Tetrapod Zoology

Welcome to another article on the Matamata Chelus fimbriatus. Yay!

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In the previous episode we looked briefly at the Matamata’s long, thick neck and on a few aspects of Matamata evolution (a brief introduction to what the Matamata is, and where it lives, can be found here) [in the composite image shown above, the skull and neck is from digimorph while the photo of the live animal is from wikipedia]. This time, we’re going to look at the anatomy of the skull and hyoid skeleton (do stick with me here, it’s well worth it). I made the point previously that, despite being comparatively well-known as turtles (and animals) go, I just wasn’t able to find a good, illustrated description of the neck because such a thing doesn’t exist (though Hoffstetter & Gasc (1969) did at least figure the neck vertebrae). In contrast, the skull has been well described… and it’s surreal.

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As you see from these diagrams [from Gaffney (1977)], it’s really broad across the palate, quadrates and otic capsules (in fact, the skull is about as broad as it is long), and very flattened overall, particularly in the facial region. Gaffney (1977) described the skull as looking like it had been “run over by a truck” (this in an otherwise technical description of cranial anatomy) [skull in left lateral view shown below (from Gaffney (1977)) The eye socket is the opening right down near the snout-tip at left]. Some authors have described the skull as ‘arrow-shaped’ (Lemell et al. 2010): the snout is pointed, and the skull as a whole is flattened and light due both to reduction or loss of some elements and to relatively small muscles. The head can thus be thrown forward at great speed, all the while producing only a small pressure wave. Incidentally, the strong convergent similarity that the Matamata skull has with that of another aquatic-feeding tetrapod – the Surinam toad Pipa pipa – has not been lost on some (Lauder & Shaffer 1993, Sanderson & Wassersug 1993, Claude et al. 2004).

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Nasal bones are absent*, the maxillae are strongly reduced, jugal bars are absent (as is the case across Chelidae), the jaws are weak, and horny beak tissue is absent (meaning that this is a turtle devoid of a beak). Because the maxillae are really small, the ridge normally present along the edge of the upper jaw has (uniquely) moved to the palatine bones. The tongue is really small (we’ll see why in the next article). The dentaries are thin and weak compared to those of other turtles.

* In other chelids, the nasals are subrectangular bones located just posterior to the single bony nostril opening.

The hyoid bones of Chelus are enormous, heavily ossified and very distinctive [see image below, from Lemell et al. (2010)]: the apparatus as a whole is about two-thirds the length of the skull and, at its broadest point, about one-third of the skull’s width. Much of the space between the two halves of the lower jaw is filled up by the hyoid apparatus: there is a massive, vaguely cruciform hyoid body located along the midline (it has a prominent trough – the tracheal sulcus – running along most of its length), and two pairs of giant, finger-like processes (the brachial horns and their associated epibranchials) curve outwards and backwards from the anterior and posterior parts of the hyoid body. The tips of the brachial horns stretch wide apart when the jaws are opened wide, resulting in massive distension of the oesophagus. An also enormous hypoglossum – a streamlined plate of bone that looks something like an alien spacecraft – is located ventral to the hyoid body in between the rami of the lower jaws (Lemell et al. 2010).

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Left: hyoid apparatus in dorsal view. Right: in ventral view. Prling = lingual process. Fe = hyoid fenestra. Chy = hyoid body. Str = tracheal sulcus. Cbl = branchial horn I. Ebl = epibranchial I. CblI = branchial horn II. EblI = epibranchial II.

The soft tissues associated with the jaws are also really interesting [see figures below; again from Lemell et al. (2010)]. The adductors (the muscles responsible for closing the jaws) are weak, but they’re very thin and cover quite a large area on the dorsolateral surface of the skull (the external adductor extends from the posterior orbital margin all the way up to the posterior margin of the skull). The front part of the external adductor is covered by a special folded flap of skin that opens out when the jaws are opened, and then functions as a sort of cheek that helps to make the open mouth into a tunnel. This structure has been called the ‘Mundplatte’: it’s lubricated by a special layer of mucus (Lemell et al. 2010).

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Further back on the head, the geniohyoid muscle (originating on the lateral and medial surfaces of the lower jaw, as well as from part of the hyoid apparatus) is enormous: combined with the brachiomandibular and coracohyoid muscles, it allows rapid, simultaneous downward and backward rotation of the hyoid skeleton and associated expansion of the throat.

So – that’s the anatomy…. but what does the Matamata do with all of these weird cranial and hyoid features? That’s what we’ll look at next. If you can’t wait until then, Lord Geekington covered Matamata anatomy and feeding behaviour back here.

For previous Matamata articles see…

And for previous Tet Zoo articles on turtles see…

Refs – -

Claude, J., Pritchard, P., Tong, H., Paradis, E. & Auffray, J.-C. 2004. Ecological correlates and evolutionary divergence in the skull of turtles: a geometric morphometric assessment. Systematic Biology 53, 933-948.

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

Hoffstetter, R. & Gasc, J.-P. 1969. Vertebrae and ribs of modern reptiles. In Gans, C., Bellairs, A. d’A. & Parsons, T. (eds.) Biology of the Reptilia Volume 1. Academic Press (New York), pp. 201-310.

Lauder, G. V. & Shaffer, H. B. 1993. Design of feeding systems in aquatic vertebrates: Major patterns and their evolutionary interpretations. In Hanken, J. & Hall, B. K. (eds) The Skull. University of Chicago Press (Chicago), pp. 113-149.

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.

Sanderson, S. L. & Wassersug, R. 1993. Convergent and alternative designs for vertebrate suspension feeding. n Hanken, J. & Hall, B. K. (eds) The Skull. University of Chicago Press (Chicago), pp. 37-112.

Comments

#1 David Marjanović
July 30, 2010

Wow. An amniote with the palate of a baphetid (only toothless) trying to be a brachyopid or plagiosaurid. Too cool.
#2 David Marjanović
July 30, 2010

The SuperReader login doesn’t work anymore.
#3 Sven DiMilo
July 30, 2010

what does the Matamata do with all of these weird cranial and hyoid features?

I think it sucks.
#4 Bradley F
July 30, 2010

I think it’s awesome.
#5 Karl Zimmerman
July 30, 2010

Hrrm…no beak, no teeth (like all other extant turtles), weak jaws, small tongue, and a honkin big hyoid. Sounds like it must be a suction feeder.
#6 Dragon
July 30, 2010

TQ!!
WoW!!

as i read your postings i always take time to look at my very sleek RES (red eared slider).

so much is different from her compared to the matamata.

we have an abundance of box turtles here.
they are obviously tortoises, despite the misnomer.

anyway every chance i get i observe their behaviour & compare that to my RES’s slider.
obviously, the box tortoises are in the wild & my RES is captive & we have a relationship mammal to turtle.
so, i know my observations are very skewed.
i still enjoy them.

my RES was a “rescue”.
i had friends that were losing their critters to the police & i overheard them say…”hurry up & get home to hide the turtle!”

when i received her, she was the size of my hand, almost & her shell had many parasitic pin holes right through.
i thought at least she will be comfortable & in clean water until she dies.

a month later i was unable to find the pinholes & we have been good friends ever since!

again, TQ for spending your time writing about the Matamata.
i am thoroughly enjoying!!

~dragon.
#7 Cameron
July 30, 2010

Dragon:

we have an abundance of box turtles here.
they are obviously tortoises, despite the misnomer.

Terrapene Box Turtles are terrestrial Emydidae (Pond & Marsh) Turtles which, being members of the clade Emydinae, are closely related to Blanding’s, Wood, Bog, Spotted Turtles et cetera.

Cuora Box Turtles are convergent Old World Geoemydidae Turtles. Interestingly, Emydidae, Geoemydidae and true tortoises (Testudinidae) are closely related and form a clade (Testudinoidea) – which contains half of all extant turtles.
#8 Mike Habib
August 1, 2010

Greatly enjoying this latest series on one of my all-time favorite animals. Darren: let me know if you want some images or video of my matamata in action. He ate a mouse last night, but I’m sure he’s still hungry (because, well, he’s always hungry).

I leave it to Darren’s last installment to describe how matas consume whole fish, rodents, and frogs in the blink of an eye.
#9 darwinsdog
August 3, 2010

Dragon: As Cameron pointed out, box turtles are emydids not testudinids (tortoises), but what strikes me is that you say they’re abundant where you live. They were abundant where I grew up, but no longer. I was under the impression that populations have been in steep decline everywhere. I’d like to know where box turtles are still abundant but you probably shouldn’t state the location in a public forum.
#10 Jura
August 3, 2010

“Tortoise” is not a taxonomic term, but rather a common name that varies depending on your location. Europeans generally refer to all land turtles as tortoises, and all semi-aquatic/marine turtles as turtles. Americans just call all of them turtles. The only reason tortoise tends to get associated with Testudinidae is because that family is full of terrestrial members, and Europeans have named the vast majority of animals known to science.

Anyway I’m assuming that this is what Dragon was talking about, and not anything phylogenetically related.
#11 Cameron
August 3, 2010

Jura:
Europeans generally refer to all land turtles as tortoises, and all semi-aquatic/marine turtles as turtles. Americans just call all of them turtles.

Here’s an excerpt from the 2009 edition of Turtles of the United States and Canada by Ernst and Lovich (page 3):

Of the 14 living families of turtles, only one, the Testudinidae, is considered to comprise true tortoises.

All other terrestrial turtles are known as ‘box turtles’ – so ‘tortoise’ is effectively a taxonomic term in American English.

Also – British English refers to aquatic and semi-aquatic turtles as ‘terrapins’.
#12 David Marjanović
August 4, 2010

Europeans generally

Of course that’s only in English; I don’t know of another language that even has more than one term.

(Even though lots of languages have some kind of frog/toad and salamander/newt distinction. And French has an extra word for the treefrogs, and German has one for the fire-bellied toads…)
#13 Daniel
August 5, 2010

Portuguese (well, Brazilian Portuguese, but still…) has jabuti for tortoises, tartaruga for turtles (which can be used as broad term including the other two) and cágado for fresh-water turtles. Maybe cágado only applies to pleurodires: it mostly does, but since we have way more of them here I’m not sure
#14 darwinsdog
August 5, 2010

All other terrestrial turtles are known as ‘box turtles’ – so ‘tortoise’ is effectively a taxonomic term in American English.

I agree that ‘tortoise’ is synonymous with testudinid in American English (at least so far as in conversation with anyone I’ve ever known) and thereby is effectively a taxonomic term. I don’t agree that box turtles (Terrapene) are necessarily or exclusively terrestrial. I have observed Eastern box turtles foraging underwater in stream pools and other aquatic habitats and have mostly found them in mesic woodlands not far from water. Even in the semiarid Western US I have never encountered an ornate box turtle far from water. Box turtles are emydids and are not much more adapted to xeric conditions than are their confamilials. I’m not sure that there is such a thing as a strictly terrestrial turtle that is not a testudinid, so I’m not sure to what a European would refer as ‘tortoise’ besides a testudinid.
#15 Jura
August 6, 2010

Regardless of typical associations, tortoise is not a taxonomic term. It is in the same category as “bird” or “bat,” and just like those words, the common meaning can change depending on the society that uses it.

Perhaps not surprising then, that the other common names for box turtles (both American and Chinese) are box tortoises. In Australia even animals like red-eared sliders would be referred to as tortoises (turtle being reserved for chelonians with flippers like Carettochelys insculpta).

As for allusions to a semi-aquatic nature for box turtles, I have read about a few subspecies of Terrapene carolina that favour streams, but I’ve never found an Ornate box turtle that wasn’t miles from the nearest water source.
#16 darwinsdog
August 6, 2010

“Bird” & “bat” may not be formal taxonomic terms but in American English nothing that isn’t a member of the monophyletic groups Avialae & Chiroptera (or whatever the clade comprised of the first volant mammal & all its descendants is called) is ever seriously conceptualized as being anything but a bird or bat, respectively. Hence, for all prctical purposes “bird” & “bat” are synonymous with the formal taxonomic denominations they represent. There are cultures that would include both birds & bats in an inclusive category of “flying things,” but I’m talking about American English here. I contend that “turtle” is functionally synonymous with Chelonian and “tortoise” with testudinid, to any English speaking American I’ve ever conversed with. “Terrapin” is usually reserved for a member of the emydid genus Malaclemys but I have heard people speak of a slider or painted turtle as being a “terrapin.” I have never heard anyone say “box tortoise” or “box terrapin.”

Sometimes box turtles will embark on overland treks away from water but usually only after heavy rains. I’ve seen ornate box turtles crossing highways remote from major bodies of water but even then, there was usually water in the ditches alongside the road. More typically, a population of ornate box turtles will be found within a riparian corridor in the semiarid West. The population within New Mexico’s Mimbres Valley, that I’m familiar with, is typical of this. Individuals can be found near the river but never in my experience upon the arid hillsides roundabout. I never provide drinking water for any of the Geochelone tortoises I keep. Try keeping a box turtle that way & it will die of thirst.
#17 Cameron
August 6, 2010

darwinsdog:

I agree, calling Box Turtles ‘terrestrial’ isn’t a fair description – perhaps ‘semi-terrestrial’ (as opposed to ‘semi-aquatic for other emydids)? In the wild, Box Turtles require humid areas (over 51%) and can even hibernate in the mud on the bottom of streams. I’ve noticed that one box turtle spends a lot of times in a makeshift pool, originally a water dish.
#18 Allen Hazen
August 6, 2010

Darwinsdog–
Good thing you specify “American English”: my impression is that testudinate nomenclature is an area where there is a good deal of dialectal variation in English. I believe that, now or in the recent past, some (regional? class? educational?) dialect of British English restricted “turtle” to sea turtles, and used “tortoise” for all the terrestrial and semiterrestrial and freshwater types with clawed feet. Jura (post before yours) claims that Australian English is like that, though the one time I interrogated an Australian informant I didn’t get a very consistent picture of usage.