This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Today we’re here because of the lacertid lizards, the Old World clade that includes Eurasian wall lizards, green lizards, fringe-toed lizards and a great number of less familiar species groups that rarely get much attention outside of the specialist literature. Yes, as you might have realised if you’re a long-term and/or regular reader, this is one of those long-running, I-produce-the-next-instalment-as-and-when-I-feel-like-it sets of articles. A few of the many lacertid lineages have been covered in previous Tet Zoo articles (see the links below). [Adjacent photo, and photo below, by Yuriy75.].
In the article here I want to talk about some members of a major group that I’ve – literally – only mentioned before; namely, the Eremiadini or Eremiinae or Eremiainae or Eremiadinae*, generally called eremiines. And this is a pretty big group containing perhaps 15 genera and over 80 species, so I’m actually only going to talk here about one ‘genus’: Eremias. The ‘best’ collective name for the Eremias lizards is racerunners, though the sometimes-used ‘desert lacertas’ isn’t too bad. The common name fringe-toed lizard is also used for some species. This name makes sense given that some species specialised for life on loose sand have distinct fringes or combs of subtriangular scales along their fingers and toes; the problem is that it’s already used for another group of lacertids: the Acanthodactylus species.
* Arnold et al. (2007) argued that formulations including ‘-iadin’ are technically correct. So, if the group is regarded as a ‘subfamily’, it should be Eremiadinae, and if it’s regarded as a ‘tribe’ within a ‘subfamily’, it should be Eremiadini. In view of this, the right vernacular term should be ‘eremiadines’ or ‘eremiadins’.
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As someone who spent formative years reading fieldguides to European reptiles, I know one racerunner – the Steppe-runner E. arguta – as an obscure ‘exotic’ lacertid that only occurs in far eastern Europe and is even missing from some books on the European lizard fauna altogether. Sadly, it has disappeared or virtually disappeared from some regions where it used to occur and has been regarded as locally extinct in parts of Romania and Ukraine. I’ve looked for it in Romania but failed to find it. Many lacertid species seem to have declined in recent decades, predominantly as a consequence of agricultural development (Gherghel et al. 2007) and habitat degradation caused by over-grazing and heavy vehicle traffic.
In general, racerunners are lizards of dry, sparsely vegetated semi-deserts, deserts and steppes, though members of some species will also live in sandy places in marshes, on coasts and in river deltas. Some tend to frequent rocky plains and the sides of wadis while others are psammophiles that inhabit sand dunes and burrow into sand when taking refuge. Arnold (2004) said that adaptation to aeolian habitats happened independently on two occasions (and see Mayer et al. 2007). Subtle specialisation for different microhabitats is definitely present in the group: there are species that prefer stabilised sand where light vegetation is growing (like Anderson’s racerunner E. andersoni), others that occur on hard, sometimes pebbly, soil covered in vegetation (like the Black-ocellated racerunner E. nigrocellata), and yet others that frequent loose sand on dunes (like the Pointed-snouted racerunner E. acutirostris). Species that inhabit mountainsides and other rocky places (like Strauch’s racerunner E. strauchi) will happily climb steep slopes (Anderson 1999). Exactly how these microhabitat specialisations correlate with anatomical variation – with scale form, digit length, claw curvature and so on – is a question of great interest since a good understanding of any correlations here can help us make predictions about lizards where we have anatomical data but no (or less) data on microhabitat preference, and vice versa. Work of this sort has been done on several lizard groups but I’m not sure that it’s been done on racerunners.
A few papers have, however, looked at how body shape, limb proportions and so on correlate with life history in racerunners. Li et al. (2011) showed how body size and limb proportions in the Multi-ocellated racerunner E. multiocellata varied between populations according to local climate, with the ones from a warmer location being faster runners than those from a cooler location.
Where? How many? And how do you tell them apart?
Racerunner species occur from southeastern Europe, across the Middle East, and all the way east to Pakistan, northern China and the Korean Peninsula. Given that we usually think of them as mostly based in Central Asia, the presence of at least one species literally on the shores of the Pacific is a bit surprising. The lizard concerned – the Mongolian racerunner E. argus – inhabits coastal dune systems on Yoobu-do Island and elsewhere on coastal South Korea, right on the edge of the Yellow Sea (Jin et al. 2013, Song et al. 2013).
A reasonable number of racerunner species are recognised (something like 38) and a few new ones have been named since 2000. These include E. montana (originally written as E. montanus but later corrected by other authors), named in 2001, E. cholistanica, named in 2006, E. karivensis, named in 2007, and E. papenfussi, named in 2011. All are from Iran except for E. cholistanica, which is from Pakistan. Another supposedly new Iranian species – ‘E. novo’, named in 2006 (mentioned by Mozaffari & Parham 2007) – was never meant to be a new species, but a shorthand way of referring to a new population now thought to belong to E. montanus. More new species are set to be named in time, since there are good indications from molecular phylogeny that some relatively widespread ‘species’ – the Rapid fringe-toed lizard E. velox is perhaps the best example – are actually species complexes (Pouyani 2009). [Adjacent photo by Yuriy75.].
As expected for any group of lizards, species predominantly differ from one another in the configuration, arrangement and number of their head shields and other scales, their pigmentation and patterns, and in the form of their subdigital scales. Head shape is reasonably variable within the group, some having far shorter, broader snouts than others. Some of the shallow-snouted ones sometimes don’t look all that different from Acanthodactylus lacertids. Hold that thought...
Szczerbak (1974) decided to recognise the diversity within the racerunners by classifying Eremias species into five subgenera: Eremias, Ommateremias, Rhabderemias, Pareremias, and Scapteira. These were later raised to generic level by some authors. Oh, and Ommateremias is a junior synonym of yet another name – Aspidorhinus – according to some authors (Guo et al. 2011). As is so often the case with subgenera, the classification of species into these groups was done predominantly on phenetic grounds (that is, on general overall similarity) and distinct anatomical or molecular characters that distinguish them weren’t identified. Having said that, studies of hemipenial anatomy are more or less in agreement with the recognition of these groups (Arnold 1989). An rRNA analysis found Pareremias and Eremias to be clades whereas Rhabderemias, Ommateremias/Aspidorhinus and Scapteira were not monophyletic (Guo et al. 2011*). The viviparous racerunners formed a clade within Pareremias. What? Viviparous species? We’ll come back to that, hold on.
* Be careful with the diagrams in that paper, since some of the taxonomic names are spelt incorrectly. [Image below by Benny Trapp.]
Life history and the viviparity thing
At least some racerunner species are reportedly short-lived, with average life expectancies of 2.5 years being given for the Rapid fringe-toed lizard (Pouyani 2009). This strikes me as surprisingly short-lived for a lizard, though I’m not wholly sure why I think this given that good longevity data on lizards is infrequently encountered in the literature. Longevity for the Mongolian racerunner is approximately 10 years (Kim et al. 2010), which is greater than that of other small lacertids.
Given the short lifespan of the Rapid fringe-toed lizard, I’m also surprised to find that it apparently only produces 2-5 eggs per year: you’d expect greater fecundity in such a small, short-lived animal. Juvenile racerunners often differ substantially from adults in colouration – a fairly common thing for lacertids that might be an evolutionary response to the different predation pressures that affect these animals at different points in their lives. Minor sexual dimorphism is present: males have proportionally larger heads than females (Li et al. 2006) and also have more prominent spots and stripes and so on in at least some species (Moravec 1994). However, the heads of males are apparently no broader than those of females (though they are longer) in Mongolian racerunners or Ordos racerunners E. brenchleyi, perhaps because head width is constrained by its use in sand-burrowing, nor are males larger or longer overall (Kim et al. 2010).
I mentioned viviparity. Three Eremias ‘species’ are viviparous: E. buechneri, E. przewalskii* (photo above by Alastair Rae) and E. multiocellata, and I put the word ‘species’ in quote marks there because E. multiocellata is one of the species complexes I mentioned earlier (it’s suspected to house as many as 8 distinct lineages that should probably be raised to ‘species’ level (Guo et al. 2010, 2011)). Viviparity in racerunners might have arisen more than once but one recent study did find the viviparous species to form a clade within Pareremias (Guo et al. 2011). Why might viviparity have evolved in these lizards in the first place? Viviparity in squamates is usually thought to be linked to specialisation for life in cool climates. Guo et al. (2011) used a molecular clock technique to come up with possible divergence times for the different racerunner clades and suggested that the viviparous clade might have originated at about the same time as the Tibetan Plateau expanded and affected climates in east Asia and elsewhere.
* Przewalski is – so I’ve been told – pronounced something like ‘shu-val-ski’. Any further pronunciation tips appreciated. [Image of Gobi racerunner below by Conrad Savy.]
How are racerunners related to other lacertids?
You might (but probably won’t) remember from the previous Tet Zoo lacertid articles (links below) that the basic structure of the lacertid tree involves an early split between Gallotiinae and a large clade that contains all the other taxa, generally (but not universally) called Lacertinae. Within the latter clade, the long-tailed Takydromus grass lizards might (Fu 1998, 2000, Harris et al. 1998, Pavlicev & Mayer 2009) form a distinct lineage that’s outside a clade that includes (1) Lacerta and its mostly Eurasian kin (but see Mayer & Pavlicev 2007), and (2) the mostly African clade that contains Acanthodactylus and the racerunners. Arnold (1989) was first to establish this basic framework and it’s since been elaborated and generally supported by subsequent studies. That second, ‘mostly African’ clade is Eremiadini or Eremiinae or Eremiainae or Eremiadinae, ugh... Eremiadini and Eremiadinae are apparently the versions that are technically correct (Arnold et al. 2007).
Arnold (1991) supported a hypothesis of relationships where Eremias is part of what he termed the “advanced Saharo-Eurasian lacertids”: the clade that also includes Acanthodactylus, Mesalina and Ophisops. These lizards share an unusual internal stiffening system within the hemipenis termed an armature and hence have also been termed the ‘armatured clade’ on occasion (Harris et al. 1998). Pedioplanis was suggested to be the sister-taxon of the armatured clade, and both it and the members of the armatured clade share a number of derived anatomical characters (like a sternal fontanelle that’s often heart-shaped, and a reduced quadratojugal process on the jugal). Pedioplanis is from southern Africa and all the outgroups to this Pedioplanis + armatured clade (Meroles, Aporosaura, Ichnotropis, Heliobolus, Latastia, Philochortus and Nucras) are African too (Arnold 1991). We thus seem to have an ‘out of Africa’ model in this eremiadin group, lineages within the clade migrating out of Africa and into Eurasia once or several times.
Or do we? Fu (1998) found racerunners and the mostly Eurasian Ophisops to form a clade that was the sister-group to the rest of the ‘Saharo-Eurasian’ clade. Given that other lacertid lineages are Eurasian, and thus that this ‘Saharo-Eurasian’ clade must have dispersed into Africa from Eurasia at some point, this position would suggest that racerunners (and Ophisops) are primitively Eurasian, not recent invaders from Africa.
A molecular analysis that combined data from several genes also supported this model, though this time Eremias was closer to Adolfus than it was to Ophisops, Meroles, Pedioplanis, Latastia or Heliobolus, and Acanthodactylus and Mesalina were a long way away (albeit still in a ‘Saharo-Eurasian’ clade) (Fu 2000). [In the adjacent and massively simplified lacertid cladogram - its topology based on that of several studies combined - Latastia by Guérin Nicolas, Eremias by Yuriy75, Takydromus by Acapella, Gallotia by Petermann.]
That same study also includes a very different cladogram (based on data from the cytochrome oxydase I gene [COI] alone) where racerunners are shown as being part of a Eurasian clade that otherwise only includes Timon, Algyroides, Podarcis and Lacerta (sensu lato) (Fu 2000). I suppose the aim in Fu’s study was to see if single genes recovered the same relationships as did a combined analysis. Anyway, other molecular studies have found Eremias to be surrounded in the tree by African taxa (Harris et al. 1998, Mayer & Pavlicev 2007, Greenbaum et al. 2011, Kapli et al. 2011), so the ‘out of Africa’ model looks more robust than the 'primitively Eurasian' one. A lot could be said about the timing and precise details of lacertid biogeography: I have to ignore that whole area for now.
Incidentally.... yes, lacertid diversity and phylogeny is confusing and ideas about the way the many constituent taxa might be related have varied substantially. One of the reasons that things are so difficult to resolve might be that the different lineages really did diversify very rapidly (Pavlicev & Mayer 2009). Among the most important studies prior to recent years are those of George A. Boulenger who published his monumental two-volume Monograph of the Lacertidae in 1920 and 1921. Arnold (1989) said the following: “This was Boulenger’s last task in a long and highly productive career. Even before the second volume of the monograph left the press, he quit the field, retired from the British Museum and returned to his native Belgium where he devoted his last years to studying roses. Anyone who has spent much time wandering in the confusing labyrinths of lacertid systematics will tend to sympathise” (p. 210).
I said earlier that I would only be talking about Eremias in this article (and, despite having written over 2200 words on them so far, there’s an awful lot more that could be said). But as a wise and responsible Tet Zoo reader, you’ve surely been thinking “but what about all those other eremiine genera that you’ve mentioned and not discussed at length?”. Yes, there are lots more
eremiineseremiadines eremiadins to talk about. One day, one day...
Tet Zoo now features some fairly reasonable coverage of squamate diversity... but there is still so much to do...
Dibamids and amphisbaenians
Amphisbaenians and the origins of mammals (April 1st article!)
Gekkotans
Gekkota part II: loud voices, hard eggshells and giant calcium-filled neck pouches
Squirting sticky fluid, having a sensitive knob, etc. (gekkotans part III)
300 years of gecko literature, and the ‘Salamandre aquatique’ (gekkotans part VI)
Whence Uroplatus and… there are how many leaf-tailed gecko species now?? (gekkotans part VII)
Ptychozoon: the geckos that glide with flaps and fringes (gekkotans part VIII)
Lacertids
The New Forest Reptile Centre (on Zootoca and Lacerta)
Iguanians
Harduns and toad-heads; a tale of arenicoly and over-looked convergence
The Squamozoic actually happened (kind of): giant herbivorous lizards in the Paleogene
Australia, land of dragons (by which I mean: agamids) (part I)
Scincomorphs
Anguimorphs
Pompey and Steepo, the world-record-holding champion slow-worms
Dinosaurs come out to play (so do turtles, and crocodilians, and Komodo dragons)
What I saw at the zoo yesterday... (more brief comments on Komodo dragons)
Perentie tries to swallow echidna. Echidna too spiky, Perentie gets horribly injured. Dies.
“Lean, green and rarely seen”: enthralling prasinoid tree monitors
Snakes
"What was that cute little Mexican snake?", and other musings...
Snake 195 mm long eats centipede 140 mm long. Centipede too big. Snake dies.
Monster pythons of the Everglades: Inside Nature's Giants series 2, part II
The more you know about colubrid snakes, the better a person you are
Love for Mastigodryas, Tomodon, Sordellina and all their buddies: you know it’s right
Refs - -
Anderson, S. C. 1999. The Lizards of Iran. Society for the Study of Amphibians and Reptiles, Saint Louis.
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.
- . 1991. Relationships of the South African lizards assigned to Aporosaura, Meroles and Pedioplanis (Reptilia: Lacertidae). Journal of Natural History 25, 783-807.
- . 2004. Overview of morphological evolution and radiation in the Lacertidae. In Pérez-Mellado, V., Riera, N. & Perera, A. (eds) The Biology of Lacertid Lizards. Evolutionary and Ecological Perspectives. Institut Menorquí d’Estudis. Recerca 8, 11-36.
- ., Burton, J. A. & Ovenden, D. W. 1992. Reptiles and Amphibians of Britain and Europe. Collins, London.
Greenbaum, E., Villanueva, C. O., Kusamba, C., Aristote, M. M. & Branch, W. R. 2011. A molecular phylogeny of Equatorial African Lacertidae, with the description of a new genus and species from eastern Democratic Republic of the Congo. Zoological Journal of the Linnean Society 163, 913-942.
Guo, X.-G., Chen, D.-L., Wan, H.-F. & Wang, Y.-Z., 2010. Review of systematics of the racerunner lizard (Lacertidae: Eremias). Sichuan Journal of Zoology 29, 665-672.
Laňka, V. & Vít, Z. 1986. Amphibians and Reptiles. Hamlyn, Twickenham.
Li, H., Ji, X., Qu, Y., Gao, J. & Zhang, L. 2006. Sexual dimorphism and female reproduction in the multi-ocellated racerunner (Eremias multiocellata) (Lacertidae). Acta Zoologica Sinica 52, 250-255.
- ., Qu, Y.-F., Ding, G.-H. & Ji, X. 2011. Life-history variation with respect to experienced thermal environments in the lizard, Eremiasmultiocellata (Lacertidae). Zoological Science 28, 332-338.
Szczerbak, N. N. 1974. Yaschurki Palearcktiki. [The Palearctic Desert Lizards] Axadeimiya Nauk Ukrainskoi SSR Institut Zoologii, Kiev.
Song, J.-Y., Chang, M.-H. & Koo, K.-S. 2013. Estimating the size of a Mongolian racerunner Eremias argus (Squamata: Lacertidae) population at Baramarae Beach, Taeanhaean National Park. Korean Journal of Herpetology 5, 9-13.