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.
At left, Potto with flexed neck, showing its cervical and thoracic spines. From Walker (1970). At right, Amargasaurus as reconstructed by Salgado (1999). Salgado imagined this to be the animal's normal posture: an idea that we find somewhat unlikely (see Taylor et al. 2009).
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.
References
- 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.
Sauropod Vertebra Picture of the Week 
October 8, 2009 at 12:48 pm
At the risk of asking a stupid question: Would Amargasaurus have been able to hold its neck upright like you’ve proposed as general for sauropods? Would those high neural spines have not gotten in the way?
October 8, 2009 at 1:04 pm
Ah, the cafeteria Amargasaurus…
October 8, 2009 at 1:05 pm
Biologist, but no paleontologist here. First impression: neck spines are not the only extensions of the spinal column. I also see spines along the back and descending spines along the tail. To me this suggests a bluff strategy: with tissues (even thin tissues) on the spines, the critter would have looked far bigger than its central core when it presented itself side-on to a predator (or competitor!). Think of how mammals and birds fluff-up when threatened.
October 8, 2009 at 1:34 pm
Christopher, why would you think that’s a stupid question? Seems to that you’re absolutely right: if the reconstructed vertebrae in the mount and the Salgado et al. figure are anything like correct, then the spines would have dramatically limited dorsal flexibility of the neck.
… unless …
I wonder whether it’s possible that each vert’s spines could slip neatly past the next vert’s, on the outside?
Probably not, actually, looking at Salgado and Bonaparte’s (1991) figures 5 and 6 of Amargasaurus cervicals in anterior view. On the other hand, their figure 13 (skeletal reconstruction) does show the neck in a more or less Vidal-compliant posture without any spines overlapping.
I guess it’s going to be impossible to tell without seeing the material.
October 8, 2009 at 1:36 pm
Phil Mannion is ‘doing’ S. America soon: we could beg him to take a close look. Phil?
October 8, 2009 at 1:38 pm
I know they are not neural spines, but ribs, but the principle seems similar,see:
http://news.bbc.co.uk/earth/hi/earth_news/newsid_8212000/8212623.stm
Here the end of the ribs is usually under the skin. When the animal feels trapped, it forces the ribs through the skin and a toxic substance is ‘injected’ in the predator. Could it be that the Potto and Argamasaurus do/did something similar
October 8, 2009 at 1:56 pm
Amphibians seem to be the only group that have gone in for this skin-piercing thing (there are also frogs that, Wolverine-style, unsheath their claw-like unguals by actually piercing through the epidermis). Pottos don’t do it, and were amargasaurs agile enough to use their spines as actual weapons? We don’t know.
The best known animals with ‘protruding’ bones are of course deer. Whether they’re at all relevant here I don’t know.
October 8, 2009 at 6:44 pm
Are there any hints on the bone surface of the spines which would give an indication how they were covered? I am no expert about this, but shouldn´t there be differences between a bone surface which was covered with skin and a bone surface which was mainly the base for a ceratinous horn or even musculature and sinews?
Oh, and are there any indications for healed fractures of the spines?
And yes, deer are well known for protuding bones, so well known that most people never realize how bloody freakish deers actually are, especially given the fact that they regrow their antlers every year. I know this is completely out of context, but as I blogged about this just I short time ago, I just could not resist to mention it.
October 8, 2009 at 8:01 pm
OK, the “Spanish ribbed newt” (Pleurodeles waltl?) is officially awesome, despite not being a sauropod. X-man Wolverine needs to change his name.
I notice A.‘s neck is conspicuously lacking ventral spines. That allows room for the Freyan air bladders.
I wonder if the function of the spines is really just to break up A‘s outline. If so, that would argue against integumentary stripes on diplodocids, because if they could manage stripes, they would be way cheaper than spines. It would also argue against sails, and say something about its feeding environment — tall grass?
October 8, 2009 at 8:28 pm
I am with djlactin. Horses manage with erect hairs on their manes to bluff their size (cheap!). I used to work with wall lizards (Podarcis), usually a very dorsoventrally flattened lizard. I was very impressed how, when males displayed to each other, their raised themselves on their legs and flattened their bodies laterally, and arched their necks to look really impressive!
October 8, 2009 at 8:29 pm
A good person to look at the spines of _A.cazaui_, would be Tobin Heironymous. He recently finished his Ph.D dissertation on osteological correlates for integument (skin, keratin etc.). I bet he could figure out if there was some kind of epidermal covering on those suckers.
October 8, 2009 at 8:53 pm
I am not sure if these spines were robust enough to deter the angry theropod. For the best effect, Amargasaurus would have to almost tuck its head between forelegs, then spines would point forward.
But giraffe bulls are known to fight by swinging necks and hitting with their short horns. Watch youtube to see how powerful it is – other bull is really pushed away by the impact. Now, imagine Amargasaurus doing the same, puncturing the rival with the row of spines!
This hypothesis is testable – look for neck mobility and eventual puncture woulds!
Additionally, the spines could be (partly) covered with the skin, froming the mega-display larger than the soft-tissue crests, which other diplodocids are known to possess.
October 8, 2009 at 9:12 pm
“flexed cervico-dorsal junction”. Is that a typo? The cervico-dorsal looks extended to me. If I’m wrong, I need these terms defined, please.
October 8, 2009 at 9:18 pm
Yes, Rob, the cervico-dorsal junction in the mounted skeleton is indeed slightly extended. I think the point Darren was making is that it is less extended than we would expect to see if Amargasaurus behaved like extant animals (but then maybe it didn’t).
For necks, extended means raised and flexed means lowered. I admit that it took me a long time to get the hang of this, and that I prefer Stevens and Parrish’s more explicit terms “dorsiflexed” and “ventriflexed”. The way I got it was to think of the neck as being like a giant knee sticking out the front of the animal. Then flex and extend mean what you think they do.
October 8, 2009 at 9:26 pm
Am I all alone in finding the notion of these spines as weaponry absurd? They’re too easily snapped off, and if not snapped off, attached to vertebrae easily crushed instead.
October 8, 2009 at 10:26 pm
Well, how easily snapped off are they?
Analogous vegetation perhaps (whatever that might be), but not grass; Amargasaurus is not much younger than the oldest known flowering plants, and some 40 Ma older than the oldest known grasses.
October 9, 2009 at 5:05 am
They don’t look easily snapped off to me; Just ’cause somthing is thin doesn’t mean it is “easily snapped off”. We must remember that the spines are solid bone, aand were probably also sheathed in keratin.
October 9, 2009 at 6:47 am
Pottos being closely related to lorises, which have venom in their inner elbows that they lick before biting, might indicate some possible toxicity potential against predators (raptors, leopards) which grasp/bite the neck/throat area. Do pottos have skin glands (or cysts) around the covered cervical spines? Did amargasaurus have venomous kin?
October 9, 2009 at 9:03 am
They also point the wrong way.
October 9, 2009 at 11:59 am
Presumably, laminae extanding up the anterior, posterior and lateral margins of the spines are indicated of laminar sheets, muscle insertion or origin regions and/or regions occupied by pneumatic diverticulae. If so, these regions at least would not be spinous in any fashion. In this case, it would apear that the basal 1/5 of the forked neural spines were not projecting beyond the tissues of the neck as spikes.
Note also that Vidal’s reconstruction proposes that the vertebral spines are, more or less, aligned parallel to one another (as they seem to be typically in the dorsum even when the column is flexed as Paul typically reconstructs them for Apatosaurus, Diplodocus etc. among sauropods) and that this would be a stable base-point to project the vertebral columns posture. Note also that it doesn’t take much to further elevate the dorsal column into the Taylor et al. “normal” posture given that the reconstruction is already elevating the dorsal column brachiosaur-like from the pelvis such that the mid to anterior dorsals are inclined, and that the neck posture as argued by Taylor et al. (curved up, then down) is approximated but muted relative to the proposition put forward there. As such, the reconstruction does not seem to fail much and Salgado’s work and Demetrios’ reconstruction was “ahead of its time.”
October 9, 2009 at 1:15 pm
Qilong: PLEASE REPEAT IN ENGLISH.
October 9, 2009 at 1:35 pm
They point the right way when the neck is curved down.
October 9, 2009 at 1:42 pm
(Just a quick note of clarification: Vidal’s never done an Amargasaurus reconstruction, at least that I know about — we use the term “Vidal-compliant” informally to describe the habitual head-and-neck posture of terrestrial amniotes as described and depicted by Vidal et al. 1986 — what Jamie’s calling Taylor er. al. “normal” posture.)
October 9, 2009 at 4:05 pm
I think the most likely answer for these spines is some sort of display — possibly defensive, more likely for mating/courtship displays. However, the side-by-side of the potto and the sauropod neck triggered a wild’n’crazy thought: it looks like a perfect defense against an attack from above. I also recall that some large birds of prey will drop on prey from above and bite through the spinal cord, killing or paralyzing the prey.
Is it possible that Amargasaurus had to deal with large predatory pterosaurs or birds that made a practice of dropping from above and striking at the vulnerable neck?
October 9, 2009 at 7:19 pm
Seems like Witmer could do an investigation of soft-tissue correlates for Amargasaurus–he just did it for centrosaurine ceratopsids.
My question is more from the perspective of a paleo-artist. The cervical spines originate from bifuricated cervical neural spines, and the dorsal neurals are also bifuricated. The sacral spines are NOT, though, and neither are the caudals. I’ve never been comfortable with the “sail-back” idea because wouldn’t the sail also extend along the dorsals? And they’d just stop at the pelvis? That just looks bad, conceptually.
I’m more in favor of a big wall of meat to the level of the dorsal neurals, and keratin coverings on the cervicals above that point.
October 9, 2009 at 7:28 pm
“Is it possible that Amargasaurus had to deal with large predatory pterosaurs or birds that made a practice of dropping from above and striking at the vulnerable neck?”
I doubt a pterosaur or bird would even think of attacking such a large animal as Amargasaurus. But I always thought theropods would try to attack the neck of sauropods to bring them down… the spines would be a great way of preventing a large theropod from getting a good hold of the Amargasaurus neck.
The comments above about poison, newts and lorises raise a fascinating question in my mind. Is it possible that there were poison glands in whatever kind of covering the spines had, or around them? Would this probably make the animal too dangerous in both ends (I’m assuming Amargasaurus had a whip-like tail as is often reconstructed but I don´t know if this is known for certain)?
In nature, “expensive” structures such as these spines are seldom used for one thing alone. I’m sure there is more to these spines than meets the eye. They were probably useful to Amargasaurus in more than one way.
October 9, 2009 at 9:40 pm
Bailey (1997) suggested these were basically the only dinosaurian neural spines to actually resemble those of sailed sphenacodonts and lizards, so was a proponent of the dual sail idea. I have to wonder though- is there any evidence Dimetrodon and such actually had sails, and if so is Amargasaurus different in these respects?
October 10, 2009 at 6:57 am
My mistake on the “Vidal-” comment. However, my use of “normal” comes from the contrast preferred between ONP and this erect posture, and the characterization in Naish et al (2009 SVP abstract) that erectile posture is comparable in habitual posture (without a description of percent of time spent in any given posture) and the attribution that ONP refers to feeding posture. Osteological posture whould be normative unless the desire is to depict an organism in an super-active state (alert or attentive, running while alert, etc.) while passive behaviors on the like of sleeping, many feeding postures, typically involve relaxation of posture and a horizontal or depressed orientation of the forward body. So the characterization of “normal” (“active” in the paper) is meant to provoke discussion on the missing aspect on the repeatedly mentioned paper (percentiles of posture in living animals).
October 10, 2009 at 7:51 am
Poisonous sauropods… what an awesome idea. Pity there’s probably no way to tell.
October 10, 2009 at 8:53 am
Jaime, I think you should re-read Taylor et al. (2009) :-). We make the point, repeatedly, that it’s NOT the case that “Osteological posture whould be normative unless the desire is to depict an organism in an super-active state” (which is what Stevens and Parrish have been assuming). In fact, osteological neutral posture tells you literally nothing at all about how an animal habitually holds it neck. Nothing.
October 10, 2009 at 5:56 pm
“Bailey (1997) suggested these were basically the only dinosaurian neural spines to actually resemble those of sailed sphenacodonts and lizards, so was a proponent of the dual sail idea. ”
Bailey (1997) also seems to think that a certain giant predatory dinosaur walked around with an enormous hump of fat on it’s back, simply because the elongated neural spines are broader front-back than those of pelycosaurs… and he comepletely ignores (or perhaps is simply unaware of) the fact that sail-backed chameleons do not posess thin pelycosaur-like rods – they have “buffalo-like” broad neural spines, just as in Spinosaurus and Ouranosaurus. Fallowing Bailey’s advice, I shall go and inform those chameleons that they should have humps rather than sails, and that they are breaking Bailey’s Law.
So… I’m saying that, with all due respect to Jack Bailey, I wouldn’t take his paper too seriously.
And to Qilong: Please see Daniella Perea’s comment. Your comments seem to be written in some kind of foreign languange and do a complete fly-by.
October 11, 2009 at 4:18 am
I have a possibly dumb question: Could that tail, which certainly looks like it would have been surprisingly tall and flat, have been used to propel Amargasaurus while it swam/walked in shallow water?
I checked Wikip on the La Amarga Formation, and the fact that the various described members all had bodies of water encourages me in this (otherwise uninformed) speculation.
A (partially) aquatic lifestyle might suggest other possible uses for neck spines/a neck sail.
October 11, 2009 at 5:49 am
That’s quite the non sequitur- you don’t believe Bailey was right about the plate-like spines of Spinosaurus being withers, thus he was wrong about the cylindrical spines of Amargasaurus being sails? I think people’s dismissive opinions are mostly due to people misunderstanding what kind of structure he proposes. It’s not a fatty hump like a camel’s hump, but rather a narrow tapered muscular ridge. After an excruciatingly long debate about this with Jaime years back on the DML, my conclusion was that the distinction between muscular ridges and skin sails is probably not all-or-nothing, and that Spinosaurus might have had a thinner ridge than Acrocanthosaurus for instance (due to its lack of transverse dorsal expansion and general transverse thinness).
In any case, what’s your reference for chameleons? This photo suggests thin spines like Dimetrodon, does it not? http://www.arkive.org/media/3C/3C5F61D2-5EA8-472F-B28E-6BA000A40023/Presentation.Large/photo.jpg
October 11, 2009 at 8:24 am
Owlmirror,
There are lots of good reasons for thinking that sauropods as a group were primarily terrestrial (although, like elephants there’s no reason to think they didn’t spend some time in water the opportunity arose).
But Sauropoda is big, diverse, disparate and long-lived clade. It seems pretty unlikely to me that among a couple of hundred species (that we know about) living on every continent across a hundred and fifty million years, there weren’t some that adopted a more strongly aquatic lifestyle. There are specific anatomical features that correlate well with that lifestyle, e.g. broad rather than slablike chest, wide feet; as far as I know, there’s no reason to think that Amargasaurus had any of these, but then I’ve not seen the material.
October 12, 2009 at 4:51 pm
Owlmirror, it’s funny you should mention that. I’ve been toying with the idea of a semi-aquatic Amargosaurus for some time now, but I’ve never said anything about it for fear of sounding, well, stupid. However…
If the skeletal in the original description of Amargosaurus is correct, then Amargosaurus apparently did have a VERY tall, laterally compressed tail (not that this automatically makes it a swimmer, mind you, but it is suggestive).
Also note tha the caudal neural spines are vertical. This feature is interesting because it is typically aquatic reptiles that posess vertical neural spjnes, while those of terrestriial reptiles typically have spines that are inclined backward. As explained by Bakker (1986):
“The difference between vertical and slanted spines is explained by ligament action. A layer of tough ligament runs along the midline of the tail, and each spine is embedded into it. When the spines slant backward, this ligament is stretched when the tail is bent sideways. Such stretching impels the tail back in the direction from which it came, so the land lizard can flex its tail back and forth quickly as it runs. Underwater, much slower, stronger flexing would be required, and the elastic-rebound effect produced by slanted spines would be useless. So specialized tails of swimmers have vertical spines.”
Phew.
Mike mentioned, correctly, that other anatomical features suggestive of an squatic lifestyle include a broad chest and wide feet. I don’t know if Amargosaurus really had these, as I have not seen the meterial either. However, if you look at this mount:
The body actually does seem very broad compared to, say, Nigersaurus. Almost hippopotamus-like, although perhaps I’m going a bit too far there. The manus, incidentally, also looks pretty wide.
Of course, skeletal mounts are often innaccurate, and I am certainly not saying that this mount is really anything to go by.
October 20, 2009 at 5:48 pm
I’ve always been intrigued by the idea of Amargasaurus and even Stegosaurs shaking their necks and tails to make loud clattering sound with their plates and spines, kinda like Dark Age soldiers ( and even riot police)to intimidate the enemy.
November 5, 2009 at 12:33 am
Passed on to me by a former anthropologist friend:
The potto does not use these structures for defense or display, but they are part of a very sensitive tactile zone according to “Nuchal adaptations in Perodicticus potto” by Alan Walker (1970).
February 17, 2019 at 12:18 am
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