The Giant Turtle Therizinosaurus

Therizinosaurus, you look... unwell. Reconstruction by K. K. Fierova, from Maleyev (1954).

I am quite fond of old, weird reconstructions, and the initial classification of Therizinosaurus cheloniformis as a "turtle-like reptile"¹ resulted in the magnificent specimen above. So how could the veritable Jabberwocky we're all familiar with be misinterpreted to such a colossal degree?

¹ This odd phrasing is mirrored in the scientific name ("saurus" = lizard, "cheloniformis" = turtle-like). Malayev (1954) linked Therizinosaurus with members of Protostegidae and thus (probably) didn't intend to suggest another clade of reptiles which converged on turtles. Bizarrely, Rozhdestvensky (1974) claimed Malayev/Maleev classified Therizinosaurus as a "turtle-like pangolin"! Rozhdestvensky (1977) does not reiterate that statement, and further notes that another worker (Sukhanov) classified Therizinosaurus as a turtle; I unfortunately cannot find that source ("The subclass Testudinata" in Osnovy Paleontologii).

Therizinosaurus in its non-turtle form. From Wikipedia Commons.

Malayev (1954) described Therizinosaurus from scrappy remains: a metacarpal fragment, 3 manual unguals, and rib fragments (Zanno 2010). One of the ribs was an estimated 1.5 meters long when complete and was used to calculate a maximum body width of 3.25 meters (10'8") and body length of 4.5 m (14'9") (Malayev 1954); this is of course quite a bit larger than even the largest known Stupendemys geographicus. The rib was noted to lack costal elements, which is curious since turtle skeletons generally look like this:

 

Common Snapping Turtle (Chelydra serpentina) skeleton. Note the plastron is missing. From Wikipedia Commons.

Surprisingly, this is not necessarily a critical flaw, as (all?) turtles have distinct ribs during development before the carapace is fully formed (Wyneken 2001, fig. 90; Sánchez-Villagra 2009, figs. 3, 4). Malayev (1954) did not mention this nor the obvious possibility of a multi-ton hatchling. Instead, the "form of the ribs" was compared to Archelon and Protostega:

Archelon skeleton. From Wikipedia Commons.

The similarity is very general and Malayev (1954) does not list any specific shared characteristics. Due to the lack of costal elements, Malayev (1954) speculated that Therizinosaurus was in a distinct clade and in life had "barely developed or almost completely absent bony armor". It is incredibly strange that the Leatherback Seaturtle (Dermochelys coriacea) was not mentioned, as it entirely lacks costal elements and instead has thousands of dermal ossicles (Cebra-Thomas et al. 2005). The skeleton (sans ossicles) looks like an attempt by turtles to become "normal" tetrapods again.. until you notice the pectoral girdle within the ribcage:

From Wikipedia Commons

The rib material used to describe Therizinosaurus cheloniformis is apparently not from a therizinosaur at all, but a sauropodomorph (Zanno 2010 citing Rozhdestvensky 1970). Isn't it a major problem that the holotype is a chimera? Whatever the case, Therizinosaurus cheloniformis has been re-described a few more times and other rib material has been referred to the species (Zanno 2010). However, all of the diagnostic traits (and most of the material) are from the forelimbs (Zanno 2010).

From Wikipedia Commons.

Malayev (1954) interpreted the metacarpal and phalanges to be "powerful swimming organs" and suggested the huge claws were used for "cutting aquatic vegetation or for another functions, constrained by movement and acquiring food". The longest phalanyx was 60-65 cm long, not including the keratin covering (Malayev 1954), which suggests that the claws were ridiculously huge in life, even for a turtle-like reptile with a 4.5 meter body. I have observed turtles using their claws to climb and tear apart food (maybe what Malayev had in mind...), but clearly claws this disproportionate were doing something special. Something like this:

I like to think that Therizinosaurus, despite not being turtle-shaped anymore, waved its giant claws seductively in the faces of prospective mates.

References:

Cebra-Thomas, J., Tan, F., Sistla, S., Estes, E., Bender, G., Kim, C., Riccio, P., and Gilbert S. F. (2005). How the Turtle Forms its Shell: A Paracrine Hypothesis of Carapace Formation. Journal of Experimental Zoology 304B, 558-569. Available.

Maleyev, E. A. (1954). A new turtle-like reptile from Mongolia. Priroda 3, 106-108. Available.

Rozhdestvensky, A. K. (1977). The study of Dinosaurs in Asia. Journal of the Palaeontological Society of India 20, 102-119. Available.

Rozhdestvensky, A. K. (1974). History of the dinosaur fauna of Asia and other continents and questions concerning paleogeography. Transactions of the Joint Soviet–Mongolia Paleontological Expedition 1, 107–131. Available.

Rozhdestvensky, A. K. (1970). On the gigantic claws of mysterious Mesozoic reptiles. Palaeontological Journal 1, 131-141.

Sánchez-Villagra, M. R., Müller, H., Sheil, C. A., Scheyer, T. M., Nagashima, H., and Kuratani, S. (2009).  Skeletal Development in the Chinese Soft-Shelled Turtle Pelodiscus sinensis (Testudines: Trionychidae). Journal of Morphology 270, 1381-1399. Available.

Wyneken, J. (2001). The Anatomy of Sea Turtles. U.S. Dept Commerce NOAA Tech Mem NMFS SEFSC-470. Available.

Zanno, L. E. (2010). A taxonomic and phylogenetic re-evaluation of Therizinosauria (Dinosauria: Maniraptora). Journal of Systematic Palaeontology 8(4), 503-543. Draft Available.

A Giant Snapper At Last!

A common cliché in fringe anecdotes is that when eyewitnesses see something beyond belief, the camera has the lens cap on/no film/failed to work/been misplaced. Logically this should be taken as a strike against veracity... but I began to wonder otherwise when it happened to me. 

Of course, I've documented a big snapping turtle before, but my subsequent failures were astounding. I saw the turtles on multiple occasions this year (alluded to here), sometimes up close (touching, in fact) and once in triplicate. On all of these occasions I didn't bring my camera because I was commuting via bike, or the turtles fled before I could get their photographs. After a couple dozen failures, I gave up. Impulsively I decided on 8 November 2011 to take a trip searching for any reptiles or amphibians still active in the abnormally warm weather (about 70° F, 21° C) and saw this (plus a frog):

Blobturtle! I saw the turtle fairly clearly, but evidently my camera didn't. Rather than leave and be disappointed for a few months and then fail to see the turtles ever again, I realized I had no other option but to go in after it. Not only was the water very cold (it had snowed earlier in the year), it was murky and muddy and possibly had other snapping turtles I couldn't see. Gradually and with little subtlety, I made my way over to the turtle which had of course noticed me, but did not attempt to escape.

Remembering previous encounters and advice on pick-pocketing from Fagin, I approached the turtle from the rear, knowing it would eventually rotate around to defend itself. I also kept in mind how to fight the Cyberdemon from Doom - it's not just the shooting, it's the circle-strafing. With the cold water being slightly less of a hindrance for me, I managed to avoid something getting amputated. 

Getting closer, I confirmed my suspicions that, yes, this turtle is really really big.

The closest thing I could get to a measurement.

Eventually the turtle kicked up large amounts of silt and released gas (from... somewhere) and became impossible to see. I "ran" off, knowing that my luck in succeeding with this ill-conceived shenanigan was running out.

I know I'm never going to get an accurate length or weight measurement from this turtle... not without one or both of us getting hurt. Even if this specimen was a record (and there's no guarantee), it would not be worth risking the life of an old reptile to revise the SCLmax of 49.4 cm for Chelydra serpentina. From now on I'm leaving these turtles alone, my curiosity is satiated, and bothering them further will have no benefits. I'll have to live with the wonder that despite inhabiting a polluted body of water and having human hunt them and compete for their resources, things like this still exist.

Picture of the Indiscriminate Interval #000003 - Invasion of the Sliders

Whilst I'm in the midst of designing the most flamboyant Cooter (turtle) ever and trying to not horrendously reconstruct cetaceans, I've decided to resurrect this nearly-forgotten gimmick to stymie the ol' blog from gathering too much dust. How has it gotten to one-post-a-month? I feel like I'm always in the process of writing something up.

At Brickyard Pond, Barrington, Rhode Island, I was in the process of stalking Snapping Turtles when I noticed what was unmistakably an invasive Red-Eared Slider (Trachemys scripta elegans) resting about a meter offshore in thick vegetation. Despite facing the shore, the head was retracted, and I was able to casually walk up to and capture the turtle before it started its futile escape dash. I was surprised to see that the little male (SCL ~ 12-13 cm) had its left arm amputated above the elbow.

Despite the horrendous-looking injury and the lackluster escape attempt, the turtle appeared to be in decent condition. Not having the capability to care for another Slider (see below), I returned the male back to its point of capture (roughly where the back end is pointing in the photo above), and was surprised that it made no attempt to flee, and did not even emerge from its shell for a few minutes. I had recently observed a large Snapping Turtle in the immediate vicinity, which makes me wonder if the Slider's presence so close to shore and apparent tenacity to hold its position had to do with the potential predator. Either that, or it was more damaged than what I had thought.

I cannot find any literature on the frequency of Trachemys scripta elegans losing limbs - let alone in an invasive context - however it has been occasionally documented in other species. As discussed in Sewer Turtles, some Phrynops geoffroanus individuals missing their forelimbs could survive and even feed themselves. Saumere (2001) observed a female Snapping Turtle in Quebec with both forelimbs amputated at the elbow nesting in two years out of three. For whatever reason, most literature on turtle limb loss concerns Wood Turtles (Glyptemys insculpta); one population from Quebec was observed to have amputation rates of 9.6% for a single limb and 3.2% for two limbs, which was comparable to rates reported in other populations (Walde et al. 2010). However, another Quebec population had 32.3% and 13% rates for single and double amputations, respectively, which may have been caused by either predator efficiency and/or density (Saumere and Bider 1998). The recapture rate for amputee Wood Turtles in a northern Michigan study was significantly lower for non-amputees, and while some were recaptured multiple times (Harding 1985), it would overall suggest that limb loss is a significant hazard to survival.

There's no way of telling just how the Slider lost its arm, although I'd say predation would be more likely that some run-in with a lawnmower or other equipment since the shell was unharmed. Any number of mammals could have been the culprits - as they have been for unfortunate Wood Turtles - although interactions with snapping turtles or even Blue Crabs (yes, they can live in freshwater) can't be ruled out either. I didn't really wan't to return the specimen, but I lack the capacity to care for such a turtle and have heard it is difficult to find anyone willing to accept Sliders of any sort. If anybody out there knows an exception, please let me know!

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As for why I couldn't cram any more turtles into my life, I had already captured a female of possible breeding size (SCL = 19 cm) from the same pond. I had seen it around for a few months, although its shell did not have any readily-visible patterning and it was generally facing away from me, so I was not certain if it was a Red-Eared Slider or not. On one mid-November afternoon, I observed it rather unwisely basking in cool weather (45 F, 7.2 C) on a log ~2 m offshore while facing away from said shore. I'd be stupid not to sneak up on it, catch it, take it home, clean it off, and christen it as my new pet.

Kevin (named after actress Kevin Casey, of The Skydivers infamy) is still with me, although I'm honestly surprised. 165 days into my ownership, I noticed a piece of metal sticking out of the cloaca. Not knowing what to expect, I wound up pulling a sinker, line, and a partially-digested hook out of the turtle. Despite the potential to puncture internal organs from the hook and the line and the possibility of lead poisoning from the sinker, Kevin showed no signs of blood or really any indication that something that potentially-traumatic had just occurred. Still, it was probably lucky that it wasn't attempting to pass foreign object in the wild.

As for what damage a hook can do to a turtle, one snapping turtle which swallowed multiple hooks and a sinker was treated for lead poisoning and intestinal perforations (from the fishing line) (Borkowski 1997). There's not much information out there on non-marine turtles getting hooked, but I'd wager that a turtle surviving an internal hook with no obvious damage is one lucky punk.

References:

Borkowski, R. (1997). Lead poisoning and intestinal perforations in a snapping turtle (Chelydra serpentina) due to fishing gear ingestion. Journal of Zoo and Wildlife Medicine 28(1), 109-113. Abstract.

Harding, J. H. (1985). Clemmys insculpta (Wood Turtle). Predation-mutilation. Herpetological Review 16, 30. Available.

Saumere, R. A. (2001). Limb Mutilations in Snapping Turtles, Chelydra serpentina. The Canadian Field-Naturalist 115, 182-184. Available.

Saumere, R. A., and Bider, J. R. (1998). Impact of Agricultural Development on a Population of Wood Turtles (Clemmys insculpta) in Southern Québec, Canada. Chelonian Conservation and Biology 3, 37-45. Available.

Walde, A. D., Bider, J. R., Daigle, C., Masse, D., Bourgeois, J-C., Jutras, J., and Titman, R. D. (2010). Ecological Aspects of a Wood Turtle, Glyptemys insculpta, Population at the Northern Limit of its Range in Québec. The Canadian Field-Naturalist 117, 377-388. Available.

Sewer Turtles

Yes, really.

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Turtles are in serious trouble. The IUCN Red List investigated 207 out of ~300 species and arrived at these assessments:

Click to enlarge. This is an unofficial chart of my own construction - for a prior version see the Turtle Conservation Fund. The number of unassessed species is estimated.

95 of the species were last assessed over 10 years ago and are in need of updates (IUCN 2010); this unfortunately suggests the present situation could be worse than illustrated above. It also needs to be pointed out that 'Unassessed' is not necessarily synonymous with 'Least Concern'. For instance, the unassessed Common Snapping Turtle (Chelydra serpentina) is unprotected throughout most of its range and commonly assumed to be in no danger, but in reality requires conservation effort (Ernst and Lovich 2009).


With the situation looking grim, it then comes as a shock that some turtles not only survive in anthropogenically-altered environments, but thrive.

Geoffroy's side-necked turtle (Phrynops geoffroanus) is a moderately-large (max SCL = 35 cm, 13.8") pleurodire which lives east of the Andes in the Orinoco, Amazonas, São Francisco, and Paraná rivers basins ('Turtles of the World', Baldo et al. 2007). Souza (2005), however, interprets the distribution as patternless, and coupled with the diversity of habitat, reiterated a prior suggestion that P. geoffroanus is a complex of sister species. For the sake of not having to construct awkward sentences for the rest of this article, I'll refer to whatever complex may exist as a single species. P. geoffroanus inhabits streams, rivers, lakes and lagoons* with soft bottoms and abundant vegetation ('Turtles of the World', Bonin et al. 2006). The diet is strongly carnivorous, including fish, aquatic insects, snails, and other invertebrates ('Turtles of the World', Bonin et al. 2006). The turtles are shy and flee from humans whom are less than 50 meters (165 feet) away (Bonin et al. 2006). They have been spared from large-scale hunting due to being generally unpalatable, but large numbers are still collected for the pet trade (Bonin et al. 2006). The IUCN does not list the species.


*Making this one of a surprisingly large number of turtles tolerant of saline conditions.

Phrynops geoffroanus from Wikipedia Commons. Phrynops species are commonly called Toad-Head Turtles thanks to their wide dorso-ventrally compressed head.

Souza and Abe (2000) investigated P. geoffroanus populations in Ribeirão Preto Stream, which runs through a town of over half a million and as a result receives an estimated 25-28 tons of sewage per day, as well as dead animals, pesticides, and assorted domestic waste including food scraps, furniture, and tires. The stream is muddy to the degree that at a 30 cm (1 foot) depth, the bottom cannot be seen. Only around 1 kilometer out of the 40 km stretch (0.6 out of 25 miles) is canalized, allowing the grass Panicum maximum to dominate the banks. Up to 75 turtles were present in a 0.1 hectare (0.25 acre) area surveyed; median figures gave a more modest 170-230 turtles/hectare (420-569/acre) or a biomass of 255-345 kg/hectare (1388-1878 lbs/acre). Thus, the 40 km stretch averaging 10 m (33 feet) wide has a population of around 3000 turtles. Surprisingly, neotropical turtles living in lakes may have much higher densities, but in comparison with other streams, the Ribeirão Preto turtles are extremely abundant. It is unfortunate Souza and Abe (2000) did not survey P. geoffroanus in unaltered streams to determine differences in abundance and life history.


So how were the turtles apparently thriving in what essentially amounts to an open-air sewer? Terrestrial prey such as snails and cockroaches were taken, along with carrion and items such as (chicken?) meat and rice from human residences. However, the chironomid Chironomus plumosus was found in 100% of the stomachs surveyed and appears to make up the bulk of the diet. Juvenile turtles - which have a more varied diet than adults - primarily consumed pupal C. plumosus, whereas adult turtles consumed the larvae, suggesting niche partitioning. Due to almost none of the original vegetation remaining in the region, the river otters that would typically prey on the turtles are either locally extinct or scare. Piranhas have been observed to mutilate P. geoffroanus at the stream mouth, but turtles with severe wounds, including damaged or absent forelimbs, can still apparently survive on carrion and/or their small insect prey.


Living in a polluted stream is obviously not without its risks. Souza and Abe (2000) warn that further pollution will eventually kill off C. plumosus and that future canalization will destroy nesting habitat - although it is unlikely the whole 40 km stretch will be so modified. Turtles from the urbanized Anhanduizinho River were found to have a huge mortality rate from roadways (Souza et al. 2008). Chironomid larvae have been observed to live on (and in?) turtles in polluted streams (Marques et al. 2008), but it is not clear what sort of impact this has. Urban P. geoffroanus were found to have a high rate of leech parasitism compared to those from agricultural areas (with no leeches) (Brites and Rantin 2003); another study found that individuals parasitized by leeches and injured by boat strikes showed no sign of disease, although it was suspected they were sub-clinical (Ferronato et al. 2009). Piña et al. (2009) studied P. geoffroanus individuals from the Piracicaba River and found the highest blood serum levels of Cu and Pb for any studied reptile, which was remarkable since there were no obvious clinical or reproductive impacts. The authors warned that the contamination may have been recent enough that any impact, which will likely disrupting reproduction, may eventual appear within a few years.


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For anyone disappointed about a more literal Sewer Turtle not showing up, there's hope. Actinemys marmorata, a vulnerable species, has lost habitat due to urbanization and other anthropic changes, but thrives in sewage treatment plants (Germano 2010). The author suggested the facilities could be used to stock up populations to re-introduce to more natural environments. I wish I have access to this one...






References:


Baldo, D., Martinez, P., Boeris, J. M., Giraudo, A. R. (2007). Reptilia, Chelonii, Chelidae, Phrynops geoffroanus Schweigger, 1812 and Mesoclemmys vanderhaegei (Bour, 1973): Distribution extension, new country record, and new province records in Argentina. Check List 3 (4), 348-352. Available. 


Bonin, F., Devaux, B. Dupré, A. (2006). Turtles of the World. Baltimore, Maryland: John Hopkins University Press. Partially Available.


Brites, V. L. C. and Rantin, F. T. (2003). The Influence of Agricultural and Urban Contamination on Leech Infestation of Freshwater Turtels, Phrynops geoffroanus, taken from Two Areas of the Uberabinha River. Environmental Monitoring and Assessment 96(1-3), 273-281. DOI: 10.1023/B:EMAS.0000031733.98410.3c


Ernst, C. H., and Lovich, J. E. (2009). Turtles of the United States and Canada. John Hopkins University Press: Baltimore, Maryland. ISBN 13:978-0-8018-9121-2

Ernst, C. H., Altenburg, R. G. M., and Barbour, R. W. "Phrynops geoffroanus". Turtles of the World.
http://nlbif.eti.uva.nl/bis/turtles.php?selected=beschrijving&menuentry=soorten&record=Phrynops%20geoffroanus

Ferronato, B. O., Genoy-Puerto, A., Piña, C. I., Souza, F. L., Verdade, L. M., and Matushima, E. R. (2009). Notes on the hematology of free-living Phrynops geoffroanus (Testudines: Chelidae) in polluted rivers of Southeastern Brazil. Zoologia (Curitiba, Impresso) 26(4). doi: 10.1590/S1984-46702009000400027


IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. www.iucnredlist.org


Germano, D. J. (2010). Ecology of Western Pond Turtles (Actinemys marmorata) at Sewage-Treatment Facilities in the San Joaquin Valley, California. The Southwestern Naturalist 55(1), 89-97.

doi: 10.1894/GC-196.1

Marques, T. S., Ferronato, B. O., Guardia, I., Longo, A. L. B., Trivinho-Strixino, S., Bertoluci, J., and Verdade, L. M. (2008). First record of Chironomus inquinatus larvae Correia, Trivinho-Strixino & Michailova (Diptera, Chironomidae) living on the shell of the side-necked turtle Phrynops geoffroanus Schweigger (Testudines, Chelidae). Biota Neotropica 8(4). doi: 10.1590/S1676-06032008000400019. 

Piña, C. I., Lance, V. A., Ferronato, B. O., Guardia, I., Marques, T. S., and Verdade, L. M. Heavy Metal Contamination in Phrynops geoffroanus (Schweigger, 1812) (Testudines: Chelidae) in a River Basin, Sao Paulo, Brazil. Bulletin of Environmental Contamination and Toxicology 83, 771-775. Available.


Souza, F. L., Raizer, J., da Costa, H. T. M., and Martins, F. I. (2008). Dispersal of Phrynops geoffroanus (Chelidae) in an Urban River in Central Brazil. Chelonian Conservation and Biology 7(2), 257–261. Available.


Souza, F. L. (2005). Geographical distribution patterns of South American side-necked turtles (Chelidae), with emphasis on Brazilian species. Revista Española de Herpetología 19, 33-46. Available.


Souza, F. L., and Abe, A. S. (2000). Feeding ecology, density and biomass of the freshwater turtle, Phrynops geoffroanus, inhabiting a polluted urban river in south-eastern Brazil. Journal of Zoology 252, 437-446. DOI: 10.1111/j.1469-7998.2000.tb01226.x

Turtle Conservation Fund. (2002). A global action plan for conservation of tortoises and freshwater turtles. Strategy and funding prospectus 2002–2007. Washington, DC: Conservation International and

Chelonian Research Foundation. Available. 

The Tiny Turtles of North America

Clemmys guttata (Spotted Turtle), a native of the Eastern United States and among the smallest turtles. Taken from my Flickr.

Thanks to Turtles of the United States and Canada, I wondered if North America has an unusually high diversity of small turtles. While Spotted Turtles have a maximum strait carapace length of only 14.25 cm (5.6"), there are 8 smaller species on the continent and several of similar size. But, what is "small" for a turtle? To find out - and possibly demonstrate an ascension from geek to nerd - I used the Turtles of the World website to obtain maximum size data for 305 species* and placed them in size categories at 5 cm intervals (e.g. 10-15 cm, 15-20 cm), rounding up. The number crunching resulted in this:

* I upgraded Trachemys scripta subspecies to full species and used data from TotUSaC where available.

Minimum = 9.6 cm (Homopus signatus)
Maximum = 291 cm (Dermochelys coriacea)

The mode size category is 20-25 cm* (~19% of the total), although the average is 38.39 cm with a standard deviation of 32.44 cm. Since no turtles are less than a standard deviation from the average (thanks to seaturtles and island-dwelling tortoises) I'll consider the bottom 10% "small", which is just under 15.5 cm and roughly includes individuals in the 5-10 and 10-15 cm categories. As for how size varies within major clades:

* I apologize to any of my countrymen reading this, providing conversions from metric makes this even more unreadable. 

Kinosternidae range 12-37.9 cm. Mode 15-20 cm (52%). Average 17.01 cm (stdev = 5.5 cm).

Geoemydidae range 13-80 cm. Mode 20-25 cm (35%). Average 27.02 cm (stdev = 14.96 cm).

Emydidae range 11.5-60 cm. Mode 25-30 cm (25%). Average 28.47 cm (stdev = 9.38 cm).

Pleurodira range 12-89 cm. Mode 30-35 cm (22%). Average 29.99 cm (stdev = 11.29).

Testudinidae range 9.6-130 cm. Mode 20-25 cm (12.5%). Average 50.3 cm (stdev = 36.96 cm).

Trionychidae range 25-200 cm. Mode 60-65, 65-70% (25% total). Average 77.06 cm (stdev = 43.87 cm)

Including only these clades, one standard deviation less than the average is now about 18 cm, or 15 cm sans the freakishly big softshells. The remaining "family"-level clades have few species and extremely large body sizes (Cheloniida, Dermochelyidae, Chelydridae, Carettochelyidae, Dermatemydidae), with the notable exception of Platysternidae. So, let's consider turtles below 15 cm (6") small; I'll get back to this in a bit, but first, how do North America's turtles stack up against other continents*?

* This does not include seaturtles. 

Eurasia range 13-200 cm. Mode 20-25 cm (23%). Average 38.6 cm, stdev = 34.09 cm

North America range 11.6-80 cm. Mode 15-20, 20-25 cm (41% total). Average 26.84 cm, stdev = 12.66 cm

Central/South America range 12-89 cm. Mode 20-25 25-30 cm (33% total). Average 32.52 cm, stdev = 15.63 cm

Africa range 9.6-101.5 cm. Mode 20-25 cm (20%). Average 30.53 cm, stdev = 20.69 cm

It certainly appears that North America's turtles are smaller, and consistently so. It's worth noting that Turtles of the United States and Canada often had considerably larger figures than Turtles of the World, so it is possible that the maximum sizes for the other continents are understated. Now, to put that jumble of numbers into a more comprehensible form:

Note that these totals are percentages. Eurasia has 78 species, North America 68, Central/South America 55, and Africa 39. The patterns still occur with actual numbers, but are less apparent.

And now for that ever-trendy third dimension.

North America certainly does appear to have a trend towards smallness, although admittedly it isn't a strong one. Or is it. In accordance with action film tropes, there's a major aspect of this discussion I've suspiciously failed to mention - some turtles display the most extreme sexual size dimorphism of any tetrapod*. Barbour's Map Turtle (Graptemys barbouri) females are over twice the size of males (max strait carapace length of 33 cm vs. 13.5 cm) and Spiny Softshell (Apalone ferox) females display an even more pronounced dimorphism (54 cm vs. 21.6 cm) (Ernst and Lovich 2009); such linear differences imply females weigh at least 15 times as much as males. According to Turtles of the World, females from the geoemydid species Hardella thurjii reach an SCL of 61 cm while males only reach 17.5 cm - with females 3.5 times the linear dimensions of males, this implies a difference of at least 40 times in mass! For the most part it appears that North American emydids (i.e. most of them) have particularly pronounced sexual dimorphism, especially the numerous map turtles (Graptemys) (Gibbons and Lovich 1990). Unfortunately, digging up data for the remaining 200+ species of turtle without readily available data on sexual size dimorphism is far too much for this already ludicrous blog post, so I'm going to assume that there aren't dozens of hyper-dimorphic geoemydids out there.

* The record is typically given to the Green Anaconda (Eunectes murinus), although a survey of 177 males and 48 females found that in regards to means, females were 1.41 times longer and 4.68 times as massive; in regards to largest sizes, the female was 1.55 times longer and weighed 5.77 times as much. The study was found on Jesus Rivas's website, although I am not sure where it was published.

North American turtle sexual size dimorphism. Not every case involves females larger than males.

Counting males and females as separate "forms", suddenly a quarter of United States and Canada* turtles are in the 10-15 cm category, which seems unlikely for any other region to exceed. As to what conditions in North America would be ideal for small turtles - I have no idea. It seems unlikely to be predation (most of the species overlap in range with alligators, and all overlap with Chelydra) or climate... maybe it could just be a phylogenetic fluke?

* The data was not available for most Mexican turtles, hence I couldn't say "North American"

Glyptemys muhlenbergii, taken from Sophro's Flickr stream.

Stay tuned to follow-ups regarding the world's smallest turtle(s) and turtle sexual size dimorphism!

References:

Ernst, C. H., and Lovich, J. E. (2009). Turtles of the United States and Canada. John Hopkins University Press: Baltimore, Maryland. ISBN 13:978-0-8018-9121-2

Gibbons, J. W., and Lovich, J. E. (1990). Sexual Size Dimorphism in Turtles with Emphasis on the Slider Turtle (Trachemys scripta). Herpetological Monographs 4, 1-29. Available.

Giant Snappers, Take 3

There aren't many pictures of very large Common Snapping Turtles (Chelydra serpentina) - let alone with decent angles or objects that can be used for scale - so I feel obliged to share a series of photos taken in Rhode Island's Blackstone River in May, 1986:

I have no prior experience with gun identification, but this appears to be a Ruger MK II with a 4 in (10 cm) bull barrel; this scale gives realistic measurements of the man in the photograph, who is roughly the same size I am. Thus, the strait carapace length is approximately 16.5 inches (42 cm), which isn't record size (49.4 cm/19.4 inches), but then, the same body of water reportedly holds numerous other individuals which are even larger. The weight was estimated to be around 80 pounds (36 kg).

The carapace appears to have three low keels, which seems remarkable for a turtle of this size. Supramarginals are obviously not present, so this cannot be an out of place Alligator Snapping Turtle (Macrochelys temminckii). The head:carapace ratio is difficult to determine, but appears to be larger than 1:3, judging by the last photo. The tail is rather short and slender for a snapping turtle - could this individual be female? The record for that gender is an SCL of only 36.6 cm (14.4 inches) - in which case this individual would be quite remarkable (Ernst and Lovich 2009 - citing Gibbons and Lovich 1990)

Small (8 inch/20 cm SCL) female Snapping Turtle finishing up a nest. Photo by me.

Snapping turtle with ~40 cm (15.7 inch) SCL - note how the tail has a post-carapace 'bulge' and is overall much thicker than that of the Blackstone Specimen. Taken from Flickr user Karim Rezk. Similar photos can be found here and here.

Males snappers have an anal vent past the carapace rim and a pre-anal tail length of over 120% the length of the posterior lobe; females have a vent beneath or slightly under the rim and have a pre-anal tail length under 110% of the lobe (Ernst and Lovich 2009 - illustrated here). Males also have longer and thicker tails, a smaller plastron, and narrower bridge (see Chelydra.org). Unfortunately, most of these traits are not observable in the specimen and I am uncertain if the tail morphology is within the range of variation for males.  Still, it is a remarkable animal, and it certainly isn't every day that a turtle has a shell the size of a human torso.

Since this is such an interesting topic, I will start on a sub-page of this blog that focuses on snappers which are potentially larger than record size. If anyone reading has any stories, I will be highly interested.

Many thanks to the source for the photograph!

References:

Ernst, C. H., and Lovich, J. E. (2009). Turtles of the United States and Canada. John Hopkins University Press: Baltimore, Maryland. ISBN 13:978-0-8018-9121-2

Gibbons, J., and Lovich, J. (1990). Sexual dimorphism in turtles with emphasis on the slider turtle (Trachemys scripta). Herpetol. Monogr. 4, 1-29.

Giant Snappers, Take 2

At the Audubon Society of Rhode Island's Environmental Education Center, I couldn't help but notice an enormous Common Snapping Turtle (Chelydra serpentina) skull when I was placing a complete Corn Snake shed into a specimen drawer. All I could determine about this specimen is that it's from Auburn, Maine and rivals my prior giant snapper in size.

Ventral view of the skull. Using ImageJ, I calculated the distance from the tip of the premaxilla (i.e., the beak) to the end of the supraoccipital to be 14.74 cm or 5.8 inches. The currency - which refused to smoothen out - is there to establish rough scale.

Dorsal view of skull. These measurements slightly exceed the ventral view, probably due to the highly raised supraoccipital. The bill has somehow become even more crinkled.

Note the enormous temporal/otic notches and damage to the prefrontal.

Frontal view. The posterior portion of the head was probably considerably wider in life.

Data from Herrel and O'Reilly (2006) indicates their largest Chelydra had a 11.8 cm (4.65") head corresponding with a carapace length of 38.6 cm (15.6"), giving a head:SCL ratio of 1:3.27. This implies that the Auburn Specimen (head length ~14.7 cm) has an SCL of at least 48 cm (19") - as snapping turtle heads appear to get proportionally smaller with increased SCL. So how does Gamera stack up?

The specimens appear to be nearly identical in size - and somehow, angle. 

The official maximum size* of Chelydra serpentina, as given by Ernst and Lovich (2009), is an SCL of 49.4 cm (19.4") (Ernst and Lovich 2009) - a length both of these specimens appear to have approached, or slightly exceeded. Considering just about everybody has a story about giant snappers, this seems to imply that such lengths are not uncommon; the ease in which I found the two very large specimens appears to support this. Ferri (2002) claims the "normal" maximum for Chelydra is 47 cm SCL, but specimens may reach 60 cm (2 feet); while this claim was not substantiated as far as I can tell, it seems plausible.

* One wild specimen with a 47 cm (18.5") SCL weighed 34 kg (75 pounds)... and was known for attacking horses! (Ernst and Lovich 2009) - presumably the specimens I ran across are/were similarly massive and potentially traumatogenic.

More on this subject soon.

References:


Ernst, C. H., and Lovich, J. E. (2009). Turtles of the United States and Canada. John Hopkins University Press: Baltimore, Maryland. ISBN 13:978-0-8018-9121-2

Ferri, Vincenzo. (2002). Turtles and Tortoises. Firefly Books: Buffalo, New York. ISBN 978-1552096314

Herrel, A. and O'Reilly, J. (2006). Ontogenetic Scaling of Bite Force in Lizards and Turtles. Physiological and Biochemical Zoology 79(1), 31–42. DOI: 10.1086/498193

A Most Peculiar Turtle

Shortly after 8 a.m. on June 20th, 2010, at approximately this location, I happened across a melanistic turtle with an ~8 inch/20 cm carapace which had just successfully crossed the East Bay Bike Path. It appeared to be an emydid, but somehow I was unable to pin down the identification. Could it be a variant, or something more unusual? Or am I just crazy?

My best approximation of a dorsal view. The fourth vertebral scute has been damaged (and patched up by people?) and some of the costal ('rib') scutes appear to be abnormally shaped. Traits relevant for classification include the 'sculpted' appearance of the scutes, the vertebral ridge, and patternless dark brown coloration.  

The jaws appear to be particularly thick and are the widest point of the head - which is brown/black/white and distinct from the otherwise greyish skin. The ventral surface of the carapace is orange and black, and the plastron is orange-ish and unpatterned.

A lateral view demonstrating that the lower margin of the upper jaw is rimmed with ivory white, the same shade as the lower jaw.

This specimen is clearly not an Eastern Box Turtle, Spotted Turtle, Painted Turtle, or Slider, which leaves two remaining candidates... assuming an exotic isn't involved.

Wood Turtle?

Wood turtles (Glyptemys insculpta) doing their thing. Note the difference in shell pattern (and lack thereof). From Flickr user man of mud. Original.

Wood Turtles frequently reach an SCL of 20 cm (Walde et al. 2003) have a dark sculpted carapace, subtle vertebral ridge, a primarily orange plastron, and somewhat similar facial coloration as the Warren turtle. However, the Warren turtle only had access to brackish water, which Wood Turtles apparently avoid, and lacked extensive orange or red pigmentation. That in itself is not conclusive, but facial morphology is:

From Flickr user ajschu. Original.

Wood Turtles lack the massive jaws of the Warren turtle, and have two projections on the upper beak clearly not present in that specimen. There's a possibility that a Wood x Blanding's Turtle hybrid could have head morphology more similar to the Warren turtle, but as the Blanding's half of such an individual is not native to Rhode Island*, such an individual would be an extreme oddity. 

While we can dismiss the species as a candidate, this Wood Turtle site is still worth checking out. I should probably give them proper coverage at some point.

* They are, however, present in nearby Massachusetts.

Diamondback Terrapin?

Northern Diamondback Terrapin, Malaclemys terrapin terrapin from Flickr user nicoleym. Original.

I had seen (and removed) a road-killed terrapin two days before the Warren turtle, which looked comparable to the above individual, and at the local Audubon I occasionally fed some hatchlings (which were getting a 'jump start'). While the coloration pattern is very different from the Warren turtle, the shell and head morphology looks very similar. Northern Terrapins in particular are highly variable, so do any out there resemble the Warren turtle? Yes they do:

From Flickr user sandy richard. Original.

So there you have it, the Warren turtle in unambiguously a dark-morph Northern Diamondback Terrapin and not some bizarre exotic. Terrapins are only known to lay eggs at one site - two miles away - so the individual I observed may have been attempted re-colonization. Increased melanin in turtles may protect sexual organs from ultraviolet radiation and is correlated with territoriality and aggression (see abstract by Dominy) - although of course the study has yet to take place. More on terrapins soon...

References:

Walde, A., Bider, J., Daigle, C., Masse, D., Bourgeois, J.-C., Jutras, J., and Titman, R. (2003). Ecological Aspects of a Wood Turtle, Glyptemys insculpta, Population at the Northern Limit of its Range in Québec. Canadian Field-Naturalist 117: 377-388. Available.