Convergent Trajectories in the Evolution of Bipedality in Desert Rodents

Bipedal desert rodents have long been a textbook example of convergent evolution. Australian hopping mice (Muridae), Kangaroo rats (Heteromyidae), and Jerboas (Dipodidae) are all capable of bipedal locomotion, construct underground burrows, do not need to drink water, and are crepuscular foragers. However, upon closer inspection, there are significant differences in diet, locomotion, and physiology that have led some researchers to propose that they are not convergent after all. To better understand how the concept of convergence relates to this clade, I collected morphological data on members of each group, closely related quadrupeds, and other rodents, totaling 158 species. Performing a phylogenetic Principal Components Analysis revealed that increase in metatarsal length paired with decrease in humeral length (pPC2) provides a reliable indicator of bipedal locomotion ability. I found that the best fit to the data was an Ornstein-Uhlenbeck model with multiple optima: one for quadrupedal and another for bipedal species. I then found that in each lineage, the maximum value of pPC2 is correlated with time since bipedal locomotion first evolved. In fact, when aligned by acquisition of bipedal locomotion, the pattern of trait variation is nearly identical across all three groups. I conclude that, instead of convergence being a binary designation with a specific threshold similarity, the bipedal desert rodents represent different timepoints on convergent trajectories of adaptive evolution in response to desert environments. 

@inproceedings{moore2025convergent,
  title={Convergent Trajectories In the Evolution of Bipedality in Desert Rodents},
  author={Moore, T},
  booktitle={JOURNAL OF MORPHOLOGY},
  volume={286},
  year={2025},
  organization={WILEY 111 RIVER ST, HOBOKEN 07030-5774, NJ USA}
}