Anatomical Record-Advances in Integrative Anatomy and Evolutionary Biology最新文献

Thescelosaurines are a group of early diverging, ornithischian dinosaurs notable for their conservative bauplans and mosaic of primitive features. Although abundant within the latest Cretaceous ecosystems of North America, their record is poor to absent in earlier assemblages, leaving a large gap in our understanding of their evolution, origins, and ecological roles. Here we report a new small bodied thescelosaurine—Fona herzogae gen. et sp. nov.—from the Mussentuchit Member of the Cedar Mountain Formation, Utah, USA. Fona herzogae is represented by multiple individuals, representing one of the most comprehensive skeletal assemblages of a small bodied, early diverging ornithischian described from North America to date. Phylogenetic analysis recovers Fona as the earliest member of Thescelosaurinae, minimally containing Oryctodromeus, and all three species of Thescelosaurus, revealing the clade was well-established in North America by as early as the Cenomanian, and distinct from, yet continental cohabitants with, their sister clade, Orodrominae. To date, orodromines and thescelosaurines have not been found together within a single North American ecosystem, suggesting different habitat preferences or competitive exclusion. Osteological observations reveal extensive intraspecific variation across cranial and postcranial elements, and a number of anatomical similarities with Oryctodromeus, suggesting a shared semi-fossorial lifestyle.

The mammalian inner ear contains the sensory organs responsible for balance (semicircular canals, utricle, and saccule) and hearing (cochlea). While these organs are functionally distinct, there exists a critical structural connection between the two: the ductus reuniens (DR). Despite its functional importance, comparative descriptions of DR morphology are limited, hindering our understanding of the evolutionary diversification of hearing and balance systems among mammals. Using virtual 3D models derived from micro-CT, we examine the morphology of the DR and its relationship to the bony labyrinth in humans compared to that in a commonly used animal model, the guinea pig. Anatomical reconstructions and univariate measurements were carried out in the software 3D Slicer. Data indicate similarities in DR morphology between humans and guinea pigs in terms of overall shape. However, there are considerable differences in relative DR length and width between humans and guinea pigs. Humans possess a relatively shorter and narrower DR but with wider openings to the saccule and cochlear duct. This results in a relatively more constricted DR lumen in humans which may differentially limit fluid transfer between the saccule and cochlea. Our results reveal previously hidden morphological diversity in the communication between the hearing and balance systems of the mammalian inner ear which may indicate alternative strategies for isolating the Organ of Corti from the peripheral vestibular system throughout mammalian evolution.

Headbutting is a combative behavior most popularly portrayed and exemplified in the extant bighorn sheep (Ovis canadensis). When behaviorally proposed in extinct taxa, these organisms are oft depicted Ovis-like as having used modified cranial structures to combatively slam into one another. The combative behavioral hypothesis of headbutting has a long and rich history in the vertebrate fossil literature (not just within Dinosauria), but the core of this behavioral hypothesis in fossil terrestrial vertebrates is associated with an enlarged osseous cranial dome-an osteological structure with essentially no current counterpart. One confounding issue found in the literature is that while the term "headbutting" sounds simplistic enough, little terminology has been used to describe this hypothesized behavior. And pertinent to this special issue, potential brain trauma and the merits of such proposed pugilism have been assessed largely from the potential deformation of the overlying osseous structure; despite the fact that extant taxa readily show that brain damage can and does occur without osteological compromise. Additionally, the extant taxa serving as the behavioral counterpart for comparison are critical, not only because of the combative behaviors and morphologies they display, but also the way they engage in such behavior. Sheep (Ovis), warthogs (Phacochoerus), and bison (Bison) all engage in various forms of "headbutting", but the cranial morphologies and the way each engages in combat is markedly different. To hypothesize that an extinct organism engaged in headbutting like an extant counterpart in theory implies specific striking:contacting surfaces, speed, velocity, and overall how that action was executed. This review examines the history and usage of the headbutting behavioral hypothesis in these dome-headed fossil taxa, their respective extant behavioral counterparts, and proposes a protocol for specific behavioral terms relating to headbutting to stem future confusion. We also discuss the disparate morphology of combative cranial structures in the fossil record, and the implications of headbutting-induced brain injury in extinct taxa. Finally, we conclude with some potential implications for artistic reconstructions of fossil taxa regarding this behavioral repertoire.

The rough teiid or water cork lizard (Echinosaura horrida) is a small reptile from Colombia and Ecuador placed in a genus that contains eight species and well-known phylogenetic relationships. Here we provide a detailed description and illustrations, bone by bone, of its skull, while we discussed its intraspecific variation by comparing high-resolution computed tomography data from two specimens and the variation within the genus by including previously published data from Echinosaura fischerorum. This allowed to propose putative diagnostic character states for Echinosaura horrida and synapomorphies for Echinosaura. In addition, our discussion includes broader comparisons of new character transformations of the jugal, vomer, orbitosphenoid, and hyoid. These characters are important for diagnosing clades at different levels of the Gymnophthalmoidea phylogeny.

Humboldt's woolly monkey (Lagothrix lagortricha) is a ceboid primate that more frequently engages in plantigrade quadrupedalism (~89%) but is, like most other members of the subfamily Atelinae, capable of suspensory postures and “tail assisted” brachiation. That taxon's decreased reliance on suspension is reflected in the skeletal anatomy of the upper limb which is less derived relative to more frequently suspensory atelines (Ateles, Brachyteles) but is in many ways (i.e., phalangeal curvature, enlarged joint surfaces, elongated diaphyses) intermediate between highly suspensory and quadrupedal anthropoids. Although it has been suggested that muscle may have morphogenetic primacy with respect to bone this has not been explicitly tested. The present study employs analyses of Lagothrix upper limb muscle fiber length, relative physiological cross-sectional area and relative muscle mass to test whether muscular adaptations for suspensory postures and locomotion in Lagothrix precede adaptive refinements in the skeletal tissues or appear more gradually in conjunction with related skeletal adaptations. Results demonstrate that Lagothrix upper limb musculature is most like committed quadrupeds but that limited aspects of the relative distribution of segmental muscle mass may approach suspensory hylobatids consistent with only a limited adaptive response in musculature prior to bone. Results specific to the shoulder were inconclusive owing to under-representation of quadrupedal shoulder musculature and future work should be focused more specifically on the adaptive and functional morphology of the muscular anatomy and microstructure of the scapulothoracic joint complex.

It is presumed that the unusual central location of mesencephalic trigeminal neurons is a specialization that allows them to receive synaptic input. However, relatively few synaptic terminals were observed on the somata of mesencephalic trigeminal neurons in macaque monkeys via electron microscopy. This leaves the question of dendritic synaptic terminals open. Unlike the pseudounipolar neurons found in the trigeminal ganglion, some mesencephalic trigeminal neurons have been reported to be multipolar cells exhibiting a number of dendritic processes in non-primate species. To examine whether this morphological feature was also present in macaque monkeys, we retrogradely filled these cells with biotinylated dextran amine by injecting it into the trigeminal nerve entry zone. A portion of the mesencephalic trigeminal neurons exhibited short, poorly branched, dendritic processes. They also exhibited very fine, short processes believed to be somatic spines. Thus, primate trigeminal mesencephalic neurons appear to have specializations aimed at increasing the membrane surface area available for synaptic input.

The existence of a previously unrecognized subarachnoid lymphatic-like membrane (SLYM) was reported in a recent study. SLYM is described as an intermediate leptomeningeal layer between the arachnoid and pia mater in mouse and human brains, which divides the subarachnoid space (SAS) into two functional compartments. Being a macroscopic structure, having missed detection in previous studies is surprising. We systematically reviewed the published reports in animals and humans to explore whether prior descriptions of this meningeal layer were reported in some way. A comprehensive search was conducted in PubMed/Medline, EMBASE, Google Scholar, Science Direct, and Web of Science databases using combinations of MeSH terms and keywords with Boolean operators from inception until 31 December 2023. We found at least eight studies that provided structural evidence of an intermediate leptomeningeal layer in the brain or spinal cord. However, unequivocal descriptions for this layer all along the central nervous system were scarce. Obscure names like the epipial, intermediate meningeal, outer pial layers, or intermediate lamella were used to describe it. Its microscopic/ultrastructural details closely resemble the recently reported SLYM. We further examined the counterarguments in current literature that are skeptical of the existence of this layer. The potential physiological and clinical implications of this new meningeal layer are significant, underscoring the urgent need for further exploration of its structural and functional details.

Batoids (rays and skates) are cartilaginous fishes whose jaws are not articulated directly to the neurocranium. The only point of contact between them are the hyomandibular cartilages, resulting in a unique mandibular suspension called euhyostyly. Due to this decoupling of the jaws from the skull, muscles play an essential role in modulating mandibular movements during the feeding process, especially during mandibular protrusion. The main objectives of our study were: (1) to examine the mandibular musculature of eight batoid species from different orders in the Batoidea and (2) establish a standardized musclulature terminology for future comparative myological studies in batoids. For each muscle bundle, the general characteristics of each cranial muscle were described and their origin and insertions were identified. The number of muscle bundles differed intraspecifically. On the dorsal surface, we reported the first evidence of the presence of the precranial muscle (PCM) in U. halleri, as well as the ethmoideo-parethmoidalis muscle (ETM) in R. velezi, P. glaugostigma and Z. exasperata; in addition, the insertion of the spiracularis muscle (SP) extended to the ventral surface of the oropharyngeal tract in myliobatiforms. On the ventral surface of the head, both N. entemedor and M. californica exhibited additional muscles in the mandibular area. These muscles were renamed as part of the standardization of mandibular terminology: the depressor mandibularis minor (DMM) in N. entemedor and the adductor mandibulae profundus (AMP) in M. californica. The standardization of terminology is essential for futures studies of the mandibular apparatus in batoids, to facilitate the morphological description of muscles in species without anatomical accounts and for continuity in broader comparative analyses.

A new specimen of Haplocanthosaurus is described based on bones excavated from the Late Jurassic Dry Mesa Dinosaur Quarry near Delta, Colorado. The specimen consists of seven dorsal vertebrae and a right tibia and is identified as Haplocanthosaurus based on the dorsally angled transverse processes, tall neural arch peduncles, low parapophyses relative to the diapophyses in the posterior dorsal vertebrae, and the robustness of the tibia combined with a greatly expanded distal articular surface. The discovery adds to our understanding of the biostratigraphy of Haplocanthosaurus, showing this genus is definitively present in the Brushy Basin Member of the Morrison Formation, and making this individual the geologically youngest Haplocanthosaurus specimen on the Colorado Plateau. The identification of this genus adds to the known diversity of sauropods at Dry Mesa Dinosaur Quarry (DMDQ), which is at least six distinct genera, making DMDQ the most diverse single locality of sauropods in the Morrison Formation and the world.

The morphological evolution of the appendicular skeleton may reflect the selective pressures specific to different environments, phylogenetic inheritance, or allometry. Covariation in bone shapes enhances morphological integration in response to ecological specializations. In contrast to previous multivariate studies using classical linear morphometry, we use a geometric morphometric approach to explore the morphological diversity of long bones and examine relationships between ecological categories and morphological characters in a species-rich and ecomorphologically diverse group of rodents. We examined the humerus, ulna, femur, and tibiofibula of 19 sigmodontine species with different locomotor types (ambulatory, quadrupedal-saltatorial, natatorial, semifossorial and scansorial) to investigate the influence of locomotor type and phylogeny on limb bone shape and morphological integration of the appendicular skeleton. This study represents the most detailed examination of the morphological diversity of long bones in sigmodontines, employing geometric morphometrics within an ecomorphological framework. Our results indicate that functional demands and evolutionary history jointly influence the shape of forelimb and hindlimb bones. The main variation in bone shape is associated with a slenderness-robustness gradient observed across all ecological categories. Quadrupedal-saltatorial species, with their need for agility, possess slender and elongated limbs, while natatorial and semifossorial species exhibit shorter and more robust bone shapes, suited for their respective environments. This gradient also influences bone covariation within limbs, demonstrating interconnectedness between elements. We found functional covariation between the ulna-tibiofibula and humerus-tibiofibula, likely important for propulsion, and anatomical covariation between the humerus-ulna and femur-tibiofibula, potentially reflecting overall limb structure. This study demonstrates that the versatile morphology of long bones in sigmodontines plays a critical role in their remarkable ecological and phylogenetic diversification.