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!

---

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.

Cryptozoological Case File #0004 - The Hanoi Sea Serpent

I already discussed this encounter way back in my Many-Finned days, but I just thought of a novel explanation that segues into another topic I've got in the works.

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Conversions and hyperlinks are my own.

Heuvelmans (1968) citing Ouest-Eclair inquiry from unnamed Captain (possibly P. Merlees):

In June 1908 I was captain of the steamer Hanoi belonging to A. R. Marty of Haiphong and at about 6 in the morning was about 5 miles [8 km] east of the Norway islands which lie at the entrance to the Along Bay (Tongking), and I was steering to pass between these islands and the land when I saw it.

I saw, some way ahead, a black mass which at first I took for a capsized boat. On approaching and examining it with binoculars, I found it had a strange shape. This resembled a framework over which sail had been tightly stretched. The ribs were very marked. Seen from the side and from some way off it would certainly look indented, for the ridges were very sharp. I had a three-quarter view which enabled me to make a rough estimate of its size.

The colour was black; the length about 16 feet [4.9 m] and the width about 5 feet [1.5 m]. It was quite motionless.

 As I wondered what it could be I kept coming closer and clearly distinguished all its features. When I reached some thirty yards [27 m] away a huge head emerged some 4 or 5 yards [3.6 or 4.6 m] from what I could see, and therefore nearer to me.

Although surprised by this sudden apparition, I could observe it very well, and it was very like the head of a turtle, but longer and certainly 2 feet [0.6 m] wide by 3 feet [0.9 m] long; it had two very bright black and white eyes and large nostrils. It was blackish like the rest. I could not see the jaw, the mouth being shut, but the mouth was clearly marked on the sides of large dimensions.

 The head turned to look at the ship, blew noisily without spouting water and at once dived, the rest following and making a big wash. 

When I reached where the animal had been I could see nothing but the wash in the water, and that was all.

Given the dimensions of this animal it could not possibly be confused with a turtle. For one thing it certainly had no scales, of that I am sure. The skin was more like old tanned leather, and with my binoculars I could see it very well.

The head appeared for a few seconds only, and I did not look at it with my binoculars, but it was very close, perhaps 25 yards [23 m] away, and what struck me most were the eyes. The turtle has only very small eyes, veiled by a membrane, and not big bright eyes like these. And so far as I know there are no turtles of this size.

From the head to the end of the visible part was a good 30 feet [9 m]; so it was indeed an extraordinary animal. 

From the disturbance of the water at the moment when it dived and from the part of the body that I saw, the shape of the body must be: a very long and flexible neck, indicated by the distance of the head from the visible part of the body, and by the head which turned without the middle part moving; then a much broader part in the middle, the part that I saw; and finally a fairly long tail which did not show above the surface, but was clearly marked by the disturbance of the water.

Observation was hindered by the fact that the sun was partly hidden behind small clouds and made a white reflection on the surface which prevented one from seeing to any depth.

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Heuvelmans 1968:

The poor light may perhaps explain some of the differences between this and other reports of the Along Bay dragon. The projecting ribs and spine are certainly the most interesting feature here. They remind one of the parallel ridges on the leathery turtle and the basking shark, which had [sic] a stabilizing effect, except those are longitudinal-in any case the beast is too big for a leathery turtle, and the basking shark has no neck. It is, however, hard to believe that the ridges across the spine could be taken for a jagged crest, and one cannot help wondering whether the beast's condition was normal. Sea-mammal are, for obvious reasons, usually fat, protected against the cold by a thick layer of blubber. Might not this specimen be wasted away by age or illness? It is hardly likely. The explanation I shall be putting forward is that this emaciated appearance may be due to transverse bands of armour, as on the armadillos.

Heuvelmans' analysis is bullshit. It is painfully obvious he was guilty of the very 'pigeonholing' and 'mental gymnastics' he had scorned; the Hanoi encounter bears no resemblance to the Halong Bay cryptids and neither of them can be plausibly connected with encounters of 'Many-Finned' cryptids, namely by lacking multiple fins. This encounter appears to be the genesis of the 'armored Many-Finned' concept which, aside from the very surreal Tran Van Con report (or dream?), has gone unmentioned in other accounts. This doesn't indicate that cryptid categorizations are fundamentally flawed, but more critical focus is needed on individual reports is fundamental. Who knows, it may turn up something interesting, albeit non-cryptozoological...


It also needs to be repeated that reported size in an encounter should not be taken as an actual figure. With that in mind, I wondered if the encounter actually was of a Leatherback Seaturtle which was mistakenly interpreted as having transverse ridges and a long neck. It still is a possibility, but there is a more parsimonious explanation out there:

Florida Softshell Turtle (Apalone ferox) from Flickr user dotpolka.

Nile softshell (Trionyx triunguis) from Flickr user xor74.

Obviously neither of these non-Asian species is a candidate for a sighting in Vietnam, but they demonstrate that trionychids could fulfill most of the observed traits. A head quite some distance from the main body (and inferred long neck), leather-like skin, prominent nostrils, big eyes, 'ribs', and ridge all fit perfectly. The long tail is problematic, although since it wasn't actually observed, it could have been the wake. The reported body width (about 1/3 length) is much more narrow than the carapace width relative to SCL in a softshell (typically closer to 1/1), so explanations could be that the carapace was partially submerged, or the inferred length included a non-existent tail. The illustration shows a domed structure, which could either be a misremembered or exaggerated carapace. As for Vietnamese softshell candidates:


Palea steindachneri is moderately sized for a softshell (max SCL = 44.5 cm) and is apparently restricted to freshwater (Ernst and Lovich 2009). Pelodiscus sinensis is small to moderately sized (max SCL = 33 cm, possibly 40-45 cm formerly), and has not been recorded at sea (Ernst and Lovich 2009) - but is tolerant of brackish water. Amyda cartilaginea is large (max SCL = 83 cm) but only recorded from freshwater. Rafetus swinhoei reaches a max SCL of at least 80 cm - possibly much larger for the Hoan Kiem Lake individual - but is too poorly known to determine if its (former) habitat included oceans. Pelochelys cantorii reportedly can reach gargantuan proportions (max SCL = 200 cm), and has been found at sea according to Turtles of the World. Radhakrishnan and Badrudeen (1975) report an individual P. bibroni caught in a trawl 5 kilometers off Mandapam (India), which lived an additional 14 days in a saltwater aquarium. It is worth noting their specimen with a 57 cm carapace (39 cm bony portion) had a head that was 13.8 cm long by 8.2 cm wide - similar in proportions to the reported 3 foot long by 2 foot wide head of the Hanoi animal - eyes that were 1 cm wide, and a proboscis that was 0.2 cm long by 0.9 cm wide. Presuming P. cantorii is at all similar in habitat and appearance, which it is, its similarity with the Hanoi cryptid would be very striking indeed.

Aside from the reported length (explainable by the omnipresent human tenancy to exaggerate), the dark coloration (explainable by the lighting), and the shell proportions, the most parsimonious explanation for the encounter is a large softshell, probably Pelochelys cantorii.  It is possible the Hanoi encounter documented rare surface behavior in a marine setting for this species - possibly multiple - which is/are now endangered thanks to the ravaging Asian turtle market and habitat loss.



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


Heuvelmans, B. (1968). In the Wake of the Sea-Serpents. New York: Hill and Wang.


Radhakrishnan, P. N., and Badrudeen, M. (1975). On the occurrence of the soft-shelled turtle, Pelochelys bibroni (Owen) in marine environment. Indian Journal of Fisheries 22 (1&2), 270-274. 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.

Sliders? In My Neighborhood?

Me with non-native Pond Slider (Trachemys scripta).

What exactly is Trachemys scripta? Most sources treat it as a 'megaspecies' composed of 15 subspecies ranging from Virginia to New Mexico to Colombia (e.g. Turtles of the World), however this notion is an unfortunate holdover from The Age of Lumping. Seidel (2002) argues that differences in breeding behavior, broadly non-overlapping distributions, and distinct morphology* imply many of the 'subspecies' are in fact full species; a phylogeny determined from 52 morphological traits placed United States Sliders (scripta, troostii, elegans) in a distinct clade, causing Seidel to restrict Trachemys scripta to the three subspecies and moving all others to new or previously existing species. The molecular phylogeny in Stephens and Wiens (2004) also supports a scripta/troostii/elegans clade and shows the traditional "Trachemys scripta" to be strongly polyphyletic; curiously "Trachemys" itself was shown to be paraphyletic, but this was not directly commented on. Bickham et al. (2007) used the taxonomy proposed by Seidel (2002), making it about as 'canonical' as a proposed taxonomy can get, so from here on out I will use Trachemys scripta in the strictest sense.

* According to Turtles of the World, some 'subspecies' barely reach an SCL of 20 cm (troostii, taylori, cataspila) while grayi reaches a colossal 60 cm (2 feet), and presumably weighs over 30 times as much. If the traditional Trachemys scripta species concept was valid, it would have to take the cake for size variation within a species.

T. scripta is the only Trachemys species with black markings on the plastron (Seidel 2002).

Trachemys scripta naturally ranges across a considerable portion of the United States east of the Continental Divide*, but thanks to human introductions, breeding colonies are now established on every continent except Antarctica, as well as several major island groups (Ernst and Lovich 2009). In addition to being the world's most widely distributed turtle species, Pond Sliders are also one of the most genetically variable vertebrates (Scribner et al. 1995). To demonstrate, here are three possibly related individuals:

* It's easier to show than describe.

The middle individual is the same one I'm holding at the top, approx SCL of 20 cm (8 inches).

The above turtles are residents of Wood Pond in Barrington, Rhode Island, a tiny body of water (0.16 hectares/0.4 acres) designed to collect highway runoff - note the unnatural sheen at the water's surface. Despite these factors, and undoubtedly thanks to people constantly throwing in bread, I've counted at least a dozen Sliders, a handful of Painted Turtles (Chrysemys picta picta), hundreds of Goldfish (Carassius auratus auratus), and a couple dozen Mallards (Anas platyrhynchos). Feeding waterfowl is a bad idea, so I decided to attract the turtles with a few pellets of old cat food. Sliders were present in the pond 7 years ago, and judging by how small some of them are, it seems possible this is a reproducing population. The turtle I am holding at the top of the page was stuck in a construction ditch and may have been on its way to deposit eggs. The presence of Painted Turtles raises the possibility that the Sliders can colonize local freshwater bodies of water - however the highway and brackish waterways will (hopefully) hinder their movements*. Still, if anyone wants some pet sliders, these are already fairly tame and easy to catch.

* They are occasionally present in brackish waters, but this has only been observed in Georgia and South Carolina (Ernst and Lovich 2009)

Introduced Trachemys scripta have had negative impacts on turtle populations in Europe and Western North America due to direct competition, including competition for basking sites (Ernst and Lovich 2009 - citing Cadi and Joly 2003, 2004, Spinks et al. 2003), however it is not clear what sort of impact they would have if present in areas with a multitude of other turtle species. Wild T. scripta prefers shallow freshwater habitats with plentiful basking sites and aquatic vegetation such as lakes, swamps, sloughs, and slow moving rivers where they feed on assorted plant and animal matter, shifting towards the former with maturity (Ernst and Lovich 2009, also citing various). While I though a density of about 30/hectare looked like a lot in Wood Pond, only one population density study cited by Ernst and Lovich (2009) was similar (28/hectare in a small pond) and several were much larger, the largest being 983/hectare! T. scripta also take up a large percentage of the total number of turtles in many areas, the studies cited in Ernst and Lovich (2009) generally observed over 50% T. scripta, with a low of 0.06% and a high of 87%. Despite the propensity towards invasiveness, anthropogenic influences (habitat destruction, pollution, roadways, over-collection) are causing decreases in wild populations (Ernst and Lovich 2009). I don't think there's a species of turtle out there that can't be described by the previous sentence.

References:

Bickham, J.W., Iverson, J.B., Parham, J.F., Philippen, H-D, Rhodin, A.G.J., Shaffer, H.B., Spinks, P.Q., van Dijk, P.P. (2007). An Annotated List of Modern Turtle Terminal Taxa with Comments on Areas of Taxonomic Instability and Recent Change. Chelonian Research Monographs 4, 173-199. Available.

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. Turtles of the World. World Biodiversity Database.

Scribner, K.T., Morreale, S., Smith, M.H., Gibbons, J.W. (1995). Factors contributing to temporal and age-specific genetic variation in the freshwater turtle Trachemys scripta. Copeia. 1995, 970-977.

Seidel, M.E. (2002). Taxonomic Observations on Extant Species and Subspecies of Slider Turtles, Genus Trachemys. Journal of Herpetology 36(2), 285-292. Available.

Stephens, P.R., and Wiens, J.J. (2004). Convergence, Divergence, and Homogenization in the Ecological Structure of Emydid Turtle Communities: The Effects of Phylogeny and Dispersal. The American Naturalist 164(2), 244-254. Available.

Secondary References:

Cadi, A. and Joly, P. (2004). Impact of the introduction of the red-eared slider (Trachemys scripta elegans) on survival rates of the European pond turtle (Emys orbicularis). Biodiversity and Conservation 13, 2511-2518.

Cadi, A., and Joly, P. (2003). Competition for basking places between the endangered European pond turtle (Emys orbicularis galloitalica) and the introduced red-eared slider (Trachemys scripta elegans). Canadian Journal of Zoology 81(1), 392-398.

Spinks, P.Q., Pauly, G.B., Crayon, J.J., Shaffer, H.B. (2003). Survival of the western pond turtle (Emys marmorata) in an urban California environment. Biological Conservation 113, 257,267