SVP 1 – Quetzalcoatlus and Azhdarchids

This post begins a review of select SVP abstracts from the recent convention.

Andres and Langston (2015 abstract)
limit the number of taxa referred to azhdarchidae (Quetzalcoatlus + Azhdarcho) to Turonian (Early Late Cretaceous, 90 mya) taxa using phylogenetic analysis. By definition and age that includes Zhejiangopterus (81 mya) as earlier work by Andres and Myers (2013) did so as well. I’m glad someone is continuing the work started by Wann Langston (RIP). Although the Andres tree is ripe with problems, this node is not a problem.

Azhdarchids and Obama

Figure 1. Click to enlarge. Here’s the 6 foot 1 inch President of the USA alongside several azhdarchids and their predecessors. Most were knee high. The earliest examples were cuff high. The tallest was twice as tall as our President.

From the abstract
“Over the past 30 years, [the azhdarchidae] has had hundreds of fragmentary specimens referred to it, spanning over 85 million years from the Late Jurassic to the latest Cretaceous. Newly described material of Azhdarcho and Quetzalcoatlus combined with a phylogenetic analysis of referred azhdarchid specimens, allows better resolution of the evolutionary relationships and history of the azhdarchid pterosaurs.”

“The earliest reported occurrences of azhdarchids in the Late Jurassic and Early Cretaceous are of ctenochasmatoids. [not sure which taxa Andres and Langston refer to here]. Despite a tendency to refer most Late Cretaceous pterosaur material to the Azhdarchidae, the clade only dates back to the Turonian. A tapejarid, ornithocheiran, thalassodromine, and the pteranodontids also survive to the early Late Cretaceous. Most of the specimens previously referred to the Azhdarchidae, but now recovered outside of the group, are on the azhdarchid branch as non-azhdarchid neoazhdarchians {again, which taxa?]. These specimens range from the Aptian, when the lineage would have split from the chaoyangopterids at the latest, to the latest Cretaceous, and so comprise the last surviving pterosaurs along with the Azhdarchidae and one Nyctosaurus specimen. The giant and smaller morphs of Quetzalcoatlus are recovered as sister taxa and so are closely related as either a single species or sister species.”

In the large pterosaur tree, there is a continuous lineage in the ancestry of azhdarchid pterosaurs going back to a sister to Huehuecuetzpalli (a basal tritosaur) and Macrocnemus (Middle Triassic tritosaur). Quetzalcoatlus and the azhdarchids were derived from a sister to Zhejiangopterus, Chaoyangopterus, Microtuben, Jidapterus, Sos 2428 (the flightless pterosaur), tiny B St 1911 I 31, CM 11 426, Ardeadactylus (which gave rise to Huanhepterus), Beipiaopterus, tiny and short legged TM 10341 and the SMNS 50164 specimen attributed to Dorygnathus (Fig. 1, Middle Jurassic). Nowhere in this lineage are any ctenochasmatoids, although Huanhepterus has been mistakenly referred to that clade.

Figure 1. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Figure 2. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen. These specimens demonstrate isometric growth in pterosaurs – which is heretical as these specimens are conveniently overlooked by the data deniers among pterosaur workers. 

This clade of pre-azhdarchids is remarkable
for demonstrating isometry during ontogeny in Zhejiangopterus (Fig. 2) and isometry during phylogeny starting with long-legged and long-necked B St 1911 I 31 (Fig. 3).

Pterodactylus? elegans? BSPG 1911 I 31 (no. 42 in the Wellnhofer 1970 catalog)

Figure 3. Pterodactylus? elegans? BSPG 1911 I 31 (no. 42 in the Wellnhofer 1970 catalog). Note the scale bar and the azhdarchid-like proportions in this tiny Late Jurassic azhdarchid precursor.

Brian Andres is the third of three pterosaur workers to have their cladogram of pterosaur phylogeny published on Wikipedia. Although all three have a similar topology (they all retain “The Pterodactyloidea”) at certain nodes, none have a similar topology in the broad sense. None include fenestrasaurs as outgroup taxa. None include several species (distinct specimens) from single genera and and none include the tiny pterosaurs found in the large pterosaur tree. As we learned earlier, phylogenetic miniaturization marked the genesis of several pterosaur clades, so the tiny pterosaurs are key to understanding phylogenetic relationships. We looked at the tree of Andres and Myers (2013) earlier here.

References
Andres B and Langton W 2015. Morphology and phylogeny of Quetzalcoatlus (Pterosauria: Azhdarchidae) Journal of Vertebrate Paleontology Abstracts 2015. 

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