Journal: Anatomical record (Hoboken, N.J. : 2007)
The charismatic and diverse ornithischian dinosaurs exhibited some of the most extreme examples of cranial anatomy, inspiring decades of investigation into their muscular anatomy. Current ornithischian jaw muscle reconstructions, although parsimonious, pose concerns of small adductor muscles and caudally-displaced insertions relative to mandibular proportions. Here, craniomandibular material of ornithischian genera spanning all subclades are reexamined for osteological correlates indicative of intracranial and oral soft tissues. M. adductor mandibulae externus (mAME) has traditionally been reconstructed as solely inserting along the caudal margin of the coronoid process for jaw closure. Here, a new mAME reconstruction is proposed in derived ornithischians, with the superficial-most mAME layer reconstructed as a rostrolabial expansion of muscle, exiting the cranium rostroventrally beneath a unique, laterally flaring jugal and inserting along the lateral surface of the coronoid process and its rostrally extending, shelf-like labial dentary ridge (LDR). Through previous dental microwear and morphological studies, ceratopsians, hadrosaurids, and ankylosaurs are known to have implemented a major palinal feeding component in their jaw motions, unlike other primarily basal ornithischians. This rostral fan-like extension of muscle in these derived clades would create a greater mandibular support system and mechanical advantage along the labial margin of the jaw, cradling the entire mandible while lifting it up into occlusion and retracting it. In hadrosaurids and ankylosaurs, this rostrolabially expanding muscle also acts in medial rotation of the dentaries about their long-axes. With these new reconstructions, the notion of a novel, unparsimonious “cheek” muscle is rejected, with further discussion of plausible buccal soft tissues. This article is protected by copyright. All rights reserved.
Here we describe an extremely large and relatively complete (roughly 65%) skeleton of Tyrannosaurus rex (RSM P2523.8). Multiple measurements (including those of the skull, hip, and limbs) show that RSM P2523.8 was a robust individual with an estimated body mass exceeding all other known T. rex specimens and representatives of all other gigantic terrestrial theropods. Histological sampling of the fibula confirms that RSM P2523.8 is skeletally mature. The prevalence of incompletely coossified elements contradicts previous assertions that such unfused elements can be taken as indicators of somatic immaturity. As an extreme example of both ontogenetic maturity and osteological robustness, RSM P2523.8 offers support for prior hypotheses that a sampling bias occurs throughout the Dinosauria, making it likely that most taxa grew to significantly greater size than current known specimens indicate. This article is protected by copyright. All rights reserved.
Extant baleen whales (Mysticeti) share a distinct suite of extreme and unique adaptations to perform bulk filter feeding, such as a long, arched skull and mandible and the complete loss of adult dentition in favor of baleen plates. However, mysticetes still develop tooth germs during ontogeny. In the fossil record, multiple groups document the transition from ancestral raptorial feeding to filter feeding. Fetal specimens give us an extraordinary opportunity to observe when and how this macroevolutionary transition occurs during gestation. We used iodine-enhanced and traditional CT scanning to visualize the internal anatomy of five fetuses of humpback whale representing the first two-thirds of gestation, and we combine these data with previously published reports to provide the first comprehensive qualitative description of the sequence of developmental changes that characterize the skull and dentition. We also employ quantitative methods based on 3D landmarks to investigate the shape changes in the fetuses in relation to a juvenile cranial morphology. We found similarities in the ossification patterns of the humpback and other cetaceans (dolphins), but there appear to be major differences when comparing them to terrestrial artiodactyls. As for the tooth germs, this developmental sequence confirms that the tooth-to-baleen transition occurs in the last one-third of gestation. Analysis of cranial shape development revealed a progressive elongation of the rostrum and a resulting posterior movement of the nasals relative to the braincase. Future work will involve acquisition of data from other species to complete our documentation of the teeth-to-baleen transition. This article is protected by copyright. All rights reserved.
The intromittent organs of most amniotes contain variable-volume hydrostatic skeletons that are stored in a flexible state and inflate with fluid before or during copulation. However, the penis in male crocodilians is notable because its shaft does not seem to change either its shape or bending stiffness as blood enters its vascular spaces before copulation. Here I report that crocodilians may have evolved a mechanism for penile shaft erection that does not require inflation and detumescence. Dissections of the cloaca in sexually mature male American alligators (Alligator mississippiensis) show that the cross section of the proximal shaft of the alligator penis contains dense collagenous tissues that do not significantly change shape when fluid is added to the central vascular space. The large amount of collagen in the wall and central space of the alligator penis stiffen the structure so it can be simply everted for copulation and rapidly retracted at its completion. Because no muscles insert directly onto the penis, eversion and retraction must be produced indirectly. My results suggest that the contraction of paired levator cloacae muscles around the anterior end of the cloaca rotates the penis out of the cloacal opening and strains the ligamentum rami that connect the base of the penis to the ischia. When the cloacal muscles relax, the elastic recoil of the ligamentum rami can return the penis to its original position inside the cloaca. Anat Rec, 296:488-494, 2013. © 2013 Wiley Periodicals, Inc.
The novel observation of a palatal retial organ in the bowhead whale (Balaena mysticetus) is reported, with characterization of its form and function. This bulbous ridge of highly vascularized tissue, here designated the corpus cavernosum maxillaris, runs along the center of the hard palate, expanding cranially to form two large lobes that terminate under the tip of the rostral palate, with another enlarged node at the caudal terminus. Gross anatomical and microscopic observation of tissue sections discloses a web-like internal mass with a large blood volume. Histological examination reveals large numbers of blood vessels and vascular as well as extravascular spaces resembling a blood-filled, erectile sponge. These spaces, as well as accompanying blood vessels, extend to the base of the epithelium. We contend that this organ provides a thermoregulatory adaptation by which bowhead whales (1) control heat loss by transferring internal, metabolically generated body heat to cold seawater and (2) protect the brain from hyperthermia. We postulate that this organ may play additional roles in baleen growth and in detecting prey, and that its ability to dissipate heat might maintain proper operating temperature for palatal mechanoreceptors or chemoreceptors to detect the presence and density of intraoral prey. Anat Rec, 2013. © 2013 Wiley Periodicals, Inc.
Modern crocodylians possess a derived sense of face touch, in which numerous trigeminal nerve-innervated dome pressure receptors speckle the face and mandible and sense mechanical stimuli. However, the morphological features of this system are not well known, and it remains unclear how the trigeminal system changes during ontogeny and how it scales with other cranial structures. Finally, when this system evolved within crocodyliforms remains a mystery. Thus, new morphological insights into the trigeminal system of extant crocodylians may offer new paleontological tools to investigate this evolutionary transformation. A cross-sectional study integrating histological, morphometric, and 3D imaging analyses was conducted to identify patterns in cranial nervous and bony structures of Alligator mississippiensis. Nine individuals from a broad size range were CT-scanned followed by histomorphometric sampling of mandibular and maxillary nerve divisions of the trigeminal nerve. Endocast volume, trigeminal fossa volume, and maxillomandibular foramen size were compared with axon counts from proximal and distal regions of the trigeminal nerves to identify scaling properties of the structures. The trigeminal fossa has a significant positive correlation with skull length and endocast volume. We also found that axon density is greater in smaller alligators and total axon count has a significant negative correlation with skull size. Six additional extant and fossil crocodyliforms were included in a supplementary scaling analysis, which found that size was not an accurate predictor of trigeminal anatomy. This suggests that phylogeny or somatosensory adaptations may be responsible for the variation in trigeminal ganglion and nerve size in crocodyliforms. Anat Rec, 00:000-000, 2013. © 2013 Wiley Periodicals, Inc.
Previous research has revealed significant size differences between human male and female carpal bones but it is unknown if there are significant shape differences as well. This study investigated sex-related shape variation and allometric patterns in five carpal bones that make up the radiocarpal and midcarpal joints in modern humans. We found that many aspects of carpal shape (76% of all variables quantified) were similar between males and females, despite variation in size. However, 10 of the shape ratios were significantly different between males and females, with at least one significant shape difference observed in each carpal bone. Within-sex standard major axis regressions (SMA) of the numerator (i.e., the linear variables) on the denominator (i.e., the geometric mean) for each significantly different shape ratio indicated that most linear variables scaled with positive allometry in both males and females, and that for eight of the shape ratios, sex-related shape variation is associated with statistically similar sex-specific scaling relationships. Only the length of the scaphoid body and the height of the lunate triquetrum facet showed a significantly higher SMA slope in females compared with males. These findings indicate that the significant differences in the majority of the shape ratios are a function of subtle (i.e., not statistically significant) scaling differences between males and females. There are a number of potential developmental, functional, and evolutionary factors that may cause sex-related shape differences in the human carpus. The results highlight the potential for subtle differences in scaling to result in functionally significant differences in shape. Anat Rec, 2013. © 2012 Wiley Periodicals, Inc.
The avian Herbst corpuscles are the equivalent of the Pacinian corpuscles in mammals, and detect vibration and the movement of joints and feathers. Therefore, they can be regarded as rapidly adapting low-threshold mechanoreceptors. In recent years, it has been establish that some ion channels are involved in mechanosensation and are present in both mechanosensory neurons and mechanoreceptors. Here we have used immunohistochemistry to localize some putative mechanoproteins in the Herbst corpuscles from the rictus of Columba livia. The proteins investigated were the subunits of the epithelial Na(+) channel (ENaC), the transient-receptor potential vanilloid 4 (TRPV4), and the acid-sensing ion channel 2 (ASIC2). Immunoreactivity for ENaC subunits was never found in Herbst corpuscles, while the axon expressed ASIC2 and TRPV4 immunoreactivity. Moreover, TRPV4 was also detected in the cell forming the inner core. The present results demonstrate for the first time the occurrence of mechanoproteins in avian low-threshold mechanoreceptors and provide further evidence for a possible role of the ion channels in mechanosensation. Anat Rec, 2012. © 2012 Wiley Periodicals, Inc.
This study concerns the morphological differentiation between double outlet right ventricle (DORV) and aortic dextroposition (AD) defects, namely tetralogy of Fallot and Eisenmenger anomaly. Indeed, despite the similar condition in terms of sequential ventriculo-arterial connections, DORV and AD are two distinct morphological entities. It is proposed that the borderline between these two groups of malformations is represented by the specific insertion of the infundibular septum into the left anterior cranial division of the septomarginal trabeculation (or septal band) occurring in ADs and lacking in DORV. Furthermore, the spiraliform versus straight parallel arrangement of the great arteries in the two groups of anomalies is emphasized as an additional and distinctive morphological feature. Emphasis is also given to the association of straight parallel great arteries conotruncal malformations, DORV and transposition of the great arteries, with the asplenia type of heterotaxy laterality defects. Within this context, the absence of subaortic ventricular septal defect and concomitantly of spiraliform great arteries in the asplenia group of heterotaxy anomalies, as detected by this study, further substantiates our belief of not mixing collectively the ADs with the DORV in clinico-pathological diagnosis. Anat Rec, 00:000-000, 2013. © 2013 Wiley Periodicals, Inc.
Fossils from the Jehol Group (Early Cretaceous, Liaoning Province, China) are integral to our understanding of Paraves, the clade of dinosaurs grouping dromaeosaurids, troodontids, and avialians, including living birds. However, many taxa are represented by specimens of unclear ontogenetic age. Without a more thorough understanding of ontogeny, evolutionary relationships and significance of character states within paravian dinosaurs may be obscured and our ability to infer their biology restricted. We describe a complete specimen of a new microraptorine dromaeosaur, Wulong bohaiensis gen. et sp. nov., from the geologically young Jiufotang Formation (Aptian) that helps solve this problem. Phylogenetic analysis recovers the specimen within a monophyletic Microraptorinae. Preserved in articulation on a single slab, the type specimen is small and exhibits osteological markers of immaturity identified in other archosaurs, such as bone texture and lack of fusion. To contextualize this signal, we histologically sampled the tibia, fibula, and humerus and compared them with new samples from the closely related and osteologically mature Sinornithosaurus. Histology shows both specimens to be young and still growing at death, indicating an age for the new dinosaur of about 1 year. The holotype possesses several feather types, including filamentous feathers, pennaceous primaries, and long rectrices, establishing that their growth preceded skeletal maturity and full adult size in some dromaeosaurids. Comparison of histology in the new taxon and Sinornithosaurus indicates that macroscopic signs of maturity developed after the first year, but before cessation of growth, demonstrating that nonhistological indicators of adulthood may be misleading when applied to dromaeosaurids. Anat Rec, 2020. © 2020 American Association for Anatomy.