Small African primate possibly sheds light on soft-tissue morphology of Cretaceous diplodocoid
October 8, 2009
One of the most bizarre of sauropods – and arguably one of the most bizarre of dinosaurs – is the Patagonian dicraeosaurid diplodocoid Amargasaurus cazaui Salgado & Bonaparte, 1991. Here’s a picture of a replica specimen, provided by Nizar Ibrahim. You’ll note that this skeleton has been posed with an extended cranio-cervical junction, and a slightly extended cervico-dorsal junction: virtually the opposite of what you’d expect in ‘normal’ posture (Taylor et al. 2009).
Thanks to its appearance in virtually every post-1991 book on dinosaurs, Amargasaurus is a relatively familiar animal these days, which is sort of a shame: we’ve somehow forgotten how frikkin’ weird it is. We’ve looked at Amargasaurus on SV-POW! before: in this article we drew attention to the fact that its dorsals are pretty interesting too, and as usual with sauropods we could write whole essays on all manner of its vertebral osteology. Perhaps, in time, we will.
However, let’s be honest and note that it’s those ridiculous cervical spines that keep us awake at night. What the hell did the animal do with these structures, and exactly what did it look like when alive? Early reconstructions (most notably Brian Franczak’s drawing from 1992 (see Hecht 1992)) all went with the idea of two paired sails, running in parallel along the length of the neck. All artists thereafter followed suit. Until 1994, when Greg Paul noted that the circular cross-sections of the spines and tapering tips might suggest that the paired neural spines instead protruded from the neck as horn-covered spikes (Paul 1994). Greg also suggested that having paired sails along the neck might be a really bad idea as it could restrict neck mobility, but this idea never made much sense as the tissue between the spines would presumably be flexible and hence not such a problem (the circular cross-section is not really a problem either, since other animals that are thought to have had skin sails, like Dimetrodon, also have rounded neural spines). Since 1994 few opinions have been expressed on this subject, but those that have have sided with Greg in noting that spines are more likely than sails (Salgado 1999).
At SVP Bristol last month, your favourite blog authors spent many happy hours discussing sauropods and their vertebrae. And, inevitably, the subject of Amargasaurus and its weird cervical spines came up. Fact is, sails AND spines are both equally stupid, and the idea of independent neck spines is particularly stupid because animals just don’t ever have their neural spines poking out beyond the musculature and skin of the neck. Right?
Wrong. Hardly known and rarely mentioned is that the last four (or so) cervical neural spines and first three thoracic spines of the Potto Perodicticus potto (a peculiar African strepsirrhine primate, closely related to the Asian lorises) protrude from the skin of the neck and shoulders, have sharply pointed tips, and are usually stated to serve a defensive function [potto skeleton above provided by Mo Hassan]. The spines don’t protrude as naked bone (though this was claimed by Ivan Sanderson), but are covered with skin and some hair, and form a series of tubercles in the live animal. When threatened, a potto is supposed to hide its head and point those protruding neck spines towards the danger, sometimes even butting the predator or aggressor with the spines. Other functions have been suggested for the spines, but a defensive function remains most popular and in the absence of any special knowledge I’ll go with the majority.
You might wonder, quite reasonably, whether the anatomy of a small arboreal modern primate has any bearing whatsoever on the soft-tissue morphology of a Cretaceous sauropod (even a ‘small’ one). The point is, however, that neural spines can protrude from the neck after all (albeit sheathed in skin and other tissue), and hence there is at least some precedent for this sort of thing. All that’s needed now is for someone to study the histology and microscopic surface texture of those protruding potto spines and see if there are any correlates for their protruding nature (so far as I can tell this hasn’t been done). Then go look at Amargasaurus. There’s clearly a paper in this, please report back and include me on the authorship, thanks.
- Hecht, J. 1992. Dollars for dinosaurs. New Scientist 136 (1845), 50.
- Paul, G. S. 1994. Dinosaur art & restoration notes: dicraeosaurs. The Dinosaur Report Summer 1994, 8.
- Salgado, L. 1999. The macroevolution of the Diplodocimorpha (Dinosauria; Sauropoda): a developmental model. Ameghiniana 36, 203-216.
- Taylor, M. P., Wedel, M. J. & Naish, D. 2009. Head and neck posture in sauropod dinosaurs inferred from extant animals. Acta Palaeontologica Polonica 54, 213-220.
- Walker, A. 1970. Nuchal adaptations in Perodicticus potto. Primates 11, 135-144.