Huaxiapterus (Sinopterus) benxiensis enters the LPT basal to Tapejaridae

Lü et al. 2007
introduced us to the nearly complete crushed skeleton of Huaxiapterus benxiensis (Figs. 1, 2, BXGM V 0011) in a short paper with a short, three-sentence abstract.

Figure 1. Huaxiapterus benxiensis (BXGM V 0011) in situ, largely complete, crushed and articulated.

Figure 1. Huaxiapterus benxiensis (BXGM V 0011) in situ, largely complete, crushed and articulated.

From the Lü et al. abstract
“A new species of Huaxiapterus: H. benxiensis sp. nov. is erected based on the new specimen. The diagnostic characters of Huaxiapterus benxiensis are well-developed premaxillary crest and parietal spine, the crest and spine parallel and extending posterodorsally, and a shallow groove present on the dorsal surface of the anterior portion of the mandibular symphysis. The different skull morphologies of Chinese tapejarid pterosaurs indicate that they are much more diverse than the previous thought.”

As in all known specimens of pterosaurs, no two adults are alike. That fact gives us an excellent view of microevolution at work in this and other pterosaur clades.

Unfortunately, other workers refuse to add pertinent largely complete taxa shown in the large pterosaur tree (LPT, 256 taxa), nor have they added valid outgroups with correct scores. So the taxonomy and nomenclature in those smaller studies tends to get confused.

Figure 2. DGS reconstruction from the low resolution in situ image in figure 1. Note the brevity of the distal wing phalanges, the robust hind limbs and the gracile humerus.

Figure 2. DGS reconstruction from the low resolution in situ image in figure 1. Note the brevity of the distal wing phalanges, the robust hind limbs and the gracile humerus.

Huaxiapterus benxiensis (Lü et al. 2007, Early Cretaceous, BXGM V 0011, aka Sinopterus benxiensis) nests as the last common ancestor of the Tapejara clade + the Tupuxuara clade. Recently here, here and here we looked at other specimens assigned to Huaxiapterus that were later switched over to Sinopterus. This one (the BXGM specimen, Figs. 1, 2) is among those. They do nest closer to Sinopterus dongi (the holotype) than to Huaxiapterus jii, (the holotype), but H jii was also switched over to Sinopterus.

Almost flightless?
Different from other related pterosaurs Huaxiapterus benxiensis had shorter distal wing phalanges (m4.2, 4.3 and 4.4), a slender humerus and robust hind limbs. Together these traits suggest a trend to a reduced flight ability. Other, more clearly flightless pterosaurs are documented here, here, here and here.

Figure 4. Tapejaridae in the LPT.

Figure 4. Tapejaridae in the LPT. The BXGM specimen shows in the enlargement. It was about the size of Sinopterus dongi at the genesis of the Tupuxuara clade. 

A poor flyer at the base of the flying Tapejaridae
is possible, given that H. benxiensis is probably not the real last common ancestor, but more likely close to the real last common ancestor. It likely evolved its own way. The small size of H. benxiensis is in keeping with phylogenetic miniaturization at the start of other pterosaur clades and major clades in general.


References
Lü JC, GAo YB, Xing LD, Li ZX and Ji Q 2007. A New Species of Huaxiapterus (Pterosauria: Tapejaridae) from the Early Cretaceous of Western Liaoning, China. Acta Geol Sinica – English 81: 683-687.

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