Anatomical Record最新文献

Many fish use a set of pharyngeal jaws in their throat to aid in prey capture and processing, particularly of large or complex prey. In this study-combining dissection, CT scanning, histology, and performance testing-we demonstrate a novel use of pharyngeal teeth in the ocean sunfish (Mola mola), a species for which pharyngeal jaw anatomy had not been described. We show that sunfish possesses only dorsal pharyngeal jaws where, in contrast to their beaklike oral teeth, teeth are recurved spikes, arranged in three loosely connected rows. Fang-like pharyngeal teeth were tightly socketed in the skeletal tissue, with shorter, incompletely-formed teeth erupting between, suggesting tooth replacement. Trichrome staining revealed teeth anchored into their sockets via a combination of collagen bundles originating from the jaw connective tissue and mineralized trabeculae extending from the teeth bases. In resting position, teeth are nearly covered by soft tissue; however, manipulation of a straplike muscle, running transversely on the dorsal jaw face, everted teeth like a cat's claws. Adult sunfish suction feed almost exclusively on gelatinous prey (e.g., jellyfish) and have been observed to jet water during feeding and other activities; flume experiments simulating jetting behavior demonstrated adult teeth caught simulated gelatinous prey with 70%-100% success, with the teeth immobile in their sockets, even at 50x the jetting force, demonstrating high safety factor. We propose that sunfish pharyngeal teeth function as an efficient retention cage for mechanically challenging prey, a curious evolutionary convergence with the throat spikes of divergent taxa that employ spitting and jetting.

We provide an ontogenetically-based comparative description of mandibular remains from Last Interglacial deposits (MIS 5e) at Baume Moula-Guercy and examine their affinities to European and Middle Eastern Middle-to-Late Pleistocene (≈MIS 14-MIS 1) Homo. Description of the M-G2-419 right partial mandibular corpus with M_1-3 (15-16.0 years ±0.5 years) and mandibular fragments M-F4-77 and M-S-TNN1 is with reference to original fossils, casts, CT scans, literature descriptions, and virtual reconstructions. Our comparative sample is ontogenetically based and divided into a Preneanderthal-Neanderthal group and a Homo sapiens group. These groups are subdivided into (1) Preneanderthals (≈MIS 14-9), Early Neanderthals (MIS 7-5e), and Late Neanderthals (MIS 5d-3), and (2) Middle (MIS 5) and Upper (MIS 3-Pre-MIS 1) Paleolithic and recent H. sapiens. Standard techniques were employed for developmental age and sex determinations and measurements. The M-G2-419 mandible possesses corpus features that link it most closely with the Sima de los Huesos Preneanderthal and Early Neanderthal groups. These include mental foramen position, number, and height on the corpus, anterior marginal tubercle position, and mylohyoid line orientation. Metrically, the M-G2-419 mandibular corpus is small relative to adults in all groups, but the thickness/height relationship is like the adult condition. The thickness of the corpus is more like Neanderthal children than adolescents. Molar crown features suggest affinities with the Preneanderthal-Neanderthal group. The Moula-Guercy mandibles possess a combination of Neanderthal-associated features that provides insights into MIS 7-5e paleodeme variation and the timing of appearance of MIS 5d-3 Neanderthal facial features.

Long bone ecomorphology has proven effective for paleohabitat reconstructions across a wide range of mammalian clades. Still, there is no comprehensive framework to allow interpretation of long bone morphological variation within and between different monophyletic groups. Here, we investigated the use of humerus morphometry to classify living members of the orders Carnivora and ungulates based on their preferred habitats. Using geometric morphometrics, we extracted three different kinds of humerus shape data describing interspecific variation with and without accounting for evolutionary allometry and phylogenetic signal. The traditional a priori categorization of species in open, mixed, and closed habitats was employed in combination with selected subsets of shape variables to identify the best-predictive models for habitat adaptation. These were identified based on the statistical performance of phylogenetic and non-phylogenetic discriminant analyses and then applied to predict habitats on a subsample of fossil species. Size-free shape data combined with phylogenetic discriminant analyses showed the highest rate of accuracy in habitat classification for a combined sample of carnivorans and ungulates. Conversely, when the two groups were investigated separately, traditional shape data analyzed with phylogenetic discriminant function analyses provided models with the greatest predictive power. By combining carnivorans and ungulates within the same methodological framework we identified common adaptive features in closed habitat-adapted species that show compressed epiphyses, while open habitat-adapted species have expanded epiphyses. These morphologies evolved to allow significant degree of direction switches during locomotion in closed habitats compared to open habitat-adapted species whose forelimb joints evolved to stabilize articulations for increasing speed.

Caudate nucleus (CN) neurons in camels and humans were examined using modified Golgi impregnation methods. Neurons were classified based on soma morphology, dendritic characteristics, and spine distribution. Three primary neuron types were identified in both species: rich-spiny (Type I), sparsely-spiny (Type II), and aspiny (Type III), each comprising subtypes with specific features. Comparative analysis revealed significant differences in soma size, dendritic morphology, and spine distribution between camels and humans. The study contributes to our understanding of structural diversity in CN neurons and provides insights into evolutionary neural adaptations.

Frontal size variation is comparatively poorly sampled among sub-Saharan African populations. This study assessed frontal sinus size in a sample of Khoe-San skeletal remains from South African Later Stone Age contexts. Volumes were determined from CT scans of 102 adult crania; individual sex could be estimated in 82 cases. Sinus volume is not sexually dimorphic in this sample. The lack of frontal sinus aplasia is concordant with the low incidences recorded for other sub-Saharan African and most other global populations save those that inhabit high latitudes. There is considerable variation in frontal sinus size among global populations, and the Khoe-San possess among the smallest. The Khoe-San have rather diminutive sinuses compared to sub-Saharan Bantu-speaking populations but resemble a northern African (Sudanese) population. Genetic studies indicate the earliest population divergence within Homo sapiens to have been between the Khoe-San and all other living groups, and that this likely occurred in Africa during the span of Marine Isotope Stages 8-6. There is scant information on frontal sinus development among Late Quaternary African fossils that are likely either closely related or attributable to Homo sapiens. Among these, the MIS 3 cranium from Hofmeyr, South Africa, exhibits distinct Khoe-San cranial affinities and despite its large size has a very small frontal sinus. This raises the possibility that the small frontal sinuses of the Holocene South African Khoe-San might be a feature retained from an earlier MIS 3 population.

Turbinals are key bony elements of the mammalian nasal cavity, involved in heat and moisture conservation as well as olfaction. While turbinals are well known in some groups, their diversity is poorly understood at the scale of placental mammals, which span 21 orders. Here, we investigated the turbinal bones and associated lamellae for one representative of each extant order of placental mammals. We segmented and isolated each independent turbinal and lamella and found an important diversity of variation in the number of turbinals, as well as their size, and shape. We found that the turbinal count varies widely, from zero in the La Plata dolphin, (Pontoporia blainvillei) to about 110 in the African bush elephant (Loxodonta africana). Multiple turbinal losses and additional gains took place along the phylogeny of placental mammals. Some changes are clearly attributed to ecological adaptation, while others are probably related to phylogenetic inertia. In addition, this work highlights the problem of turbinal nomenclature in some placental orders with numerous and highly complex turbinals, for which homologies are extremely difficult to resolve. Therefore, this work underscores the importance of developmental studies to better clarify turbinal homology and nomenclature and provides a standardized comparative framework for further research.

African wild dogs (Lycaon pictus) are unique among canids in their specialized hunting strategies and social organization. Unlike other, more omnivorous canids, L. pictus is a hypercarnivore that consumes almost exclusively meat, particularly prey larger than its body size, which it hunts through cooperative, exhaustive predation tactics. Its bite force is also among the highest reported for carnivorans. Here, we dissected an adult male L. pictus specimen and conducted diffusion iodine contrast-enhanced computed tomography (diceCT) scans to evaluate and describe its masticatory and oral cavity musculature. Muscles of mastication in L. pictus are separated by deep layers of thick intermuscular fascia and deep insertions. The superficial surface of m. masseter is entirely covered by an extremely thick masseteric fascia. Deep to m. masseter pars reflexa and superficialis are additional bellies, m. masseter pars profunda and zygomaticomandibularis. Musculus temporalis in L. pictus, divides into suprazygomatic, superficial, and deep bellies separated by a deep layer of thick intermuscular fascia, and it inserts along the entire rostral margin of the mandibular ramus. Musculus digastricus appears to comprise a single, large fusiform belly which appears to receive its innervation exclusively from CN V3 (nervus mandibularis, division of nervus trigeminus). Musculus pterygoideus medialis and lateralis are each composed of a single, deep belly. However, despite its great bite force, the jaw adductor muscle mass in L. pictus is not increased for its body size over other canid taxa. This finding suggests there are other architectural adaptations to hypercarnivory beyond increased muscle volume (e.g., pennation angle, greater strength, optimization of lever arms for mechanical advantage).

Cardiac regeneration is a natural phenomenon that occurs in many species outside of humans. The goldfish (Carassius auratus) is an understudied model of cardiac wound response, despite its ubiquity as pets as well as its relationship to the better-studied zebrafish. In this study, we examined the response of the goldfish heart to a resection injury. We found that by 70 days post-injury, goldfish scarlessly heal cardiac wounds under a certain size, with local cardiomyocyte proliferation driving the restoration of the myocardial layer. We also found the upregulation of extracellular matrix components related to cardiac regeneration in the injury site. This upregulation correlated with the level of cardiomyocyte proliferation occurring in the injury site, indicating an association between the two that warrants further exploration.

The potential connection between trends of within species variation, such as those of allometric change in morphology, and phylogenetic divergence has been a central topic in evolutionary biology for more than a century, including in the context of human evolution. In this study, I focus on size-related shape change in craniofacial proportions using a sample of more than 3200 adult Old World monkeys belonging to 78 species, of which 2942 specimens of 51 species are selected for the analysis. Using geometric morphometrics, I assess whether the divergence in the direction of static allometries increases in relation to phyletic differences. Because both small samples and taxonomic sampling may bias the results, I explore the sensitivity of the main analyses to the inclusion of more or less taxa depending on the choice of a threshold for the minimum sample size of a species. To better understand the impact of sampling error, I also use randomized subsampling experiments in the largest species samples. The study shows that static allometries vary broadly in directions without any evident phylogenetic signal. This variation is much larger than previously found in ontogenetic trajectories of Old World monkeys, but the conclusion of no congruence with phylogenetic divergence is the same. Yet, the effect of sampling error clearly contributes to inaccuracies and tends to magnify the differences in allometric change. Thus, morphometric research at the boundary between micro- and macro-evolution in primates, and more generally in mammals, critically needs very large and representative samples. Besides sampling error, I suggest other non-mutually exclusive explanations for the lack of correspondence between allometric and phylogenetic divergence in Old World monkeys, and also discuss why directions might be more variable in static compared to ontogenetic trajectories. Even if allometric variation may be a poor source of information in relation to phylogeny, the evolution of allometry is a fascinating subject and the study of size-related shape changes remains a fundamental piece of the puzzle to understand morphological variation within and between species in primates and other animals.

Masticatory gape and bite force are important behavioral and ecological variables. While much has been written about the highly derived masticatory anatomy of Smilodon fatalis, there remains a great deal of debate about their masticatory behaviors. To that end, we establish osteological proxies for masticatory adductor fascicle length (FL) based on extant felids and apply these along with previously validated techniques to S. fatalis to provide estimates of fascicle lengths, maximum osteological gapes, and bite force. While the best correlated FL proxies in extant felids do not predict particularly long fascicles, these proxies may be of value for less morphologically distinct felids. A slightly less well correlated proxy predicts a temporalis FL 15% longer than that of Panthera tigris. While angular maximum bony gape is significantly larger in S. fatalis than it is in extant felids, linear gape at the canine tip and carnassial notch were not significantly different from those of extant felids. Finally, we produce anatomical bite force estimates of 1283.74 N at the canine and 4671.41 N at the carnassial, which are similar in magnitude to estimates not of the largest felids but of the much smaller P. onca, with S. fatalis producing slightly less force at the canines and more at the carnassials. These estimates align with previous predictions that S. fatalis may have killed large prey with canine shearing bites produced, in part, by force contributions of the postcranial muscles.