If you know anything about turtles you’ll know something of the geoemydids – formerly called batagurines. This is a large group of Eurasia and the Americas that don’t really have a popular collective name but is sometimes called the Asian river turtles or Old World pond turtles, even though both names are technically incorrect. One species – the Malayan box turtle Cuora amboinensis – occurs in Sulawesi and the Moluccas, putting it on the Australasian side of Wallace’s Line. There are about 70 living geoemydid species. Asian box turtles (Cuora), roofed and painted terrapins or turtles (Batagur), Old World pond turtles (Mauremys) and Neotropical wood turtles (Rhinoclemmys) are among the better known species clusters within the group.
Geoemydids include some of the most attractive turtles of all, there being many species with bold and colourful head markings used in mating displays or perhaps, in cases, in warning off potential predators (Orenstein 2001). Some of the markings look crazy: I’m thinking of the prominent spots of the Four-eyed turtle Sacalia quadriocellata in particular. The markings also increase in intensity and brightness on a seasonal basis; the species concerned can look bland and dull at some times of the year, or when kept in captivity and (so it’s thought) maintained on an insufficient diet. Some species undergo a whole-body colour change as they enter the breeding season, males of some Batagur species (including those formerly given the separate genus Callagur) changing in head, body and shell colour. They can look resplendent and amazing in full breeding condition.
Geoemydids tend to be amphibious, freshwater animals, though some occur in coastal marine environments and some are fairly terrestrial and inhabit damp woodlands and grasslands. Some of the terrestrial species (they include some of those Cuora box turtles) have a tall, domed carapace; flatter shells are more typical in the group, and some (like the Spiny turtle Heosemys spinosa) have thorn-like projections that grow outwards from the marginal scutes around the shell’s edges. Longitudinal ridges on the carapace are common and some Cuora species have a kinetic plastron that allows the shell to be completely sealed – an excellent example of convergent evolution with the (only distantly related) emydid box turtles.
A few shell characters are diagnostic for the group (Claude & Tong 2004), including a small pygal (the midline bone at the posterior end of the carapace) and the presence of musk ducts within the peripherals (the bones that lines the outer margins of the carapace). Yes, musk ducts – turtles of many sorts secrete musk through various ducts on the shell, and sometimes smell very strongly. Most geoemydids have carapace lengths of 20 cm or so but the Malayan giant turtle Orlitia borneensis can have a carapace 80 cm long.
Most geoemydids are predominantly animalivorous, eating worms, molluscs, crustaceans and fish but some (like some Batagur species) are omnivorous and eat fungi, fruits and leaves as well.
As expected for a group that inhabits tropical Asia, new species are named on a fairly regular basis. On that note, a number of species named as brand new during the 1990s and deemed highly desirable in the pet trade (‘Ocadia glyphistoma’, ‘O. philippeni’ and ‘Sacalia pseudocellata’) now appear to be hybrids generated in captivity and fraudulently sold as exotic novelties (Stuart & Parham 2006) – I’ve been saying since about 2007 that I’d write about those cases at Tet Zoo and yet here we are. As also expected for a group that occurs through tropical Asia, geoemydids of many species have been, and are being, horrendously over-exploited for the restaurant trade but also for use as good luck charms and pets. Several are now critically endangered as a result of over-exploitation and some are extinct or suspected to be so. The plight of turtles in tropical Asia is a matter of urgency and much needs to be done.
Phylogeny and fossils. Geoemydids are testudinoids: that is, part of the turtle clade that includes marsh turtles (Emydidae) and tortoises (Testudinidae), and molecular data indicates that they’re especially closely related to tortoises, the two forming the clade Testuguria (Crawford et al. 2013). That might be surprising in view of the traditional idea that geoemydids are close to – if not part of – Emydidae, but there we go. The shape of the phylogeny means, incidentally, that tortoises likely descended from amphibious or aquatic ancestors. Yes, Platysternon – the big-headed turtle – is shown here as a testudinoid following Crawford et al. (2013). That’s an interesting thing that warrants further discussion, but it will have to wait to later.
Geoemydids have a pretty good fossil record that extends back more than 40 million years into the Eocene and includes species from Europe and central and eastern Asia. Some taxa now restricted to tropical Asia – I’m thinking of the Geoemyda leaf turtles – are known from fossils to have been present across Europe and right across Asia (from Ukraine to Japan) from the Eocene onwards, a complication being that the palaeontological concept of Geoemyda is now different from the neontological one (Geoemyda now has a far narrower content than it used to).
So there we have it, a brief introduction to geoemydids. Some of the material here is based on the relevant section of the in-prep textbook, on which go here. For other Tet Zoo articles on turtles, see…
- Hard-shelled sea turtles and a diet of glass
- Gilbert White's pet tortoise, and what is 'grey literature' anyway?
- Giant African softshells - wow!
- Giraffe-necked giant tortoises
- Matamata: turtle-y awesome to the extreme
- The familiar Matamata, known to us all since the 1700s, and its long, fat neck (matamatas part II)
- "Adaptation perfected" (possibly) in a turtle's head (matamatas part III)
- Turtles that suck, turtles that blow (matamatas part IV)
- Giant fossil matamata turtles (matamatas part V)
- Necks for sex? No thank you, we're sauropod dinosaurs (includes brief discussion of Galapagos tortoises)
- The goat-eating hot water bottle turtles
- In case you forget, softshell turtles are insanely weird
- Terrifying sex organs of male turtles
- A very quick history of turtles
- Turtles that eat bone, rocks and soil, and turtles that mine
- Turtles I Have Recently Seen
- J.Lo and Other Araripemydid Pleurodires
- Letters from the World of Turtle Evolution
Refs - -
Claude, J. & Tong, H. 2004. Early Eocene testudinoid turtles from Saint-Papoul, France, with comments on the early evolution of modern Testudinoidea. Oryctos 5, 3-45.
Crawford, N. G., Parham, J. F., Sellas, A. B., Faircloth, B. C., Glenn, T. C., Papenfuss, T. J., Henderson, J. B., Hansen, M. H. & Simison, W. B. 2014. A phylogenomic analysis of turtles. Molecular Phylogenetics and Evolution 83, 250-257.
Orenstein, R. 2001. Turtles, Tortoises & Terrapins: Survivors in Armor. Firefly Books, New York.
Stuart, B. L. & Parham, J. F. 2006. Recent hybrid orign of three rare Chinese turtles. Conservation Genetics 8, 169-175.