The Choices We Make as Paleontologists

A recent paper by Dr. Mark Witton (2012) re-reconstructed the skull of Istiodactylus latidens (Hooley 1912) based on the recovery of a central portion of the maxilla and mandible.

 

Istiodactylus skulls

Figure 1. Istiodactylus skull bones (center). As reconstructed by yours truly (left) with restored areas in gray. As reconstructed by Witton (2012, right). Compare these to the skulls of Nurhachius, Istiodactylus sinensis and SMNK PAL 1136.

The Choices We Make
Witton (2012) chose to minimize the missing bones and so determined that Istiodactylus had a shorter skull than previously imagined and also relatively shorter and taller than the skull of other istiodactylids. I chose to add more missing material to more closely match the apparent margins and to match sister taxa, like SMNK PAL 136Nurhachius and Istiodactylus sinensis. So, ironically in this case, I was the traditional guy and Witton (2012) was the heretic.

Witton (2012) also chose not to delineate the various skull sutures, even though they were visible. Witton (2012) deepened the posterior mandible. I did not. Again, it’s good to do comparative studies with sisters if doubts persist.

These are the choices all paleontologists make. Those that can be supported, all other things being equal, will usually win out.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Andres B and Ji Q 2006. A new species of Istiodactylus (Pterosauria, Pterodactyloidea) from the Lower Cretaceous of Liaoning, China. Journal of Vertebrate Paleontology, 26: 70-78.
Hooley RW 1913. On the skeleton of Ornithodesmus latidens. An ornithosaur from the Wealden shales of Atherfield (Isle of Wight)”, Quarterly Journal of the Geological Society, 69: 372-421
Howse SCB, Milner AR and Martill DM 2001. Pterosaurs. Pp. 324-335 in: Martill, D. M. and Naish, D., eds. Dinosaurs of the Isle of Wight, The Palaeontological Association
Witton MP 2012. New Insights into the Skull of Istiodactylus latidens (Ornithocheiroidea, Pterodactyloidea). PLoS ONE 7(3): e33170. doi:10.1371/journal.pone.0033170 

wiki/Istiodactylus

Addendum
Dr. Mark Witton commented on this blog today. His remarks are important and I thank him for them. He said many things, but, unfortunately, did not offer more detailed image evidence to back up his statements. Below, some images that may help explain my “choices.” I revised the rostrum of Istiodactylus because I no longer see sufficient evidence for fenestrae. I deepened the posterior mandible because Dr. Witton mentioned it was broken on its ventral rim, but I did not deepen it to the extent Dr. Witton did. I tried to keep in accord with Nurhachius and other sister taxa.

Istiodactylus snout.

Figure x. Istiodactylus snout. Note the clear delineation of the premaxilla from the rest of the rostrum. This is more distinct than I have seen in many taxa. The rest of the rostrum appears to be splintered, but splintered nearly identically on both sides. Thus many of these breaks can be interpreted as sutures. In this way the jugal and nasal extends anterior to the antorbital fenestra, a configuration not recognized by other workers because they have not yet cared to note the details in the material and duplicated in all other sister taxa. Witton's (2012) skull reconstruction showed no sutures whatsoever, which is the typical and traditional way to present pterosaur skulls. In any case, it should important for paleontologists to delineate bone sutures when they can. I look forward to further changing my reconstruction if and when appropriate data comes in.

The skull and mandibles of Nurhachius.

Figure y. The skull and mandibles of Nurhachius. Note the left mandible appears to artificially deepen the right mandible, which may be the reason why Witton (2012) deepened the posterior mandible of Istiodactylus. The two mandibles are color coded here. The anterior mandible is purple because it is preserved in dorsal view beyond the break. The posterior mandible is narrow, as reconstructed above in Istiodactylus. The ventral rim of the posterior mandible may be broken, but there can't be much more to it, if it is to match sister taxa.

1 thought on “The Choices We Make as Paleontologists

  1. Dave,

    I can only assume from this post that you haven’t read my paper or examined the material in question. Your skull reconstruction shows the broken margin of the dentary as the ventral limit of the mid-mandible, but this can be clearly seen to be a broken margin by anyone who’s looked at photos of the specimen or the real thing (see http://www.plosone.org/article/slideshow.action?uri=info:doi/10.1371/journal.pone.0033170&imageURI=info:doi/10.1371/journal.pone.0033170.g002). The posterior mandible is also broken, so I based this part of my reconstruction on the complete (and relatively deep) models of other istiodactylids. Again, the incomplete nature of the posterior mandible is incontroverible when you examine the fossil itself, or even a good photograph.

    I make the point that the broken portions of the various jaw elements are actually very consistent with each other dimensionally, morphologically and in terms of the displacement of the mandible. At least 7 colleagues of mine have corroborated this. It is likely, therefore, that very small dimensions of jaw are missing, and most unlikely that the longer lengths you have indicated were present. I am also confused why you consider it more parsimonious to reconstruct the jaw from close relatives when good direct evidence of I. latidens jaw metrics already exist. You can also find evidence in my paper showing that the rostrum of NHMUK R3877 is heavily fractured and not indicative of its in vivo appearance, which you have also ignored in your reconstruction. You have also mistaken some of the more extensive fracturing for fenestrae in the rostrum. In short, your work would strongly benefit from actually looking at this material, and perhaps closely reading what others (who _have_ worked with the fossils in question, an experience for which no photographs are a substitute) have said on such matters.

    Cheers,

    Mark

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