September 14, 2013 | 34
I said a while back that I intended to make some overdue headway into the diversity of lacertid lizards: Lacertidae being the clade that includes many of the more familiar, conventionally ‘lizard-shaped’ lizards of Europe, Asia and Africa. Beleaguered by commitments and absolutely unable to produce anything lengthy for Tet Zoo (and unwilling to repost an old article from the archives), I thought I’d produce a shortish article on a lacertid I haven’t written about before: Takydromus… though, seeing as this taxon contains something like 21 species, I’m actually talking about a whole group of lacertids, not a stand-alone singleton. [Image above by Materialscientist.]
Actually… about that number of species. There are a few cases where people have reported northern, temperate-climate Takydromus taxa from tropical places (example: specimens referred to the Russian-Korean-Chinese species T. wolteri have been ‘identified’ in Vietnam), leading some to suggest that the tropical identifications are erroneous, hinting at the existence of additional, cryptic species (Lin et al. 2002). Indeed, two such species – previously included within T. formosanus – were named from Taiwan in 2008 (Lue & Lin 2008). At the time of writing the newest species is T. hani, named this year from Vietnam.
In general appearance, these lizards – typically called grass lizards or oriental racers – are greenish or brownish, have a distinctly depressed head and a really long tail. That tail can be as much as five times as long as the combined length of the head, neck and body. This means that the centre of gravity is placed well back, a fact which allows for some mean acrobatic feats (read on). The keels on the large, plate-like dorsal scales form continuous longitudinal rows in many species. Many details of the scalation in Takydromus are unusual and unique within lacertids (Arnold et al. 2007).
If you know squamates, you’ll know that hemipenis structure is important in working out how species might be related to another. Surprise surprise, Takydromus has weird hemipenes: the lobes at the tips are unusually thick-walled and – so far as we know – the hemipenes don’t change shape much across the seasons. Oh yeah, did I say that squamate hemipenes normally change in size and shape according to season? As you might predict, they are biggest and most elaborately ornamented during the breeding season.
Takydromus species occur across eastern Asia, from Japan in the north down to Sumatra and Java in the south. About half of all species inhabit islands along the Pacific margin of Asia, including Taiwan, Japan and the Ryukyu Islands. This distribution means that there are species of humid tropical climates, cool temperate ones and everything in between. The high island-endemicity of the group also makes them potentially vulnerable to the sorts of anthropogenic problems associated with being restricted to islands (to my knowledge, little is known of the conservation status of these lizards, nor of how vulnerable they might be to extinction risk).
Some Takydromus species are forest-dwelling lizards while others occur in open habitats and show a preference for climbing among tall grasses. In fact, some are mostly ground-dwellers (e.g., T. amurensis and T. sylvaticus) while others are highly agile, acrobatic climbers that wind their tails around branches or grass blades when climbing. The more proficient of the climbers (like T. sexlineatus and T. dorsalis) are able to project the body stiffly outward from the object they’re climbing, the forelimbs laid back against the flanks (Arnold 1997). Bipedal standing, again with the forelimbs flat against the body, is practised in the longer-tailed species (like T. sexlineatus) when they’re trying to catch airborne or elevated prey. Arnold (1997) described this pose as ‘penguin-like’. He also suggested that the large, continuously overlapping dorsal and ventral scales might help provide stiffness for the body when the animals stand in this pose.
One of the most interesting things about these lizards is that they have tricuspid teeth at the back of the jaws (a feature that, elsewhere within Lacertidae, is also present in Gallotia and the Miocene taxon Miolacerta… wow, imaginative name on that one). All Takydromus species are arthropod predators and all (so far as we know) are oviparous.
As for where Takydromus fits within Lacertidae, a general similarity with Zootoca vivipara – the Palaearctic Viviparous lizard – has led to the idea that they’re somewhere within the lacertid clade Lacertinae, and close to Zootoca (Arnold 1989). Exactly this relationship was recovered by Arnold et al. (2007) in their morphology-based analysis, though things were rather less tidy in the molecular ones: they preferred topologies where Takydromus is the sister-taxon of all other lacertines excepting the members of Eremiadini (ah yes, them. Another time, ok?). Fu (1998, 2000) found Takydromus to be the sister-taxon to all other lacertines.
There’s no definite fossil record for Takydromus but Miolacerta might be a close relative or stem-member of the lineage (Arnold et al. 2007). It’s inferred that Takydromus descends from an ancestor that moved east from the more westerly area where lacertids mostly evolved, and then diversified extensively in eastern Asia and along the Pacific margin.
Arnold (1997) provided a wealth of data on the anatomy of the Takydromus species and produced a morphology-based phylogenetic hypothesis for the clade. As is typical for species that contain numerous species, there have been suggestions from time to time that certain of said species should get their own genera, so both Platyplacopus Boulenger, 1917 and Apeltonotus Boulenger, 1917 are today regarded as synonyms of Takydromus. Arnold (1997) found Takydromus to group into two main clades and he hence suggested that the name Platyplacopus could be applied to the clade that includes its type species (T. keunei from southern China, Hainan and Taiwan). However, molecular phylogenies have not supported this tidy division and Platyplacopus now seems to be polyphyletic (Lin et al. 2002, Ota et al. 2002). [Image below by TANAKA Juuyoh.]
So, for now, I can rest, secure in the knowledge that I’ve written about another group of lacertids at Tet Zoo. Only another 15-20 major lineages to go.
For previous Tet Zoo articles on lacertids, see…
Refs – -
Arnold, E. N. 1989. Towards a phylogeny and biogeography of the Lacertidae: relationships within an Old-World family of lizards derived from morphology. Bulletin of British Museum of Natural History (Zoology) 55, 209-257.
-. 1997. Interrelationships and evolution of the east Asian grass lizards, Takydromus (Squamata: Lacertidae). Zoological Journal of the Linnean Society 119, 267-296.
- ., Arribas, O. & Carranza, S. 2007. Systematics of the Palaearctic and Oriental lizard tribe Lacertini (Squamata: Lacertidae: Lacertinae), with descriptions of eight new genera. Zootaxa 1430, 1-86.
Bhupathy, S., Chettri, B. & Bauer, A. M. 2009. Rediscovery and revalidation of Takydromus sikkimensis (Günther, 1888) (Squamata: Lacertidae) from Sikkim, India. Journal of Herpetology 43, 267-274.
Fu, J. 1998. Toward the phylogeny of the family Lacertidae: implications from mitochondrial DNA 12S and 16S gene sequences (Reptilia: Squamata). Molecular Phylogenetics and Evolution 9, 118-130.
- . 2000. Toward the phylogeny of the family Lacertidae – why 4708 base pairs of mtDNA sequences cannot draw the picture. Biological Journal of Linnean Society 71, 203-217.
Lin, S.-M., Chen, C. A. & Lue, K.-Y. 2002. Molecular phylogeny and biogeography of the grass lizards genus Takydromus (Reptilia: Lacertidae) of East Asia. Molecular Phylogenetics and Evolution 22, 276-288.
Lue, K.-Y. & Lin, S.-M. 2008. Two new cryptic species of Takydromus (Squamata: Lacertidae) from Taiwan. Herpetologica 64, 379-395.
Ota, H., Honda, M., Chen, S.L., Hikida, T., Panha, S., Oh, H.-S. & Matsui, M. 2002. Phylogenetic relationships, taxonomy, character evolution and biogeography of the lacertid lizards of the genus Takydromus (Reptilia: Squamata): a molecular perspective. Biological Journal of the Linnean Society 76, 493-509.