When a paper with the title, “how the pterosaur got its wings”
(Tokita 2014, Harvard U.) shows up, you know I’ll be interested. This one reviews the literature on morphology and heads straight into the world of molecules, a first for a fossil taxon last seen 65 mya. I’ve been chided for speculation, but here Tokita has a golden ticket.
As usual the author starts off with analogous birds descending from theropods and bats descending from unknown ‘small arboreal mammals.’ See the real story here.
When the Tokita gets down to pterosaurs, he reports the following, “Although the phylogenetic position of pterosaurs within reptiles still remains controversial (Unwin, 2006), a close relationship with a lineage of Archosauria such as the Late Triassic Scleromochlus, a member of the clade that includes birds and dinosaurs (Ornithodira), has been suggested (Hone & Benton, 2007; Witton, 2013).” As you’ll recall, these references are among the worst sources out there for pterosaur ancestry. No references were made to the one and only validated ancestry of pterosaurs among the tritosaur – fenestrasaurs, the one that keeps getting ignored.
See, folks, publication is not all its cracked up to be.
Tokita repeats the traditional propaganda, “However, as for bats, transitional fossils with intermediate anatomical features linking pterosaurs with ancestral reptiles remain to be found. The scenario that pterosaurs evolved from an arboreal tetrapod with gliding (parachuting) ability was inferred from data on limb functional morphology and has been widely accepted (Bennett, 1997, 2008; Unwin, 2006; Witton, 2013).”
As occasional readers will realize, nothing could be further from the truth.
Tokita wishes to “speculate about the potential developmental basis of pterosaur wing evolution given recent advances in the developmental biology of other flying vertebrates as well as of non-volant vertebrates” or “infer potential cellular and molecular mechanisms underlying phenotypic evolution in extinct vertebrates.”
Repeating the sins of Bennett (2003, 2008) without a critical eye
Tokita (2014, figs. 2, 3) colorizes the oddly reconstructed forelimb of Anhanguera from Bennett (2003, 2008) in which Bennett runs the tendons of extension and flexion across the anterior and posterior wrist when in every other tetrapod these cross the dorsal and palmar sides while rotating the free fingers palmar side anteriorly, which is not found in any pterosaur fossil. Bennett also removes the pteroid from the deltopectoral tendon when it is ideally placed to receive it. And totally out of his imagination, Bennett switches flexors with extensors to fold the wing finger. This is the topsy-turvy world we live in guyz! I’d cry if I was five years old again. The side-by-side illustrations of bats and birds that Tokita includes are very instructive in this matter, but the question of the many dissimilarities with pterosaurs (as Bennett reconstructs them) was never raised.
Compare all five fingers, not just the three easy ones.
Tokita compares the first three fingers to putative ancestors among the Archosauriformes. Euparkeria, Scleromochlus and Lagosuchus, completely oblivious to the fact that in these three taxa finger four is a vestige if present at all.
Tokita mistakenly refers to the pteroid bone
as unique to pterosaurs, ignoring the literature (Peters 2002, 2009) that reports it in Cosesaurus and for that matter all basal lepidosaurs as the pteroid and preaxial carpal are simply migrated centralia (Peters 2002, 2009).
Tokita repeats the propaganda
without evidence that the brachiopatagium stretched to the anterior surface of the ankle. Of course this ignores Zittel (1882) as Elgin, Hone and Frey (2011) did earlier.
Tokita reports, “The first finger of bats is inconspicuous, like the anterior three fingers of pterosaurs.” Few scientists think so. The thumb is not a vestige, it’s just not gigantic. Maybe the term, ‘inconspicuous,’ is just a poor choice of words.
Then Tokita finishes that chapter with a report on bat and bird wing muscles and the elongation of digit 4. At this point, Tokita gets into the cellular and molecular mechanisms underlying digit identify and I’m lost. But so is Tokita. His figure 4 orients the first three digits of a hypothetical early stage pterosaur embryo anteriorly, rather than parallel to the rest. This busts both the Peters and Bennett pterosaur finger orientation hypotheses and goes off in a different direction.
Then he moves to the pectoral girdle.
Tokia reports, that pterosaurs retained the architectural pattern found in non-avian tetrapods, including lizard, crocodiles and mammals. Actually pterosaurs converge a great deal with avians. So again, very topsy-turvy here. Not sure he ever put two 3d skeletons side by side, because birds and pterosaur pectoral girdles are extremely similar. Rather he states “in pterosaurs…architectural pattern was similar to those in primitive tetrapods rather than those in birds.”
Hmmm. So all the textbooks on convergence in vertebrate flight are wrong?
I don’t think Tokita understands
that the clavicles wrapped posteriorly around the sternum, unlike any other reptiles other than fenestrasaurs. The terms “clavicle” or “sternal complex” do no show up with regard to pterosaurs in his paper. He also doesn’t understand the the pterosaur coracoids were ventrally locked in place, like bird coracoids, unlike basal amniote coracoids, that ride their medial slot. And he didn’t not that the scapulae in pterosaurs were strap-like, as in birds, not as in basal amniotes.
Tokita reports, “At the later origin of the Pterodactyloidea, a drastic change occurred in the metacarpals, which changed from being the shortest and least variable in length of the major wing elements in non-pterodactyloids to being the longest and most variable in length (Witton, 2013; Andres et al., 2014).” Actually this is never true. Manual 4.1 is always as long or longer than metacarpal 4. Tokita has no clue that the origin of longer metacarpals occurred in the hatchlings of the smallest of the pterodactyloids at the base of each of the four pterodactyloid-grade clades.
Let us also remember that at least two referees and a few editors approved this.
Bennett SC 2003. Morphological evolution of the pectoral girdle of pterosaurs: myology and function. In Evolution and Palaeobiology of Pterosaurs, Geological Society Special Publications 217 (eds E. Buffetaut and J.-M. Mazin), pp. 191–215. Geological Society of London, London.
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E Buffetaut and DWE Hone eds., Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Prondvai E and Hone DWE 2009. New models for the wing extension in pterosaurs. Historical Biology DOI: 10.1080/08912960902859334
Tokita M 2014. How the pterosaur got its wings. Biological Reviews doi: 10.1111/brv.12150
Unwin DM 2005. The Pterosaurs: From Deep Time. Pi Press, New York.
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.
Witton M. 2013. Pterosaurs. Princeton University Press. 291 pages.
Zittel KA 1882. Über Flugsaurier aus dem lithographischen Schiefer Bayerns. Palaeontographica 29: 7-80.