Biology subjects

Coates, M. I.

Publications and source records attributed to Coates, M. I..

4 recordsLinked to original sources

bioRxiv2025

Teeth Outside the Jaw: Evolution and Development of the Toothed Head Clasper in Chimaeras

Chimaeras (Holocephali) are an understudied group of mostly deep-ocean cartilaginous fishes (Chondrichthyes) with unique characteristics that distinguish them from their distant relatives, sharks, skates, and rays. Unlike sharks, chimaeras lack scales and do not have serially replacing rows of serrated teeth crowned with enameloid. Instead, they possess a fused dentition of dentine toothplates. Additionally, male chimaeras develop an articulated cartilaginous facial appendage, the tenaculum, which is covered in an arcade of tooth-like structures. These seeming extraoral teeth remain poorly understood, and their evolutionary origin is unclear. We investigate the development of the tenaculum and its teeth throughout the ontogeny of the Spotted Ratfish, Hydrolagus colliei, to assess homology and convergence between this novel craniofacial feature and oral jaws. Our study aims to: (1) describe the development of the tenaculum, (2) assess tenaculum tooth development in comparison to oral teeth and denticles, and (3) characterize the genes and tissues responsible for tenaculum tooth emergence. We found that juvenile male chimaeras develop a full tenaculum before tooth development is complete and that only mature males possess a fully toothed tenaculum. These extraoral teeth emerge from within the tenaculum rather than from the surrounding epithelium. We integrate our developmental data with fossil evidence of the tenacula dentition from the Carboniferous holocephalan Helodus simplex. Our findings show that the tenaculum is closely associated with the upper jaw and that tenacula dentition resembles separate shark-like oral tooth whorls more than modified dermal denticles. Significance StatementThe development and evolutionary history of extraoral dentition in vertebrates remain largely unexplored. This study investigates the ontogeny of the male tenaculum, a unique feature of chimaeras, revealing a tooth development pathway similar to the oral dentition in sharks. By integrating fossil data and molecular techniques, we hypothesize that tenaculum teeth are homologous to oral teeth rather than modified skin denticles, providing key insights into the plasticity of odontogenesis and craniofacial diversity in vertebrates.

developmental biology↗

bioRxiv2025

Development of the zebrafish anterior lateral line system is influenced by underlying cranial neural crest

The mechanosensory lateral line system of aquatic vertebrates comprises a superficial network of distributed sensory organs, the neuromasts, which are arranged over the head and trunk and innervated by lateral line nerves to allow detection of changes in water flow and pressure. While the well-studied zebrafish posterior lateral line has emerged as a powerful model to study collective cell migration, far less is known about development of the anterior lateral line, which produces the supraorbital and infraorbital lines around the eye, as well as mandibular and opercular lines over the jaw and cheek. Here we show that normal development of the zebrafish anterior lateral line system from cranial placodes is dependent on another vertebrate-specific cell type, the cranial neural crest. We find that cranial neural crest and anterior lateral lines develop in close proximity, with absence of neural crest cells leading to major disruptions in the overlying anterior lateral line system. Specifically, in the absence of neural crest neither supraorbital nor infraorbital lateral lines fully extend, such that the most anterior cranial regions remain devoid of neuromasts, while supernumerary ectopic neuromasts form in the posterior supraorbital region. Both neural crest and cranial placodes contribute neurons to the lateral line ganglia that innervate the neuromasts and in the absence of neural crest these ganglia, as well as the lateral line afferent nerves, are disrupted. Finally, we establish that as ontogeny proceeds, the most anterior supraorbital neuromasts come to lie within neural crest-derived frontal and nasal bones in the developing cranium. These are the same anterior supraorbital neuromasts that are absent or mislocated in specimens lacking neural crest cells. Together, our results establish that cranial neural crest and cranial placode derivatives function in concert over the course of ontogeny to build the complex cranial lateral line system. HighlightsO_LIThe anterior lateral line and cranial neural crest develop in close proximity C_LIO_LIAbsence of neural crest disrupts anterior lateral line development C_LIO_LIAbsence of neural crest disrupts lateral line ganglion morphology and innervation C_LIO_LIEarly interactions of neural crest and placodes prefigure later anatomical interactions C_LI O_FIG O_LINKSMALLFIG WIDTH=196 HEIGHT=200 SRC="FIGDIR/small/637483v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@ce9c43org.highwire.dtl.DTLVardef@7511e5org.highwire.dtl.DTLVardef@1e9e208org.highwire.dtl.DTLVardef@1f6af7d_HPS_FORMAT_FIGEXP M_FIG C_FIG

developmental biology↗

bioRxiv2025

The lower jaw of Devonian ray-finned fishes (Actinopterygii): anatomy, relationships, and functional morphology

Actinopterygii is a major extant vertebrate group, but limited data are available for its earliest members. Here we investigate the morphology of Devonian actinopterygians, focusing on the lower jaw. We use X-Ray Computed Tomography (XCT) to provide comprehensive descriptions of the mandibles of 19 species, which span the whole of the Devonian and represent roughly two thirds of all taxa known from more than isolated or fragmentary material. Our findings corroborate previous reports in part but reveal considerable new anatomical data and represent the first detailed description for roughly half of these taxa. The mandibles display substantial variation in size, spanning more than an order of magnitude. Although most conform to a generalized pattern of a large dentary and one or two smaller infradentaries, XCT data reveal significant differences in the structure of the jaw and arrangement of teeth that may be of functional relevance. We report the presence of a rudimentary coronoid process in several taxa, contributed to by the dentary and/or infradentaries, as well a raised articular region, resulting in a mandible with an offset bite and that functions as a bent level arm. Among the most striking variation is that of tooth morphology: several taxa have heterodont dentary teeth that vary in size and orientation, and multiple variations on enlarged, whorl-like and posteriorly-oriented anterior coronoid dentition are observed. We use these new data to revise morphological characters that may be of phylogenetic significance and consider the possible functional implications of these traits. The observed variation in mandible form and structure suggests previously unappreciated functional diversity among otherwise morphologically homogenous Devonian ray-finned fishes.

paleontology↗

bioRxiv2022

Exceptional fossil preservation and evolution of the ray-finned fish brain

Brain anatomy provides key evidence for ray-finned fish relationships1, but two key limitations obscure our understanding of neuroanatomical evolution in this major vertebrate group. First, the deepest branching living lineages are separated from the groups common ancestor by hundreds of millions of years, with indications that aspects of their brain morphology-like other aspects of their anatomy2,3-are specialised relative to primitive conditions. Second, there are no direct constraints on brain morphology in the earliest ray-finned fishes beyond the coarse picture provided by cranial endocasts: natural or virtual infillings of void spaces within the skull4-8. Here we report brain and cranial nerve soft-tissue preservation in {dagger}Coccocephalichthys wildi, a [~]319-million-year-old (Myr) ray-finned fish. This oldest example of a well-preserved vertebrate brain provides a unique window into neural anatomy deep within ray-finned fish phylogeny. {dagger}Coccocephalichthys indicates a more complicated pattern of brain evolution than suggested by living species alone, highlighting cladistian apomorphies9 and providing temporal constraints on the origin of traits uniting all extant ray-finned fishes9-11. Our findings, along with a growing set of studies in other animal groups12-16, point to the significance of ancient soft tissue preservation in understanding the deep evolutionary assembly of major anatomical systems outside of the narrow subset of skeletal tissues17-20.

paleontology↗