Anat Rec Research Articles

Isolation and Characterization of Mammalian Otic Progenitor Cells that Can Differentiate into Both Sensory Epithelial and Neuronal Cell Lineages.

The mammalian inner ear mediates hearing and balance and during development generates both cochleo-vestibular ganglion neurons and sensory epithelial receptor cells, that is, hair cells and support cells. Cell marking experiments have shown that both hair cells and support cells can originate from a common progenitor. Here, we demonstrate the lineage potential of individual otic epithelial cell clones using three cell lines established by a combination of limiting dilution and gene-marking techniques from an embryonic day 12 (E12) rat otocyst. Cell-type specific marker analyses of these clonal lines under proliferation and differentiation culture conditions demonstrate that during differentiation immature cell markers (Nanog and Nestin) were downregulated and hair cell (Myosin VIIa and Math1), support cell (p27Kip1 and cytokeratin) and neuronal cell (NF-H and NeuroD) markers were upregulated. Our results suggest that the otic epithelium of the E12 mammalian inner ear possess multipotent progenitor cells able to generate cell types of both sensory epithelial and neural cell lineages when cultured under a differentiation culture condition. Understanding the molecular mechanisms of proliferation and differentiation of multipotent otic progenitor cells may provide insights that could contribute to the development of a novel cell therapy with a potential to initiate or stimulate the sensorineural repair of damaged inner ear sensory receptors. Anat Rec, 303:451-460, 2020. © 2019 American Association for Anatomy.

A Regenerative Medicine Approach to the Treatment of Hearing, Balance, and Olfactory Disorders: What Is in the Future for Otolaryngology?

Regenerative medicine is being applied to many fields of medicine and is now starting to be considered and developed for application to treat hearing, balance, olfaction, and voice disorders. This special issue of the Anatomical Record with a series of over 20 papers covers many aspects of gene and stem cell therapies as they are developed for clinical applications in both in vitro and in vivo laboratory studies. These studies cover a wide range of approaches from gene editing in zebrafish with the latest technology (i.e., CRISPR/Cas9) to the isolation of human inner ear progenitor cells, to tracking transplanted human umbilical cord stem cells in mini pigs, to the in vitro building of graft tissues to repair tracheal defects with adipose tissue-derived stem cells. Anat Rec, 303:385-389, 2020. © 2019 American Association for Anatomy.

Hearing Preservation Following Repeated Adenovector Delivery.

Factors influencing the damage to the inner ear can include the surgical approach used for vector delivery, the volume of vector used, the buffer that the vector is suspended in as well as the host response to the vector capsid and vector genes that are transferred. We evaluated the effect of Ad5 capsid adenovectors on hearing function after delivery to the perilymph of adult C57Bl/6 mice. Hearing was evaluated before surgery and 3 days post-surgery by auditory brain stem response (ABR) and distortion product otoacoustic emissions (DPOAE). A second group of mice underwent repeated delivery of adenovector two times to determine if a preliminary exposure to an Ad vector could induce an inflammatory response leading to further loss. The first adenovector (Ad.11D.LacZ) was delivered to the posterior semicircular canal or via round window. In the second surgery, a second adenovector (Ad.11D.gfp) was delivered to the horizontal semicircular canal. The functional outcome was tested prior, 7 days post first vector delivery, and 3 days post second vector delivery via ABR and DPOAE. Dual delivery via the semicircular canals resulted in preservation of hearing suggesting that pre-exposure to Ad5 capsid does not predispose to hearing loss. Delivery to the round window resulted in hearing loss that was worsened after the second vector delivery, suggesting that delivery route and prior injury to the inner ear rather than the repetition of delivery predisposes to further hearing loss. Anat Rec, 303:600-607, 2020. © 2019 American Association for Anatomy.

Transcriptomic Analyses of Inner Ear Sensory Epithelia in Zebrafish.

Analysis of gene expression has the potential to assist in the understanding of multiple cellular processes including proliferation, cell-fate specification, senesence, and activity in both healthy and disease states. Zebrafish model has been increasingly used to understand the process of hearing and the development of the vertebrate auditory system. Within the zebrafish inner ear, there are three otolith organs, each containing a sensory macula of hair cells. The saccular macula is primarily involved in hearing, the utricular macula is primarily involved in balance and the function of the lagenar macula is not completely understood. The goal of this study is to understand the transcriptional differences in the sensory macula associated with different otolith organs with the intention of understanding the genetic mechanisms responsible for the distinct role each organ plays in sensory perception. The sensory maculae of the saccule, utricle, and lagena were dissected out of adult Et(krt4:GFP)sqet4 zebrafish expressing green fluorescent protein in hair cells for transcriptional analysis. The total RNAs of the maculae were isolated and analyzed by RNA GeneChip microarray. Several of the differentially expressed genes are known to be involved in deafness, otolith development and balance. Gene expression among these otolith organs was very well conserved with less than 10% of genes showing differential expression. Data from this study will help to elucidate which genes are involved in hearing and balance. Furthermore, the findings of this study will assist in the development of the zebrafish model for human hearing and balance disorders. Anat Rec, 303:527-543, 2020. © 2019 American Association for Anatomy.

Congenital Middle Ear Malformation with Common Deafness Gene Mutation Analysis: A Review of 813 Profound Sensorineural Hearing Loss Child Patients.

Deafness gene variants play a key role in inner ear malformations. However, the relationship between congenital middle ear malformations and common deafness genes (GJB2, SLC26A4, and mtDNA) in profound sensorineural hearing loss (SNHL) child patients remains poorly investigated. Here we showed that there was no statistical significance in the total mutation frequency of the three common deafness genes in the middle ear malformation group (21.2%, 41/193) in comparison with the normal middle ear and inner ear group (21.0%, 116/553) (χ2 = 0.0061, p = 0.940). Moreover, the mutation ratio of GJB2 and SLC26A4 in the middle ear malformation group (18.7%, 36/193; 2.6%, 5/193) was not significantly different from that in the normal middle ear and inner ear group (17.7%, 98/553; 2.4%, 13/553) (χ2 = 0.084, p = 0.772; χ2 = 0.0000, p = 1.000). The mutation ratio of GJB2 235delC and GJB2 79G>A in the middle ear malformation group (8.8%, 17/193; 8.8%, 17/193) was almost the same to that in the normal middle ear and inner ear group (8.6%, 48/553; 6.7%, 37/553) (χ2 = 0.0030, p = 0.957; χ2 = 0.9556, p = 0.328). The high jugular bulb subgroup analysis also showed the same results. Our findings suggested that GJB2, SLC26A4, and mtDNA mutations might not be related to the middle ear malformations in profound SNHL child patients. Anat Rec, 303:594-599, 2020. © 2019 American Association for Anatomy.

Extreme Anatomy: The Lottery Winners, Specialists, and Extreme Adaptations That Are No More.

This special issue of The Anatomical Record explores extravagant adaptions that vertebrates have evolved from their base groups to survive in the most challenging environments. It stems from a symposium entitled "Extreme Anatomy: Living beyond the edge," which was held April 23, 2017, at the annual meeting of the American Association for Anatomy, in Chicago, IL. In Part 1 of this issue, we examined extreme morphologies that allow exploration of new niches. In this issue, we return to the evolution of terrestriality by digging deeply into the fossil history of the piscine antecedent of tetrapods. These were truly "lottery winners" among vertebrates. This issue also bears on extreme specialists that once thrived but are now long extinct and some extant species that thrive in the hottest terrestrial niches. Herein, several contributions discuss developmental strategies that facilitate later demanding locomotor regimens and feeding strategies for accessing nutrients from less than ideal food sources. From mole-rats to short-faced breeds of domestic dogs, we encounter another host of the most unusual of earth's creatures, who have much to teach us about our world. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:214-217, 2020. © 2019 American Association for Anatomy.

Computational Fluid Dynamics Reveals a Unique Net Unidirectional Pattern of Pulmonary Airflow in the Savannah Monitor Lizard (Varanus exanthematicus).

This report models pulmonary airflow in the savannah monitor (Varanus exanthematicus) using computational fluid dynamics simulations, which are based on computed tomography data. Simulations were validated by visualizing the flow of aerosolized lipids in excised lungs with good but not perfect agreement. The lung of this lizard has numerous successive bronchi branching off a long intrapulmonary bronchus, which are interconnected by intercameral perforations. Unidirectional flow has been documented in the lateral secondary bronchi of the savannah monitor, but patterns of airflow in the rest of the lung remain unknown, hindering our understanding of the evolution of pulmonary patterns of airflow in tetrapods. These results indicate that the lung contains a unique net unidirectional flow, where the overall flow scheme is similar during expiration and late inspiration, but dissimilar during early inspiration. Air is transported net caudally through the intrapulmonary bronchus and net craniad through secondary bronchi, much like the pattern of flow in birds. The simulations show that many chambers feature flow in multiple directions during parts of the respiratory cycle, but some regions also show robust unidirectional airflow. Air moves craniad through secondary bronchi and between adjacent secondary bronchi through intercameral perforations. The first secondary bronchus, the hilar-cranial bronchus, contains tidal flow that may improve ventilation of the central and dorsal lung parenchyma. These results expand our understanding of flow patterns in varanid lungs and suggest lungs with net unidirectional flow as an evolutionary pathway between tidal flow and complete unidirectional flow in multicameral lungs. Anat Rec, 2020. © 2019 American Association for Anatomy Anat Rec, 303:1768-1791, 2020. © 2019 American Association for Anatomy.

Anatomy and Flight Performance of the Early Enantiornithine Bird Protopteryx fengningensis: Information from New Specimens of the Early Cretaceous Huajiying Formation of China.

The Early Cretaceous (∼131 Million Years Ago) Protopteryx fengningensis is one of the oldest and most primitive enantiornithine birds; however, knowledge of its anatomy has largely been limited to the succinct description of two specimens (holotype and paratype). This study describes two new specimens of P. fengningensis preserving most of the skeleton and plumage, and it therefore adds significantly to understanding the morphology of this important species and the character evolution of enantiornithine birds. The well-preserved plumage of these specimens also affords a quantitative assessment of the flight performance of P. fengningensis. Our aerodynamic considerations indicate that this early enantiornithine was capable of intermittent flight (bounding or flap-gliding), thus marking the earliest occurrence of such energy-saving aerial strategy. Anat Rec, 303:716-731, 2020. © 2019 American Association for Anatomy.

Osteology of the Late Triassic Bipedal Archosaur Poposaurus gracilis (Archosauria: Pseudosuchia) from Western North America.

Poposaurus gracilis is a bipedal pseudosuchian archosaur that has been poorly understood since the discovery of the holotype fragmentary partial postcranial skeleton in 1915. Poposaurus. gracilis is a member of Poposauroidea, an unusually morphologically divergent clade of pseudosuchians containing taxa that are bipedal, quadrupedal, toothed, edentulous, and some individuals with elongated thoracic neural spines (i.e., sails). In 2003, a well preserved, fully articulated, and nearly complete postcranial skeleton of P. gracilis was discovered with some fragmentary cranial elements from the Upper Triassic Chinle Formation of Grand Staircase-Escalante National Monument of southern Utah, USA. The aim of this work is to describe the osteology of this specimen in detail and compare P. gracilis to other closely related pseudosuchian archosaurs. The open neurocentral sutures throughout the majority of the vertebral column, the small size of this individual, and the presence of seven evenly spaced cyclic growth marks in the histologically sectioned femur indicate that this specimen was a skeletally immature juvenile, or subadult when it died. The pes of P. gracilis contains multiple skeletal adaptations and osteological correlates for soft tissue structures that support a hypothesis of digitigrady for this taxon. When coupled with the numerous postcranial characters associated with cursoriality, and the many anatomical traits convergent with theropod dinosaurs, this animal likely occupied a similar ecological niche with contemporaneous theropods during the Late Triassic Period. Anat Rec, 303:874-917, 2020. © 2019 American Association for Anatomy.

Cranium and Vertebral Column of Xingxiulong chengi (Dinosauria: Sauropodomorpha) from the Early Jurassic of China.

The Lower Jurassic Lufeng Formation in Yunnan Province of southwestern China provides one of the most abundant records of sauropodomorphs in the world. However, most of them have not been fully described. Xingxiulong chengi is among the most complete non-sauropodan sauropodomorphs ever discovered from Lufeng Formation and is represented by three partial skeletons. Here, we provide a detailed osteological description of its axial skeleton, including both the cranial and postcranial elements, and compare its anatomy with that of other known non-sauropodan sauropodomorphs. In general, the cranium of Xingxiulong is more similar to those of more basal sauropodomorphs than to sauropodiforms, as evidenced by features such as an only slightly concave dorsal margin of the postorbital, a caudally placed rostral margin of the infratemporal fenestra not extending below the orbit, and long and slender basipterygoid processes divergent from each other at an angle of approximately 80 degrees. However, its postcranial axial skeleton possesses some unique or relatively derived features among basal sauropodomorphs, such as four sacral vertebrae and caudal dorsal vertebrae with laterally expanded neural spine tables. This provides future workers with a reassessment of non-sauropodan sauropodomorphs through the lens of Xingxiulong chengi, which will serve to increase our knowledge on the anatomy, phylogeny, and furthermore, evolution of sauropodomorph dinosaurs. Anat Rec, 303:772-789, 2020. © 2019 American Association for Anatomy.

The Anatomy of Asilisaurus kongwe, a Dinosauriform from the Lifua Member of the Manda Beds (~Middle Triassic) of Africa.

The diagnosis of Dinosauria and interrelationships of the earliest dinosaurs relies on careful documentation of the anatomy of their closest relatives. These close relatives, or dinosaur "precursors," are typically only documented by a handful of fossils from across Pangea and nearly all specimens are typically missing important regions (e.g., forelimbs, pelves, skulls) that appear to be important to help resolving the relationships of dinosaurs. Here, we fully describe the known skeletal elements of Asilisaurus kongwe, a dinosauriform from the Middle Triassic Manda Beds of the Ruhuhu Basin of Tanzania. The taxon is known from many disarticulated and partially articulated remains and, most importantly, from a spectacularly preserved associated skeleton of an individual containing much of the skull, pectoral and pelvic girdles, forelimb and hindlimb, and parts of the vertebral column including much of the tail. The unprecedented detail of the anatomy indicates that Asilisaurus kongwe had a unique skull that was short and had both a premaxillary and dentary edentulous margin, but retained a number of character states plesiomorphic for Archosauria, including a crocodylian-like ankle configuration and a rather short foot with well-developed metatarsals I and V. Additionally, character states present across the skeleton of Asilisaurus kongwe suggest it is more closely related to Silesaurus opolensis than to dinosaurs; thus suggesting high homoplasy and parallel trends within Silesauridae and within lineages of early dinosaurs. The anatomy of Asilisaurus kongwe and detailed description of early members of clades found outside Dinosauria are clearly needed to untangle the seemingly complex character evolution of the skeleton within avemetatarsalians. Anat Rec, 303:813-873, 2020. © 2019 American Association for Anatomy.

Osteohistology and Life History of the Basal Pygostylian, Confuciusornis sanctus.

More than a thousand specimens of Confuciusornis sanctus have been recovered from the Early Cretaceous Jehol Group of Northeastern China. Here, we investigate the bone microstructure of 33 long bones sampled from 14 C. sanctus specimens in an attempt to assess the life history patterns of this basal pygostylian bird. Analysis of the histology of various skeletal elements (femur, humerus, tibia, radius, and ulna) revealed differences in the histology of their bone walls. Based on the osteohistology, we coded the examined specimens into five histology age classes. We found that histological age was not strictly correlated with body size. The variability in the histology of multiple bones from single skeletons suggests differences in the growth rate of the skeleton in response to allometry, functional demands, and pathology. We show that although fibrolamellar bone is widespread across birds, the extent and duration of this rapid phase of bone deposition is highly variable. Comparisons among Mesozoic birds confirm that early ontogenetic growth was rapid, but that later post-hatching growth was strongly influenced by the ontogenetic age of the individual, body size, and local environment, as well as taxonomy. Our findings indicate that C. sanctus experienced rapid growth from early ontogeny until almost fully grown, and thereafter transitioned to slow, episodic growth (for at least 3-4 years) to reach skeletal maturity. Anat Rec, 303:949-962, 2020. © 2019 American Association for Anatomy.

Clavicle in Carnivorans: A Forgotten Bone.

The clavicle is a bone whose development is related to the versatility of the thoracic limbs in mammals. Studies with vestigial structures are scarce and controversial, especially in the order Carnivora. The objective of this study was to verify the presence and to investigate the shape and constitution of the clavicle in neotropical carnivores. In order to do this, 108 cadavers of 19 different species were collected dead on highways and were analyzed. The clavicles were submitted to dissections, longitudinal length measurements, radiographs, histological sections and, in some cases, diaphanization. Sixteen of the 19 species had clavicles in both sides, being significantly larger (P < 0.05) and distinctly more radiopaque in the felids than in the other families. There were no macro or microscopic evidence of clavicle in the specimens of Nasua nasua (n = 6), Conepatus semistriatus (n = 2), and Conepatus chinga (n = 1). The clavicle of the males of Lycalopex gymnocercus, Galictis cuja, and Leopardus geoffroyi was significantly larger (P < 0.05). The predominating contour of the clavicles was a thin stick with cranial convexity. The histological sections demonstrated compact bone consisting of trabecula and lamellae filled by bone marrow and different levels of occupation by chondroid matrix. It can be proposed the clavicles of the order Carnivora, although vestigial and rarely absent, have their presence, constitution and shape more associated with the phylogenetic proximity and evolutionary history of the species than to the variety of movements the thoracic limbs perform in free-living conditions. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:1831-1841, 2020. © 2019 American Association for Anatomy.

Cetacean Orbital Muscles: Anatomy and Function of the Circular Layers.

Dissections of cetacean orbits identified two distinct circular muscle layers that are uniquely more elaborate than the orbitalis muscles described in numerous mammals. The circular orbital muscles in cetaceans form layers that lie both external and internal to the rectus extra ocular muscles (EOMs). A cone-shaped external circular muscle (ECM) that invests the external surface of the rectus EOMs was found in all cetacean specimens examined. The cetacean ECM corresponds generally to descriptions of the musculus orbitalis in various mammals but is more strongly developed and has more layers than in noncetaceans. A newly identified internal circular muscle (ICM) is located internal to the rectus EOMs and external to the retractor bulbi (RB). The RB is massive in cetaceans and is encased in a connective tissue layer containing convoluted bundles of blood vessels. The most robust ECM and ICM layers were in sperm whale (Physeter macrocephalus) where they form complete rings. Surprisingly, histological analysis showed the sperm whale ECM to contain both smooth and striated (skeletal) muscle layers while the ICM appeared to contain solely skeletal muscle fibers. The extreme development of the ECM (orbitalis) and RB suggest a co-evolved system mediating high degrees of protrusion and retraction in cetaceans. We know of no homolog of the ICM but its function seems likely related to the complex vascular structures surrounding and deep to the retractor muscle. Skeletal muscle components in orbital circular muscles appear to be highly derived specializations unknown outside of cetaceans. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:1792-1811, 2020. © 2019 American Association for Anatomy.

Extreme Anatomy: Gear for the Pioneer.

This special issue of The Anatomical Record explores extravagant adaptions that vertebrates have evolved from their base groups to survive in the most challenging environments. The special issue stems from a symposium entitled "Extreme Anatomy: Living beyond the edge," which was held April 23, 2017, at the annual meeting of the American Association of Anatomists, (now called the American Association for Anatomy), in Chicago, IL. In part 1 of this issue, we encounter fossorial mammals and cave-dwelling fish and salamanders that have reduced visual systems accompanied by a variety of mechanosensory adaptations. In rivers and seas, teeth may not suffice in the pursuit of prey: aquatic vertebrates are adorned with armor or weaponry or elaborate keratinous sieves. As vertebrates exploit a great diversity of niches, selection has favored a dizzying array of specialized sensory and locomotor adaptions for deep diving, rapid flight, and navigation through dark and complex settings. Each special adaptation, some seemingly quite "extreme" deviations from an original Bauplan, becomes a tool for a pioneer-like diversification of vertebrates. Anat Rec, 2019. © 2019 American Association for Anatomy.

DiceCT Analysis of the Extreme Gouging Adaptations Within the Masticatory Apparatus of the Aye-Aye (Daubentonia madagascariensis).

Relative to all other primates, the aye-aye (Daubentonia madagascariensis) exists at the extremes of both morphology and behavior. Its specialized anatomy-which includes hypselodont incisors and highly derived manual digits-reflects a dietary niche, unique among primates, which combines tap-foraging with gouging to locate and extract wood-boring larvae. Here, we explore the impact of this extreme dietary ecology upon the masticatory musculature of this taxon with reference to a second, similarly sized but highly generalist lemuriform-the mongoose lemur (Eulemur mongoz). Using non-destructive, high-resolution diffusible iodine-based contrast-enhanced computed tomography techniques, we reconstruct the three-dimensional volumes of eight masticatory muscles, and, for the first time in strepsirrhines, isolate and visualize their constituent muscle fascicles in situ and in three dimensions. Using these data, we report muscle volumes, forces, and fascicle lengths from each muscle portion, as well as their orientation relative to two standardized anatomical planes. Our findings demonstrate the overbuilt nature of the aye-aye's masticatory apparatus, in which each muscle possesses an absolutely and relatively larger muscle volume and PCSA than its counterpart in the mongoose lemur. Likewise, for several adductor muscles, aye-ayes also possess relatively greater fascicle lengths. Finally, we note several unusual features within the lateral pterygoid of the aye-aye-the muscle most responsible for jaw protrusion-that relate to force maximization and reorientation. As this jaw motion is critical to gouging, we interpret these differences to reflect highly specific specializations that facilitate the aye-aye's extreme subsistence strategy. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:282-294, 2020. © 2019 American Association for Anatomy.

Skull Anatomy and Pneumaticity of the Enigmatic Coelurosaurian Theropod Bicentenaria argentina.

The enigmatic basal coelurosaur Bicentenaria argentina is a small theropod that comes from the Upper Cretaceous of Patagonia. It is constituted by more than 130 elements, including cranial remains. These are represented by an incomplete snout, palate, dermatocranium, and lower jaws still in articulation. The skull material of Bicentenaria was preliminarily studied by previous authors. In this study, we conducted a CT scan of the holotype of Bicentenaria, which allowed us to fully describe all preserved skull bones, including some previously unknown elements. The morphological analysis indicates that Bicentenaria shares many cranial features with other basal coelurosaurs as compsognathids, Ornitholestes, and tyrannosauroids. Otherwise, results of this analysis show that Bicentenaria exhibits a set of traits unique to this taxon. Furthermore, several pneumatic recesses were closely matched with those pneumatic features present in many derived coelurosaurs, particularly tyrannosauroids. This new information, together with future discoveries, will improve our knowledge about the muscular correlates of Bicentenaria and other coelurosaurs, and may shed light about the phylogenetic relationships of this group. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:1884-1900, 2020. © 2019 American Association for Anatomy.

Quantitative Analysis of the Timing of Development of the Cerebellum and Precerebellar Nuclei in Monotremes, Metatherians, Rodents, and Humans.

We have used a quantitative statistical approach to compare the pace of development in the cerebellum and precerebellar systems relative to body size in monotremes and metatherians with that in eutherians (rodents and humans). Embryos, fetuses, and early postnatal mammals were scored on whether key structural events had been reached in the development of the cerebellum itself (CC-corpus cerebelli; 10 milestones), or the pontine and inferior olivary precerebellar nuclear groups (PC; 4 milestones). We found that many early cerebellar and precerebellar milestones (e.g., formation of Purkinje cell layer and deep cerebellar nuclei) were reached at a smaller absolute body length in both metatherians and eutherians together, compared to monotremes. Some later milestones (e.g., formation of the external granular layer and primary fissuration) were reached at a smaller body length in metatherians than eutherians. When the analysis was performed with proportional body length expressed as a natural log-transformed ratio of length at birth, milestones were reached at a much smaller proportional body length in rodents and humans than in the metatherians or monotremes. The findings are consistent with the slower pace of metabolic activity and embryonic development in monotremes. They also indicate slightly advanced maturation of some early features of the cerebellum in some metatherians (i.e., early cerebellar development in dasyurids relative to body size), but do not support the notion of an accelerated development of the cerebellum to cope with the demands of early birth. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:1998-2013, 2020. © 2019 American Association for Anatomy.

Sex and Ontogenetic Variation in the Crest of Numida meleagris: Implications for Crested Vertebrates.

Crested vertebrates are known from a wide variety of modern and fossil taxa, however, the actual formation and function of the crest is still debatable. Among modern birds, the globally distributed guinea fowl (Numida meleagris) is characterized by having a cranial bony crest (overlain by keratin), but surprisingly little is known about its development. Here, we studied the crest of 202 wild guinea fowl from the same population, using anatomical measurements as well as 2D-morphometry. Our results show that juveniles have smaller skulls than adults and have smaller, simpler crests that are visible even in very young individuals. Among adults, female skulls are smaller than males, and they have smaller, simpler shaped crests, which permit a discrimination between the sexes of 93% when the keratin is preserved with the bony crest, and of 89% when only the bony crest is available. By extrapolation, these results confirm that the crest can be used as an ontogenetic character, as well as for sex discrimination in the fossil record. Our results also show that the overlying keratin does not always mimic the underlying bony crest, which should be considered when reconstructing extinct crested vertebrates. Anat Rec, 303:1018-1034, 2020. © 2019 American Association for Anatomy.

Vertebromedullary Topography of the Red‐Rumped Agouti (Dasyprocta leporina Linnaeus, 1758)

The agouti is a wild rodent located almost throughout the Brazilian territory, with great scientific importance and high reproductive potential when farmed. In the clinical routine, clinical and surgical procedures are performed on the nervous system of these animals, such as epidural anesthesia and cerebrospinal fluid (CSF) collection; however, data available are limited in literature on the main points of these procedures in this species. In this aspect, the objective was to describe the vertebromedullary topography of the agouti in order to identify and quantify it, with the intention of expanding the information regarding the clinical-surgical procedures in this system. Ten animals were incised longitudinally in the dorsal median line, removing the skin, the musculature, and dorsal fascia of the vertebral column; then, removed the vertebral arches and consequent exposure of the spinal cord and meninges. The morphometry of the animals was done by obtaining the total length, body length, and crown-rump length, as well as the total length of the spinal cord and its segments. The cervical intumescence in the agouti is located between C4-T1 and measures 2.45 cm. The lumbar intumescence is between L5-L7 and is 2.52 cm long. The cauda equina arises from S2 and the filum terminale from S3. As for the medullary cone, it is located between L7-S1 and is 2.52 cm long. The suggested localization for epidural anesthesia or CSF puncture for laboratory tests in agoutis is the lumbosacral space, with the insertion of the needle to be carried out at angle of 90° in the sphinx position. Anat Rec, 303:1472-1477, 2020. © 2019 American Association for Anatomy.