Earlier we discussed many of the sins of omission and commission in the new book, “Pterosaurs” by Mark Witton (2013). Here we’ll take a look at the family tree of pterosaurs that Witton presents. It also includes several sins of omission and commission.
Witton’s (2013) book includes a family tree of the Pterosauria (Fig. 1 above). Unfortunately it has no outgroups. As Witton noted earlier, he follows traditional paleontologists in assuming, without testing, that pterosaurs nested with archosaurs. They don’t. On the other hand, the large pterosaur tree and large reptile tree (modified from Peters 2007, also see Fig. 6) includes more than a dozen outgroup taxa within and beyond the Lepidosauriformes, all demonstrating a gradual serial acquisition of pterosaurian traits.
Sins of Commission
Witton’s two basal taxa (Dimorphodontidae and Anurognathidae) do not include any Triassic taxa. So his Jurassic pterosaurs are more primitive than his Triassic pterosaurs.
Witton’s third clade up, the Campylognathoididae, includes Triassic pterosaurs with many multi-cusped teeth. This is a primitive trait inherited from Longisquama, a basal fenestrasaur. Witton’s nesting of campylognathoidids makes it an unlikely sister clade to Anurognathidae, which have only a few widely spaced simple teeth. (Fig. 2). Eudimorphodon does not preserve a tail, but other campylognathoidids have the largest tails among all pterosaurs, which is distinct from anurognathids. In the large pterosaur tree (Fig. 6), the common ancestor of these two clades is closer to the base of all pterosaurs, deep in the Triassic.
Witton follows earlier workers in lumping super-sharp-snouted pteranodontids with toothy ornithocheirids (Fig. 3) rather than with other sharp-snouted germanodactylids. Witton’s nesting is based largely on the warped deltopectoral crest, which basal taxa in both clades don’t have. And this is the danger that comes from using suprageneric clades.
Witton’s tree lumps long-necked, long-legged azhdarchids and chaoyangopterids together with short-necked, short-legged tapejarids and thalassodromids largely based on the shared trait of an enlarged antorbital fenestra (Fig. 4). The large pterosaur tree found this trait to be convergent between tapejarids and azhdarchids and the tiny anurognathid, Anurognathus.
Witton’s tree nests sharp-snouted dsungaripterids with toothy ctenochasmatids based on the presence of a sometimes shared rostral crest (Fig. 5). Considering the many differences between these two strange bedfellows, there are much better matches, according to the large pterosaur tree results.
Witton’s Wukongopteridae includes Darwinopterus, his transitional taxon with a pterodactyloid head and neck and rhamphorhynchoid tail and toes. No taxa in Witton’s tree are shown to gradually evolve toward Darwinopterus or beyond it. The Peters tree (Fig. 1 below) nests the sterile clade, Wukongopteridae, with Scaphognathus (Fig. 6), which begets many descendant clades. In that sense, Darwinopterus and its kin sort of jumped the gun, gaining certain pterodactyloid traits before the Pterodactloidea actually arose.
The Sin of Omission – The Tiny Pterosaur Issue
Witton’s tree (Fig. 1) includes no tiny pterosaurs. Peters’ tree found tiny pterosaurs to be transitional taxa at the bases of several clades (Fig. 1). Certain paleontologists have strongly suggested that tiny pterosaurs should not be included in phylogenetic analysis. Deleting them is no problem. Here (Fig. 6) are the results. In detail the tree topology changes very little. Overall, however, a monophyletic Pterodactyloidea is recovered. That’s a big difference. See notes below.
When you delete 40+ tiny pterosaurs
from the large pterosaur tree you get 1050+ most parsimonious trees (Fig. 6). There is some loss of resolution here and there, chiefly in Dorygnathus. The biggest change is the return of a monophyletic and traditional Pterodactyloidea in the abridged tree. Here (Fig. 6) Darwinopterus nests with Scaphognathus in a distinct clade, far from the base of the new “Pterodactyloidea.” The little pterosaur nicknamed “Rhamphodactylus” (Fig 7) nests as the basalmost pterodactyloid in the abridged tree.
Distinct from the Witton tree, here (Fig. 6) all the sharp-nosed taxa nest together. Tapejarids and dsungaripterids are derived from Germanodactylus. Azhdarchids and ctenochasmatids are basal clades close to Beipiaopterus, Huanhepterus and the outgroup Dorygnathus. Without tiny pterosaurs, it’s still a large morphological leap from Dorygnathus to “Rhamphodactylus.” And… there is a size reduction (Fig. 7).
By deleting tiny pterosaurs, anurognathids are still derived from dimorphodontids. Rhamphorhynchus is still derived from Campylognathoides.
The Pterodactylus clade becomes topsy-turvy with the former larger derived taxa nesting at the base and giving rise to smaller taxa. We’ve seen that flip happen before, in Mortimer’s theropods.
The Germanodactylus clade (including Pteranodontia, Dsungaripteridae and Tapejaridae) remains essentially untouched with tiny pterosaurs gone, but then it never included many tiny pterosaurs, except at its base.
Tiny pterosaurs are not essential for uncovering many pterosaurian lineages, but if you want full resolution in your family tree, they are key. These transitional taxa need to be included, and no longer ignored, in future analyses. The Peters’ tree, based on more specimens, has more gradual changes and fewer strange bedfellows than the Witton tree (Fig. 1), based on suprageneric taxa and too few characters.
Peters D 2007. The origin and radiation of the Pterosauria. Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27.
Witton M. 2013. Pterosaurs. Princeton University Press. 291 pages.