It is unlikely that direct competition over food resources with rodents played a major role in the extinction of carpolestids and saxonellids, as members of these families were capable of consuming a range of foods that were not accessible to rodents. Although several plesiadapid species overlap with rodents in their range of DNE values, only three overlap in time. One of these (Plesiadapis cookei) may have been too large to be in direct competition with rodents, another (Plesiadapis dubius) has DNE values substantially different (higher) than those of rodents, whereas the third, Chiromyoides, has teeth of both a similar size and DNE value to those of Clarkforkian rodents. If dietary niche overlap with rodents played a direct role in the decline of plesiadapiforms, it can only have potentially done so for Chiromyoides.

No abstract

Dental topographic metrics provide quantitative, biologically meaningful data on the threedimensional (3D) form of teeth. In this study, three dental topographic metrics (Dirichlet normal energy (DNE), relief index (RFI), and orientation patch count rotated (OPCR)) are used to evaluate the presence of dietary niche overlap between North American plesiadapoid primates (Plesiadapidae, Carpolestidae, and Saxonellidae) and early rodents. Calculation of these metrics requires researchers to modify the 3D surface models of the teeth by cropping them to a region of interest and/or orienting them. The current study therefore also examines the error introduced by cropping and orientation, and evaluates the contribution of these metrics to the niche overlap hypothesis. Our results indicate that cropping creates significantly more variation in RFI than DNE. Furthermore, orientation is an even larger source of variation in the calculation of RFI than cropping. Orientation does not strongly influence OPCR values. However, none of these sources of error are significant enough to undermine the extent to which these metrics can speak to the niche overlap hypothesis. The DNE and RFI results suggest that carpolestids and saxonellids had very different molar morphologies from early rodents, and thus these groups were not adapted to consume the same resources. Some plesiadapids show similar levels of occlusal curvature, relief, and complexity to early rodents. The plesiadapid Chiromyoides, which has distinctively low cusps and weak shearing crest development, has molars that are the most rodent-like of all taxa compared. This suggests that Chiromyoides had a dietary niche that overlapped with early rodents and would have been the most likely to be competing over food resources. Results from the plesiadapoid-rodent dental topographic analysis highlight the utility of DNE for detecting more fine-scaled differences in occlusal surface morphology than OPCR, whereas RFI provided valuable data on the degree to which teeth were high crowned.

Our knowledge of muscle anatomy and physiology in vertebrates has increased dramatically over the last two-hundred years. Today, much is understood about how muscles contract and about the functional meaning of muscular variation at multiple scales. Progress in muscle anatomy has profited from the availability of broad comparative samples, advances in microscopy have permitted comparisons at increasingly finer scales, and progress in muscle physiology has profited from many carefully designed and executed experiments. Several avenues of future work are promising. In particular, muscle ontogeny (growth and development) is poorly understood for many vertebrate groups. We consider which types of advances in muscle functional morphology are of use to paleobiologists. These are only a modest subset for muscle anatomy and a very small subset for muscle physiology. The relationship between muscle and bone - spatially and mechanically-is critical to any future advances in "paleomyology". Anat Rec, 301:538-555, 2018. © 2018 Wiley Periodicals, Inc.

No abstract

Herein, we compared the developmental maturity of the cranium, limbs, and feeding apparatus in a perinatal common vampire bat relative to its mother. In addition, we introduce a method for combining two computed tomographic imaging techniques to three‐dimensionally reconstruct endocasts in poorly ossified crania. The Desmodus specimens were scanned using microcomputed tomography (microCT) and diffusible iodine‐based contrast‐enhanced CT to image bone and soft tissues. Muscles of the jaw and limbs, and the endocranial cavity were segmented using imaging software. Endocranial volume (ECV) of the perinatal Desmodus is 74% of adult ECV. The facial skeletal is less developed (e.g., palatal length 60% of adult length), but volumes for alveolar crypts/sockets of permanent teeth are nearly identical. The forelimb skeleton is uniformly less ossified than the distal hind limb, with no secondary centers ossified and an entirely cartilaginous carpus. All epiphyseal growth zones are active in the brachium and antebrachium, with the distal radius exhibiting the greatest number of proliferating chondrocytes arranged in columns. The hind limb skeleton is precociously ossified from the knee distally. The musculature of the fore limb, temporalis, and masseter muscles appear weakly developed (6–11% of the adult volume). In contrast, the leg and foot musculature is better developed (23–25% of adult volume), possibly enhancing the newborn's capability to grip the mother's fur. Desmodus is born relatively large, and our results suggest they are born neurally and dentally precocious, with generally underdeveloped limbs, especially the fore limb.

Diet has been suggested to play an important role in developmental pacing. Somatic growth and dental development are expected to be slow in frugivorous primates because of seasonal food shortages and greater competition for food with adults, whereas folivorous primates are expected to grow more rapidly because food resources are less limited and/or because folivores need to be better equipped than frugivorous weanlings to break down fibrous foods. Here, we present the first dataset on the mass and fiber architecture of jaw adductors in newborn strepsirrhines to assess differences in the developmental maturity of the chewing muscles. We predicted that chewing muscle maturity at birth would be more advanced in folivores, which tend to be more dentally precocious at birth, than in the more dentally‐delayed frugivores.The study sample includes four strepsirrhine species: Varecia rubra (frugivore), Eulemur macaco (frugivore/folivore), Lemur catta (frugivore/folivore), and Propithecus coquereli (folivore). The masticatory muscles of infant strepsirrhines were dissected to collect muscle mass and fiber length (FL) data, and to calculate physiological cross‐sectional area (PCSA). PCSA provides an estimate of muscle force. Muscle data were compared to a published dataset on adult strepsirrhines. Muscle mass, FL, and PCSA maturity were operationalized as a ratio (i.e., infant FL/adult FL).At birth, there is already considerable variation among species in the masticatory muscles. No muscle stands out as being more developmentally advanced than the others; notably, contrary to published hypotheses, temporalis is not always the most mature muscle at birth. However, in all cases FL was found to be closer to the adult condition in newborns than muscle mass or PCSA. This is likely because FL growth is so strongly tied to bony growth.Propithecus coquereli was found to have the most mature temporalis and masseter muscles (in terms of mass, FL, and PCSA), but not the most mature medial pterygoid muscles. Furthermore, Varecia rubra, the most frugivorous taxon in the sample, generally has more mature jaw adductors at birth than the more folivorous Lemur catta. In addition, jaw adductor muscle maturity at birth does not appear to be influenced by adult muscle mass, FL, or PCSA – for example, the taxon with the largest temporalis in adulthood does not necessarily have the largest temporalis at birth. These results suggest that chewing muscle maturity is not necessarily more advanced in folivores than in frugivores. Although Propithecus coquereli is more dentally advanced at birth than the other lemur taxa in this study, the jaw adductors do not all follow this pattern. Chewing muscles might be following different developmental and functional cues than are the teeth; for example, they are subject to geometric rearrangements of the cranium and mandible during development. Future work will explore these patterns in additional strepsirrhine species and match changes in muscle geometry to changes in skull geometry.Support or Funding InformationDuke Lemur Center Director's Fund Award to KA PrufrockThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The mammalian feeding system is made up of multiple components that influence facial variation, including the masticatory muscles, bony jaw apparatus, and teeth. However, it is not fully understood how the development of these components are coordinated and are impacted by life history and diet. Bats are the only mammals that continue to nurse until they are almost adult size, and often after they become volant. Common vampire bats (Desmodus rotundus) have a relatively prolonged juvenile period among bats, can nurse up to nine months, and later solely subsist off of blood. Feeding system maturity may therefore be delayed in bats, and particularly delayed in Desmodus, as a result of their lengthy juvenile period and liquid diet. In this study, we examine the developmental maturity of the cranium and feeding apparatus in the late fetus of a common vampire bat (Desmodus rotundus) relative to an adult (its mother). The heads of each specimen were microCT scanned twice. Conventional microCT was used to image mineralized tissues. Diffusible iodine‐based contrast‐enhanced CT (diceCT) imaging was used to image soft tissues. Cranial length and palate length measurements were acquired from unstained scans to evaluate size and jaw apparatus development. Masticatory muscles (e.g., medial pterygoid, zygomaticomandibularis) and permanent tooth crypt volumes were acquired from stained tissue scans to evaluate masticatory muscle and tooth development. Developmental maturity of these structures was assessed by calculating a percentage of the growth completed (i.e., [fetal muscle volume/adult muscle volume]*100). In the fetus, permanent tooth crypt volume is already comparable to the adult condition despite cranial length and palate length being <75% of adult size. Masticatory muscle volume maturity is highest in the lateral pterygoid muscle (~35%), whereas other masticatory muscles are far less developed (e.g., medial pterygoid volume maturity, ~20%; temporalis profundus volume maturity, ~20%; temporalis medius volume maturity, ~6%). These results reveal highly precocious permanent tooth development in Desmodus. Although this may facilitate transition to hematophagy, Desmodus do not fly until eight to ten weeks, so the precocious incisors may primarily aid the infant to grip its mother’s skin. Differential development of the masticatory muscles may also be influenced by the need for young bats to use their mouths to help anchor themselves to their mother early in life. This may explain the advanced maturity of the lateral pterygoid muscle, which would protrude the jaw and help to facilitate a more secure grip.