Rachel H. Dunn

Ecological divergence and talar morphology in gorillas.

Gorillas occupy a variety of habitats from the west coast to eastern central Africa. These habitats differ considerably in altitude, which has a pronounced effect on forest ecology. Although all gorillas are obligate terrestrial knuckle-walking quadrupeds, those that live in lowland habitats eat fruits and climb more often than do those living in highland habitats. Here we test the hypothesis that gorilla talus morphology falls along a morphocline that tracks locomotor function related to a more inverted or everted foot set. This proposed morphocline predicts that gorillas living in lowland habitats may have a talocrural joint configured to facilitate a more medially oriented foot during climbing, suggesting that they may be more adaptively committed to arboreality than gorillas living in highland habitats. To quantify the relative set of the foot in gorillas, we chose two three-dimensional measurements of the talocrural joint: mediolateral curvature of the trochlea and relative surface area of the lateral malleolus. Our results show that, in comparison to their eastern counterparts, western gorillas have talar features that reflect a more medially directed sole of the foot. This morphology likely facilitates foot placement in a wider range of positions and minimization of shearing stresses across the joint when the foot is loaded on more curved or vertically oriented substrates as occurs during climbing and other arboreal behaviors. In contrast, eastern gorilla talar morphology is consistent with habitual placement of the foot with the sole directed more inferiorly, suggesting more effective loading during plantigrade push-off on terrestrial substrates.

Skeletal morphology and locomotor behavior of Pseudotomus eugenei (Rodentia, Paramyinae) from the Uinta Formation, Utah

Abstract A new skeleton of Pseudotomus eugenei is described and compared to extant large bodied rodents and those fossil manitshines represented by postcranial material (Pseudotomus robustus, Pseudotomus petersoni, and Manitshatanka). The postcranial skeleton of P. eugenei is unspecialized in terms of individual joint function as well as in overall proportions. The forelimb is heavily muscled with a generalized shoulder but with some distinctive features of the elbow and manus. These include an extremely broad distal humerus, long olecranon process, short proximal and middle phalanges and long, uncompressed ungual phalanges. The hind limb of P. eugenei is also generalized, but departs from those of earlier manitshines in the deeper patellar groove and femoral condyles, and in the size reduction of the peripheral metatarsals, suggesting a stronger commitment to terrestrial life. A quantitative analysis of limb proportions indicates that P. eugenei and the other manitshines generally resemble terrestrial rather than arboreal rodents. This is especially evident in the shape of the radial head, and in the shape and relatively greater lengths of the olecranon process, phalanges and metapodials. These features of the forelimb together with the long and uncompressed ungual phalanges of the manus suggest that when P. eugenei diverges from other manitshines, it is in a semi-fossorial direction. Here it is reconstructed as a generalized terrestrial rodent with fossorial tendencies.

Additional postcranial remains of omomyid primates from the Uinta Formation, Utah and implications for the locomotor behavior of large-bodied omomyids

Most omomyids are relatively small bodied (e.g. <500g), but beginning in the middle Eocene, some omomyids began to grow larger. The largest omomyids occur in the late middle Eocene during the Uintan NALMA, reaching an estimated body mass over 1kg. The hind limb skeleton of small omomyids is relatively well known, and is generally thought to show active arboreal quadrupedal and leaping adaptations. New postcranial specimens of previously unknown elements from the larger Uintan omomyids, Ourayia (two species), Chipetaia lamporea, and Mytonius hopsoni have recently been recovered from the Uinta Formation, Utah, and from the Mission Valley Formation, California, and they provide additional information concerning their locomotor behavior. The new specimens include several distal tibiae, partial calcanei, a complete talus and a proximal first metatarsal of Chipetaia; distal femora, distal tibiae, cuboids, and partial calcanei of Ourayia uintensis; a complete calcaneus of Ourayia sp.; and a partial calcaneus and talus of Mytonius. Metric analysis of these elements, together with qualitative observations of non-metric traits, indicate that Ourayia and Chipetaia show equal or greater development of traits associated with leaping behavior (including elongation of the calcaneus, navicular and cuboid) than do smaller omomyids from North America. The elements of Mytonius, although fragmentary, lack some leaping features that are well-developed in Ourayia and Chipetaia, suggesting that Mytonius may have relied more on arboreal quadrupedal locomotion than on leaping.

Skeletal Morphology of a New Genus of Eocene Insectivore (Mammalia, Erinaceomorpha) from Utah

Abstract A new genus and 2 new species of erinaceomorph insectivores from the Eocene of Utah are named and described. Both come from Member B of the Uinta Formation, which consists of terrestrially deposited rocks of Early Uintan age. The best specimen consists of dentaries, a few teeth, and several associated elements of the postcranial skeleton; additional dental and postcranial remains also have been recovered. Dentally, the new genus resembles the smaller erinaceomorphs known from earlier in the Rocky Mountain region of North America rather than the contemporary large ones from southern California, indicating that large body size and omnivory evolved independently in different regions of North America during the Eocene. The new genus is primitive in lacking many specializations of the ankle seen in extant erinaceids and other Eocene insectivores. The morphology of the forelimb suggests some digging behavior in having an expanded entepicondyle and the presence of distinct tubercles for insertion of the extensor carpi radialis on the bases of metacarpals II and III. The hind limb exhibits a mosaic of features typical of terrestrial runners, such as anteroposteriorly deep femoral condyles and a deep patellar groove, along with features seen in arboreal climbers, such as a medially and plantarly inflected calcaneal heel. We conclude that the new genus was terrestrial, perhaps moving rapidly over an uneven substrate such as a littered forest floor, but it could probably dig and climb as well.

Hemiacodon engardae, a new species of omomyid primate from the earliest Uintan Turtle Bluff Member of the Bridger Formation, southwestern Wyoming, USA

In this paper, we describe a new species of Hemiacodon known only from University of Colorado Museum Loc. 92189 (Donnas Locality) in the Turtle Bluff Member of the Bridger Formation, Green River Basin, southwestern Wyoming. Donnas locality has yielded a diverse mostly small-bodied mammalian assemblage of Bridgerian and first appearance Uintan mammalian taxa, as well as range-through taxa. Together with H. engardae sp. nov., the faunal assemblage from Donnas Locality and more recently discovered localities in the same stratigraphic interval provides the first conclusive paleontological evidence of an earliest Uintan age (Ui1A biochron) for the Turtle Bluff Member of the Bridger Formation. The new species is represented by a sample of 11 specimens consisting of well-preserved upper and lower premolars and lower molars. H. engardae is distinct from H. gracilis on the basis of overall larger size as well as a combination of features of the premolars and molars related to a greater development of shearing crests. This suggests that H. engardae may have incorporated more foliage into its diet than the Bridgerian species, H. gracilis.

Scaling of the corpus callosum in wild and domestic canids: Insights into the domesticated brain

All domesticated mammals exhibit marked reductions in overall brain size, however, it is unknown whether the corpus callosum (CC), an integral white matter fiber pathway for interhemispheric cortical communication, is affected by domestication differentially or strictly in coordination with changes in brain size. To answer this question, we used quantitative magnetic resonance imaging to compare the midsagittal cross‐sectional areas of the CC in 35 carnivore species, including eight wild canids and 13 domestic dogs. We segmented rostro‐caudal regions of interest for the CC and evaluated correlations with brain mass. The results of this study indicate that under the influence of domestication in canids, the CC scales to brain size in an allometric relationship that is similar to that of wild canids and other carnivores, with relatively high correlation coefficients observed for all regions, except the rostrum. These results indicate that architectural and energetic considerations are likely to tightly constrain variation in caudal components of the CC relative to overall brain size, however fibers passing through the rostrum, putatively connecting prefrontal cortex, are less constrained and therefore may contribute more toward species‐specific differences in connectivity. Given the species diversity of the Canidae and the resurgence of interest in the brain of the domestic dog, further studies aimed at characterizing the neural architecture in domesticated species is likely to provide new insights into the effects of domestication, or artificial selection, on the brain.

Multivariate Craniodental Allometry of Tarsiers

Evolutionary allometry describes size and shape differences across taxa matched for developmental stage (e.g., adulthood). Allometric studies can identify subtle differences among species, and therefore help researchers interested in small-bodied, cryptic species such as tarsiers. Recent taxonomic revision has emphasized size differences among three possible tarsier genera inhabiting different island regions: Sulawesi (genus: Tarsius), Borneo (genus: Cephalopachus), and the Philippines (genus: Carlito). We examined seven craniodental measures of 102 museum specimens of adult tarsiers representing these three regions. We found that the allometric patterns within groups do not predict the observable differences among groups. Crania of the largest-bodied genus, Cephalopachus, are characterized by relatively short skulls and small orbits, with wider palates and molars than predicted by allometric increase from the smaller-bodied Tarsius. Overall, we found tarsier skulls stay the same shape as they increase in size. This may reflect shared developmental and biomechanical adaptations across tarsier groups filling an extreme leaping, faunivorous niche with hypertrophied orbits and subtle dietary differences in prey selection. These shared adaptations of tarsiers may severely limit the range of body sizes in tarsiers and impose further constraints on cranial shape. Despite their deep divergence times in the Miocene, living tarsier groups are united by a common craniodental form across a limited size range. Adaptations to extreme niches might result in a hyperconservatism of the cranium. Future primate allometric studies should explore cranial variation in other taxa to determine how adaptations to specific niches affect the size and shape of the cranium.

Neuropil Distribution in the Anterior Cingulate and Occipital Cortex of Artiodactyls: NEUROPIL DISTRIBUTION IN ARTIODACTYLS

Relatively little neuroscience research has been focused on artiodactyls. Recent observations of complex social interactions in domestic and wild species suggest that analyses of artiodactyl brain anatomy would be of comparative value. In this study, we examined how the distribution of cortical neuropil space (a proxy for connectivity) varies across representative members of this diverse clade. Using image analysis techniques, we quantified the neuropil space in the anterior cingulate cortex (ACC) and the occipital (putative primary visual) cortex (OC) of 12 artiodactyl species from adult specimens. Additionally, we conducted a preliminary investigation of variation in ACC neuropil space in a developmental series of five white‐tailed deer (Odocoileus virginianus). Results indicate a consistent pattern of greater neuropil space in the ACC in comparison to the OC among all species, and a gradual increase in ACC neuropil space toward maturity in the white‐tailed deer. Given the taxa that have the greatest cortical neuropil space, we hypothesize that such enhanced connectivity might be needed to support behaviors such as group foraging and attentiveness to conspecifics. These results help advance a broader understanding of diversity in neural circuitry in artiodactyls and point to the need for more in‐depth comparisons of cortical neuron morphology and organization in this relatively understudied taxonomic group. Anat Rec, 301:1871–1881, 2018.

Evolution of early Eocene Palaeosinopa (Mammalia, Pantolestidae) in the Willwood Formation of the Bighorn Basin, Wyoming

Abstract. Species-level diversity and evolution of Palaeosinopa from the Willwood Formation of the Bighorn Basin is reassessed based on substantial new material from the Bighorn, Powder River, and Wind River basins. We recognize three species of Palaeosinopa in the Willwood Formation of the Bighorn Basin: P. lutreola, P. incerta, and P. veterrima. The late Wasatchian species P. didelphoides is not present in the Bighorn Basin. The Willwood species can be differentiated based only on size. P. veterrima is the most common and wide-ranging species and is the most variable in size and morphology: the stratigraphically lowest individuals are smaller, with narrower, more crestiform lower molars; whereas the highest are larger, with wider, more bunodont teeth. Although it could be argued that these represent distinct species, we demonstrate that this morphological evolution occurred as the gradual and mosaic accumulation of features, suggesting in situ anagenetic evolution. The two smaller species are present only low in the section (biochrons Wa0–Wa4) and show no discernable evolution in size or morphology. A new skeleton of Palaeosinopa veterrima from the Willwood Formation is described, and other new postcrania are reported. The skeleton is the oldest associated skeleton of Palaeosinopa known, yet it is remarkably similar to those of younger, more derived pantolestids, the primary disparities being minor differences in proportions of the innominate, femur, and tibia, and co-ossification of the distal tibia and fibula. Either P. incerta or P. lutreola was likely the ancestral population that gave rise to the other Wasatchian Palaeosinopa. Alternatively, P. veterrima may have migrated into the Bighorn Basin from the Powder River Basin.