Search

The treefrog Boana exastis was tentatively included in B. faber group based on its morphological similarity to B. lundii and B. pardalis. This species was only recently included in a molecular phylogeny, confirming its placement in this group; however, its phylogenetic relationships have been poorly explored. Herein, we describe the larval external morphology, buccopharyngeal cavity, and skeleton of B. exastis, and assess its phylogenetic placement and genetic similarity between disjunct populations. Additionally, we describe the larval skeleton of the two closely related species, B. lundii and B. pardalis. The larval morphology of B. exastis is congruent with the other Boana species, reinforcing a high larval similarity across species of the B. faber group. The three species showed differences in color and in rows of marginal papillae. Comparing the chondrocranium of the three species, we found that B. exastis is more similar to B. pardalis than to B. lundii, contrary to what has been previously proposed, based on acoustic data. Phylogenetically, B. exastis was found to be more related to B. pardalis than to B. lundii. Despite presenting a disjunct distribution, the populations of Boana exastis show a very low mitochondrial genetic divergence, indicating that they are the same taxon. [ABSTRACT FROM AUTHOR]

Elasmobranchs are common, iconic species in public aquaria; their wild counterparts are key members of marine ecosystems. Post-mortem examination is a critical tool for disease monitoring of wild elasmobranchs and for management of those under human care. Careful necropsy of the head, with a focus on clinically relevant anatomy, can ensure that proper samples are collected, increasing the chance of presumptive diagnoses prior to slower diagnostic workup. Immediate feedback from a thorough head necropsy allows for faster management decisions, often identifying pathogens, routes of pathogen entry, and pathogenesis, which are current shortcomings in published literature. This article proposes a protocol for necropsy of the elasmobranch chondrocranium, emphasizing unique anatomy and careful dissection, evaluation, and sampling of the endolymphatic pores and ducts, inner ears, brain, and olfactory system as part of a complete, whole-body necropsy. Extensive use of cytology and microbiology, along with thorough sample collection for histology and molecular biology, has proven effective in identifying a wide range of pathogens and assisting with characterization of pathogenesis. The cause of mortality is often identified from a head necropsy alone, but does not replace a thorough whole-body dissection. This protocol for necropsy and ancillary diagnostic sample collection and evaluation was developed and implemented in the necropsy of 189 wild and aquarium-housed elasmobranchs across 18 species over 13 years (2011--2023) in California. Using this chondrocranial approach, meningoencephalitis was determined to be the primary cause of mortality in 70% (118/168) of stranded wild and aquarium-housed elasmobranchs. Etiology was largely bacterial or protozoal. Carnobacterium maltaromaticum bacterial meningoencephalitis occurred in salmon sharks (Lamna ditropis), shortfin mako sharks (Isurus oxyrinchus), common thresher sharks (Alopias vulpinus), and one Pacific electric ray (Tetronarce californica). Miamiensis avidus was the most common cause of protozoal meningoencephalitis and found almost exclusively in leopard sharks (Triakis semifasciata) and bat rays (Myliobatis californica) that stranded in San Francisco Bay. Bacterial pathogens were found to use an endolymphatic route of entry, while protozoa entered via the nares and olfactory lamellae. Trauma was the second most common cause of mortality and responsible for 14% (24/168) of wild shark strandings and deaths of aquarium-housed animals. [ABSTRACT FROM AUTHOR]

The first record of well-preserved chondrocranial elements in mosasaurids is here described. These elements are preserved in situ in a Coniacian skull found in north-central Colombia, inside a calcareous concretion. Based on a 3D model generated from computed tomography scans, we identified elements of the nasal and orbitotemporal regions. Our descriptions show that in this specimen, the chondrocranium was reduced, more so than in most lacertilians (including their closest recent relatives, the varanids), but not as severely as in snakes or amphisbaenians (which have an extremely reduced chondrocranium and limbs). The new evidence suggests that the reduction in the chondrocranium in mosasaurids could be related to modification of their limbs when adapting to aquatic environments, but also that in mosasaurids, the olfactory tract was reduced, and the optic muscle insertions occurred mainly in the interorbital septum. The exceptional preservation of the chondrocranial elements in the specimen is facilitated by a gray mineralization covering them. XRD analysis and thin section observations indicated that this mineralization is composed of microcrystalline quartz and calcite. We infer that this material was produced by a partial silicification process promoted by lower pH microenvironments associated with bacterial breakdown of non-biomineralized tissues during early diagenesis. [ABSTRACT FROM AUTHOR]

Elasmobranchs are common, iconic species in public aquaria; their wild counterparts are key members of marine ecosystems. Post-mortem examination is a critical tool for disease monitoring of wild elasmobranchs and for management of those under human care. Careful necropsy of the head, with a focus on clinically relevant anatomy, can ensure that proper samples are collected, increasing the chance of presumptive diagnoses prior to slower diagnostic workup. Immediate feedback from a thorough head necropsy allows for faster management decisions, often identifying pathogens, routes of pathogen entry, and pathogenesis, which are current shortcomings in published literature. This article proposes a protocol for necropsy of the elasmobranch chondrocranium, emphasizing unique anatomy and careful dissection, evaluation, and sampling of the endolymphatic pores and ducts, inner ears, brain, and olfactory system as part of a complete, whole-body necropsy. Extensive use of cytology and microbiology, along with thorough sample collection for histology and molecular biology, has proven effective in identifying a wide range of pathogens and assisting with characterization of pathogenesis. The cause of mortality is often identified from a head necropsy alone, but does not replace a thorough whole-body dissection. This protocol for necropsy and ancillary diagnostic sample collection and evaluation was developed and implemented in the necropsy of 189 wild and aquarium-housed elasmobranchs across 18 species over 13 years (2011–2023) in California. Using this chondrocranial approach, meningoencephalitis was determined to be the primary cause of mortality in 70% (118/168) of stranded wild and aquarium-housed elasmobranchs. Etiology was largely bacterial or protozoal. Carnobacterium maltaromaticum bacterial meningoencephalitis occurred in salmon sharks (Lamna ditropis), shortfin mako sharks (Isurus oxyrinchus), common thresher sharks (Alopias vulpinus), and one Pacific electric ray (Tetronarce californica). Miamiensis avidus was the most common cause of protozoal meningoencephalitis and found almost exclusively in leopard sharks (Triakis semifasciata) and bat rays (Myliobatis californica) that stranded in San Francisco Bay. Bacterial pathogens were found to use an endolymphatic route of entry, while protozoa entered via the nares and olfactory lamellae. Trauma was the second most common cause of mortality and responsible for 14% (24/168) of wild shark strandings and deaths of aquarium-housed animals.

3D-printed models (3DPMs) are being increasingly utilized as learning aids in medical and comparative anatomy education. Research suggests that 3DPMs can significantly improve students' accuracy in recognizing important anatomical landmarks and provide a low-cost alternative to expensive or fragile specimens. The use of 3DPMs can also alleviate conservation concerns for certain endangered species. Additionally, 3DPMs provide a unique interactive experience in viewing structures that may otherwise be difficult to observe or handle directly by students. A novel 3DPM has been developed to help biology students learn the anatomy of the Squalus acanthias (S. acanthias), or dogfish shark, chondrocranium and brain. This feasibility study evaluated the perceived utility of these new 3DPMs in an undergraduate-level comparative chordate anatomy lab (BIOL 351) at Iowa State University in Spring 2023. Students responded to a questionnaire comprising Likert and open-ended long-form questions that uncovered their perceptions of and experience interacting with the 3DPMs. Two separate surveys were administered, one for the chondrocranium (29 responses) and one for the brain (16 responses). Students indicated a strong preference for using the 3DPMs as compared to the dissected and preserved specimens, citing the 3DPMs' size, durability, and the ability to handle and rotate them as beneficial for understanding relevant anatomy. Further investigation is required to understand how the 3DPM improves students' learning outcomes; however, this study confirms the model's utility and biology students' desire to have access to additional 3DPMs in the comparative chordate anatomy lab. [ABSTRACT FROM AUTHOR]

In this study, we morphologically examine larval specimens of Ranitomeya variabilis, which were breed in captivity and genetically determined to belong to the French Guiana population. We provide detailed data on the external morphology, chondrocranium, cranial muscle systems and inner organs of the tadpoles. Additionally, we provide essential characteristics for the recognition of the tadpoles of the different Ranitomeya species. The external morphology of the R. variabilis tadpoles was assessed by measurements and photographs of the specimens. Internal morphology was analyzed using µCT images, µCT-based three-dimensional reconstructions, and dissection of specimens for organ and muscle descriptions. The majority of the muscle configurations observed herein for larval specimens of R. variabilis are consistent with data presented in previous studies for larvae of other Ranitomeya species. In addition, several of the observed morphological characters are defined for different taxonomic levels within Dendrobatidae, e.g., the reduction of tectal cartilages and the insertion of the M. rectus cervicis on the third or fourth branchial arch. The absence of the anterolateral process of the ceratohyal in Ranitomeya and Dendrobates further strengthens their close relationship, in contrast to the more distantly related Epipedobates and Phyllobates where this structure is present. The absence of the M. levator arcuum branchialium I and II, the M. interhyoideus posterior and the M. diaphragmatopraecordialis might be defining traits for Ranitomeya. The specific characters observed in this study for R. variabilis, are the fusion of the superficialis and profundus portion of the musculus levator longus larvae and the absence of the parotic crista. [ABSTRACT FROM AUTHOR]

The craniofacial skeleton of vertebrates is a major innovation of the whole clade. Its development and composition requires a precisely orchestrated sequence of chondrification events which lead to a fully functional skeleton. Sequential information on the precise timing and sequence of embryonic cartilaginous head development are available for a growing number of vertebrates. This enables a more and more comprehensive comparison of the evolutionary trends within and among different vertebrate clades. This comparison of sequential patterns of cartilage formation enables insights into the evolution of development of the cartilaginous head skeleton. The cartilaginous sequence of head formation of three basal anurans (Xenopus laevis, Bombina orientalis, Discoglossus scovazzi) was investigated so far. This study investigates the sequence and timing of larval cartilaginous development of the head skeleton from the appearance of mesenchymal Anlagen until the premetamorphic larvae in the neobatrachian species Bufo bufo. Clearing and staining, histology, and 3D reconstruction enabled the tracking of 75 cartilaginous structures and the illustration of the sequential changes of the skull as well as the identification of evolutionary trends of sequential cartilage formation in the anuran head. The anuran viscerocranium does not chondrify in the ancestral anterior to posterior direction and the neurocranial elements do not chondrify in posterior to anterior direction. Instead, the viscerocranial and neurocranial development is mosaic‐like and differs greatly from the gnathostome sequence. Strict ancestral anterior to posterior developmental sequences can be observed within the branchial basket. Thus, this data is the basis for further comparative developmental studies of anuran skeletal development. Research highlights: The anuran viscerocranium develops mosaic‐like.Posterior neurocranial elements extend anteriorly and anterior elements extend posteriorly.Posterior to anterior growth of the parachordal and initial development of the lateral wall of the otic capsule are shared gnathostome features. [ABSTRACT FROM AUTHOR]

The first record of well-preserved chondrocranial elements in mosasaurids is here described. These elements are preserved in situ in a Coniacian skull found in north-central Colombia, inside a calcareous concretion. Based on a 3D model generated from computed tomography scans, we identified elements of the nasal and orbitotemporal regions. Our descriptions show that in this specimen, the chondrocranium was reduced, more so than in most lacertilians (including their closest recent relatives, the varanids), but not as severely as in snakes or amphisbaenians (which have an extremely reduced chondrocranium and limbs). The new evidence suggests that the reduction in the chondrocranium in mosasaurids could be related to modification of their limbs when adapting to aquatic environments, but also that in mosasaurids, the olfactory tract was reduced, and the optic muscle insertions occurred mainly in the interorbital septum. The exceptional preservation of the chondrocranial elements in the specimen is facilitated by a gray mineralization covering them. XRD analysis and thin section observations indicated that this mineralization is composed of microcrystalline quartz and calcite. We infer that this material was produced by a partial silicification process promoted by lower pH microenvironments associated with bacterial breakdown of non-biomineralized tissues during early diagenesis.

3D-printed models (3DPMs) are being increasingly utilized as learning aids in medical and comparative anatomy education. Research suggests that 3DPMs can significantly improve students’ accuracy in recognizing important anatomical landmarks and provide a low-cost alternative to expensive or fragile specimens. The use of 3DPMs can also alleviate conservation concerns for certain endangered species. Additionally, 3DPMs provide a unique interactive experience in viewing structures that may otherwise be difficult to observe or handle directly by students. A novel 3DPM has been developed to help biology students learn the anatomy of the Squalus acanthias (S. acanthias), or dogfish shark, chondrocranium and brain. This feasibility study evaluated the perceived utility of these new 3DPMs in an undergraduate-level comparative chordate anatomy lab (BIOL 351) at Iowa State University in Spring 2023. Students responded to a questionnaire comprising Likert and open-ended long-form questions that uncovered their perceptions of and experience interacting with the 3DPMs. Two separate surveys were administered, one for the chondrocranium (29 responses) and one for the brain (16 responses). Students indicated a strong preference for using the 3DPMs as compared to the dissected and preserved specimens, citing the 3DPMs’ size, durability, and the ability to handle and rotate them as beneficial for understanding relevant anatomy. Further investigation is required to understand how the 3DPM improves students’ learning outcomes; however, this study confirms the model’s utility and biology students’ desire to have access to additional 3DPMs in the comparative chordate anatomy lab.

The chondrocranium is a key structure of the skull, but our knowledge of its embryonic development is based mostly on investigations of few stages across taxa. Variation of chondrocranial features is known across species, but little is known about intraspecific variation, or its evolution in the context of domestication. Here, we investigated two specific structures of the chondrocranium in three windows of embryonic development. The anatomy of one of these structures was also compared among adult skulls of chickens and their wild ancestor (red junglefowl [RJF]). The proccesus tectalis and the prenasal process, along with the surrounding area of the orbitonasal foramina, presented variation throughout the ontogeny and in the adults. The processus tectalis showed distinct variation from the earliest stage studied to the adult. The numbers of orbitonasal foramina were also found to be variable in the ancestor and breeds studied. Furthermore, during early embryonic development, the prenasal process is similar across breeds and RJF, but later in embryonic development this structure presents variable states. The embryonic and adult variation found herein could be an example of intraspecific variation under domestication, resulting from different types of tissue interrelationship during development. Research Highlights: Comparing the living ancestor of chickens (red junglefowl) and four chicken breeds, the chondrocranium was found variable during embryonic development and adults, contrasting former studies on particular structures of the chicken chondrocranium.The embryonic variation found here could be linked to the adult skull anatomy and to behavior in chickens too. This variation might come from different types of tissue interrelationship during embryonic development that give rise to complex structures.This study offers a first step for future examinations on the effect of domestication and the chondrocranium, as also the study of the underlying developmental mechanisms of morphological variation. [ABSTRACT FROM AUTHOR]

Abstract Background The craniofacial skeleton is an evolutionary innovation of vertebrates. Due to its complexity and importance to protect the brain and aid in essential functions (e.g., feeding), its development requires a precisely tuned sequence of chondrification and/or ossification events. The comparison of sequential patterns of cartilage formation bears important insights into the evolution of development. Discoglossus scovazzi is a basal anuran species. The comparison of its chondrocranium (cartilaginous neuro- & viscerocranium) development with other basal anurans (Xenopus laevis, Bombina orientalis) will help establishing the ancestral pattern of chondrification sequences in anurans and will serve as basis for further studies to reconstruct ancestral conditions in amphibians, tetrapods, and vertebrates. Furthermore, evolutionary patterns in anurans can be studied in the light of adaptations once the ancestral sequence is established. Results We present a comprehensive overview on the chondrocranium development of D. scovazzi. With clearing and staining, histology and 3D reconstructions we tracked the chondrification of 44 elements from the first mesenchymal Anlagen to the premetamorphic cartilaginous head skeleton and illustrate the sequential changes of the skull. We identified several anuran and discoglossoid traits of cartilage development. In D. scovazzi the mandibular, hyoid, and first branchial arch Anlagen develop first followed by stepwise addition of the branchial arches II, III, and IV. Nonetheless, there is no strict anterior to posterior chondrification pattern within the viscerocranium of D. scovazzi. Single hyoid arch elements chondrify after elements of the branchial arch and mandibular arch elements chondrify after elements of the branchial arch I. Conclusions In Osteichthyes, neurocranial elements develop in anterior to posterior direction. In the anurans investigated so far, as well as in D. scovazzi, the posterior parts of the neurocranium extend anteriorly, while the anterior parts of the neurocranium, extend posteriorly until both parts meet and fuse. Anuran cartilaginous development differs in at least two crucial traits from other gnathostomes which further supports the urgent need for more developmental investigations among this clade to understand the evolution of cartilage development in vertebrates.

Background: The craniofacial skeleton is an evolutionary innovation of vertebrates. Due to its complexity and importance to protect the brain and aid in essential functions (e.g., feeding), its development requires a precisely tuned sequence of chondrification and/or ossification events. The comparison of sequential patterns of cartilage formation bears important insights into the evolution of development. Discoglossus scovazzi is a basal anuran species. The comparison of its chondrocranium (cartilaginous neuro- & viscerocranium) development with other basal anurans (Xenopus laevis, Bombina orientalis) will help establishing the ancestral pattern of chondrification sequences in anurans and will serve as basis for further studies to reconstruct ancestral conditions in amphibians, tetrapods, and vertebrates. Furthermore, evolutionary patterns in anurans can be studied in the light of adaptations once the ancestral sequence is established. Results: We present a comprehensive overview on the chondrocranium development of D. scovazzi. With clearing and staining, histology and 3D reconstructions we tracked the chondrification of 44 elements from the first mesenchymal Anlagen to the premetamorphic cartilaginous head skeleton and illustrate the sequential changes of the skull. We identified several anuran and discoglossoid traits of cartilage development. In D. scovazzi the mandibular, hyoid, and first branchial arch Anlagen develop first followed by stepwise addition of the branchial arches II, III, and IV. Nonetheless, there is no strict anterior to posterior chondrification pattern within the viscerocranium of D. scovazzi. Single hyoid arch elements chondrify after elements of the branchial arch and mandibular arch elements chondrify after elements of the branchial arch I. Conclusions: In Osteichthyes, neurocranial elements develop in anterior to posterior direction. In the anurans investigated so far, as well as in D. scovazzi, the posterior parts of the neurocranium extend anteriorly, while the anterior parts of the neurocranium, extend posteriorly until both parts meet and fuse. Anuran cartilaginous development differs in at least two crucial traits from other gnathostomes which further supports the urgent need for more developmental investigations among this clade to understand the evolution of cartilage development in vertebrates. [ABSTRACT FROM AUTHOR]

On the basis of selected osteological markers, Patterson (1936) identified two pathways (here designated A and B) along which the internal carotid artery in notoungulates was said to travel in order to enter the skull and supply the brain. The existence of these pathways, at least as Patterson defined them, has been disputed but no substantive alternatives have been proposed. Using comparative embryological and morphological evidence based on conditions in extant mammals, we find that pathway A (intratympanic) is not supported. Pathway B (enclosed extratympanic) is supportable, but as far as is now known applies only to a small number of notoungulate taxa. On the basis of new evidence, we propose another route, pathway C, briefly mentioned by Scott (1912) but subsequently ignored, that may apply to the majority of notoungulates. In pathway C (unenclosed extratympanic) the internal carotid passed directly into the endocranium via a naturally unossified area of the basicranium, the piriform fenestra, rather than coursing through or alongside the middle ear in a canal. The absence of a separate, bony carotid foramen on the basicranium's ventral surface may explain the hesitancy of previous workers to consider this routing. There is no evidence that the function of the internal carotid artery was supplanted by another vessel (e.g., external carotid artery) in any notoungulate. Conditions in other major clades of South American native ungulates are poorly investigated, but some clearly differed from notoungulates in carotid patterning, pointing to the existence of substantial intertaxon disparities. [ABSTRACT FROM AUTHOR]

Several types of bone development are present in the Australian lungfish, Neoceratodus forsteri , the only extant member of the family Neoceratodontidae. In this species, dermal and parachondral bones form around the chondrocranium and mandible, to protect the brain and sense organs, to support the dentition and to facilitate oral function. The notochord persists throughout life. The quadrate and Meckel's cartilage remain cartilaginous, as does the chondrocranium. Anterior elements of the hyoid arch, the basihyal and hypohyals, do not ossify. The ceratohyal, which articulates with the hypohyals, ossifies perichondrally, as do the exoccipital bone and the ribs of the trunk, including the cranial rib. The exoccipital bone is embedded in the chondrocranium in the adult fish, and the cranial rib is immobile. Some elements of the skeleton, such as the pectoral and pelvic fins, and the pelvic girdle, remain cartilaginous, and the skeletal elements in these fins resemble the structure of the tail. Fully developed bone is trabecular or lamellar, and does not include vascular elements. Endochondral ossification does not occur in the living Australian lungfish. The Australian lungfish, Neoceratodus forsteri , belongs to an ancient group of fish, and is not close to the evolution of land animals, which appeared while lungfish were still living in the sea. Bone formation is not based on endochondral ossification of cartilage, as in mammalian long bones, and the paired fins have no bone, and no fingers or toes. Photograph by Anne Kemp. [ABSTRACT FROM AUTHOR]

Using histological cross-sections, the chondrocranium anatomy was reconstructed for two developmental stages of Hermann's tortoise (Testudo hermanni). The morphology differs from the chondrocrania of most other turtles by a process above the ectochoanal cartilage with Pelodiscus sinensis being the only other known species with such a structure. The anterior and posterior processes of the tectum synoticum are better developed than in most other turtles and an ascending process of the palatoquadrate is missing, which is otherwise only the case in pleurodiran turtles. The nasal region gets proportionally larger during development. We interpret the enlargement of the nasal capsules as an adaption to increase the surface area of the olfactory epithelium for better perception of volant odors. Elongation of the nasal capsules in trionychids, in contrast, is unlikely to be related to olfaction, while it is ambiguous in the case of Sternotherus odoratus. However, we have to conclude that research on chondrocranium anatomy is still at its beginning and more comprehensive detailed descriptions in relation to other parts of the anatomy are needed before providing broad-scale ecological and phylogenetic interpretations., (© 2024 The Author(s). Journal of Morphology published by Wiley Periodicals LLC.)

Corythomantis greeningi is a hylid widely distributed in the xerophilic and sub-humid morphoclimatic regions of northeastern Brazil. The morphology of C. greeningi tadpoles were described from specimens collected in the Bahia, however, we observed some differences in morphology of individuals from Piauí, northeastern Brazil. The tadpoles were collected during the 2019 rainy season and 14 individuals were used to compare the larval characters. We observed differences in external, internal oral and chondrocranial morphology in relation to specimens previously described, especially in oral disc, number and shape of oral cavity papillae and some chondrocranium structures, suggesting a heterochrony in the development of the species. Further studies involving a greater number of tadpoles at different stages, combined with genetic, acoustic, and morphological factors of adult may establish the variation degree of C. greeningi in different regions of northeastern Brazil. [ABSTRACT FROM AUTHOR]

Background: In vertebrates, the skull evolves from a complex network of dermal bones and cartilage—the latter forming the pharyngeal apparatus and the chondrocranium. Squamates are particularly important in this regard as they maintain at least part of the chondrocranium throughout their whole ontogeny until adulthood. Anguid lizards represent a unique group of squamates, which contains limbed and limbless forms and show conspicuous variation of the adult skull. Results: Based on several emboadryonic stages of the limbless lizards Pseudopus apodus and Anguis fragilis, and by comparing with other squamates, we identified and interpreted major differences in chondrocranial anatomy. Among others, the most important differences are in the orbitotemporal region. P. apodus shows a strikingly similar development of this region to other squamates. Unexpectedly, however, A. fragilis differs considerably in the composition of the orbitotemporal region. In addition, A. fragilis retains a paedomorphic state of the nasal region. Conclusions: Taxonomic comparisons indicate that even closely related species with reduced limbs show significant differences in chondrocranial anatomy. The Pearson correlation coefficient suggests strong correlation between chondrocranial reduction and limb reduction. We pose the hypothesis that limb reduction could be associated with the reduction in chondrocrania by means of genetic mechanisms. Key Findings: Taxonomic comparisons indicate that even closely related species with reduced limbs show significant differences in the chondrocranial anatomy.Limb rudimentation lead to the diversification of the orbitotemporal region complexity.The Pearson correlation coefficient suggests strong correlation between chondrocranial reduction and limb reduction.Limb reduction could be associated with the reduction in chondrocrania by means of genetic mechanisms. [ABSTRACT FROM AUTHOR]

The evolutionary success of anurans can be partially explained by the occurrence of free‐living larvae. Tadpoles occupy several distict habitats, including the terrestrial environment. Semiterrestriality appears to have evolved seven times in anurans, and tadpoles of distantly related lineages have converged in a set of phenotypic characters, such as a depressed body, ventral mouth, massive, well‐keratinized and laterally compressed jaw sheaths, low fins, and well‐developed hind limbs. The semiterrestrial tadpoles of the South American family Cycloramphidae remain poorly studied. In this work, we perform a comparative analysis of the external and internal morphology of these larvae, we comment on the systematic and evolutionary implications for the family, and finally, we discuss the convergent evolution of semiterrestrial tadpoles in anurans. We studied the external, buccopharyngeal, and musculoskeletal morphology of semiterrestrial tadpoles of 14 species of Cycloramphidae. These tadpoles are highly modified and present several character‐states associated with semiterrestrial life. Most of them are unique and restricted to the family, such as the novel configuration of the muscles subarcualis rectus I, rectus abdominis, and levator arcuum branchialium III. We propose 13 new synapomorphies for Cycloramphidae and one for Thoropa. The presence of similar, homoplastic, character‐states in all semiterrestrial tadpoles of unrelated phylogenetic lineages seems to suggest that these character‐states are adaptations for semiterrestriality. [ABSTRACT FROM AUTHOR]

We studied the larval morphology of the dendrobatid frog genus Silverstoneia and closely related species of Colostethinae. After describing external, buccopharyngeal, larval muscle, and chondrocranium morphology, we delimit 17 new larval characters, including the following 12 new unambiguously optimized synapomorphies of Silverstoneia: (a) medial emargination on the upper and (b) lower labia, (c) distinct gamma‐shaped crest in prenarial arena, (d) postnarial papillae oblique, (e) lateral ridge papillae keel‐like, (f) dermal crest on buccal floor arena, (g) additional slip of the m. subarcualis obliquus inserting on a medial aponeurosis, (h) fibers of the m. subarcualis rectus I inserting on a medial aponeurosis, (i) fibers of the rectus cervicis inserting on a medial aponeurosis, (j) complete fusion of the suprarostral corpus and alae, (k) adrostral tissue mass with cartilaginous core, and (l) basihyal free. We also identify the fusion of suprarostral corpora above the distal line as a novel larval synapomorphy for Epipedobates. Finally, we discuss the ecomorphology and convergent evolution of funnel‐mouthed tadpoles, which evolved at least seven times in six families. [ABSTRACT FROM AUTHOR]

The head represents the most complex part of the body and a distinctive feature of the vertebrate body plan. This intricate structure is assembled during embryonic development in the four-dimensional process of morphogenesis. The head integrates components of the central and peripheral nervous system, sensory organs, muscles, joints, glands, and other specialized tissues in the framework of a complexly shaped skull. The anterior part of the head is referred to as the face, and a broad spectrum of facial shapes across vertebrate species enables different feeding strategies, communication styles, and diverse specialized functions. The face formation starts early during embryonic development and is an enormously complex, multi-step process regulated on a genomic, molecular, and cellular level. In this review, we will discuss recent discoveries that revealed new aspects of facial morphogenesis from the time of the neural crest cell emergence till the formation of the chondrocranium, the primary design of the individual facial shape. We will focus on molecular mechanisms of cell fate specification, the role of individual and collective cell migration, the importance of dynamic and continuous cellular interactions, responses of cells and tissues to generated physical forces, and their morphogenetic outcomes. In the end, we will examine the spatiotemporal activity of signaling centers tightly regulating the release of signals inducing the formation of craniofacial skeletal elements. The existence of these centers and their regulation by enhancers represent one of the core morphogenetic mechanisms and might lay the foundations for intra- and inter-species facial variability.

Objectives: Magnitudes of morphological integration may constrain or facilitate craniofacial shape variation. The aim of this study was to analyze how the magnitude of integration in the skull of Macaca fascicularis changes throughout ontogeny in relation to developmental and/or functional modules. Materials and methods: Geometric morphometric methods were used to analyze the magnitude of integration in the macaque cranium and mandible in 80 juvenile and 40 adult M. fascicularis specimens. Integration scores in skull modules were calculated using integration coefficient of variation (ICV) of eigenvalues based on a resampling procedure. Resultant ICV scores between the skull as a whole, and developmental and/or functional modules were compared using Mann–Whitney U tests. Results: Results showed that most skull modules were more tightly integrated than the skull as a whole, with the exception of the chondrocranium in juveniles without canines, the chondrocranium/face complex and the mandibular corpus in adults, and the mandibular ramus in all juveniles. The chondrocranium/face and face/mandibular corpus complexes were more tightly integrated in juveniles than adults, possibly reflecting the influences of early brain growth/development, and the changing functional demands of infant suckling and later masticatory loading. This is also supported by the much higher integration of the mandibular ramus in adults compared with juveniles. Discussion Magnitudes of integration in skull modules reflect developmental/functional mechanisms in M. fascicularis. However, the relationship between "evolutionary flexibility" and developmental/functional mechanisms was not direct or simple, likely because of the complex morphology, multifunctionality, and various ossification origins of the skull. [ABSTRACT FROM AUTHOR]

The morphological diversity of anuran larvae made them an important source of information for evolutionary and systematic studies. For the monotypic frog genus Lithodytes , which has an interesting taxonomic history, including its past synonymizing with Adenomera and its placement as a subgenus of Leptodactylus , the information provided from its larvae can help to understand its systematics interrelationships and also provide insights about its evolutionary trajectories. Herein, we provide a detailed description of the larval morphology of Lithodytes lineatus , including novel data of internal morphology (buccopharyngeal cavity and skeleton), and discuss some morphological and evolutionary aspects in relation to other members of the subfamily Leptodactylinae. Despite the overall similar larval morphology with others members of the subfamily, we identified four autapomorphic traits for Lithodytes and seven purported homoplastic traits with a subclade of the Leptodactylus pentadactylus species group that likely evolved convergently. Some of these traits have been previously associated with a carnivorous diet. Putative homoplastic and autapomorphic characters served as additional diagnostic traits for Lithodytes, supporting its recognition as a distinct genus within Leptodactylidae. [ABSTRACT FROM AUTHOR]

Abstract Background The study of chondrocrania has a long tradition with a focus on single specimens and stages. It revealed great interspecific diversity and a notion of intraspecific variation. As an embryonic structure, the chondrocranium is subject to major changes in ontogeny with resorption and ossification of different cartilaginous structures. The cupula nasi anterior is the anteriormost portion of the cartilaginous nasal capsule and is expected to mirror much of the animal's life history and lifestyle. Its diversity in mammals is reflected in the external nasal anatomy of newborns. Marsupials and placentals show marked differences, likely related to breathing and suckling behavior. Results We examined histological sections of five marsupial and three placentals species and traced the development of the cupula nasi anterior and the anterior nasal capsule. We found ontogenetic variation for nearly 50% of the 43 characters defined herein. By comparing to the literature and considering ontogenetic variation, we performed an analysis of character evolution in 70 mammalian species and reconstructed the nasal anatomy of the therian ancestor. Conclusions At birth, marsupials have a complete but simple cupula nasi anterior, whereas placentals display a more diverse morphology due to reductions and variations of chondrocranial elements. The more compact nasal capsule in marsupials is related to a long and strong fixation to the mother’s teat after birth. Within marsupials and placentals, several derived characters distinguish major taxa, probably related to developmental and functional constraints. The reconstructed ancestral anatomy of the cupula nasi anterior supports the hypothesis that the therian ancestor was placental-like and that the marsupial lifestyle is more derived.

The mammalian skull is composed of the calvarial bones and cartilages. Malformation of craniofacial cartilage has been identified in multiple human syndromes. However, the mechanisms of their development remain largely unknown. In the present study, we identified Pdgfra as a novel player of chondrocranial cartilage development. Our data show that Pdgfra is required for normal chondrocranial cartilage development. Using tissue-specific genetic tools, we demonstrated that Pdgfra is essential for chondrocyte progenitors formation, but not in mature chondrocytes. Further analysis revealed that Pdgfra regulates chondrocytes progenitors development at two stages: in embryonic mesenchymal stem cells (eMSCs), Pdgfra directs their differentiation toward chondrocyte progenitors; in chondrocytes progenitors, Pdgfra activation promotes cell proliferation. We also found that excessive Pdgfra activity causes ectopic cartilage formation. Our data show that Pdgfra directs eMSCs differentiation via inhibiting Wnt9a transcription and its downstream signaling, and activating Wnt signaling rescues ectopic cartilage phenotype caused by excessive Pdgfra activity. In summary, our study dissected the role of Pdgfra signaling in chondrocranial cartilage formation, and illustrated the underlying mechanisms at multiple stages. • Pdgfra is a novel regulator of chondrocranial development. • Pdgfra directs eMSCs differentiation towards chondrocyte progenitor fate. • Pdgfra regulates eMSCs differentiation via Wnt9a transcription and Wnt signaling. • Alteration of Wnt signaling rescues ectopic cartilage caused by excessive Pdgfra activity during TTR development. Our study identified Pdgfra as a novel regulator of chondrocranial cartilage development and revealed that Pdgfra directs eMSCs fate via inhibiting Wnt/beta catenin signaling in this process. [ABSTRACT FROM AUTHOR]

Boana atlantica was described based on morphological characters to acommodate populations from Bahia state, Brazil, previously referred to as B. punctata. However, its taxonomic validity is questionable due to inconsistencies in bioacoustic data. Here, we integrate molecular, cytogenetic and morphological data to re-evaluate the taxonomic status of B. atlantica. Molecular analyses provided strong support for the hypothesis that B. atlantica is a valid species, being, however, nominal populations from Bahia state paraphyletic with respect to individuals of B. atlantica collected in Alagoas and Pernambuco states. These populations shown high genetic divergence in the 16S rRNA mitochondrial fragment, and we consider populations from Alagoas and Pernambuco as a putative new candidate species of Boana punctata group. The external and internal morphology of the tadpoles of these lineages were similar, but Nucleolar Organizer Regions (NOR) was sited in different chromosomes. Our results indicate that B. atlantica is paraphyletic and may be a complex of species. Morphological of adult and/or bioacoustical data should be further assessed to find diagnostic characters to tease these lineages apart and name them properly. [ABSTRACT FROM AUTHOR]

Chrondrocranium, the cartilaginous skull, is one of the major innovations that underlie evolution of the vertebrate head. Control of the induction and shaping of the cartilage is a key for the formation of the facial bones and largely defines facial shape. The appearance of cartilage in the head enabled many new functions such as protection of central nervous system and sensory structures, support of the feeding apparatus and formation of muscle attachment points ensuring faster and coordinated jaw movements. Here we review the evolution of cartilage in the cranial region and discuss shaping of the chondrocranium in different groups of vertebrates. [ABSTRACT FROM AUTHOR]

Little is known about the embryonic development and variation of the chondrocranium in Crocodylia and there are no works on any Caiman species. Due to the importance of cranial features in the systematics of this clade, investigating the development of the skull in embryonic stages is essential. In this study, we present for the first time the development of the cartilaginous skull of two extant Caiman species. Anatomical descriptions of the embryonic chondrocranium of Caiman latirostris and Caiman yacare were made, paying special attention to their inter‐ and intraspecific variation. For this purpose, pre‐hatching ontogenetic cranial series of these two caiman species were prepared with a double staining and diaphanization technique. The main differences with other crocodylian species were observed in the palatoquadrate, and interspecific variation within the genus was recorded in the hyobranchial apparatus and larynx. Some characters may be distinctive of Caiman (posterior and ventral surface of the otic process of the palatoquadrate articulated with the dorsal process of the columella auris, and otic process articulated with the lateral wall of the auditory capsule), Alligatoridae (presence of an epiphanial foramen) or C. latirostris and C. yacare (Corpus hyoidei with different number and position of foramina and different shapes of its anterior contour and anterior and posterior notch, different degrees of broadening of the distal end of the Cornu branchiale I, and presence/absence of a notch in the posteroventral surface of the cricoid). Homologies of the elements belonging to the hyobranchial apparatus could not be confirmed. As in other tetrapods the trachea consists of incomplete cartilaginous rings. Morphological changes and dissimilarities found in this study are useful as a context to start studying phylogenetic constraints. Moreover, in a heterochronic context, variations may be involved. [ABSTRACT FROM AUTHOR]

This study provides a comprehensive description of chondrocranial development before, during and after larval metamorphosis in the tongue sole Cynoglossus semilaevis, a commercially valuable flatfish in China. Samples were collected at regular intervals ranging from 1 to 23 days post hatching (dph). Based on observations of cleared and double‐stained specimens and images from sections stained with safranin O–fast green, major morphological events during early development were described. No cartilaginous structure was visible at hatching. From 2 dph onwards, cartilaginous structures such as the trabecular bar and some elements of the mandibular, hyoid and branchial arches appeared. At this time also, cartilaginous structures of the neurocranium started to form. Hypertrophic chondrocytes could be observed in many splanchnocranium elements at 5 dph. The start of ossification was indicated by alizarin red stain visible at 14 dph. At 17 dph, most of the cartilaginous skeleton was ossified. Soon after, the right eye started to migrate and pass through a slit beneath the dorsal‐fin base and above the skull. Metamorphosis was complete at 20 dph, at which time the dorsal‐fin base cartilage extended onto the anterior region of the head. Meanwhile, extremities of the hyoid and branchial arch elements remained cartilaginous. At 23 dph, endochondral ossification of the splanchnocranium was nearly complete. Unlike previous observations of other Pleuronectiformes, our study indicates that endochondral ossification of C. semilaevis skull cartilage occurs before metamorphosis. [ABSTRACT FROM AUTHOR]

We describe the formation of the chondrocranium and the ossification pattern of the skull of the Black Caiman (Melanosuchus niger (Spix, 1825)). The embryos were cleared and double-stained with Alizarin Red S and Alcian Blue 8GX. Additionally, they were visualized by histological hematoxylin and eosin staining and computed tomography imaging. The chondrocranium of M. niger comprised the nasal capsule, orbitotemporal, and optic–occipital regions. Its development began at stage 9, with the chondrification of the acrochordal cartilage, trabeculae, and mandibular cartilage. The optic capsule was formed in the caudolateral portion of the chondrocranium at stage 13. The basal plate appeared at stage 14, with foramina for the hypoglossal. The chondrocranium was completely formed at stage 16. The first osteogenic events were noted at stage 13, in the bones, maxilla, jugal, postorbital, and pterygoid. The quadratojugal, prefrontal, frontal, and squamosal began their ossification at stage 14. The parietal bone began to ossify only at stage 20. The basisphenoid began at stage 15 and the parasphenoid began at stage 16. The jaw bones ossified between stages 13 and 16. The dermal elements started their ossification prior to the endochondral bones. [ABSTRACT FROM AUTHOR]

The avian viscerocranium has been described by several investigators. It was perceived that a review on the ontogeny of the avian viscerocranium would be very useful to enrich the knowledge on this subject. The present article casts light on the avian viscerocranium starting from the early stages up to fairly late ones.

Achondroplasia, the most common chondrodysplasia in humans, is caused by one of two gain of function mutations localized in the transmembrane domain of fibroblast growth factor receptor 3 (FGFR3) leading to constitutive activation of FGFR3 and subsequent growth plate cartilage and bone defects. Phenotypic features of achondroplasia include macrocephaly with frontal bossing, midface hypoplasia, disproportionate shortening of the extremities, brachydactyly with trident configuration of the hand, and bowed legs. The condition is defined primarily on postnatal effects on bone and cartilage, and embryonic development of tissues in affected individuals is not well studied. Using the Fgfr3 Y367C/+ mouse model of achondroplasia, we investigated the developing chondrocranium and Meckel's cartilage (MC) at embryonic days (E)14.5 and E16.5. Sparse hand annotations of chondrocranial and MC cartilages visualized in phosphotungstic acid enhanced three-dimensional (3D) micro-computed tomography (microCT) images were used to train our automatic deep learning-based 3D segmentation model and produce 3D isosurfaces of the chondrocranium and MC. Using 3D coordinates of landmarks measured on the 3D isosurfaces, we quantified differences in the chondrocranium and MC of Fgfr3 Y367C/+ mice relative to those of their unaffected littermates. Statistically significant differences in morphology and growth of the chondrocranium and MC were found, indicating direct effects of this Fgfr3 mutation on embryonic cranial and pharyngeal cartilages, which in turn can secondarily affect cranial dermal bone development. Our results support the suggestion that early therapeutic intervention during cartilage formation may lessen the effects of this condition., (© 2023 The Authors. The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

Abstract: Objectives: Assessing the strength of integration among different regions of the modern human nasal complex is important for developing a more thorough understanding of the determinants of nasal morphology. Given the morphogenetic influence of cartilage on adjacent intramembranous growth sites, the interaction between chondrocranial‐ versus intramembranous‐derived nasal structures may have a significant influence on patterns of nasal variation. The purpose of this study is to examine integration between the chondrocranial‐ and intramembranous‐derived regions of the nasal complex. Materials and methods: Using computed tomograph (CT) scans, we collected three‐dimensional coordinate landmark data from a static adult sample (n = 62). First, using centroid size, and the symmetric and asymmetric components of shape variation, we examined the strength of integration between landmarks representing chondrocranial‐derived structures (e.g., ethmoid, external nasal cartilages) and landmarks representing intramembranous‐derived structures (nasal floor, anterior nasal aperture, etc.). Second, given that the strength of integration is a relative measure, we compared integration between chondrocranial‐ and intramembranous‐derived structures to the more modularized external and internal regions of the nasal complex. Results: There was significant moderate morphological integration between chondrocranial‐ versus intramembranous‐derived regions of the nasal complex. Moreover, integration between chondrocranial‐ versus intramembranous‐derived structures was consistently stronger when compared to external versus internal regions for both the symmetric and asymmetric components of variation. Thus, more covariation within the nasal complex could be explained by the relationship between chondrocranial‐ and intramembranous‐derived structures. Conclusions: Our results suggest that the interaction between chondrocranial‐ and intramembranous‐derived structures may be an important determinant in the patterning of nasal complex variation. [ABSTRACT FROM AUTHOR]

Abstract: Dalatiid sharks are members of a family of predominantly small, midwater meso‐ and bathypelagic chondrichthyans. The family is notable for both its number of monotypic genera and high morphological disparity. Three of the seven dalatiid genera are known only from holotype specimens (Mollisquama parini) or from only a handful of specimens (Euprotomicroides zantedeschia, Heteroscymnoides marleyi), with the only detailed anatomical work consistent across all taxa being studies of dentition. Here, we present detailed anatomical description of the second‐ever specimen of Mollisquama (Mollisquama sp.) covering chondrocranial, jaw, dental, and muscular anatomy, derived from a phase‐contrast synchrotron microtomographic scan. Mollisquama sp. is unique among dalatiids in possessing a deep carinal process, extending ventrally from the bar between the subethmoid region and basal angle in squaloid sharks, containing a large fenestra infiltrated by the suborbitalis muscle. Mollisquama sp. also exhibits additional possibly diagnostic features, including a planar configuration of the labial cartilages and the absence of labial folds; a pad‐like orbital process on the palatoquadrate; and the origination of the suborbitalis muscle solely on the carina, rather than the intraorbital wall. Character optimization of anatomical data onto a phylogeny of dalatiid sharks suggests Mollisquama sp. to be among the most specialized in the family, expanding the existing dalatiid morphospace. However, the functional significance of such transformations remains unclear. Synchrotron‐derived data, which do not require chemical pretreatment of specimens, may elucidate soft‐tissue functional correlates in future studies of undersampled taxa, such as dalatiids. [ABSTRACT FROM AUTHOR]

Herein, we provide external and internal morphological data of Scinax skuki tadpoles from its type locality. The benthic tadpole of S. skuki has eyes and nostrils positioned dorsally, vent tube dextral and reaching the free margin of the ventral fin, oral disk ventral with posterior margin concave when partially closed, labial tooth row formula 2/3, and the presence of nonpigmented spurs behind the lower jaw. These characters, together with the absence of a tectum parietale, and the shapes of the pars articularis quadrati and suprarostral, are useful for species identification and may be informative for systematic purposes. [ABSTRACT FROM AUTHOR]

Cartilaginous structures are at the core of embryo growth and shaping before the bone forms. Here we report a novel principle of vertebrate cartilage growth that is based on introducing transversally-oriented clones into pre-existing cartilage. This mechanism of growth uncouples the lateral expansion of curved cartilaginous sheets from the control of cartilage thickness, a process which might be the evolutionary mechanism underlying adaptations of facial shape. In rod-shaped cartilage structures (Meckel, ribs and skeletal elements in developing limbs), the transverse integration of clonal columns determines the well-defined diameter and resulting rod-like morphology. We were able to alter cartilage shape by experimentally manipulating clonal geometries. Using in silico modeling, we discovered that anisotropic proliferation might explain cartilage bending and groove formation at the macro-scale.

Palaeospondylus gunni Traquair, 1890 is an enigmatic Devonian vertebrate whose taxonomic affinities have been debated since it was first described. Most recently, Palaeospondylus has been identified as a stem-group hagfish (Myxinoidea). However, one character questioning this assignment is the presence of three semicircular canals in the otic region of the cartilaginous skull, a feature of jawed vertebrates. Additionally, new tomographic data reveal that the following characters of crown-group gnathostomes (chondrichthyans + osteichthyans) are present in Palaeospondylus: a longer telencephalic region of the braincase, separation of otic and occipital regions by the otico-occipital fissure, and vertebral centra. As well, a precerebral fontanelle and postorbital articulation of the palatoquadrate are characteristic of certain chondrichthyans. Similarities in the structure of the postorbital process to taxa such as Pucapampella, and possible presence of the ventral cranial fissure, both support a resolution of Pa. gunni as a stem chondrichthyan. The internally mineralized cartilaginous skeleton in Palaeospondylus may represent a stage in the loss of bone characteristic of the Chondrichthyes.