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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.

Traditional Dipodomys (sub)species identification uses geography, phenotype, and external/skull measurements. Such measurements are correlated with size and thus redundant. I assessed the value of scaled cranial shape, based on two‐dimensional landmarks (analyzed using geometric morphometric methods) in distinguishing Dipodomys taxa, and in summarizing their variation. My dataset includes 601 adult specimens from 20 species (49 operational taxonomic units ‐ OTUs) across 190 localities. Cranial shape was highly useful in classifying Dipodomys taxa without considering geography. The auditory bulla was the most variable region—taxa differed in its hypertrophy, accompanied by different degrees of nearby structure crowding. Cranial shape was weakly allometric, with no significant sexual dimorphism. Weak size dimorphism was detected. (Sub)specific taxonomy is not reflective of shape variation, as the number of subspecies per species is not associated with disparity. Shape had significant phylogenetic signal, but subspecies did not always cluster with conspecifics and species did not always cluster according to phylogenetic relationship/taxonomy. Shape variation was correlated with climate, and species differed in morphological disparity and degree of specialization, which may contribute to divergence in shape variation patterns from phylogeny. D. deserti was the most specialized species, diverging greatly from the genus mean; D. heermanni was the least specialized. This study provides new insights into morphological variation of North American keystone species, several of conservation interest, for example, D. heermanni berkeleyensis, D. h. dixoni, D. nitratoides brevinasus, and D. n. nitratoides. [ABSTRACT FROM AUTHOR]

Recent phylogenetic studies amended the taxonomy of three-toed jerboas (subfamily Dipodinae), including raising subspecies to full species. Here, we use geometric morphometrics to compare scaled-shape differences in dipodine crania while considering their revised taxonomy. We sampled Dipus deasyi , D. sagitta halli , D. s. sowerbyi , Jaculus blanfordi blanfordi , J. hirtipes , J. jaculus , J. loftusi , J. orientalis gerboa , J. o. mauritanicus , and Stylodipus andrewsi. Crania were not sexually dimorphic. Common allometry explained some of the shape variation, for example, reduced braincases in larger specimens. Most operational taxonomic unit pairs differed in both size and shape. Dipus and Stylodipus clustered together based on their cranial shape. Jaculus differed from the aforementioned genera by its larger tympanic bulla, broader braincase, larger infraorbital foramen, along with reduced molars and rostra. Jaculus orientalis differed from other Jaculus by its broader face versus reduced cranial vault. Jaculus blanfordi (subgenus Haltomys) resembles members of the subgenus Jaculus more than its consubgener (J. orientalis). Jaculus loftusi , previously considered a synonym of J. jaculus , clearly differed from the latter by its shorter rostrum, smaller infraorbital foramen, and more caudolaterally expanded tympanic bulla. Jaculus hirtipes , another recent synonym of J. jaculus , resembled J. blanfordi more in scaled cranial shape than it did J. jaculus. Dipus sagitta halli and D. s. sowerbyi were indistinguishable, but they clearly differed from D. deasyi (recently raised to full species) with the latter having a larger molar row, more inflated tympanic bulla, and shorter, slenderer rostrum. Ecological explanations for detected cranial shape differences are considered, including diet and habitat (particularly substrate). [ABSTRACT FROM AUTHOR]

Molecular phylogenies support the monophyly of Desmodilliscus braueri and Pachyuromys duprasi as a clade basally split from all other gerbillines. While this monophyly supports their placement in a single tribe (Desmodilliscini), no morphological synapomorphies exist among desmodilliscines. This study compares the scale-independent cranial shapes of these two species using geometric morphometrics to determine how they differ and/or converge. Tribal synapomorphies, should they exist, may appear as interspecifically invariable cranial regions. No such invariable cranial regions were detected. The two species significantly differed in cranial size and shape. A small part of shape variation was allometric, with a weak unique allometric effect. No sexual size nor shape dimorphism was found. The sister taxa greatly differed in almost all cranial features, with Pachyuromys (when compared to Desmodilliscus) having a larger-sized cranium, with a larger bulla and suprameatal triangle, a more posteriorly placed palatine foramina, and more anteriorly shifted (and reduced) rostral cranial structures, due to being crowded by the hypertrophied bulla. Cranial variation patterns are consistent with the literature. The extreme morphological divergence among these species is explained by the distant divergence time and ecological differences. Absence of cranial shape synapomorphies does not preclude synapomorphies in other craniodental morphological features (e.g., detailed morphology of the dentition and cranial foramina) or in other morphological structures, such as the postcranial skeleton. [ABSTRACT FROM AUTHOR]

Half of the ten Australian hopping mice (Notomys) species have become extinct following the European colonisation of Australia, and most of the rest are threatened. This makes the study of their present diversity paramount. Although recent molecular phylogenies improved our understanding of the relationships among the species, detailed interspecific phenotypic comparisons are still lacking. This is the aim of the present study. Geometric morphometric methods were used to compare the crania of all five extant species (N. alexis , N. aquillo , N. cervinus , N. fuscus , and N. mitchellii) along with the extinct N. longicaudatus. Although previous work (based on traditional approaches) find intragenerically conserved crania, the present study discovers significant differences in cranial size and shape among Notomys species, with the ventral view being more distinct than the dorsal view. There was no evidence of sexual dimorphism in cranial size nor shape, and only a weak allometric effect. Most aspects of cranial shape differed among the species. The extant species pair that differed in cranial shape the most was N. aquilo – N. cervinus , differing in the foramen magnum, tympanic bulla, orbit, incisive foramen, and rostrum, along with cranial width, potentially a consequence of N. cervinus ' phylogenetic position, and N. aquilo 's s ecological uniqueness. Half of the ten Australian hopping mice (Notomys) species have become extinct recently, and most of the rest are threatened, making the study of their present diversity paramount. Using geometric morphometric methods, I find significant differences in cranial size and shape among Notomys species. The species pair that differed the most (N. aquilo – N. cervinus), potentially caused by the N. cervinus being evolutionarily distant from other Notomys and N. aquilo having a more distinct ecology than the other sampled species. [ABSTRACT FROM AUTHOR]

Phodopus is the smallest cricetine genus, consisting of the dwarf hamsters (Phodopus sungorus , Phodopus campbelli , and Phodopus roborovskii) of arid central and east Asia. Persistent taxonomic issues in this genus include (1) whether P. sungorus and P. campbelli are con- or heterospecific and (2) whether P. roborovskii is con- or heterogeneric with the aforementioned species. To shed new light on these questions, the crania of Phodopus species were compared to each other using geometric morphometrics. Furthermore, to determine what cranial traits are shared by Phodopus crania, they were compared to the more 'typical' small hamster Nothocricetulus migratorius. The three Phodopus species significantly differed in cranial size and shape from each other and from N. migratorius. A large part of shape variation was allometric with only weak evidence for unique allometries. All four species lacked sexual dimorphism in cranial size and shape. As a genus, Phodopus is characterized by small-sized crania, that are broad, short, and with flaring zygomatic arches. They also have reduced rostra and enlarged foramina magna. P. roborovskii was the most distinct Phodopus , characterized by its smaller-sized cranium, with greater breadth, a rounder braincase and orbit, a shorter incisive foramen and rostrum, a larger foramen magnum, and smaller bulla with a longer eustachian tube. The crania of P. sungorus and P. campbelli are very similar, but they do diverge in relatively minor (statistically nonsignificant) features, such as cranial roundness, as well as the size of the molar row, bulla, zygomatic arch, and incisive foramen. Shape differences conformed to phylogenetic distance and with habitat differences. [ABSTRACT FROM AUTHOR]

Global desert rodent communities were examined for evidence of phylogenetic and morphological community structure. Using geographical distribution data of desert rodents (within 15 assemblages), a composite molecular phylogeny and a geometric morphometric dataset of skulls, the mean pairwise distance and mean nearest taxon distance were calculated for each assemblage and compared with null communities. Community structure metrics detected phylogenetic clumping in two out of the 15 desert assemblages, indicating that co-occurring rodents were more closely related than expected by chance. No other assemblages showed a significant phylogenetic structure. Skull morphology had different structuring patterns, but overall, most examined desert assemblages were not significantly structured in skull morphology. Similar overall lack of community structure patterns was observed at the regional scale in both the phylogenetic and the body mass datasets. We also directly tested the association between phylogenetic and morphological structure and found it to be significant. The association between phylogenetic distance and increased diversity that we observed might indicate that niche partitioning facilities coexistence in diverse assemblages. [ABSTRACT FROM AUTHOR]

Jirds (Meriones) are a mostly desert-adapted genus of gerbils, with a wide geographic range, through which it encounters various climatic conditions, which may influence their morphology. In this study, we quantified cranial morphometric variation both within and among seven jird species (M. meridianus, M. hurrianae, M. crassus, M. tristrami, M. persicus, M. libycus and M. vinogradovi), based on a two-dimensional landmark-based geometric morphometric analysis of 972 specimens, covering their entire geographic distribution. The aforementioned analysis was used to compare sexual dimorphism in size and shape within each species, as well as the relationship between size and shape (i.e. allometry) for each species. Despite greatly overlapping in morphospace (when examined visually), statistical analysis indicates significant differences in both size and shape among the seven examined jird species. UPGMA and CVA both show two main species clusters. Deformation grids indicate that these two clusters differ mostly in the relative size of the tympanic bulla, along with differences in the extent of nasal elongation, and the broadness of the zygomatic arch. Allometric changes in shape were analyzed in all species that show an allometric relationship. Sexual dimorphism in shape and size was detected in only three of the seven jird species. A visual inspection of the data indicates high overlap in shape space, and that male skulls are significantly larger than female skulls. When specimens were divided by sex, we found significant allometry in six of the seven species (for both sexes). A factorial multivariate analysis of covariance (MANCOVA) indicated that even when taking size variation into account, the residual shape variation was also significantly different among the sexes of the examined species. The outcome of this study confirms the presence of cranial variation in the examined jirds, and that the patterns of sexual dimorphism and allometry vary considerably among jird species. [ABSTRACT FROM AUTHOR]

The taxonomy of Gerbillus, the most speciose gerbil genus, is highly debated. Of particular contention is the relationship of Dipodillus to Gerbillus; some consider it to be a closely related genus, while others synonymize it with Gerbillus—either with or without recognizing it as a subgenus. The main objective of this study is to test the validity of common taxonomic groupings within the Gerbillus-Dipodillus species complex, which was achieved by using geometric morphometrics to examine cranial and mandibular variation in 34 out of the 52 Gerbillus-Dipodillus species. Craniomandibular size and shape were highly correlated, indicating strong allometric patterns in shape variation. The common taxonomic groups were significantly different in craniomandibular size and shape, yet they did overlap considerably in morphospace. A notable exception was the extreme divergence of Monodia (G. mauritaniae) from all other species in the occlusal view of the mandible. Morphospace overlap is likely a consequence of both phylogenetic history and environmental adaptation. Only the ventral cranium was associated with climate, particularly in areas related to resource acquisition. Geographic distance was not significantly associated with craniomandibular morphometric distance, and the groups overlapped greatly in their geographic range. Cranial and mandibular regions differed in discrimination power—the ventral cranium had among the highest, while the dorsal cranium and the occlusal mandible had the lowest. Craniomandibular regions varied in association with climate, phylogeny, and size—previous studies suggest this difference may be a consequence of different genetic controls for shape variation. [ABSTRACT FROM AUTHOR]