SVP abstracts – Ornithocheirid hip range of motion (ROM)

Griffin et al. 2019 report on their study
of the Coloborhynchus (Figs. 3) pelvis during a hypothetical launch. We looked at this issue earlier here following publication of Witton and Habib 2010.

From the abstract:
“Pterosauria includes the largest animals to achieve powered flight. How medium to large-sized pterosaurs were able to launch into the air is a matter of debate.”

Oh, no. Not this invalid hypothesis again. Griffin et al. believe that giant azhdarchids could fly. They could not. Look how short their wings are compared to volant giant seabirds, pteranodontids and ornithocheirids (Fig. 1).

Figure 1. Click to enlarge. The largest flying and non-flying birds and pterosaurs to scale.

Figure 1. Click to enlarge. The largest flying and non-flying birds and pterosaurs to scale.

Griffin et al. continue:
“Birds employ their legs to accelerate their bodies into the air, but the difficulties large birds face in becoming airborne suggests take-off may limit the maximum size of birds. It has been suggested that pterosaurs employed their fore and hindlimbs in take-off, the so-called quadrupedal launch mechanism, overcoming the size constraint.”

That suggestion is not documented in the fossil record. Quad launch is not only dangerous, it is untenable and clearly inferior to using both the wings and legs to produce massive amounts of thrust as large volant birds do. Flightlessness in man-sized and smaller birds made possible flightless giant birds. The same was true for pterosaurs. All the giant pterosaurs had clipped wings (vestigial distal phalanges).

Unsuccessul Pteranodon wing launch based on Habib (2008).

Figure 2. Unsuccessul Pteranodon wing launch based on Habib (2008) in which the initial propulsion was not enough to permit wing unfolding and the first downstroke.

Griffin et al. continue
“Range of motion (ROM) studies are a common way of determining the viability of hypothetical poses in extinct animals. Here we use ROM mapping of the hip joint of a mid-sized pterosaur, Coloborhynchus (SMNK PAL 1133. Fig. 2) to test whether the joint surfaces of the acetabulum and femur were capable of achieving a bipedal and/or a quadrupedal stance during the range of motion required for take-off.” 

Figure 2. GIF animation showing stages in the bipedal take off of Coloborhynchus. Please imagine the wings talking their first mighty flap at the moment of takeoff, relieving the hind limbs from most of the stress.

Figure 3. GIF animation showing stages in the bipedal take off of Coloborhynchus. Please imagine the wings talking their first mighty flap at the moment of takeoff, relieving the hind limbs from most of the stress. In the invalid quadrupdal pose, note the proximal wing finger makes an impression, which never happens in pterosaur tracks.

Griffin et al. continue:
“Using the software programs Maya and MATLAB, possible intersections and orientations between different bones of the hip joint were identified and coded as viable or unviable. Osteological ROM mapping reveals a quadrupedal stance is more likely in launch, with maximum crouch during quadrupedal launch and flight positions being possible.”

See, they had a preconceived bias and did not comparatively test the bipedal configuration. Remember, in the bipedal pose the wings are ready to provide thrust BEFORE the legs launch the pterosaur into the air (Fig. 3). So the legs are not working alone. By contrast in the quad launch scenario, the wings are not unfolded, and not raised above the shoulders when the pterosaur is at the apogee of whatever feeble take-off abducting the antebrachium can provide (Fig. 2).

Figure 1. The as yet undescribed SMNS PAL 1136 specimen is much larger than comparable bones in the new specimen, MPSC R 1221.

Figure 4. The as yet undescribed SMNS PAL 1136 specimen is much larger than comparable bones in the new specimen, MPSC R 1221. This is a resting pose. When walking or preparing to flap the wings would have to rise off the substrate. This sort of giant-winged, small footed, volant creature rarely landed, IMHO.

Griffin et al. continue:
“However, it is important to consider not just osteological ROM but also the effects of soft tissues. ROM simulations can approximate the effect of different soft tissue such as ligamentous constraints and joint cartilage. We find that the required orientation for bipedal launch was not possible without the presence of cartilage. In order to achieve a bipedal stance in this specimen, a minimum of 3 mm of cartilage is required to sufficiently increase the ROM.”

3mm. That’s not very much, and well within the range of possibilities for a large pterosaur. I look forward to seeing their bipedal launch configuration. Having dealt with pterosaur workers cheating morphology to support their bias (e.g. Elgin, Hone and Frey 2011), I’m always suspicious  based on reputation and history.

“A ROM study that included ligaments in addition to cartilage reduced the available viable orientations. This ROM generated in this study does not rule out the possibility of a quadrupedal launch in pterosaurs, and provide greater support for the quadrupedal rather than the bipedal launch hypothesis.”

These authors mistakenly believe that pterosaurs were archosaurs. Testing reveals they are lepidosaurs (Peters 2007). Ligament issues need to based on lepidosaur pelves and hind limbs, not archosaur. Did the authors sprawl the femora, matching femoral head axis to pelvic socket axis? Having built several pterosaur skeletons, I can tell you, the bipedal stance works best. The ROM at the hips is the LEAST of their worries if they are trying to launch a pterosaur with ventrally folded wings.


References
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Griffin BW et al. 2019.
Simulated range of motion mapping of different hip postures during launch of a medium-sized ornithocheirid pterosaur. Journal of Vertebrate Paleontology 2019.
Peters D 2007.The origin and radiation of the Pterosauria.Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27
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. PLoS ONE 5(11): e13982. https://doi.org/10.1371/journal.pone.0013982

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.