Turtles that suck, turtles that blow (matamatas part IV)

In the previous Matamata article I discussed the very scary skull and hyoid anatomy of this singular South American turtle. The 'ugly' look of the Matamata is well known, but hopefully you now know that the Matamata should also be famous for its large size, for its massively thick, long neck, for its pivotal historical role in our understanding of pleurodire turtle diversity, and for its freakish, flat-faced skull [illustrations above from Patrick Lemell's website].

As you'll no doubt already know, the remarkable morphology of the Matamata's head and neck correlates with a remarkable feeding behaviour. Like various other turtles that lurk, concealed, on the bottoms of ponds, lakes and rivers, matamatas are (usually!) cryptic lunge-feeders that wait for small prey (typically fish) to come close. They don't possess worm-like lures on their lower jaws, as shown in this old drawing by L. R. Brightwell (not sure where Brightwell got that idea from: plausibly from confusion with Alligator snappers).

Once the prey is within range, the Matamata engages in dynamic suction-feeding: a feeding Matamata gapes its jaws really wide (opening them to an angle of about 80°), and rapidly expands its throat to suck in a huge quantity of water - hopefully containing the prey. Structures normally present on the pleurodire palate (and apparently restricting their gapes to between 40-65°) have been strongly reduced (as discussed in the article on skull and hyoid anatomy). It's fairly easy to get a Matamata to indulge in this behaviour if you tease it with bits of meat, or wiggle your fingers around in front of its face. Ordinarily, this sort of thing is only recommended when there's a sheet of glass in the way, but it's reported by people who have experienced matamata 'attacks' that their bites aren't actually that painful. And they shouldn't be, given the weak jaws, absence of beak tissue, and importance of suction and engulfment of water.

The speeds involved are phenomenal, as should be clear from this sequence of photos (from Lemell et al. 2002). Within the space of 20 milliseconds, the turtle has lunged at and fully engulfed the prey, and by 44 milliseconds the throat is fully extended and filled with a large amount of engulfed water (containing the prey item). For some awesome film of a feeding event, see below... After engulfment, the neck is relaxed into its pre-strike posture, the hyoids return to their resting positions, and the mouth is slightly opened so that the engulfed water can be expelled. The prey is then jiggled around in the throat by repeated sucking in and blowing out of more water: the turtle retains the prey between its hyoid rods and only opens its mouth slightly when expelling water. It does this expelling very slowly. Incidentally, I'm reliably informed that Matamatas can also expel large quantities of air when out of water: a loud hissing noise is the result (M. Habib, pers. comm.).

In the wild, live fish are the usual prey (probably characins), but captive Matamatas have often been fed live frogs and rodents, and there's some suggestion that wild ones might eat carrion if the opportunity arises. Very little is known about Matamata diet in the wild; it's assumed that they mostly eat small prey, but there's no reason why they can't take larger animals. The only real limit on prey size is the vertical distance between the carapace and plastron. In keeping with this, it seems that they're reluctant to accept prey similar in size to, or larger than, their own heads (Mike Habib, pers. comm.).

A whole list of unusual features are therefore combined to make the Matamata a supreme suction-feeder. In the opinion of some authors, it's an animal where adaptation has been perfected (Lemell et al. 2010). We see a weird, flattened, lightweight arrow-shaped skull; jaws that can be opened exceptionally wide exceptionally quickly; a near-absent tongue; a long, thick and distensible neck; and a gigantic, heavily ossified hyoid apparatus that allows massive distension of the oesophagus

The descriptions I've given here of Matamata feeding behaviour and anatomy are brief and very much introductory: for more information the reader is directed to Gaffney (1977) and Lemell et al. (2002, 2010). I'm not the first person to discuss Matamata behaviour and anatomy in the blogosphere: Lord Geekington covered the species back here.

Despite all those specialisations, and that remarkable feeding behaviour, Matamatas are actually quite adaptable and don't just rely on crypsis and ambush. Formanowicz et al. (1989) showed that Matamatas are prepared to move around quite a bit when prey density is low; in other words, they actively forage for prey, most typically by moving around the edges of shorelines and objects. However, the presence of other Matamatas has a 'dampening' effect on this behaviour: it seems that these turtles avoid bumping into each other if possible.

Some authors think that Matamatas deliberately 'herd' prey: either by corralling them when hunting close to shorelines (Holmstrom 1978), or by gradually herding the prey toward a barrier and strongly tilting the carapace upwards such that the prey is confronted with a 'wall' of turtle shell (Holmstrom 1991) [the photo above, from Holmstrom (1991), shows a Matamata engaging in this behaviour]. They may even wave their forelimbs to - apparently - prevent fish from escaping the corralled area. Other authors have contended that this herding behaviour is unlikely simply because they failed to observe it (Wise et al. 1989). That doesn't strike me as very convincing: as Holmstrom (1991) said, different Matamatas may behave in different ways when confronted with different prey in different conditions.

Also worth noting is that the Matamata is not restricted to what you might regard as a stereotypical habitat (say, big, slow-moving rivers). Quiet creeks, oxbow lakes and ponds are all haunted by Matamatas, and live individuals washed up on the coast of Trinidad had barnacles on their shells and must have been living at sea for a while (Pritchard 2008) [adjacent photo courtesy of Mark Hollowell].

Finally (for now).... for all their weirdosity compared to other pleurodires, matamatas are actually pretty ancient and with a good fossil record - a, shall we say, very interesting fossil record. I have to stop there... all will be revealed but, as usual, will those in the know PLEASE refrain from spoiling everything in the comments section!!

For previous articles in the Matamata series, see...

• 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)

And for previous Tet Zoo articles on turtles see...

• Giraffe-necked giant tortoises
• Giant African softshells - wow
• Gilbert White's pet tortoise, and what is 'grey literature' anyway?
• The goat-eating hot water bottle turtles
• Hard-shelled sea turtles and a diet of glass
• Terrifying sex organs of male turtles

Refs - -

Formanowicz, D. R., Brodie, E. D., Wise, S. C. 1989. Foraging behavior of matamata turtles: the effects of prey density and the presence of a conspecific. Herpetologica 45, 61-67.

Gaffney, E. S. 1977. The side-necked turtle family Chelidae: a theory of relationships using shared derived characters. American Museum Novitates 2620, 1-28.

Holmstrom, W. (1978). Preliminary Observations on Prey Herding in the Matamata Turtle, Chelus fimbriatus (Reptilia, Testudines, Chelidae) Journal of Herpetology, 12 (4) DOI: 10.2307/1563365

- . 1991. Further observations on Matamata prey herding. Journal of Herpetology 25, 363-364.

Lemell, P., Beisser, C. J., Gumpenberger, M., Snelderwaard, P., Gemel, R. & Weisgram, J. 2010. The feeding apparatus of Chelus fimbriatus (Pleurodira; Chelidae) - adaptation perfected? Amphibia-Reptilia 31, 97-107.

- ., Lemell, C., Snelderwaard, P., Gumpenberger, M., Wochesländer, R. & Weisgram, J. 2002. Feeding patterns of Chelus fimbriatus (Pleurodira: Chelidae). The Journal of Evolutionary Biology 205, 1495-1506.

Pritchard, P. C. H. 2008. Chelus fimbriatus (Schneider 1783) - Matamata turtle. In Rhodin, A. G. J., Pritchard, P. C. H., van Dijk, P. P., Saumure, R. A., Buhlmann, K. A. & Iverson, J. B. (eds) Conservation Biology of Freshwater Turtles and Tortoises: A Compilation Project of the IUCN/SSC Tortoise and Freshwater Turtle Specialist Group. Chelonian Research Foundation, pp. 020.1-020.10.

Wise, S. C., Formanowicz, D. R. & Brodie, E. D. 1989. Matamata turtles ambush but do not herd prey. Journal of Herpetology 23, 297-299.