Picture of the Day – Camel Teeth

Dromedary Camel (_Camelus dromedarius_) at Roger Williams Park Zoo.

My younger and more naïve self was under the impression that camel mouths housed an irregular mess of pegs and spikes, not unlike a certain national stereotype. Camel dentition is more orderly that what brief glimpses into their mouths suggests but, as usual, they’re still really really weird.

_Camelus_ sp. at Harvard Museum of Natural History.

First off, is it me, or does this dorsal-ish view of a camel skull make it look weirdly Basilosaurus–like? This is giving me bad ideas for highly unconventional reconstructions. Anyways, this view demonstrates that spatulate incisors are located only on the mandible and that there are well-developed canines. Pronounced canines are not unique among artiodactyls – note the Greater Mouse Deer to the right – but camels are remarkable for having additional canine-like teeth. Lots of them.

After the true canines in both jaws are caniniform first premolars, and before the canines in the upper jaw only are caniniform incisors (Fowler 2011). As for what these teeth are used for, the true canines are most developed in males and apparently adaptations for intraspecific aggression (Fowler 2011). Camels also bite humans – sometimes fatally – and bite marks on extremities leave a distinct “4 dot sign” (Abu-Zidan et al. 2011), which suggests at least one of the other pairs of caniniform teeth can be used to inflict damage.

References:

Abu-Zidan, F. M. et al. (2011) Camel bite injuries in United Arab Emirates: A 6 year prospective study. Injury http://dx.doi.org/10.1016/j.injury.2011.10.039

Fowler, M. E. (2011) Medicine and Surgery of Camelids. Wiley-Blackwell

Picture of the Day – Linnaeus’s Two-Toed Sloth

_Choloepus didactylus_

This Linnaeus’s Two-Toed Sloth (Choloepus didactylus) is kindly demonstrating the suspensory locomotion that extant sloths (Choloepus, Bradypus) typically engage in. Two- and Three-Toed Sloths are distant relatives and since no known fossil sloths were suspensory, this suggests the unusual method of locomotion evolved convergently (Pujos et al. 2012). As for how the 400+ extinct sloths got around, it was much more variable than the “ground sloth” label implies; some burrowed (Scelidotherium, Glossotherium), had some bipedal capability (Megatherium), were tree climbers (some Antillean species), rock climbers (Diabolotherium), and even aquatic and semi-aquatic (Thalassocnus) (Pujos et al. 2012).

References:

Pujos, F., et al. (2012) Recent Advances on Variability, Morpho-Functional Adaptations, Dental Terminology, and Evolution of Sloths. Journal of Mammalian Evolution DOI: 10.1007/s10914-012-9189-y

Picture of the “Day” – Returning Terrapin

A shoddy Internet connection and trip to Maine have thwarted my attempts to get content out there more frequently, let alone my lofty goal of once per day. I will have to look into this ‘stockpiling’ I’ve read so much about…

Anyways, today I managed to observe a Northern Diamondback Terrapin (Malaclemys terrapin terrapin) at Nockum Hill in Barrington, Rhode Island. Nockum Hill is the only known nesting site in the state (they’re endangered) and this is the first time I’ve seen one there. I have previously seen a roadkilled individual on a highway across the Barrington River from the nesting site and another wandering around a few miles south, so it was a relief to see that the species was still out there and nesting in protected areas.

Picture of the Day – Centenarian Box Turtles?

A New York Zoological Society photograph, from Oliver (1955).

Box Turtles (Terrapene) do not seem like the most likely creatures to live for over 100 years. Compared to Aldabra and Galápagos giant tortoises they’re minuscule (note the human hand in the above photo) and adults have predators, although few are effective (Ernst and Lovich 2009). The hardest data on Box Turtle longevity appear to be from Henry (2003) who documented that individuals of the Eastern subspecies (T. carolina carolina) marked in a 1945 study were still alive. Miller (2001) found that Three-Toed Box Turtles (T. c. triunguis) estimated to be over 60 years of age were gravid and had clutch sizes similar to those of younger individuals. If Box Turtles really do age at a negligible rate as their continued reproduction suggests, this makes the remarkable age claims more plausible. Oliver (1955) noted that while some impossible dates have been carved into Box Turtle shells (e.g. 1492) he argued that some unquestionably demonstrated (somehow…) that the turtles can live 50 to 80 years. The photograph above is of an Eastern Box Turtle collected in Rhode Island in 1953 with the dates ‘1844’ and ‘1860’ carved into the plastron, implying it was over 100 years of age (Oliver 1955). It is not clear what happened to this individual. Oliver (1955) credits Eastern Box Turtles with a maximum known age of 138 years, but how this was determined is left unsaid.

As for whether or not Box Turtles are abnormal, Congdon (2003) claimed that “evidence for senescence in turtles is weak” and found that Painted Turtles (Chrysemys picta) lived to at least 61 and increased offspring quality with age. I suspect that Box Turtles are not unusually long-lived but rather just easier to mark and recapture. This makes me wonder about some of the turtles I see out basking or cruising on a regular basis, and just how much living they’ve experienced.

References:

Congdon, J. et al. (2003) Testing hypotheses of aging in long-lived painted turtles (Chrysemys picta). Experimental Gerontology 38, 765–772. Available.

Ernst, C. H. & Lovich, J. E. (2009) Turtles of the United States & Canada. John Hopkins University Press.

Henry, P. (2003) The eastern box turtle at the Patuxent Wildlife Research Center 1940s to the present: another view. Experimental Gerontology 38(7), 773–776.

Miller, J. (2001) Escaping senescence: demographic data from the three-toed box turtle (Terrapene carolina triunguis). Experimental Gerontology 36(4-6), 829-32.

Oliver, J. (1955) The Natural History of North American Amphibians and Reptiles. D. Van Nostrand Company.

Picture of the Day – Those Bendy-Necked Giraffes

In the last post I observed that the horrendously awkward drinking stance of Giraffes isn’t due to neck inflexibility but rather proportionally very long legs. When drinking, Giraffes appear to hold their necks at around the same angle as those of other ungulates (to be on alert for predators?) and I managed to photograph one individual bending its neck down at a more extreme angle for no clear reason. Giraffe necks are most certainly not rigid beams which can barely flex downward from the familiar browsing posture, and the contortions they can achieve are astonishing.

Masai Giraffe (_Giraffa tippelskirchi_) at Roger Williams Park Zoo.

For an animal with seven elongate neck vertebrae, this is a pretty impressive arc. It also makes me wonder if autogrooming is an overlooked behavior in extinct long-necked animals – I don’t think I’ve ever seen a reconstructed sauropod engaging in such behavior.

Masai Giraffe (_Giraffa tippelskirchi_) at Roger Williams Park Zoo.

The sharp bend in this Giraffe’s neck is truly ridiculous – a better angle of the same posture shows just how sudden and extreme it is. Are Giraffes seriously capable of a 90 degree bend between two cervical vertebrae? I’m fairly certain I did not observe the absolute extremes of Giraffe flexibility and I’m curious just what their limits are.

I must point to SV-POW!’s dissection of a baby Giraffe neck which revealed nearly one fifth of the length was from cartilage. Adults are presumably less extreme than this, but still, wow.

Picture of the Day – Those Stumpy-Necked Giraffes

I suspect many people are under the impression that Giraffe necks are rigid beams which can barely bend down enough to allow the poor hyper-specialized creature to drink.

Angolan Giraffe (_Giraffa angolensis_) and Black-Faced Impala (_Aepyceros melampus petersi_) at the ol’ watering hole. From Wikipedia Commons.

A bit of behavioral comparison suggests that Giraffes have roughly the same neck posture as other ungulates while drinking and that the horribly awkward stance is due to the legs being very long proportionally, even more so than the neck. As for whether or not Giraffes can bend their necks further down than their drinking posture, yes, they can.

Masai Giraffe (_Giraffa tippelskirchi_) at Roger Williams Park Zoo

As for whether or not this Giraffe managed to get its mouth to the ground and why it would place such a strain on its nuchal ligament, rete mirabile, and who knows what else, I really don’t know. This was a young individual, so perhaps it was just playing around and exploring its limits. I did observe other neck-related wackiness in this individual, but that’s a story for another day, probably tomorrow.

Picture of the Day – Salty Snapping Turtle

Popular literature frequently claims Diamondback Terrapins (Malaclemys terrapin) are the only US turtles to inhabit brackish waters (e.g. Brennessel 2006) however it would be more accurate to say that terrapins are the species most adapted for brackish conditions. Several other US turtles can occur in brackish waters and some populations of Common Snapping Turtles (Chelydra serpentina) and Eastern Mud Turtles (Kinosternon subrubrum) are apparently adapted for brackish conditions (Ernst and Lovich 2009). I found the almost-hatchling-sized (SCL 3.5 cm) snapper pictured above (literally) beached and lying motionless in a pile of Bladderwrack, which made me wonder if it was in the best condition. Hatchlings can grow well in brackish water, but not beyond 14.35 ppt (Dunson 1986); the snapper I found was near water with a salinity of 22-25 ppt and was hundreds of meters from the mouth of a tidal stream. I reasoned that the turtle would probably not have survived much longer and decided to give it a head-start, getting it as large as possible over the summer and then releasing it into the tidal stream where it would have a better chance of successfully osmoregulating and avoiding predation.

 

References:

Brennessel, B. (2006) Diamonds in the Marsh: A Natural History of the Diamondback Terrapin. University Press of New England

Dunson, W. A. (1986) Estuarine populations of the snapping turtle (Chelydra) as a model for the evolution of marine adaptations in reptiles. Copeia 1986, 741-756.

Ernst, C. & Lovich, J. (2009) Turtles of the United States and Canada. John Hopkins University Press.