The Pterosaur Family Tree part 1 – basal members/early attempts

Following our previous introduction to the origin of pterosaurs (Figure 1) and some of the transitional taxa, it’s now time to take a closer look at the rest of the pterosaur family tree (Figure 2) and the most basal pterosaur now known (Figure 3). To learn more about the various pterosaurs not figured here click on the blue links.

 

The origin of the Pterosauria from basal Fenestrasauria

Figure 1. The origin of the Pterosauria from basal Fenestrasauria

Family trees (Figure 2, see below) are created using software, such as PAUP*, which take so many taxa and so many character scores placed into a matrix of data (employing software such as MacClade) to create a more or less resolved family tree. The computer does all the work in the end, but getting to the end can be difficult. The way taxa are chosen and scores are selected can be anywhere from black-and-white to somewhat subjective. Data may be collected from first-hand observations or images and descriptions in the literature. It is best not to combine two different specimens as one taxa and similarly, it is best not to code for taxa above the genus or species. Coding on specimens is the ideal, even if they lack a skull or other important parts. Low resolution usually means your matrix of data needs more taxa, more characters or perhaps some mistakes have crept in. High resolution is the ideal. After all, there was only one family tree produced by Nature and our job is to model it as closely as possible.

 

Pterosaur family tree

Figure 2. Click to enlarge. The pterosaur family tree.

Prior pterosaur family trees beginning with Unwin (2003) and Kellner (2003) and continuing with all subsequent studies building on these two, have not provided sufficient resolution. That has been frustrating. While many nestings are no doubt valid within these studies, both these and the several that followed suffered from too many mismatches and illogical associations. The key problem remains: not including enough taxa. Here are three solutions.

No prior traditional studies have included fenestrasaurs as basal taxa. You can’t figure out which clades are the most primitive if you don’t start with the correct outgroup taxa.

No prior traditional studies have included several specimens within a single genus, such as Dorygnathus, Rhamphorhynchus, Pteranodon and Pterodactylus, despite subtle and not-so-subtle differences in certain specimens within each genus. Some of these difference only became apparent after a reconstruction put the bones back together. The present heretical study (Figure 2.) decided to take a chance and include several variations within a single genus as a test to see if those differences meant something or not. Subsequent analysis revealed that most variations documented phylogenetic lineages within each genus (from primitive to derived) and that several of these newly recovered lineages linked one genus to another.

No prior studies included the tiny pterosaurs that virtually all workers excluded believing they were juveniles of larger taxa. The present heretical study (Figure 2) decided to take a chance and include them as a test to see if the tiny pterosaurs would nest with their purported adult counterparts. Subsequent analysis demonstrated that the tiny pterosaurs were indeed adults, distinct from the larger taxa, similar to other tiny to mid-sized taxa and the keys to pterosaur survival! Embryo pterosaurs (we’ll look at these closer in future blogs) and juveniles with proportions virtually identical to those of larger sister prove pterosaurs matured isometrically. Most tiny pterosaurs appear at the bases of virtually all of the derived clades while their larger ancestors faded to extinction (below). This sort of size reduction pattern plays out again and again in the evolution of reptiles, mammals and birds, all of which originated as smaller taxa than their contemporaries and ancestors.

Note that the highly promoted pterosaur Darwinopterus, does NOT nest as a transitional taxon. Rather, it represents the end of its particular line (see Figure 2).

The most primitive pterosaur

Figure 3. Click to enlarge. The most primitive known pterosaur, the Milan specimen, MPUM 6009.

The most primitive known pterosaur is the Milan specimen, MPUM 6009, from the Late Triassic of southern Europe (Figure 3). This specimen was considered a juvenile Eudimorphodon by Wild (1978), and as a variation on Carniadactylus by Dalla Vecchia (2009). It is the pterosaur most like the outgroup sister taxon, Longisquama: It had the longest legs and shortest arms of any pterosaur. Soft tissue frills were retained above its spine. The feet were smaller than in Longisquama, but the relative proportions of the metatarsals and phalanges were quite similar. The tail was extraordinarily slender. Like Longisquama and other fenestrasaurus.

As always, I encourage readers to see the 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:
Dalla Vecchia FM 2009. Anatomy and Systematics of the pterosaur Carniadactylus gen. n. rosenfeldi ) Dalla Vecchai, 1995). Rivista Italiana di Paleontologia e Stratigrafia 115:159-188.
Kellner AWA 2003. Pterosaur phylogeny and comments on the evolutionary history of the group. In: Buffetaut E. & J-M. Mazin, Eds. Evolution and Palaeobiology of Pterosaurs. London, Geological Society Special Publication 217: 105-137.
Unwin DM 2003. On the phylogeny and evolutionary history of pterosaurs. In: Buffetaut E. & J-M. Mazin, Eds. Evolution and Palaeobiology of Pterosaurs. London, Geological Society Special Publication 217: 139-190.
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.

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