That weird little face was, indeed, that of a turtle – but it wasn’t that of a matamata Chelus fimbriatus, it was instead that of a softshell turtle (a trionychid), and specifically that of a narrow-headed softshell Chitra indica (though read on). Well done Lars, Johannes and Emile, and particularly Hai-Ren. Chitra has to be one of the most amazing turtles: a big to enormous, long-skulled rubbery animal that hardly ever leaves the water.
Unlike all other turtles, softshells have reduced the bony carapace to such an extent that the margins of their shell are flexible: in some species, the bony carapace only occupies half of the entire, errr, carapace, and the rest is cartilage and skin (trionychids are unique in that they’ve lost the peripheral bones that normally form the bony carapace margin). While Chitra has big, flipper-like forelimbs, its hindlimbs are often obscured by the flexible rear margin of the carapace. All in all, it reminds me a giant rubber hot water bottle… and if you grew up in the tropics and don’t know what a rubber hot water bottle is, one is shown below with a Chitra chitra. Striking resemblance.
A predator of fish, molluscs and crustaceans (though it also may eat plants on occasion), Chitra is noted by some authors as having a particularly nasty bite. Others say that captive individuals are really quite nice when you get to know them (Ernst & Barbour 1989). As is the case with all big freshwater turtles, some fantastic anecdotes are attached to these turtles. My favourite is that they can catch and overturn goats (Alderton 1988). Quite what the significance of the ‘overturning’ is I’m not sure. As is clear from the skull you can see at the top, the orbits of Chitra are placed unusually far forwards, even for a softshell. In life, a short mobile proboscis extends from the bony nostrils and is used as a snorkel. Females lay 60-110 eggs in a go. Despite this fecundity, they are – like so many Asian turtles – declining due to their use as luxury food items and in Chinese medicine, and they are also endangered by habitat loss, pollution and the construction of dams. Some species are critically endangered and will probably follow other Asian turtle species into extinction in the near future. About half of all Asian turtle species are endangered.
Not only are narrow-headed softshells notable in looking so bizarre, they’re also well known for reaching huge sizes. If, until now, you’ve been imagining softshells to be little things perhaps only 30 or 60 cm long, prepare to be shocked, as the biggest species exceed 100 cm in carapace length and 200 kg in weight. A female Siamese narrow-headed softshell C. chitra (aka Striped narrow-headed softshell or Nutphand’s narrow-headed softshell) captured in 1967 had a carapace length of 123 cm (carapace length, not total length) and a weight of 152 kg, and another caught in Thailand in 1986 weighed 202 kg (Kitimasak et al. 2005). For photos of some real big ones, go here. You will doubtless have heard of the reportedly immense softshells from Hoan Kim Lake in Vietnam. They’re not narrow-headed softshells: instead they belong to Rafetus, another genus of big Asian softshells. A lot of claims have been made about these turtles: that they approach 3 m in length and are as big as a double bed, that they live to be over 500 years old, that they are the same turtles mentioned in a story from the 1400s, and that they represent a new species (R. leloii). We await more information. The head of one of these turtles is shown in the adjacent image: there aren’t many good photos of these turtles, and this one gets used a lot, so apologies if you’ve seen it before.
Finally, while the skull shown above was labelled C. indica, we can be confident that this is correct because I know the skull comes from India. The narrow-headed softshells from Thailand and Myanmar, previously included within C. indica, have recently been shown to represent separate species (Engstrom et al. 2002, McCord & Pritchard 2002). C. chitra, which you’ve seen mentioned and pictured above, was separated from C. indica and named in 1986. The Myanmar population was only named as a new species, Van Dijk’s narrow-headed softshell C. vandijki, in 2002 (McCord & Pritchard 2002).
Softshells have a pretty good fossil record, and in fact Chitra is reasonably well represented in, for example, the Pliocene deposits of the Indian Siwalik Hills (Chitra-like fossils come from rocks as old as the Eocene, but whether they’re specifically allied to Chitra remains unsure). Softshells as a whole have a fossil record extending back to the Cretaceous, and in the past they were present in Australia (Gaffney & Bartholomai 1979); today they don’t occur there, but are ‘limited’ to North America, Africa and Asia. Crown-group softshells have conventionally been divided into two groups, the trionychines and the Afro-Indian flap-shelled turtles, or cyclanorbines (Meylan 1987). These differ from trionychines in being able to hide their feet under flaps of skin that extend from the plastron. Among trionychines, Chitra has conventionally been regarded as closely related to the Asian giant softshell Pelochelys bibroni, and a recent analysis by Engstrom et al. (2004) confirmed this, grouping them together in a trionychine clade dubbed Chitraina (Engstrom et al. (2004) followed the PhyloCode convention of putting all clade names in italics. I appreciate that this is all to do with abandoning ranks, but it so jars with traditional taxonomy that I’m still not keen on it). The next closest relative to Chitraina was Trionyx, and all of these taxa were then found to form a well-supported clade for which another ridiculous-looking new taxon name was created: Gigantaestuarochelys, the giant estuarine turtles (though they mis-spelt it Gigantaesuarochelys [sic] in their Fig. 5, the first place it appears in the paper). Incidentally, the adjacent image shows Pelochelys bibroni to scale with a lady. Remind me to elaborate one time on the noble tradition of using Oriental ladies as scale bars for assorted large animals, seriously.
And, dammit, once more I failed to produce a short 100-odd words.
For previous Tet Zoo turtle pieces, there’s the Green turtle article here, and the famous turtle phallus article here. The ver 1 series on snapping turtles starts here, and the hololissa article is here. Still araripemydid pleurodires, meiolaniids and tortoises to come at some point in the future.
Refs – -
Alderton, D. 1988. Turtles & Tortoises of the World. Blandford, London.
Engstrom, T. N., Shaffer, H. B. & McCord, W. P. 2002. Phylogenetic diversity of endangered and critically endangered southeast Asian softshell turtles (Trionychidae: Chitra). Biological Conservation 104, 173-179.
- ., Shaffer, H. B. & McCord, W. P. 2004. Multiple data sets, high homoplasy, and the phylogeny of softshell turtles (Testudines: Trionychidae). Systematic Biology 53, 693-710.
Ernst, C. H. & Barbour, R. W. 1989. Turtles of the World. Smithsonian Institution Press, Washington, D. C. & London.
Gaffney, E. S. & Bartholomai, A. 1979. Fossil trionychids of Australia. Journal of Paleontology 53, 1354-1360.
Kitimasak, W., Thirakhupt, K., Boonyaratpalin, S. & Moll, D. L. 2006. Distribution and population status of the Narrow-headed softshell turtle Chitra spp. in Thailand. The Natural History Journal of Chulalongkorn University 5, 31-42.
McCord, W. P. & Pritchard, P. C. H. 2002. A review of the softshell turtles of the genus Chitra, with the description of new taxa from Myanmar and Indonesia (Java). Hamadryad 27, 11-56.
Meylan, P. A. 1987. Phylogenetic relationships of soft-shelled turtles (Family: Trionychidae). Bulletin of the American Museum of Natural History 186, 1-101.