. Except its face looks really goofy, unlike the always-elegant pygopods.
External limbs do occasionally appear in cetaceans
Case in point:
Judging from Wikipedia, Lissodelphis isnt notably elongated compared to other delphinids.
Good point about insulation.
Hang on. Even given that, yes yes, genera and subjective and not real, how can it possibly be that Chamaesaura aenea and Chamaesaura macrolepis are classified as belonging to the same genus when one has legs and the other doesn't?
Lissodelphis borealis doesn't seem too elongated, but it is shockingly attenuated. Apparently in some areas it has even earned the name "snake porpoise". The most illustrative photo I could find came from:
Perrin, William F. 1991. Why are there so many kinds of whales and dolphins? BioScience vol. 41 n. 7, 460-461.
It seems that the flukes are also rather small on this species as well.
how can it possibly be that Chamaesaura aenea and Chamaesaura macrolepis are classified as belonging to the same genus when one has legs and the other doesn't?
Easy: in lizards, this character is not diagnostic at the generic level. :-Þ
See how subjective it is?
(BTW, there have really been people who really believed in such associations between characters and ranks. I've seen monospecific genera described where separate and non-overlapping diagnoses were given for the genus and for the species. It's astounding what ranks can do to your head.)
Regarding hind limbs in pythons - they are not necessarily non-functional, I have read that they perform a role in reproduction.
Oh wow! I was just thinking about doing a post on armadillo lizards after reading Zach's post about his gecko. I had one as a kid...his name was Merv. He died of some disease that caused him to have white spots. He never curled up once.