Leiosaurid Lizards: South America, Land of Iguanians

I like iguanian lizards…. who doesn’t? But among this enormous group are a great many lineages and species that you hardly ever hear anything about. In my continuing efforts to rescue material from the Tet Zoo archives and republish it here, at ver 4, let’s look today at the leiosaurids. This article was previously published at ver 3 (a wayback machine version is here)…

Caption: leiosaurid species observed in the wild. The ‘shark tooth’ pattern on the dorsal surface shows that these are both (I think) individuals of L. bellii, sometimes called Bell’s iguana or (bizarrely) Bell’s anole. What… who calls these anoles? I don’t know why these individuals are so different in the intensity of their markings: is this a regional difference or sexual dimorphism? Images: Oliver Rauhut, used with permission; Marien Béguelin, CC BY 4.0 (original here).

Today, we’re going to look at the endemic Argentinean iguanian Leiosaurus, the type genus of Leiosauridae. I did a quick check online and was surprised to find that there’s hardly any information out there on these neat little South American lizards, most sources saying that little is known about them. Well, ain't that helpful.

All Leiosaurus species are stout-bodied, insectivorous, terrestrial iguanians, easily identifiable due to their proportionally big, wide, well-muscled heads, a tail that’s slightly longer than the body, relatively smooth-looking skin (hence the name: it means ‘smooth lizard’) and a unique dorsal pigmentation pattern that involves large spots or blotches on or on either side of the vertebral midline. These blotches form so-called ‘shark tooth’ or ‘fleur-de-lis’ patterns in some species. They’re lizards of arid and semi-arid places.

Caption: the same L. bellii shown above (at left), in oblique right lateral view. Some idea of what a lizard’s intentions and mood are (is it extremely alert and preparing to run away, is it trying to lose heat, or retain or gain heat, and so on) can be obtained from the pose it’s adopting. Image: Oliver Rauhut, used with permission.

Four Leiosaurus species are currently recognised (L. bellii, L. caramarcensis, L. jaguaris, and L. paronae). L. jaguaris is the newest, having been named in 2007 (Laspiur et al. 2007a). Its name reflects the superficial similarity between its bold dorsal patterning and that of its namesake, the big cat Panthera onca. Several additional species once included within Leiosaurus seem to be part of a closely related taxon, Diplolaemus. Some phylogenies indicate that Diplolaemus is closer to Pristidactylus than to Leiosaurus (Frost et al. 2001) though these authors recovered some topologies where Leiosaurus was paraphyletic with respect to the Diplolaemus + Pristidactylus clade. Abdala et al. (2009) incorporated a lot more data, however, and supported the monophyly of Leiosaurus. Good support for the monophyly of Leiosaurus comes from its complicated gular musculature (Abdala et al. 2009). The name Aperopristis Peracca, 1897 is available for the L. caramarcensis + L. paronae clade, should anyone want to use it (at the moment, they don’t). Leiosaurus and its relatives are closely related to the enyaliines, a group I’ll ignore for now.

Caption: a leiosaurid closely related to Leiosaurus, this is a representative of Diplolaemus, specifically the Smooth-headed Patagonian lizard or Bibron’s iguana D. bibronii. Four Diplolaemus species are known, all endemic to far southern South America. One of them (D. sexcinctus of southern Chile) was named in 2003. Image: Matias Cabezas, CC BY 4.0 (original here).

Incidentally, an alleged fossil species of Leiosaurus (L. marellii Rusconi, 1937), based on vertebrae from the Pleistocene of San Isidro in Argentina, is not a leiosaurid at all but a misidentified member of Amphisbaena (Torres & Montero 1998).

These lizards possess a large sesamoid on the palm of the hand, embedded in the tendinous sheet associated with the flexor tendons (funny how you don’t ever hear much about sesamoids in lizards). In Leiosaurus, the palmar sesamoid is especially large, perhaps because the terrestrial, arid-land lifestyle of these lizards has encouraged the evolution of features that enhance the rigidity of the hand. Climbing leiosaurid species have smaller palmar sesamoids, presumably because this permits an enhanced ability to flex the fingers (Abdala et al. 2009).

Caption: palmar view of a Leiosaurus hand (specifically, of L. catamarcensis), showing the large palmar sesamoid. The scale bar isn’t labelled in the paper but I think it might be 5 mm. Image: Abdalla et al. (2009).

Another neat (and poorly known) thing about these lizards is that they vocalise, making distinct warning noises and combat sounds. The warning vocalisations are associated with postural behaviour: an animal jerks backwards and erects its tail while making these sounds (Laspiur et al. 2007b). Leiosaurus is not unique among iguanians in making noises of this sort, since Pristidactylus species do as well. Vocalisations have not been much reported across Iguania but there are indications that they’re more widespread than currently thought.

The whole ‘Iguanidae Thing’, again. Where and how these lizards are classified varies depending on which source you consult. Tradition has it that pleurodont iguanians (that is, those iguanians that are outside of Acrodonta, the acrodont-toothed clade that includes chameleons and agamas) are classified within a super-inclusive version of Iguanidae that’s then carved up into numerous ‘subfamilies’. Leiosaurus used to be included in Polychrotinae, a group imagined (prior to the late 1980s) to include an array of arboreal, chameleon-like and anole-like iguanians – sometimes termed para-anoles – as well as the terrestrial, shorter-bodied, cryptically coloured leiosaurines. The Leiosaurus species were sometimes called either ‘leiosaur polychrotids’ back in those days, or ‘pristidactylines’ due to the idea that Leiosaurus forms a clade with Pristidactylus as well as Diplolaemus.

Caption: conventional taxonomy would have it that all of these lizards – and a huge number of others too – should be grouped together in a massively inclusive version of Iguanidae. You can stick with that view if you want to (taxonomy is still mostly subjective), but I agree with those who think that it’s more useful to recognize numerous different ‘family-level’ groups here. The animals shown here are (clockwise from top left) Iguana, Anolis, Sceloporus, Sauromalus, Liolaemus (in middle), Enyalius, Basiliscus. Images (clockwise from top left): Darren Naish Iguana, Anolis, Liolaemus (in middle); Sceloporus Alan Schmierer, CC0; Sauromalus H. Zell, CC BY-SA 3.0 (original here); Enyalius Renato Augusto Martins, CC BY-SA 4.0 (original here), Basiliscus Bernard Dupont, CC BY-SA 2.0 (original here).

Nowadays, Leiosaurus and a few close relatives are generally classified within a group variously termed Leiosaurinae or Leiosauridae and taken to include both pristidactylines and enyaliines (Frost et al. 2001, Abdala et al. 2009, Pyron et al. 2013). Some authors argue that we should emphasise monophyly and stick with a conservative taxonomy where possible: according to this view, it’s wise to maintain a super-inclusive Iguanidae that contains a Leiosaurinae and numerous other subfamily-level divisions. Other authors argue that maintaining a super-inclusive Iguanidae is misleading, since it downplays the diversity and disparity of these lizards (some authors have also wanted to avoid using ‘Iguanidae’ in the grand, inclusive sense since there were concerns that it referred to a paraphyletic grade. That no longer seems to be the case though, since modern phylogenies find pleurodont iguanians to be a clade).

Caption: the chunk of Pyron et al.’s (2013) squamate phylogeny showing the position of leiosaurids. Here, they’re close to oplurids (the spiny-tailed Madagascan iguanas), and the oplurid + leiosaurid clade is close to Liolaemidae. At right, representatives of various of the clades here, from top to bottom: Polychrus, Enyalioides, Leiosaurus, Liolaemus. Images: Polychrus, J-Mass, CC BY-SA 2.0 (original here); Enyalioides Venegas et al., CC BY 3.0 (original here); Leiosaurus Oliver Rauhut; Liolaemus Lauchaseca, CC BY-SA 3.0 (original here).

I think that the decision to avoid the old, super-inclusive version of ‘Iguanidae’ is desirable, since including all of these many lineages within one ‘family’ is inappropriate when we compare their diversity with that of mammals and birds (where just about every distinct taxon is considered special enough to get its own higher-level taxonomic entity). Of course, invertebrate workers usually make witty retorts at this stage, saying that all of tetrapod diversity could hypothetically be included within a single nematode genus or whatever. Well, we’re not talking about making tetrapod taxonomy consistent with that of midges or snails, but consistent with that of other tetrapods. Some say that this stuff doesn’t matter as long as we know which taxa we’re talking about. I can agree with that, but I also think that it does matter since we’re still lumbered with a wholly anachronistic and inaccurate view of biodiversity whereby people think that living amphibians and non-avian reptiles are substantially less diverse than mammals and birds.

One last thing. Why did I write this article? Because my colleague Oliver Rauhut happened to share some nice photos of Leiosaurus on Facebook. Thank you, Oliver. I love writing about obscure squamate taxa, so – dear readers – please keep me in mind if you have good photos that you’re prepared to let me use.

Caption: one final view of Leiosaurus bellii, in dorsal view. Image: Oliver Rauhut, used with permission.

For previous Tet Zoo articles on iguanians, see…

My research and writing (including the material that appears here) is supported by the contributions I receive via patreon. If you value what I do, please consider supporting it here.

Refs - -

Abdala, V., Manzano, A. S. & Nieto, L. 2009. Comparative myology of Leiosauridae (Squamata) and its bearing on their phylogenetic relationships. Belgian Journal of Zoology 139, 109-123.

Frost, D. R., Etheridge, R., Janies, D. & Titus, T. A. 2001. Total evidence, sequence alignment, evolution of polychrotid lizards, and a reclassification of the Iguania (Squamata: Iguania). American Museum Novitates 3343, 1-38.

Laspiur, A., Carlos Acosta, J. & Abdala, C. S. 2007a. A new species of Leiosaurus (Iguania: Leiosauridae) from central-western Argentina. Zootaxa 1470, 47-57.

Laspiur, A., Sanabria, E. & Carlos Acosta, J. 2007b. Primeros datos sobre vocalización en Leiosaurus catamarcensis (Koslowsky, 1898) y Pristidactylus scapulatus Burmeister, 1861, (Iguania, Leiosauridae) de San Juan, Argentina. Revista Peruana Biologie 14, 2.

Pyron, R. A., Burbrink, F. T. & Wiens, J. J. 2013. A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes. BMC Evolutionary Biology 2013, 13:93 doi:10.1186/1471-2148-13-93

Torres, S. E. & Montero, R. 1998. Leiosaurus marellii Rusconi 1937, is a South American amphisbaenid. Journal of Herpetology 32, 602-604.