Longisquama: Almost Too Fascinating. And a Lot of Work!
The general morphology of Longisquama has been difficult to ascertain. Sharov (1970), Senter (2003) and Martin (2000) provided simple tracings without much resolution. Peters (2000) added details, but was unable to actually “see” many details due to inexperience. There I said it. Okay, I’m better now than I was 12 years ago. I’ve got more under my belt.
A dozen years ago I was also under the existing paradigm that the posterior half of Longisquama was missing, as Sharov (1970) reported. No one ever suspected that Longisquama had the long hind legs of a biped and the wings of a pterosaur. Even when they are traced out (Figure 1), they are still difficult to see and were mistaken for displaced plumes by Sharov (1970).
Persistence Pays Off!
A new tracing of Longisquama (Figure 1) reveals long hidden details including the tail, pelves, two hind limbs and two folded wings framed by elongated wing fingers (Figure 2). Workers who have seen this fossil claim they did not see this level of detail. That’s because the human eye, even aided by a binocular microscope, cannot segregate and aggregate all the chaos and layers of detail in this fossil. It takes a computer and DGS (digital graphic segregation) to tease out each bone one at a time. By digitally tracing the elements the details emerge and form a complete picture with matching left and right elements that confirm identification. This technique has been widely criticized, but the results speak for themselves.
Despite the “weirdness” of Longisquama, there are very few autapomorphies present. Instead, nearly every trait bridges the morphological gap between Cosesaurus and pterosaurs. It took persistence and the recognition of past errors to make these tracings come together. Follow these methods and the results should be identical.
The “proto-wings” of Longsiquama were midway in size and shape between the nonvolant forelimb of Cosesaurus and the fully-fledged wings of basal pterosaurs (Figure 3). Fingers 1-3 were quite a bit larger than those of either sister taxa. Metatarsal 4 was axially rotated so the finger four flexed in the plane of the wing, as in pterosaurs, rather than toward the palm, as in all other tetrapods. The large claws on the hands suggest an arboreal habitat.
Cosesaurus and Longisquama are the Archaeopteryx and Microraptor of pterosaurs, demonstrating the first steps in the origin of flight for the first volant vertebrate clade, the Pterosauria.
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.
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E. Buffetaut & D.W.E. 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 doi: 10.4202/app.2009.0145 online pdf
Jones TD et al 2000. Nonavian Feathers in a Late Triassic Archosaur. Science 288 (5474): 2202–2205. doi:10.1126/science.288.5474.2202. PMID 10864867.
Martin LD 2004. A basal archosaurian origin for birds. Acta Zoologica Sinica 50(6): 978-990.
Peters D 2000. 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.
Senter P 2004. Phylogeny of Drepanosauridae (Reptilia: Diapsida) Journal of Systematic Palaeontology 2(3): 257-268.
Sharov AG 1970. A peculiar reptile from the lower Triassic of Fergana. Paleontologiceskij Zurnal (1): 127–130.