Cranial variation in allactagine jerboas (Allactaginae, Dipodidae, Rodentia): a geometric morphometric study

Allactaginae is a subfamily of dipodids consisting of four- and five-toed jerboas (Allactaga, Allactodipus, Orientallactaga, Pygeretmus, Scarturus) found in open habitats of Asia and North Africa. Recent molecular phylogenies have upended our understanding of this group’s systematics across taxonomic scales. Here, I used cranial geometric morphometrics to examine variation across 219 specimens of 14 allactagine species (Allactaga major, A. severtzovi, Orientallactaga balikunica, O. bullata, O. sibirica, Pygeretmus platyurus, P. pumilio, P. shitkovi, Scarturus aralychensis, S. euphraticus, S. hotsoni, S. indicus, S. tetradactylus, S. williamsi) in light of their revised taxonomy. Results showed no significant sexual size or shape dimorphism. Species significantly differed in cranial size and shape both overall and as species pairs. Species identity had a strong effect on both cranial size and shape. Only a small part of cranial shape variation was allometric, with no evidence of unique species allometries, and most specimens fit closely to the common allometric regression vector. Allactaga was the largest, followed by Orientallactaga, Scarturus, and finally Pygeretmus. Principal component 1 (PC1) separated O. bullata+O. balikunica+S. hotsoni (with inflated bullae along with reduced zygomatic arches and rostra) from A. major+A. severtzovi+O. sibirica (with converse patterns), while PC2 differentiated Orientallactaga (with enlarged cranial bases and rostra along with reduced zygomatic arches and foramina magna) from Scarturus+Pygeretmus (with the opposite patterns). Clustering based on the unweighted pair group method with arithmetic mean (UPGMA) contained the four genera, but S. hotsoni clustered with O. bullata+O. balikunica and O. sibirica clustered with A. major+A. severtzovi, likely due to convergence and allometry, respectively.