The Gogo Formation of Western Australia preserves a unique Late Devonian (Frasnian) reef fauna. The exceptional three-dimensional preservation of macrofossils combined with unprecedented soft-tissue preservation (including muscle bundles, nerve cells, and umbilical structures) has yielded a particularly rich assemblage with almost 50 species of fishes described. The most significant discoveries have contributed to resolving placoderm phylogeny and elucidating their reproductive physiology. Specifically, these discoveries have produced data on the oldest known vertebrate embryos; the anatomy of the primitive actinopterygian neurocranium and phylogeny of the earliest actinopterygians; the histology, radiation, and plasticity of dipnoan (lungfish) dental and cranial structures; the anatomy and functional morphology of the extinct onychodonts; and the anatomy of the primitive tetrapodomorph head and pectoral fin.
Abstract Many species of lizard use caudal autotomy, the ability to self-amputate a portion of their tail, regenerated over time, as an effective anti-predation mechanism. The importance of this tactic for survival depends on the degree of predation risk. There are, however, negative trade-offs to losing a tail, such as loss of further autotomy opportunities with the regenerated tail vertebrae being replaced by a continuous cartilaginous rod. The common consensus has been that once a tail has been autotomised and regenerated it can only be autotomised proximal to the last vertebral autotomy point, as the cartilage rod lacks autotomy planes. However, anecdotal evidence suggests that although the regenerated portion of the tail is unable to autotomise, it can re-regenerate following a physical shearing event. We assessed re-regeneration in three populations of the King’s skink ( Egernia kingii ), a large lizard endemic to south-west Western Australia and surrounding islands. We show that re-regeneration is present at an average of 17.2% across the three populations, and re-regenerated tissue can comprise up to 23.3% of an individual’s total tail length. The ability to re-regenerate may minimise the costs to an individual’s fitness associated with tail loss, efficiently restoring ecological functions of the tail.
—A new genus and species of selenosteid arthrodire is described from the Late Devonian of Morocco. Driscollaspis pankowskiorum, gen. nov. sp. nov., is defined as a selenosteid with a shallow preorbital plate embayment of the central plate, a paranuchal plate embayment of the central plate as a deep embayment determined by the lateral and posterior lobe, a central plate expanded at the contact with the pineal plate as transverse anterior border, and a suborbital plate overlapping the postorbital plate. The dermal ornamentation is tubercular, forming patches of reticular ridges clustered around sensory-line canal junctions in plate centers. The sensory-line canals are distinctly raised just above the level of the dermal ornamentation, a unique character not previously recognized in any arthrodire but seen in some ptyctodontids. A new phylogenetic hypothesis supports the monophyly of the Selenosteidae within which this new taxon is resolved, but emphasizes also unresolved relationships among aspinothoracid arthrodires. The paleogeographic distribution of the Frasnian vertebrates from Morocco and especially the seleonsteids on the western margin of Gondwana and Laurussia are discussed, and the indication for a contact of both continents during the late Frasnian is emphasized.http://zoobank.org/urn:lsid:zoobank.org:pub:D0287127-C713-4BB1-9A27-242679041C22SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP
The pursuit of simple, yet fair, unbiased, and objective measures of researcher performance has occupied bibliometricians and the research community as a whole for decades. However, despite the diversity of available metrics, most are either complex to calculate or not readily applied in the most common assessment exercises (e.g., grant assessment, job applications). The ubiquity of metrics like the h -index ( h papers with at least h citations) and its time-corrected variant, the m -quotient ( h -index ÷ number of years publishing) therefore reflect the ease of use rather than their capacity to differentiate researchers fairly among disciplines, career stage, or gender. We address this problem here by defining an easily calculated index based on publicly available citation data (Google Scholar) that corrects for most biases and allows assessors to compare researchers at any stage of their career and from any discipline on the same scale. Our ε ′-index violates fewer statistical assumptions relative to other metrics when comparing groups of researchers, and can be easily modified to remove inherent gender biases in citation data. We demonstrate the utility of the ε ′-index using a sample of 480 researchers with Google Scholar profiles, stratified evenly into eight disciplines (archaeology, chemistry, ecology, evolution and development, geology, microbiology, ophthalmology, palaeontology), three career stages (early, mid-, late-career), and two genders. We advocate the use of the ε ′-index whenever assessors must compare research performance among researchers of different backgrounds, but emphasize that no single index should be used exclusively to rank researcher capability.
Fusion in the vertebral column has evolved multiple times within jawed vertebrates and for these taxa represents normal physiology, with structures such as the sacrum, notarium and pygostyle providing rigidity and support.The synarcual represents the fusion of the anterior part of the vertebral column and occurs in a number of jawed vertebrates, including a variety of placoderms, chondrichthyans and mammals.Placoderms are an entirely fossil group of armoured fishes (Silurian-Devonian), resolved phylogenetically to the base of the jawed vertebrate clade, with vertebrae comprising neural and haemal arches composed of perichondral bone.The placoderm synarcual preserves substantial developmental information from anterior (oldest) to posterior, where new vertebrae are incorporated.This developmental sequence was described recently in the phyllolepid arthrodire Cowralepis mclachlani and ptyctodonts such as Materpiscis attenboroughi, although finer developmental details were not visible.We describe the synarcual in a subadult specimen of the pachyosteomorph arthrodire Dunkleosteus terrelli, preserving 16 paired vertebral elements showing varying degrees of anteroposterior fusion along the vertebral column.Micro-CT scanning of the synarcual provides details of a transitional zone of vertebral modification (involving four of these paired vertebrae, posteriorly), providing unprecedented information on how each vertebra is altered and incorporated into the synarcual.Some of the synarcual elements still retain substantial vertebral identity, showing less fusion overall, thus being more comparable to other arthrodires such as Compagopiscis.By comparison, synarcuals of other taxa, such as the ptyctodont placoderms, along with batoids, holocephalans (Chondrichthyes) and mammals (syncervical) show more complete fusion of vertebral elements.
The ontogenetic trajectories of dermal plates of the arthrodiran placoderrns Compagopiscis crollchcri and lncisosclltllm ritchici from the Late Devonian Gogo Formation, Canning Basin, Western Australia were compared to assess the impact of heterochrony. Most characters showed peramorphosis. Allometric predisplacement occurred in: the biting division of the inferognathal; the anterior ventrolateral; and the median dorsal plate's breadth. Allometric hypermorphosis was seen in the increases of the prepineal length of the skull roof and the median dorsal plate length. Peramorphic traits contributed to a trend of skull elongation. Fewer paedomorphic features were found. Allometric postdisplacement that resulted in paedomorphosis occurred in the postmesial breadth and the orbital diameter of the skull roof. It is suggested that lengthwise growth occurs earlier in ontogeny than breadthways growth, and that dissociated heterochrony was an important mechanism in the evolution of these arthrodires.
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