Forelimb reduction and digit loss were evolutionarily decoupled in oviraptorosaurian theropod dinosaurs

TL;DR

This study shows that in oviraptorosaurian dinosaurs, the loss of certain digits and the reduction of the forelimb evolved independently, revealing a more complex evolutionary history than previously thought.

Contribution

The paper demonstrates that digit III and the rest of the forelimb in oviraptorosaurs evolved under different processes, challenging previous assumptions of a direct link.

Findings

Digit III and the rest of the forelimb in oviraptorosaurs evolved independently.

Four distinct forelimb morphotypes exist in oviraptorosaurs, not directly tied to dietary niche partitioning.

Forelimb evolution in oviraptorosaurs is more complex due to their Late Cretaceous evolutionary radiation.

Abstract

Theropod forelimbs exhibit wide morphological disparity, from the elongated wings of birds to the diminutive arms of T. rex. A wealth of work has sought to understand the evolution of bird flight via arm elongation, but despite widespread occurrences of forelimb reduction and digit loss throughout theropod dinosaurs, the evolutionary drivers behind these patterns are poorly understood. Previous studies demonstrate broad allometric trends that can account for some instances of forelimb reduction, but the repeated loss of digits, and their hypothesized link to forelimb shortening, has received less attention. Here, we evaluate evolutionary associations between digit loss and forelimb reduction in an iconic and data-rich theropod clade, Oviraptorosauria. Unexpectedly, we find that the evolution of digit III and the rest of the forelimb are decoupled. Support for different evolutionary models and a lower phylogenetic signal in digit III than the rest of the forelimb suggests these segments were subject to different evolutionary processes leading to independent morphological change. Oviraptorosaurs exhibit four distinct forelimb morphotypes, but these do not exactly correspond to patterns of dietary niche partitioning. Overall, forelimb evolution in oviraptorosaurs is more complex than anticipated, potentially as a result of an evolutionary radiation they underwent in the Late Cretaceous.

Figures