Anurognathids as Apodiform Analogs


Batrachognathus

Figure 1. Batrachognathus volans. Note the binocular fields of vision enabled by the narrow nasals not found in basal anurognathids. Also note the tiny rod-like palatal processes of the maxilla ventral to the ectopalatine (ectopterygoid + palatine) and pterygoid. These are likely touch sensors when the mouth is open during feeding. Click to learn more.

Anurognathids are different from the other pterosaurs. Forsaking the long pointed rostrum, anurognathids evolved a short wide gape that ultimately produced binocular vision with the narrowing of the nasals in derived taxa, such as Batrachognathus (Fig. 1). The wide gape has long been recognized as an excellent flying insect trap. This gape was taken to its largest arc in the vampire anurognathid pterosaur, Jeholopterus and its widest gape in the “flathead” anurognathid, mistakenly attributed to Anurognathus.

Here we’ll compare Batrachognathus with its modern analogs among birds, the swift (Apus apus, Figs. 2) and the nightjar (Caprimulgus), both members of the Apodiformes.

The skull and skeleton of Apus apus,

Figure 2. The skull and skeleton of Apus apus, the Common Swift.

Swifts and Nightjars (Nighthawks in the Western Hemisphere)
Spending most of their lives in the air, swifts feed on insects caught on the wing during daylight hours. They cling to vertical surfaces when they stop flying, never settling on the ground due to the small size of their hind limbs. By contrast, nightjars (Fig. 3) usually nest on the ground, despite their small feet, which are also of little use in walking. Nightjars feed on moths and other large flying insects and are most active nocturnally.

A nightjar with mouth wide open.

Figure 3. A nightjar with mouth wide open. Photo courtesy of Peter Sjolte Ranke.

Anurognathids
The large eyes of Batrachognathus indicate a possible nocturnal lifestyle.  Bristles surrounding the jaws were reported in Batrachognathus (Rjabinin 1948). These were compared to the rictal bristles surrounding the jaws of many birds, but are more prominent in nightjars. In Batrachognathus the tip of the short tail is nearby and thus could represent tail tip bristles. Rictal bristles are not found in sister pterosaurs, but tail tip bristles are.

In contrast to apodiforms, anurognathids retained relatively large hind limbs, so Batrachognathus would have retained excellent walking and running abilities. (Note the right angle femoral head in Batrachognathus, giving it a parasagittal stride.)

Nighthawk Wings
Flying over the crowds at Friday night football games, nighthawks (Apodiformes) find and devour moths that are attracted to the stadium lights. With their stiff, elliptical-tipped, narrow-chord wings, nighthawks remind me of anurognathids.

Your thoughts?

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.

References
Bakhurina NN 1988. [On the first rhamphorhynchoid from Asia: Batrachognathus volans Riabinin 1948, from Tatal, western Mongolia]. Abstract of paper in Bulletin of the Moscow Society for the Study of Natural History, Geological Section 59(3): 130 [In Russian].
Rjabinin AN 1948. Remarks on a Flying Reptile from the Jurassic of Kara-Tau. Akademia Nauk, Paleontological Institute, Trudy 15(1): 86-93.

wiki/Batrachognathus
wiki/Common_Swift
wiki/Nightjar

Swift skeleton based on data from skullsite.com

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