For A Few Spinosaurus More

As I intimated earlier — and to quote Monty Python — the holotype of Spinosaurus aegyptiacus has ceased to be.

Spinosaurus aegyptiacus, mount of the holotype IPHG (BSP) 1912 VIII 19. The only remaining photographic evidence known for the material. After Smith et al., 2006.

Typically, then, this makes it immeasurably difficult to compare new material to the holotype. This is not even considering the difficulty implicit in referring material to taxa for which there is not comparable element preserved in the holotype, and from which type locality no further [topotypic] material has been derived to allow supplementation of the type specimen. This means we are left with a hard choice: we can continue to use von Stromer’s excellent, but dated, plates and photographs (Smith et al., 2006) or, we can set the material aside and replace the nomenclature, entrenched as it is, with new names for the more recent taxa. This is important if, as appears to be the case with regards to Cenomanian taxa, there may be regional variation between the Moroccan and Egyptian provinces. A third possibility may be that a neotype be designated to fix the nomenclature, but so far, topotypic material is limited in diagnostic quality; most new material described has been “typical” teeth, and thus may be useless for setting a new type, almost certainly the preference would be for a vertebral specimen or series.

A specimen has been noted in preparation for description by Angela Milner from northern Africa for several years now (Milner, 2003), but another one appears from private collectors and in mounts, as seen here.

Skull of a specimen called “Spinosaurus aegyptiacus,” currently in private hands, drawing by Cristophe Hendrickx.

This material may, or may not, elucidate the quality of Spinosaurus material, but they do very little on their own to settle the issue of what is Spinosaurus aegyptiacus. It is more interesting to note that when having the opportunity to settle with new information, dal Sasso et al. (2005) chose to refer their new material despite a lack of comparable material, due to the idea that there was not quanitfiable variation among the known material. As I noted, most of that is scraps of partial vertebrae and teeth. Precisely what level of analysis needs to be used to qualify this taxonomically, and has it been done? I think it requires some morphometric analysis, and that has not yet been done. Moreover, until new material can be found that somehow matches von Stromer’s material to the best of our descriptive capability, I think it is severely unwise to refer new material to Spinosaurus aegyptiacus. Conservatively, I would prefer a new name, or a new type specimen to fix the name to, and the basis of the latter is slim indeed.

But even if we accept this material is somehow Spinosaurus, or Spinosaurus aegyptiacus, there is the issue of applying the material to a single animal:

Skull and silhouettes of Spinosaurus specimens. A, IPHG 1912 VIII 19, holotype of Spinosaurus aegyptiacus von Stromer, 1914; B, same silhouette in A with MSNM V4047 added to snout and silhouette modified to “fit”; C, same silhouette in B but scaled up to the actual size of MSNM V4047; D, same silhouette as in C but with snout elongated as in dal Sasso et al., 2005.

The material described by dal Sasso et al. (2005) represents the rostral portion of the snout. How much of the snout depends on the reconstruction, to which end few material actually helps. Spinosaurids are generally divided into two clades, primarily defined on the structure of their teeth: Spinosaurinae, and Baryonychinae. The former have unserrated teeth with distinct vertical fluting (or ribbing) and relatively smooth enamel surfaces, and relatively low recurvature, and are generally broader along the tooth than in baryonychines. Alternately, baryonychines have serrations, low fluting or ribbing, distinctly wrinkled enamel, and higher recurvature. For the record, I suspect that basal spinosaurines should have teeth much like baryonychines, as this is the ancestral condition from which such spinosaurids would arise. These taxa differ in the rostrum, as well, but it is only in recent discoveries that this data has become more available.

First, there is only one well-preserved spinosaurine skull known, the holotype of Irritator challengeri, SMNS 58022 (Martill et al., 1996). Originally described as a maniraptoran of some sort, it has since been argued to be a spinosaurid (Sereno et al., 1998 and others) based on clear data in the braincase and rostrum. This has been supported by arguments in favor of the holotype of Angaturama limai, GP/2T-5 (Kellner & Campos, 1996) as potentially consisting of the rostral fragment that is missing from SMNH 58022 (Sues et al., 2002), although Kellner has disagreed in multiple occasions due to the lack of actual overlap and purported morphological differences in the teeth and presence of a high midline rostral crest apparently absent in Irritator challengeri. While I disagree with the general criteria meant to keep the taxa apart, I would suggest that until distinct material can affirm the referral, it might be best to keep the two taxa apart.

As shown above, other undescribed skulls are known, but they are useless as either private specimens or potential chimaeric specimens. This leaves the only three well-preserved cranial remains, IPHG 1912 VIII 19MNHN SAM 124, and MSNM V4047. These specimens differ in size by a considerable degree: the nearly complete right dentary of IPHG 1912 VIII 19 is roughly 525mm long, and thus just over half a meter; MSNM V4047 is 988mm, almost 1 meter in length; while MNHN SAM 124 is around 600mm.

So there is some concern about the scaling issues involved that prevent us from simply slapping a snout onto a jaw, and calling it good. No, i do not say that dal Sasso do this; I call into question, rather, the effectiveness of simply lumping specimens from across Africa into a single taxon without a grand deal more data to back it up. Scaling the material also underscores a thing that is bothersome, but also enticing:

  1. The dentary fragment of the holotype is half the length of the referred snout fragment (MSNM V4047), and were the dentary scalable to a full jaw (about 45% or less), we’d get an enormously odd mandible. Dal Sasso et al. reconstructed this with an underslung jaw, and a large portion of the rostrum projected out over the anterior mandible, producing an overbite.
  2. This also had the odd effect of allowing the rosette of rostral teeth in the mandible to be placed lateral to the upper jaw, at the portion of the rostral “pinch” in the snout, and thus a portion of the upper dentition would be lingual to the lower jaw.

Skull and mandibles of Spinosaurus aegyptiacus von Stromer (1915) reconstructed after dal Sasso et al. (2005) (left) and me (right). Scale bars indicate the actual sizes of the two key elements. Skull is reconstructed in generalization from von Stromer (1915) and dal Sasso et al. (2005), with a portion of the nasal crest simply merged with the snout fragment.

In the above image, a generalized skull of Spinosaurus aegyptiacus is presented based on IPHG 1912 VIII 19 and MSNM V4047, illustrating the open-jawed and close-jawed positions and relationships of various bones. The skull in the upper pair of illustrations are oriented so that the long axis of the ventral margin maxilla is level, while the same is true of the jugal ventral margin of the lower pair. The latter is meant to correspond roughly to the “alert” posture of the head. On the left, I’ve rendered the jaw as dal Sasso et al. describe it, and although this is not an element of their thesis (i.e., it has no bearing on the descriptive aspects of the paper and the science therein, which is spot-on) it does bear against the reconstructions and depictions of the head as shown.

Note that when scaling the jaw up isometrically, the mandible is extraordinarily deep. There are reasons to doubt the jaw was this deep, and the main reason is that IPHG 1912 VIII 19 is from a subadult animal, despite being from one of the largest theropod specimens found, and was thus not fully gorwn. Moreover, it is likely not even close to the size of the animal represented by MSNM V4047. Does this indicate that massive size gain could be obtained? I think that dal Sasso et al. (2005) have somewhat dogded this curiosity by scaling the mandible up only so much, creating the overbite, and also due to an inference that the “subnarial gap” between premaxillary rosetta and maxilla would have aesthetically or mechanically accomodated the dentary rosette. It is, in my opinion, wrong.

Virtually all animals with a rostrally expanded jaw tip pair the upper and lower expansions; they are hardly ever displaces so much as to be one behind the other. Moreover, piscivorous animals which acquire prey using the jaw tips, includoing but not limited to the gharials, some fish such as gar,and birds such as ducks, the spoonbill, etc.

Skull of the Alligator Gar, Atractosteus spatula.

Skull of the gharial, Gavialis gangeticus, borrowed from Digimorph.

An uneven jaw, with extended upper rostrum, typically develop in animals who regularly process prey with their upper jaws to such a degree that the lower jaw tends to lack elements of the processing apparatus. This is true in most raptorial birds, if not all of them, where the upper jaw is used to hook and tear flesh, disable or immobilize or kill, etc., and is also true in frugivorous or seed-eating birds, such as parrots, which use their lower jaw primarily to aid in cracking, but otherwise are limited in this respect to the upper jaw, which does most everything else.

So an enormously underslung jaw seems unreasonable for a fish-eating theropod, if this was indeed what Spinosaurus was doing. If it was, it means the upper and lower rostral rosettes should oppose one another, and this alters the reconstruction and proposed by dal Sasso et al. (2005). If the lower dentition were acquisitors of prey, and thus useful in feeding and processing, they must have been paired with the upper jaws. My reconstruction attempts to show this, although it certainly leaves more of a gap between the upper and lower jaws, but then, this may be related to the shapes of the jaws not being compatible. In animals with upper and lower prehension in the jaws, as above, the mandibles tend to be shaped to fit; but this must also permit the upper and lower jaws to work together in the same fashion. It then raises the question of whether the jaws changed shape during ontogeny, or the possible systematic variation among spinosaurs in the Late Cretaceous of Africa. I suspect the latter, and question the referral of MSNM V4047 to Spinosaurus aegyptiacus.

And that will leave us to the final post of this little series, whose title should only be obvious.

de Broin, F., Grenot, C. & Vernet, R. 1971. Sur la découverte d’un nouveau gisement de vertébrés dans le Continental intercalaire saharien: La Gara Samani (Algérie) [On the discovery of a new deposit of vertebrates in the Saharan Continental intercalaire: Gara Samani (Algeria)]. Comptes Rendus de Academie des Sciences, Paris (Series D) 272:1219-1221.
Charig, A. J. & Milner, A. C. 1986. Baryonyx, a remarkable new theropod dinosaur. Nature 324:359-361.
Charig, A. J. & Milner, A. C. 1997. Baryonyx walkeri, a fish-eating dinosaur from the Wealden of Surrey. Bulletin of the Natural History Museum of London (Geology) 53:11-70.
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.
Kellner A. W. A. & Campos, D. A. 1996. First Early Cretaceous theropod dinosaur from Brazil with comments on Spinosauridae. Neues Jahrbuch für Geologie und Paläontologie Abhandlungen 199(2):151-166.
Martill, D. M., Cruickshank, A. R. I., Frey, E., Small, P. G. & Clarke, M. 1996. A new crested maniraptoran dinosaur from the Santana Formation (Lower Cretaceous) of Brazil. Journal of the Geological Society of London 153:5-8.
Russell, D. A. 1996. Isolated dinosaur bones from the Middle Cretaceous of the Tafilalt, Morocco. Bulletin du Muséum National d’Histoire Naturelle, Paris (4th series) 18(2–3):349–402.
Sereno, P. C., Beck, A. L., Dutheil, D., Gado, B., Larsson, H. C. E., Lyon, G. H., Marcot, J. D., Rauhut, O. W. M., Sadleir, R. W., Sidor, C. A., Varricchio, D. D., Wilson, G. P. & Wilson, J. A. 1998. A long-snouted predatory dinosaur from Africa and the evolution of the spinosaurids. Science 282:1298-1302.
Smith, J. B. 2005. Heterodonty in Tyrannosaurus rex: implications for the taxonomic and systematic utility of theropod dinosaurs. Journal of Vertebrate Paleontology 25(4):865-887.
Smith, J. B., Lamanna, M. C., Mayr, H. & Lacovara, K. J. 2006. New information regarding the holotype of Spinosaurus aegyptiacus Stromer, 1915. Journal of Paleontology 80(2):400-406.
von Stromer, E. 1915. Ergebnisse der Forschungreisen Prof. E. Stromers in den Wüsten-Ägyptens. II. Wirbeltier-Reste der Baharîje-Stufe (unterstes Cenoman). 3. Das Original des Theropoden Spinosaurus aegyptiacus nov. gen. et nov. spec. [Results of the explorations of Prof. E. Stromer in the Egyptian desert. II. Vertebrate remains of the Bahariya Formation (lowest Cenomanian). 3. The original of the theropod Spinosaurus aegyptiacus nov. gen. et nov. spec.] Abhandlungen der Königlichen Bayerischen Akademie der Wissenschaften Mathematisch-physikalische Klasse Abhandlung 28(4):1–32.
von Stromer, E. 1927. Ergebnisse der Forschungreisen Prof. E. Stromers in den Wüsten-Ägyptens. II. Wirbeltier-Reste der Baharîje-Stufe (unterses Cenoman). 9. Die Plagiostomen mit einim Anhangüber käno- und mesozoische Rückenflossenstacheln von Elasmobranchiem [Results of the explorations of Prof. E. Stromer in the Egyptian desert. II. Vertebrate remains of the Bahariya Formation (lowest Cenomanian). 9. The Plagiostomi with an appendix on the Ceno- and Mesozoic spine-bearing Elasmobranchii]. Abhandlungen der Königlichen Bayerischen Akademie der Wissenschaften Mathematisch-physikalische Klasse Abhandlung 31:1-64.
Sues, H.-D., Frey, E., Martill, D. M. & Scott, D. M. 2002. Irritator challengeri, a spinosaurid (Dinosauria: Theropoda) from the Lower Cretaceous of Brazil. Journal of Vertebrate Paleontology 22(3):535-547.
Taquet, P. & Russell, D. A. 1998. New data on spinosaurid dinosaurs from the Early Cretaceous of the Sahara. Comptes Rendus de l’Académie des Sciences, IIA: Earth & Planetary Sciences 327:347−353.

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12 Responses to For A Few Spinosaurus More

  1. Steve O'C says:

    I’m liking your posts on Spinosaurus, especally the ones about the possitions of the vertebra. There are a few things in this post I’m not sure about.

    ”..the nearly complete right dentary of IPHG 1912 VIII 19 is roughly 525mm long”

    In Stromers paper it says its about 75cm long. The Tooth row is 525mm long. I knocked up this diagram using measurments from Stromers Paper a while back. It contains several figures of the Stromer spinosaurus dentary, including the Smith et al photo and the Dal Sasso reconstruction scaled to about the same size of the holotype.

    Also I don’t think you have accurately reflected the Dal Sasso reconstruction in the first figure. It’s not as ‘long snoated’ as you show.

    I think you have drawn the lower jaw too straight and too deep in the second diagram. If you look at the photos in Smith et al you can see a slight downward kink about half way along. I also suspect you have scaled the lower jaw too small in relation to the Dal Sasso snoat. It it were larger there would be less of an over bite.

    • Steve O'C says:

      I have sent a few mins looking at your diagrams in more detail. In the first image you have scaled IPHG 1912 VIII 19 too small. You apear to have scaled the whole dentary to approximately 525mm, which according to Stromer is the length of the tooth row.

      Scaling in the IPHG 1912 VIII 19 dentary to roughly match your second diagram it seems that you havn’t drawn it too deep necessarily, it’s more the shape doesn’t match the holotype. The way you’ve drawn it, with a straighter tooth row, gives the illusion it’s deeper than it actually is.

      • Thanks for the two comments, Steve! I will attempt to respond in a single response, instead of separately.

        It is true, the scaling is somewhat approximate, yes. In the second illustration, the drawing was not designed to depict the shapes of the specimens precisely. “Skull is reconstructed in generalization….” was used specifically because I knew I wasn’t getting the mandible precisely correct, and I did this after I realized I didn’t get the mandible perfectly. In this, I was being careful due to the incompleteness of the dentary (which, of course, is inferred from the margins — I do not think the dentary is complete, nor do I think it is possible to determine otherwise, and von Stromer agrees).

        On my scaling relative to the dal-Sasso reconstruction: in both illustrations, I used the same approximate scaling of dentary to snout fragment, and used the ventral margin to estimate correct lengths of the premax-maxilla, which was used to revise the outline of the illustration from my original skeletal diagram. It was literally dumped into the drawing at scale. Even in that drawing, the scaling of the mandible to the vertebrae is exact (total length to total length) from von Stromer’s precise measurement of 660mm (aprox.) for the longest of the two mandibular rami (620mm for the other), with additional length provided by the splenial fragment which is not considered here. But consider that neither element is complete: if taken at dal Sasso et al.’s estimate, the dentary as preserved should be 50% the upper snout as preserved; von Stromer’s measurements indicate I can come close to 65% instead, and this will not severely change the relative weakness of the proportional differences between the two. I will still have to significantly scale the jaw up to the snout fragment to “fit” it.

        The jaw is given as the “overbite” in relation to the inference by dal Sasso of a “fitted” jaw, not because of any scaling issues. I only altered in the two postures the postdentary bones to show relative “fit” of the jaws. Moreover, the jaw was illustrated up to “match” dal Sasso’s reconstruction, not to match the conception of a “small” versus “proper” jaw, and this is explicit if you consider the only relative proportion was a slightly distorted posterior dentary margin to match the rescaled postdentary. Because the illustration in the third image was even more approximate than the second, though the second was an attempt to use the scaling from dal Sasso paper itself, it should be clear that the scaling elements involved are not necessarily meant to be accurate to the preserved elements.

  2. Steve O'C says:

    Thanks for the reply!

    I think it’s ok to generalize if you are just trying to demonstrate an idea, as you are in the second diagram. I got the impression from the text that you were implying that the Dal Sasso recon had a large overbite and that the diagram was trying to show the degree of over bite that Dal Sasso’s recon shows.

    In the first diagram you are showing the overall sizes to the two specimens and whilst the known peices may not be complete I still think the overall scale of A and B are too small. Using the 1m scale bar in the first diagram and photoshops measure tools I get 50.5 cm for the holotype dentary.

    Based on the measurments in Stromer it should be somthing more like this.

    I scaled in the holotype illustrations and photo into your image, note the size difference of your dentry to the photo next to it. I also inserted Dal Sasso’s recon (scaled to approximately holotype size.)

    • Understand that the skeletal reconstruction that the silhouette is based on, as I noted in the original post, is not rigorous. It was meant to approximate, rather than precisely render a scaled skeletal based on the spines, vertebrae, and mandible. It was and is my goal with these to explain the ideas, that the reconstructions offered for the new snout have a misaligned jaw, and that regardless of the scaling, the mandible must be increased in size to an arbitrary level to agree with the reconstruction. And this is excepting that given measurements (525mm for the holotype left? dentary) are not precisely accurate. It is something to note in the third and final installment of this “series.”

  3. Fabrizio says:

    Ibrahim & Sereno (2011) in their abstract of SVP wrote the it’s likely that there’s only a single species of Spinosaurus in cenomanian of north africa
    What do you think about it, sir?

    • I will for the most part prefer to wait for the publication on this. I understand that for some researchers, the subsumation of many taxa into one (such as Milner’s contention that Baryonyx contains Suchomimus) requires a bit of smoke and mirrors. This isn’t a contention of purposeful obfuscation, but that the situation is either more complex or too complex or filled with too many subjective elements to be valuable. I will eventually get to the final bit in my last post on this series, but it may be a while.

  4. ijreid says:

    Nice images! From what I know, most Spinosaurus images are hard to come by these days, especially online. Where did you find all these, specifically the first image of the skeleton?

    • The plates come from von Stromer’s original publication. The photo of the mount was a record preserved by von Stromer’s family and held is private until shared with Josh Smith, Matt Lamanna and crew during their expeditions to Egypt, then to Germany to find any remaining records of the material Markgraf collected for von Stromer in Egypt prior to World War II. We are very lucky to have this, but it is all that we have left.

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