There’s been a lot of news now about Thursday’s (Sep. 11, 2014) publication on a new specimen attributed to Spinosaurus aegyptiacus. A lot of hype rose up months back about the release of a photo of a mount of some unusual bones, and what that entailed. As with every fossil discovery, caution had to be carefully tended in regards this mount because we had no idea what it was based on. This mystery was spoiled, and it seems the culprit was wilier than we all thought.
It always pays to be cautious as a paleontologist; invested as we are in our own discoveries, we know that science is an ever-marching progress of information. Some (much!) of what we work with is very incomplete. This appears to be even more problematic when what we talk about is very, very interesting not only to other professionals but to the lay public. Spinosaurus! It’s the animal that “defeated” the king in that one movie! It had a crocodile head and a theropod body, with a giant sail on its back!
But as I wrote back in May of 2010, Spinosaurus aegyptiacus may not be as we know it. Many reconstructions suggested it was sailed only above its back, but there’s evidence to support the sail was shallower and gradual over the back. In their new paper, Ibrahim et al. (2014) provide some radical new interpretations of a specimen found in the Cenomanian of the Kem Kem of Morocco, over 3k miles from the original discovery site at the oasis of Baharija in central Egypt. On the way from its original description to today, the original material had been destroyed (but not after being well-photographed and mounted) and new material began to come to light across the northern African nations of the north Sahara regions in Tunisia, Algeria, and Morocco. These sites were unusual in that they indicated a paludal, brackish marsh water environment, much akin to the swamps of Louisiana in the United States, or the brackish lagoons of Venice.
Life in a swamp, especially if you’re a giant, requires some interesting adaptations. Maybe. The authors describe the body, preserved incompletely from some dorsals and much of a hind limb and some parts of the tail, of a fairly small individual — smaller than the original specimen from Egypt, certainly — that provides the first semi-articulated skeleton of Spinosaurus aegyptiacus. Ibrahim et al. then go on to perform a series of analyses, corroborating some hypotheses posed before them, and coming up with a few novel ideas of their own. For example, the internal anatomy of the snout MSNM V4047 (possibly the largest known Spinosaurus specimen (but maybe not necessarily Spinosaurus aegyptiacus) suggesting that the snout was very extensively innervated and thus likely surrounded in life by dense sensory tissues, the composition of the teeth allowing an isotope analysis proving a diet comprised primarily of nearshore marine fish, and some peculiar adaptations of the limbs that imply a semiaquatic lifestyle. These things are interesting, croc-like in some results, and not really all that controversial.
But the devil is in the details, and as some have been noting over the past few days, these details leave one scratching their head.
There’s the issue with the body proportions and the tiny legs and hips. This is provided in both the mount and a digital skeletal reconstruction, of an animal so inept it couldn’t walk bipedally, almost certainly a quadruped and prone to swimming more than walking. And it doesn’t appear to match the given measurements and scaling provided by the authors themselves. When scaled to their actual measurements, the slinky long body disappears, the legs are able to stand upright, and without support from the massive forelimbs.
But let us consider some additional factors. First, the forelimbs, if they are anything like normal theropod forelimbs, are completely unsuited for weight-bearing. Rather than arranged vertically, the shoulder blades are aligned across the ribs in such a way that any quadrupedal stance would shove the shoulders deep into the neck and likely behead a Spinosaurus faster than Sean Bean in his next deat–film. Rather, they were suspended as in other theropods free from the ground, to dangle as they please.
Second, the authors even provide a furcula (recovered with the spinosaur Suchomimus tenerensis) for the shoulder, and this would have kept the shoulders from moving independently of one another, meaning it is unlikely the arms were permitted to walk in anything like a natural gait or a “typical” quadruped.
Third, the forelimbs while massive have not been described in sufficient detail and appear to possess characteristic typical of other spinosaurs. If they are anything like the forearms of Baryonyx walkeri, they’d lack almost any quadrupedal attributes, especially in the metacarpus, manus, and especially in the phalanges. The authors propose a semi-knuckle-walking locomotion style, but all extant knuckle-walkers have specific adaptations of the arm to permit this (and so it appears in extinct ones, even if you include chalicotheres which may not have been knuckle-walkers), including the presence of thickened, columnar first phalanges and strong curling joints for the other phalanges to bring them out-of-the-way, as well as thickened, solid wrists. Theropods, rather, have flexible wrists due to the semilunate carpal hinge and would likely have been unable to bear weight translating through the upper into the lower arm, much less straighten the limb passively enough to bear weight in such a fashion that a knuckle-walker would require. Yet that is exactly what the authors describe.
An Unlikely Reconstruction
Ibrahim et al. (2014) make some bones about the reconstruction they provide showing evidence for a very forward center of gravity, which would have necessitated either aquatic habitus, quadrupedalism, or both. However, this reconstruction, as noted by Scott Hartman in the link at the top of the previous section, is a composite. It is composed not merely of the implied association between the holotype and the new specimen, but additionally of material von Stromer originally called “Spinosaurus B” and what Dale Russell named as Spinosaurus maroccanus as well as Sigilmassassaurus brevicollis. Caught up in all this were the work of Sereno and others who attempted to qualify the relations of these specimens to one another and t other Baharija taxa, such as Carcharodontosaurus. Sereno et al. (1996), in their description of a new skull of Carcharodontosaurus, also described a vertebra very similar to the Moroccan Sigilmassasaurus as well as the Egyptian Spinosaurus B. They then synonymized the three (Sereno et al., 1998). Later on, McFeeters et al. (2013) addressed this issue and separated Sigilmassasaurus (and Spinsoaurus B) from Carcharodontosaurus. They weren’t the same, and Sereno et al. were incorrect in their assumption that association between the skull of the carcharodontosaur and the vertebrae meant they were the same animal. They also further argued the western (Moroccan) and eastern (Egyptian) specimens represented distinct forms, possibly distinct species; they weren’t identical, even if you assumed positional variation. Ibrahim et al. (2014) however completely ignore this and instead referred Sigilmassasaurus brevicollis and Spinosaurus B into Spinosaurus aegyptiacus. This is followed by referral of the skull MSNM V4047 to aegyptiacus. Despite some taxic distinction between west and east, Ibrahim et al. have supported a contiguous north African province. Michael Mortimer has a bit more to say on this here.
This clouds their skeletal reconstruction, as it provides material from the new specimen, the Moroccan specimens listed above, and the holotype. And the scaling seems to be off. Moving from the head into the neck, it is clear that the reconstruction of the vertebral spines makes an abrupt transition from tall and spindly, as in Acrocanthosaurus and Spinosaurus‘s holotype, into the thin nubbin-like processes of Sigilmassasaurus brevicollis, then immediately back into the tall and very slender spines of the anterior dorsum of Spinosaurus‘s holotype and the new specimen. The neck seems overly long. Its high S-shaped arch is composed of the unusually strong flexure in Sigilmassasaurus brevicollis and the elongate vertebrae of Spinosaurus aeygptiacus.
Ibrahim et al. (2014) reverse the trend recently to see the last, tallest vertebral spine as a caudal (Andrea Cau, Scott Hartman, and myself) and pull the arch of the sail over the hips, and plop it right back into von Stromer’s and Lydekker’s last-dorsal position with corresponding sharp drop-off in height over the hips and into the tail. Ibrahim et al. (2014) describe new caudal material, but as it turns out none of the material represents anterior caudals, and instead the authors place the ambiguous caudal of the holotype into the most anterior (read, first caudal) position possible. As I discussed here, this is unlikely. As it is, none of the caudal vertebrae seem to be anterior further anterior than about half of the tail’s length, assuming about 50 caudals.
Then, as pointed out by Scott Hartman, the hip and hindlimbs do not correspond well to the vertebrae given the measurements in the paper itself. This may be a problem with the measuring, the scaling of the reconstruction, or a little of both. There is now ambiguity to be resolved. Yet what is clear is this: The skeleton is a chimera, and is composed of material safely ensconced in other taxa: Sigilmassasaurus brevicollis from Morocco, “Sigilmassasaurus” from Egypt, disparate forelimb material collected in the Kem Kem, the holotype from Egypt, and the referred specimen from the Kem Kem. It seems unreasonable to assume a single taxon amongst these disparate (and distinct) materials, even without so handy a specimen as a Rosetta stone as, say, the holotype of Anzu wylei serves for Caenagnathidae. Thus, the skeletal reconstruction is simply not to be trusted, and the mount it is based on almost certainly a fantasy.
Perhaps I am being overly harsh on the authors, but given the high-profile and low detail presentation of their paper and it’s extensive (and openly accessible) supplemental data, we have more questions and less certainty with this new material (very little of which is separately described in the paper or supplement) than we had before. More radical is proposed than is resolved.
A quadrupedal spinosaur? I think not. Biomechanically, the forelimbs wouldn’t allow it, and the proportions done either. This doesn’t mean the animal wasn’t adapted for wading through muck and along the marshy shores of an ancient sea. Most likely it could swim, but I’d imagine so could most theropods so this is hardly surprising. Was it some predatory hippo? More croc-like than we imagine? Probably not.
(In an interesting aside, the authors reconstruct the upper and lower jaws of Spinosaurus as having only a two-tooth overbite, a reconstruction I may add I provided a while back.)
What of Spinosaurus?
It’s no secret we lost the holotype. This leaves us a gap in our knowledge of one of the most captivating, mysterious dinosaurs (that’s a theropod; a candle to the torch that is Amphicoelias). The urge to fill this gap and provide a safe, stable container for the large spinsoaurid material for north Africa is a commendable one. Ibrahim et al. (2014) chose to go ahead and make their new specimen, FSAC-KK 11888, the neotype (or “new name bearing specimen”) of Spinosaurus aegyptiacus. Ironically, from a specimen in Morocco. This defies two points the authors raise about the necessity of this action and the steps taken to carry it through. First, that there was every effort made to ensure consistency with the original record and locality, and to preserve the original intent of the first type’s designation; and second, that there is a timely, necessary need to create a stable record for the name.
Regardless of what happened to the specimen, von Stromer was very thorough, and provides while not a perfect record of collection, preparation and microscopic details a substantive physical and superficial description with measurements and excellent illustrations. Moreover, there’s a photograph of the original mount and reference to the description reveals what is reconstructed and what is authentic. This data is strong and possibly precludes the need for a new type so readily that one might pick a specimen of a likely distinct taxon as the new name-bearing type and to then dump into this what are additional possible distinct species. Ibrahim et al. (2014) further argue that this is predicated almost entirely on the intent of von Stromer to call attention (via nomenclature) to the spines as highly distinct. Yet, I would argue (and have) that the base element, the most diagnostic and distinct element, is the mandible; and if one were to split the specimen due to speculation, I’d tie the name-bearing type to the jaw. Ibrahim et al. (2014) focus on many postcranial attributes because there is so very little cranial material to go by, and that is the prime issue involved here. We might very well expect distinct, closely related species to vary only in small details of vertebrae, as Sigilmassasaurus and Spinosaurus B do; so, too, then in the jaw.
As such, I do not think the need for a neotype is warranted; though whether or not I disagree, the authors seem to satisfy the ICZN.
Dal Sasso, C., Maganuco, S., Buffetaut, E. & Mendez, M. A. 2005. New information on the skull of the enigmatic theropod Spinosaurus, with remarks on its sizes and affinities. Journal of Vertebrate Paleontology 25 (4): 888-896.
Ibrahim, N., Sereno, P. C., Dal Sasso, C., Maganuco, S., Fabbri, M., Martill, D. M., Zouhri, S., Myhrvold, N. & Iurino, D. A, 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science (Science Express, early online, 10.1126/science.1258750)
McFeeters, B., Ryan, M. J., Hinic-Frlog, S. & Schröder-Adams, C. 2013. A reevaluation of Sigilmassasaurus brevicollis (Dinosauria) from the Cretaceous of Morocco. Canadian Journal of Earth Sciences 50 (6): 636-349.
Russell, D. A. 1996. Isolated dinosaur bones from the middle Cretaceous of the Tafilalt, Morocco. Bulletin du Muséum National d’Histoire Naturelle, Paris, Série 4 18: 349-402.
Sereno, P. C., Dutheil, D. B., Iarochene, M., Larsson, H. C. E., Lyon, G. H., Magwene, P. M., Sidor, C. A., Varricchio, D. J. & Wilson, J. A. 1996. Predatory dinosaurs from the Sahara and Late Cretaceous faunal differentiation. Science 272: 986-991.
Sereno, P. C., Beck, A. L., Dutheuil, D. B., Gado, B., Larsson, H. C. E., Lyon, G. H., Marcot, J. D., Rauhut, O. W. M., Sadleir, R. W., Sidor, C. A., Varricchio, D. J., Wilson, G. P. & Wilson, J. A. 1998. A long-snouted predatory dinosaur from Africa and the evolution of spinosaurids. Science 282: 1298-1302.
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