Pterosaurs landing in trees – part 2 – perching with their opposable digit

The traditional view holds that pterosaurs did not perch on branches, largely because they did not have an opposable digit. This is wrong. Pterosaurs had an opposable digit. It was just not like that of birds. Instead it was uniquely pterosaurian — working by extension, not flexion. Peters (2002, 2010) described how pedal digit 5 in basal pterosaurs acted like a universal wrench, extending while digits 1-4 flexed around a branch of any diameter (Fig. 1), thereby opposing the flexing digits (note the white arrows in the branch cross-section).

 

 

Figure 1. The pterosaur Dorygnathus perching on a branch. Above the pes of Dorygnathus demonstrating the use of pedal digit 5 as a universal wrench (left), extending while the other four toes flexed around a branch of any diameter and (right) flexing with the other four toes. As in birds, perching requires bipedal balancing because the medially directed fingers have nothing to grasp.

Figure 1. The pterosaur Dorygnathus perching on a branch. Above the pes of Dorygnathus demonstrating the use of pedal digit 5 as a universal wrench (left), extending while the other four toes flexed around a branch of any diameter and (right) flexing with the other four toes. As in birds, perching requires bipedal balancing because the medially directed fingers have nothing to grasp.

Pterosaur perching requires a bipedal capability
Pterosaurs could perch on horizontal branches — although not quite like birds. As in birds, the anterior toes were located below the center of balance in flight, the shoulder glenoid, so a bipedal configuration was possible without shifting or lifting the torso.

In the most primitive pterosaurs pedal 5.2 (actually a fused p5.2+p5.3) was straight. In Dorygnathus and certain other derived clades, pedal 5.2 was bent or bowed in various ways (Peters 2011). Bent or straight had little effect on the universal wrench.

Certain derived pterosaurs without a large pedal digit 5 (e.g. ctenochasmatids, pterodactylids) probably did not perch on tree branches. Footprints indicate they were beachcombers. Only those with large fingers and trenchant finger claws could also have found safe haven on tree trunks, upon which pedal digit 5 had less of an importance.

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
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2010. In defence of parallel interphalangeal lines. Historical Biology iFirst article, 2010, 1–6 DOI: 10.1080/08912961003663500

Advertisements

2 thoughts on “Pterosaurs landing in trees – part 2 – perching with their opposable digit

  1. Pingback: Pterosaur Fossils | Griffith Park Pterosaurs and Perching

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 )

Twitter picture

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

Facebook photo

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

Google+ photo

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

Connecting to %s