Among my favourite lizards are the Uromastyx agamids, variously termed mastigures, dabbs, dabs, dhubs, spinytails, spiny-tailed agamas, spiny-tailed lizards or thorny-tailed lizards. In the pet trade they’re often called ‘uros’. Here, I’ll be calling them mastigures.
Mid-sized for lizards (25 cm in total length is typical, though read on), they’re rather chunky, short-headed and wide-bodied with a proportionally short, broad tail that’s covered in 10 to 30 transverse, parallel rows of posterodistally projecting spines. The rows have a ring-like form and (rather confusingly) are typically called whorls. The tail is said to function as a ‘burrow blocker’ and also to be lashed from side to side when deterring would-be attackers. Enlarged, thorn-like scales are also present on the hindlimbs of some species. The head is short and deep by lizard standards and a neat feature is that the labial scales are large, serrated structures that sometimes look like external pseudoteeth.
Mastigures are extremely variable in colour, ranging from almost black to almost white dorsally; areas of yellow and even bright orange are present in some species, sometimes forming eye-like markings, distinct spots large or small, or transverse bands. The head may be much darker than the rest of the animal, and sometimes the tail is different in colouration too. Adding to this complexity is that individuals change colour according to temperature and time of day. The tail is variable in size: it's similar in length to the body in most species but is very short and broad in a few species, most notably the Omani spiny-tailed lizard or Thomas's mastigure U. thomasi.
The teeth are especially interesting: they’re short, low-crowned and fused to the jaw bones on their lingual (tongue) side, are largest at the back of the jaws, have crescentic shearing tips, and possess oblique wear facets that become so pronounced with age that entire teeth can be worn right down to the jaw (Cooper & Poole 1973). As you might guess, these animals do not possess regular tooth replacement of the sort we associate with reptiles (Robinson 1976). This is linked with a style of jaw movement (termed propaliny) where the lower jaw slides forwards to create a shearing bite when the jaws are closed (Throckmorton 1976). In the premaxillae, the upper central incisiforms are replaced by projecting structures that have been interpreted as bony pseudoteeth (Anderson 1999), though I don’t know if the histological work required to demonstrate this has been performed and they might be fused teeth.
Mastigures occur throughout the steppes, deserts and semi-deserts of northern Africa, the Middle East and western and central Asia. They aren’t associated with dune-fields, instead inhabiting rocky or gravel-covered regions or areas with compacted sand. They use and build burrows that are sometimes 3 m long or so, though I would expect based on data from other burrow-digging reptiles that burrows at least twice as long might exist. ‘Colonial burrows’ have been mentioned in the literature (Anderson 1999), though I don’t know if this means that many burrows were located in close proximity or if the burrows were known to contain some or many lizards.
Around 15 extant species are recognised with Uromastyx, five of which have been named since 1990: U. maliensis Joger & Lambert, 1996, U. occidentalis Mateo et al., 1999 (or 1998), U. leptieni Wilms & Böhme, 2001 (or 2000…), U. alfredschmidti Wilms & Böhme, 2001 (or 2000…) and U. yemenensis Wilms & Schmitz, 2007. The total number of recognised species is a bit vague since some taxa are regarded as subspecies by some authors and as distinct species by others. An additional three Asian species have recently been removed from Uromastyx and placed in the resurrected genus Saara, first named by Gray in 1845 (Wilms et al. 2009). Saara species possess so-called intercalary scales between the spine whorls on the tail and molecular data finds them to be the sister-group to Uromastyx (Tamar et al. 2018).
In recent years, Uromastyx mastigures have become increasingly common in the pet trade and it’s now normal to see them on show in places that sell pet reptiles. I have seen them in the wild while on fieldwork in the Sahara, but the individuals concerned were dead and I never have seen a live one in the wild.
Biology and behaviour. Mastigures are omnivorous, but they’re (seemingly) essentially herbivorous as adults, only occasionally eating arthropods or smaller lizards. The presence of symbiotic gut flora has been demonstrated for some species (a feature seen elsewhere in agamids in the Hydrosaurus sailfin dragons). Their lifestyle requires their taking refuge in rock crevices or burrows when they’re not feeding, foraging, basking or interacting socially, a behavioural syndrome where a compressed body shape and defensive spiny tail are advantageous, and one that has evolved convergently in other iguanians – the American chuckwallas and ctenosaurs and Madagascan oplurines – and in the Australian Egernia skinks and in some African corylids (Pianka & Vitt 2003).
Herbivory in lizards works best at large size for the obvious reason of how much nutrition can be recovered (though it’s worth saying that there are many exceptions to this tendency: see Espinoza et al. 2004); it follows, then, that mastigures are relatively large compared to other agamids. I don’t know if there are any studies that do demonstrate this specifically, but the fact that most species are 25-45 cm long as adults does seem large, and the biggest species – the Egyptian or Leptien’s mastigure U. aegyptia – is positively enormous, reaching 75 cm on occasion and even more (specimens nearly 1 m long have been reported… can you imagine a mastigure this size? Amazing). It’s worth saying here that an especially large Paleogene lizard – Barbaturex from the middle Eocene of Myanmar, it perhaps reached 2 m in total – appears to be an especially close relative of Uromastyx (Head et al. 2013).
Mastigures are oviparous, females laying clutches of 6-20 elliptical eggs within a burrow. The hatchlings stay within the burrow for a few weeks, possibly even for months. The mother remains in attendance across this time and her burrow-guarding behaviour might be a form of parental care (directed both at the eggs and the hatchlings). Given that these lizards possess a symbiotic gut flora, the babies are presumably coprophagous. I’ve seen this stated informally but am not aware of a study that demonstrates it. Remember that tetrapods that possess a symbiotic gut flora must obtain it from their parents, and thus must eat their parent's dung early in life. Mm-mm.
Antiquity, taxonomy, biogeography. Having mentioned fossils, jaw fragments that appear to be from Uromastyx-like agamids (though not necessarily Uromastyx itself) are known from the Lower Eocene of Kyrgyzstan (Averianov & Danilov 1996) and hence establish an age of around 50 million years for this lineage. A number of Paleocene and Eocene lizards from Mongolia and China appear to be additional uromastycines. Rather younger, Oligocene fossils from the famous Jebel Qatrani Formation of the Fayum in Egypt’s Western Desert are sufficiently mastigure-like that they’ve been identified as ‘cf. Uromastyx’ (‘cf’ is an abbreviation of the Latin ‘confer’ and, when used in a taxonomic identification, basically means ‘we think that these fossils are so comparable to [insert taxon of interest] that they might belong to it, though we can’t be sure’). They date to the Lower Oligocene and hence are around 33 million years old (Holmes et al. 2010). There’s also a Lower Oligocene Uromastyx mastigure from France – yes, a European member of the group.
This antiquity is in keeping with the idea – made on the basis of their highly distinctive anatomy – that mastigures are ‘distinct enough’ from other agamids to be worthy of their own ‘subfamily’: Uromastycinae. This view derives support from those studies that have found or inferred mastigures to be a distinct lineage outside the clade containing all remaining crown-agamids (e.g., Frost & Etheridge 1989, Macey et al. 2000, Schulte et al. 2003, Pyron et al. 2013), and perhaps even outside the clade that includes chameleons and conventional agamids (Honda et al. 2000, Gauthier et al. 2012). That last result would push mastigure origins into the Cretaceous given amber fossils that seem to be stem-chameleons.
Oh, you want Cretaceous stem-mastigures? In 2016, Apesteguía et al. (2016) described Jeddaherdan aleadonta from the Cenomanian of Morocco, and concluded that both this taxon and Gueragama sulamericana from the Upper Cretaceous of Brazil – both represented by partial lower jaws – are exactly that. Fossil evidence does, therefore, now back up the idea that these lizards were in existence before the end of the Cretaceous, and that acrodonts* (and thus iguanians more generally) had evolved at least some of their variation before the Cenozoic.
* Acrodonts (properly Acrodonta): the iguanian lizard clade that includes chameleons and agamids. They are named for their acrodont teeth: that is, those fused to the jawbones (though this condition is not fully developed across all members of the clade, and note that there are acrodont reptiles that are not part of Acrodonta).
At least some studies find mastigures to form a clade with the east Asian butterfly agamas Leiolepis (e.g., Honda et al. 2000, Hugall & Lee 2004, Gauthier et al. 2012), both then being united within Leiolepidinae*. Butterfly agamas are fascinating for all sorts of reasons and I really should write about them at some point as well.
* There’s a long and complex argument over whether Leiolepidinae/Leiolepididae or Uromastycinae/Uromastycidae should win in a priority battle. Modern authors have tended to prefer the former, since it’s 1843 as opposed to 1863 for Theobald’s Uromastycidae. Anderson (1999) argued that the 1843 use of Fitzinger’s name cannot win this battle, since it was originally ‘Leiolepides’ and was not written in its ‘modern’ form by authors pre-1900.
Anyway: here I’ll say what I usually do and remind you that if these animals were mammals or birds they’d almost definitely be considered ‘distinct enough’ to warrant their own ‘family’, a decision that would require Agamidae of tradition to be split into several ‘families’ (I put these taxonomic ranks in quotes because they’re still effectively subjective). In addition to a mastigure family and butterfly agama family, there would be one for Hydrosaurus, one for the Australasian dragons (or amphibolurines), another for the Asian draconines, and so on. A few authors – most notably Scott Moody in his studies of the early 1980s – have at least separated mastigures and butterfly agamas from remaining agamids in a version of Theobald's ‘family’ Uromastycidae.
Macey et al. (2000) assumed an Indian origin for mastigures, in which case they’re among several tetrapod groups that followed an ‘Out of India’ dispersal route hypothesised elsewhere for ostriches and certain caecilians and frogs. But this is also contradicted by fossils, since Paleocene members of the lineage – if correctly identified and correctly dated – show that members of the lineage were living in Eurasia before India docked with Eurasia during the Eocene. The best model, therefore, might be one in which mastigures moved into Eurasia at the end of the Cretaceous.
Tamar et al. (2018) posited an initial, middle Miocene diversification of the Uromastyx crown-group in south-east Asia followed by Afro-Arabian invasion and diversification. But note that this only applies to crown-group Uromastyx, not to the Saara + Uromastyx clade, nor to the mastigure lineage as a whole, and thus is not inconsistent with an earlier origin and diversification elsewhere.
Your regular dose of misanthropy. Finally, all is not well as goes the future of mastigures. As you might guess given my earlier mentions of the pet trade, the sad fact is that uncontrolled, indiscriminate and often illegal collection from the wild is a threat to many populations. Many people involved in the pet reptile trade – those at the sharp end where animals are taken from the wild and smuggled to other countries – have no scruples whatsoever as goes the ethical or managed treatment of animals, and if you don’t believe me look up articles on Anson Wong, the Malaysian wildlife smuggler known as the ‘Lizard King’ (a most inappropriate moniker, given that Kings are supposed to be worthy of respect or admiration).
Mastigures have also been much used for food, medicine and as ritual objects (a cleaned mastigure body serves as a traditional baby’s bottle in Morocco, for example), all of which is fine (in theory) when harvesting is kept to sustainable levels… but less fine when exploitation begins to outstrip supply. Those mastigures that have been studied are declining or locally extinct across their range and all species are CITES listed as of 1977. Specifically, they’re on Appendix II of CITES, which refers to species that are not necessarily in immediate danger of extinction but do nonetheless require a control in their trade.
In some countries where these lizards occur it’s considered a rite of passage for young men to go out and kill as many mastigures as they can, and if you want verification for that you can find photos online where there are great piles of tens or even hundreds of dead mastigures in the backs of trucks. That’s depressing and vile behaviour. Like Anne Frank, I do think that people are essentially good but it’s difficult to maintain a rosy view of humanity when our stated aim seems to be the denuding of wild spaces of their animals.
On that depressing note, we move on.
This article took a lot of work and quickly expanded way beyond the brief ‘here’s a picture of a lizard’ article it was originally intended to be. However, I think that articles like this are useful and would like to keep doing them. Here’s your regular reminder that I require support if this is to continue. I would do more if support allowed. Thanks to those who support me at patreon already.
Iguanian lizards have now been covered quite a few times at Tet Zoo. For previous articles see...
- Harduns and toad-heads; a tale of arenicoly and over-looked convergence, December 2006
- Ermentrude the liolaemine, February 2008
- ‘Cryptic intermediates’ and the evolution of chameleons, June 2008
- Tell me something new about basilisks, puh-lease, January 2009
- Amazing social life of the Green iguana, September 2012
- The Squamozoic actually happened (kind of): giant herbivorous lizards in the Paleogene, June 2013
- The enormous liolaemine radiation: paradoxical herbivory, viviparity, evolutionary cul-de-sacs and the impending mass extinction, June 2013
- Leiosaurus: big heads, bold patterns, October 2013
- Grassland earless dragons, January 2014
- Australia, land of dragons (by which I mean: agamids) (part I), January 2014
- Australia, land of dragons (part II), February 2014
- What's With All These New Chameleon Names?, Part 1, February 2016
- By the Horns of Trioceros, the Casque of Calumma, the Brood of Bradypodion--Chameleons, Part 2, February 2016
- Palleon, Archaius, Kinyongia, Nadzikambia--The Last Chameleons, Part 3, March 2016
- The Tropidurine Treerunners, December 2017
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Cooper, J. S. & Poole, F. G. 1973. The dentition and dental tissues of the agamid lizard Uromastyx. Journal of Zoology 169, 85-100.
Espinoza, R. E., Wiens, J. J. & Tracy, C. R. 2004. Recurrent evolution of herbivory in small, cold-climate lizards: breaking the ecophysiological rules of reptilian herbivory. Proceedings of the National Academy of Sciences 101, 16819-16824.
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