Giraffes: set for change
As the only extant long-necked terrestrial tetrapods, giraffes are much employed in debates over the neck posture of sauropod dinosaurs, and recent articles by John Martin and colleagues (Martin et al. 1998), and Kent Stevens and J. M. Parrish (2005), discuss giraffes and what they might tell us about sauropod necks. Greg Paul has recently been saying a lot about giraffe necks on the dinosaur mailing list, but I haven’t yet read his comments, and I know at least two sauropod workers who have something in the pipeline on this subject. Something is happening in the world of giraffe research that will probably be unknown to dinosaur workers, and will affect the way in which giraffes are named in the literature. It’s no big deal, but it’s worth bringing to attention: it’s the species level taxonomy. Pretty soon, it’s no longer going to be ok to talk of your giraffe as being (necessarily) a Giraffa camelopardalis. Why? Because there are studies underway which indicate that more than one extant species is present.
Nine Giraffa camelopardalis subspecies are currently recognized, and while some authors have been happy to accept all of them as valid, others have wondered whether at least some of the variation is just individual. Indeed there are photos showing individuals of different supposed ‘subspecies’ standing next to each other (Dagg 1962). For the record, the subspecies are…
G. c. angolensis (Angolan Giraffe)
G. c. antiquiorum (Kordofan Giraffe)
G. c. camelopardalis (Nubian Giraffe)
G. c. giraffa (Southern/South African Giraffe)
G. c. peralta (Nigerian/West African Giraffe)
G. c. reticulata (Reticulated Giraffe)
G. c. rothschildi (Baringo/Rothschild's/Uganda Giraffe)
G. c. thornicrofti (Thornicroft's Giraffe)
G. c. tippelskirchi (Masai Giraffe)
At least some of the observed variation is real (and not just individual variation, or clinal) – but how much of it, and what does it mean for taxonomy and phylogeny? Russell Seymour has recently been giving talks with titles like ‘How many giraffes? Temporo-spatial evolution in a "well-known" species and its implications for conservation of biodiversity’, so, reading between the lines, there is the implication that Giraffa camelopardalis is actually more than one species. Maybe one or more of the supposed subspecies is going to be elevated to species rank – or in fact restored to species rank, because at least some of the taxa were initially named as species, but later demoted when it became fashionable to lump big mammals in this way (and there’s an essay in that subject, by the way). A team involving Seymour, Rick Brenneman, David Brown, Thomas deMaar and Julian Fennessy are studying giraffe phylogeography, and their results should have bearing on this matter.
So far as I know nothing has yet been published on this – please let me know if you know otherwise. But, to those who are planning to mention giraffes in any of their writings, do keep this in mind: the giraffe you are thinking of may end up being something other than Giraffa camelopardalis. At top, the photo provides damning evidence for the assertion that the neutral neck posture of giraffes is a horizontal one (that was sort of meant to be a joke). Nick Longrich looks on, with camera.
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Dagg, A. I. 1962. The subspeciation of the giraffe. Journal of Mammalogy 43, 550-552.
Martin, J., Martin-Rolland, V. & Frey, E. 1998. Not cranes or masts, but beams: the biomechanics of sauropod necks. Oryctos 1, 113-120.
Pedley, T. J., Brook, B. S. & Seymour, R. S. 1996. Blood pressure and flow rate in the giraffe jugular vein. Philosophical Transactions of the Royal Society of
Simmons, R. E. & Scheepers, L. 1996. Winning by a neck: sexual selection in the evolution of giraffe. The American Naturalist 148, 771-786.
Solounias, N. 1999. The remarkable anatomy of the giraffe’s neck. Journal of Zoology 247, 257-268.
Stevens, K. A. & Parrish, J. M. 2005. Neck posture, dentition and feeding strategies in Jurassic sauropod dinosaurs. In Tidwell, V. & Carpenter, K. (eds) Thunder-Lizards: The Sauropodomorph Dinosaurs.
van Schalkwyk, O. L., Skinner, J. D. & Mitchell, G. 2004. A comparison of the bone density and morphology of giraffe (Giraffa camelopardalis) and buffalo (Syncerus caffer) skeletons. Journal of Zoology 264, 307-315.