Theropod to bird locomotion evolution with fibula reduction

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

A new paper:

Armita R. Manafzadeh, Stephen M. Gatesy, John A. Nyakatura & Bhart-Anjan S. Bhullar (2024)
Fibular reduction and the evolution of theropod locomotion
Nature (advance online publication)
doi: https://doi.org/10.1038/s41586-024-08251-w
https://www.nature.com/articles/s41586-024-08251-w


Since Hampé’s classic developmental experiments in the mid-twentieth century, the reduced avian fibula has sparked sustained curiosity. The fibula transformed throughout dinosaur evolution from a columnar structure into its splint-like avian form, a change long thought to be of little biomechanical consequence. Here we integrated comparative three-dimensional kinematic analyses with transitional morphologies from the fossil record to refute this assumption and show that the reduced fibula serves a crucial function in enabling extreme knee long-axis rotation (LAR). Extreme LAR is fundamental to avian locomotion and is regularly exploited by living birds to execute complex terrestrial manoeuvres. We infer that the evolution of this capacity was preceded by restriction of the knee to hinge-like motion in early theropod dinosaurs, driven by the origin of a mid-shank articulation8 that precluded ancestral patterns of tibiofibular motion. Freeing of the fibula from the ankle joint later enabled mobilization of this initially static articulation and, in doing so, established a novel pattern of tibiofibular kinematics essential to the extreme levels of LAR retained by modern birds. Fibular reduction thus ushered in a transition to LAR-dominated three-dimensional limb control, profoundly altering the course of theropod locomotor evolution.

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News:

Dinosaur drumsticks, X-ray videos and 3D models shed light on the evolution of bird motion

https://phys.org/news/2024-11-dinosaur-drumsticks-ray-videos-3d.html

[Tim Williams]

I thought the first author sounded familiar - Armita Manafzadeh was also lead author (with Kevin Padian) on the brilliant 2018 study of the range of motion (ROM) in avian hip joints, which has broad implications for ornithodiran hip mobility (doi: 10.1098/rspb.2018.0727).

For the current study on extreme knee long-axis rotation (LOR), in addition to birds using LOR to perform complex terrestrial manoeuvers, Manafzadeh et al. note that it's also potentially useful in "navigating complex arboreal substrates".  Two possible arboreal behaviors that come to mind include the branch 'sidling' of parrots, and the beak-assisted clambering of juvenile hoatzins.  

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