In 2005, Dr. David Unwin, one of the top experts on pterosaurs, authored a popular book on pterosaurs, The Pterosaurs from Deep Time. This is part 2 of the Nits and Picks. Here is part 1.
Unwin p. 230
“The exact point at which the pterosaurs branched off from other diapsid reptiles is not at all clear, and intermediate forms between pterosaurs and other reptiles have yet to poke their heads out from the fossil record (or if they have done so, they are keeping their identity well-hidden).”
This is Dr. Unwin creatively ignoring Peters (2000a, b, 2002) which introduced the fenestrasaurs, Cosesaurus, Sharovipteryx and Longisquama, plus the non-fenestrasaur Langobardisaurus, as pterosaur precursors/sisters. Why would he do this? Instead Unwin (2005, p. 231) promoted an imaginary creature, a lizard-like, tree-climbing sprawler without manual digit 5, with a hyperelongated manual digit 4, a large muscular tail and extradermal membranes between the extremities. Bizarre. Why was it lizard-like with sprawling hind limbs when Bennett (1996), Benton (1999) and Senter (2003) reported that upright, bipedal and digitigrade Scleromochlus was a pterosaur sister? Even highly criticized Cosesaurus was upright, bipedal and digitigrade. This imaginary creature seems to have been chosen only to provide a platform on which to add extensive dermal membranes (but then flying squirrels also have upright limbs!).
Unwin, p. 232
“It seems possible, then, that insects powered pterosaurs to a true flapping flight ability.” Then slightly later, “really big insects are quite common in the Carboniferous and Permian, but disappear in the Late Triassic, at just the time that pterosaurs are thought to have taken to the air. Coincidence? Perhapss, but at the moment, an insect-powered origin of flight for pterosaurs is the only reasonable theory on the table.”
Incredible! By eating giant flying insects to extinction Unwin (2005) thinks pterosaurs were “powered” to flapping flight. Gaaakk!! This doesn’t even attempt to address morphology but hangs the “important” question on diet. Unwin (2005) doesn’t mention that pre-flapping pterosaur precursors were also insect-eaters, or that the giant insects would have been larger and more agile in the air than basal pterosaurs. He also ignores the explanation for wing evolution provided by Peters (2002) based on fenestrasaur morphology and the gradual acquisition of pterosaurian traits.
Unwin p. 241
In trying to explain the extinction of long-tailed “rhamphorhynchoid” pterosaurs (after 75 million years of success), Unwin reported, “the problem lay…when rhamphorhynchoids were on the ground…with their arms and legs shackled together by the cheiropatagium and a large cruropatagium draped between the legs.”
Of course this ignores the fact that all Triassic and Early Jurassic “rhamphorhynchoids” were extinct by the Late Jurassic, so extinction was happening continually and proceeded to continue in “pterodactyloids” throughout the Cretaceous. This also hangs all the “rhamphorhynchoid” problems on the false interpretation of the Sordes uropatagium (aka cruropatagium) discussed earlier.
Unwin, p. 244
“Pterodactyloids’ appearance in the Late Jurassic is almost as dramatic as the debut of pterosaurs in the Triassic. Frustratingly, we still have no evidence for their ancestors…”
So imagine Unwin’s excitement when he was presented Darwinopterus! Lü, Unwin, Jin, Liu and Ji (2009) considered it the long-sought link. No wonder they invented “modular evolution” to explain away the “pterdactyloid” skull and neck attached to a “rhamphorhynchoid” post-cervical region. Unfortunately his cladogram recovered 500,000+ trees with no resolution surrounding Darwinopterus. That should have been a red flag.
No, “pterodactyloids” had four origins and darwinopterids represent a fifth departure from basal pterosaur patterns as demonstrated by the large study. Furthermore Unwin’s cladogram ignored the tiny pterosaurs, which are key to understanding the four origins of the “pterodactyloid”-grade pterosaurs.
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.
Lü J, Unwin DM, Jin X, Liu Y and Ji Q 2009. Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull. Proceedings of the Royal Society London B (DOI 10.1098/rspb.2009.1603.)
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos 7(1): 11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301.
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, DeKalb, IL, 1-279.
Unwin DM 2005. The Pterosaurs: From Deep Time. Pi Press, New York.
Wellnhofer P 1991. The Illustrated Encyclopedia of Pterosaurs. London: Salamander. 192 pp.