Habib, Hone and Therrien 2017
bring us new insights into a robust azhdarchid, half the wingspan of Q. northropi (Figs. 1–3), and known from a few scattered bones.
From the Habib et al. abstract:
“The Royal Tyrrell Museum of Palaeontology (TMP) houses several specimens of
relatively large azhdarchid pterosaurs with estimated wingspans of approximately 4.5
meters from the Late Cretaceous of Alberta, Canada. Most of the material appears to
belong to a single taxon, represented by well-preserved cervical vertebrae from multiple
age classes and a partial skeleton (TMP 1992.83.4) with three-dimensionally preserved
cervical vertebra, proximal wing, and partial hind limb.
Here we present on the functional morphology of TMP 1992.83.4, with focus on the load-bearing capacity of the neck and limb elements. We find that the wing morphology of TMP 1992.83.4 and Quetzalcoatlus are very similar. The robust build of TMP 1992.83.4, combined with apparent adaptations for compressive load resistance in the humerus and fourth metacarpal, are suggestive of an animal better adapted for rapid launch and burst flight than for maximally efficient soaring. While Quetzalcoatlus seems to have had a more
gracile neck, it may be the case that azhdarchids were generally more robust, burst adapted animals than previously suggested.”
The terms ‘Burst flight’ and ‘burst adapted’
are distinct from sustained flight in volant tetrapods. Marden 1994 reported: “Recent empirical data for short-burst lift and power production of flying animals indicate that mass-specific lift and power output scale independently (lift) or slightly positively (power) with increasing size. These results contradict previous theory, as well as simple observation, which argues for degradation of flight performance with increasing size. Burst flight performance capacities of even the largest extinct fliers (estimated mass 250 kg) would allow takeoff from the ground; however, limitations on sustainable power output should constrain capacity for continuous flight at body sizes exceeding 0.003-1.0 kg, depending on relative wing length and flight muscle mass.”
Given these bits of data,
one can imagine a burst-adapted azhdarchid with a more robust neck, like TMP 1992.83.4, running from predators and never taking flight, like this (Fig. 3). If so, the list of likely flightless pterosaurs keeps growing.
Habib M, Hone D and Terrien F 2017. Evaluation of flight characteristics of Canadian azhdarchid pterosaur material reveals unique functional morphology and hints at hidden azhdarchid taxonomic and ecological diversity. SVP abstracts 2017.
Marden JH 1994. From damselflies to pterosaurs: how burst and sustainable flight performance scale with size. American Journal of Physiology 266: 1077–1084.
Witton MP and Habib MB 2010. On the size and flight diversity of giant pterosaurs, the use of birds as pterosaur analogues and comments on pterosaur flightlessness. PlosOne 5(11): e13982. doi:10.1371/journal.pone.0013982