The tetrapod Caerorhachis bairdi Holmes and Carroll from the Lower Carboniferous of Scotland

The tetrapod Caerorhachis bairdi, probably from the Pendleian Limestone Coal Group in the Scottish Midland Valley, is redi agnosed and redescribed, and its affinities are discussed. Caerorachis was originally interpreted as a temnospondyl amphibian, based on characters that are now regarded as primitive for tetrapods, or of uncertain polarity. Several features of Caerorhachis (e.g. gastrocentrous vertebrae, curved trunk ribs, reduced dorsal iliac blade, L-shaped tarsal intermedium) are observed in certain primitive amniotes. In particular, Caerorhachis resembles ‘anthracosaurs’, generally considered to be among the most primitive of stem-group amniotes. The phylogenetic position of Caerorhachis is considered in the light of recently published cladistic analyses of Palaeozoic tetrapods. Most analyses place Caerorhachis at the base of, or within, ‘anthra- cosaurs’. When multiple, equally parsimonious solutions are found, its ‘anthracosaur’ affinities are shown in at least some trees, and are supported by several informative and, generally, highly consistent characters. Alternative phylogenetic placements (e.g. sister taxon to temnospondyls) are usually less well corroborated. If the fundamental evolutionary split of most early tetrapods into stem-group lissamphibians (e.g. temnospondyl s) and stem-group amniotes (e.g. ‘anthracosaurs’) is accepted, then the revised interpretation of Caerorhachi s sheds light on near-ancestral conditions for Amniota

Styracopterid ( A ctinopterygii) ontogeny and the multiple origins of post‐ H angenberg deep‐bodied fishes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/99621/1/zoj12054.pd

The skeletal completeness of the Palaeozoic chondrichthyan fossil record

Chondrichthyes (sharks, rays, ratfish and their extinct relatives) originated and diversified in the Palaeozoic but are rarely preserved as articulated or partly articulated remains because of their predominantly cartilaginous endoskeletons. Consequently, their evolutionary history is perceived to be documented predominantly by isolated teeth, scales and fin spines. Here, we aim to capture and analyse the quality of the Palaeozoic chondrichthyan fossil record by using a variation of the skeletal completeness metric, which calculates how complete the skeletons of individuals are compared to estimates of their original entirety. Notably, chondrichthyan completeness is significantly lower than any published vertebrate group: low throughout the Silurian and Permian but peaking in the Devonian and Carboniferous. Scores increase to a range similar to pelycosaurs and parareptiles only when taxa identified solely from isolated teeth, scales and spines are excluded. We argue that environmental influences probably played an important role in chondrichthyan completeness. Sea level significantly negatively correlates with chondrichthyan completeness records and resembles patterns already evident in records of ichthyosaurs, plesiosaurs and sauropodomorphs. Such observed variations in completeness highlight the impact of different sampling biases on the chondrichthyan fossil record and the need to acknowledge these when inferring patterns of chondrichthyan macroevolution

Bones, molecules, and crown- tetrapod origins

ABSTRACT The timing of major events in the evolutionary history of early tetrapods is discussed in the light of a new cladistic analysis. The phylogenetic implications of this are compared with those of the most widely discussed, recent hypotheses of basal tetrapod interrelationships. Regardless of the sequence of cladogenetic events and positions of various Early Carboniferous taxa, these fossil-based analyses imply that the tetrapod crown-group had originated by the mid-to late Viséan. However, such estimates of the lissamphibian-amniote divergence fall short of the date implied by molecular studies. Uneven rates of molecular substitutions might be held responsible for the mismatch between molecular and morphological approaches, but the patchy quality of the fossil record also plays an important role. Morphology-based estimates of evolutionary chronology are highly sensitive to new fossil discoveries, the interpretation and dating of such material, and the impact on tree topologies. Furthermore, the earliest and most primitive taxa are almost always known from very few fossil localities, with the result that these are likely to exert a disproportionate influence. Fossils and molecules should be treated as complementary approaches, rather than as conflicting and irreconcilable methods

A symmoriiform from the Late Devonian of Morocco demonstrates a derived jaw function in ancient chondrichthyans

This work is licensed under a Creative Commons Attribution 4.0 International License.The Palaeozoic record of chondrichthyans (sharks, rays, chimaeras, extinct relatives) and thus our knowledge of their anatomy and functional morphology is poor because of their predominantly cartilaginous skeletons. Here, we report a previously undescribed symmoriiform shark, Ferromirum oukherbouchi, from the Late Devonian of the Anti-Atlas. Computed tomography scanning reveals the undeformed shape of the jaws and hyoid arch, which are of a kind often used to represent primitive conditions for jawed vertebrates. Of critical importance, these closely fitting cartilages preclude the repeatedly hypothesized presence of a complete gill between mandibular and hyoid arches. We show that the jaw articulation is specialized and drives mandibular rotation outward when the mouth opens, and inward upon closure. The resultant eversion and inversion of the lower dentition presents a greater number of teeth to prey through the bite-cycle. This suggests an increased functional and ecomorphological disparity among chondrichthyans preceding and surviving the end-Devonian extinctions.Swiss National Science Foundation (project number 200020_184894)NOW Vidi grant no. 864.14.00

Rise and diversification of chondrichthyans in the Paleozoic

The Paleozoic represents a key time interval in the origins and early diversification of chondrichthyans (cartilaginous fishes), but their diversity and macroevolution are largely obscured by heterogenous spatial and temporal sampling. The predominantly cartilaginous skeletons of chondrichthyans pose an additional limitation on their preservation potential and hence on the quality of their fossil record. Here, we use a newly compiled genus-level dataset and the application of sampling standardization methods to analyze global total-chondrichthyan diversity dynamics through time from their first appearance in the Ordovician through to the end of the Permian. Subsampled estimates of chondrichthyan genus richness were initially low in the Ordovician and Silurian but increased substantially in the Early Devonian. Richness reached its maximum in the middle Carboniferous before dropping across the Carboniferous/Permian boundary and gradually decreasing throughout the Permian. Sampling is higher in both the Devonian and Carboniferous compared with the Silurian and most of the Permian stages. Shark-like scales from the Ordovician are too limited to allow for some of the subsampling techniques. Our results detect two Paleozoic radiations in chondrichthyan diversity: the first in the earliest Devonian, led by acanthodians (stem-group chondrichthyans), which then decline rapidly by the Late Devonian, and the second in the earliest Carboniferous, led by holocephalans, which increase greatly in richness across the Devonian/Carboniferous boundary. Dispersal of chondrichthyans, specifically holocephalans, into deeper-water environments may reflect a niche expansion following the faunal displacement in the aftermath of the Hangenberg extinction event at the end of the Devonian

Embryonic origin of the gnathostome vertebral skeleton.

The vertebral column is a key component of the jawed vertebrate (gnathostome) body plan, but the primitive embryonic origin of this skeleton remains unclear. In tetrapods, all vertebral components (neural arches, haemal arches and centra) derive from paraxial mesoderm (somites). However, in teleost fishes, vertebrae have a dual embryonic origin, with arches derived from somites, but centra formed, in part, by secretion of bone matrix from the notochord. Here, we test the embryonic origin of the vertebral skeleton in a cartilaginous fish (the skate, Leucoraja erinacea) which serves as an outgroup to tetrapods and teleosts. We demonstrate, by cell lineage tracing, that both arches and centra are somite-derived. We find no evidence of cellular or matrix contribution from the notochord to the skate vertebral skeleton. These findings indicate that the earliest gnathostome vertebral skeleton was exclusively of somitic origin, with a notochord contribution arising secondarily in teleosts

First shark from the late Devonian (Frasnian) gogo formation, Western Australia sheds new light on the development of tessellated calcified cartilage

Background: Living gnathostomes (jawed vertebrates) comprise two divisions, Chondrichthyes (cartilaginous fishes, including euchondrichthyans with prismatic calcified cartilage, and extinct stem chondrichthyans) and Osteichthyes (bony fishes including tetrapods). Most of the early chondrichthyan (‘shark’) record is based upon isolated teeth, spines, and scales, with the oldest articulated sharks that exhibit major diagnostic characters of the group—prismatic calcified cartilage and pelvic claspers in males—being from the latest Devonian, c. 360 Mya. This paucity of information about early chondrichthyan anatomy is mainly due to their lack of endoskeletal bone and consequent low preservation potential. Methodology/Principal Findings: Here we present new data from the first well-preserved chondrichthyan fossil from the early Late Devonian (ca. 380–384 Mya) Gogo Formation Lägerstatte of Western Australia. The specimen is the first Devonian shark body fossil to be acid-prepared, revealing the endoskeletal elements as three-dimensional undistorted units: Meckel’s cartilages, nasal, ceratohyal, basibranchial and possible epibranchial cartilages, plus left and right scapulocoracoids, as well as teeth and scales. This unique specimen is assigned to Gogoselachus lynnbeazleyae n. gen. n. sp.Conclusions/Significance: The Meckel’s cartilages show a jaw articulation surface dominated by an expansive cotylus, and a small mandibular knob, an unusual condition for chondrichthyans. The scapulocoracoid of the new specimen shows evidence of two pectoral fin basal articulation facets, differing from the standard condition for early gnathostomes which have either one or three articulations. The tooth structure is intermediate between the ‘primitive’ ctenacanthiform and symmoriiform condition, and more derived forms with a euselachian-type base. Of special interest is the highly distinctive type of calcified cartilage forming the endoskeleton, comprising multiple layers of nonprismatic subpolygonal tesserae separated by a cellular matrix, interpreted as a transitional step toward the tessellated prismatic calcified cartilage that is recognized as the main diagnostic character of the chondrichthyans

Development of Methods for Cross-Sectional HIV Incidence Estimation in a Large, Community Randomized Trial

Background Accurate methods of HIV incidence determination are critically needed to monitor the epidemic and determine the population level impact of prevention trials. One such trial, Project Accept, a Phase III, community-randomized trial, evaluated the impact of enhanced, community-based voluntary counseling and testing on population-level HIV incidence. The primary endpoint of the trial was based on a single, cross-sectional, post-intervention HIV incidence assessment. Methods and Findings Test performance of HIV incidence determination was evaluated for 403 multi-assay algorithms [MAAs] that included the BED capture immunoassay [BED-CEIA] alone, an avidity assay alone, and combinations of these assays at different cutoff values with and without CD4 and viral load testing on samples from seven African cohorts (5,325 samples from 3,436 individuals with known duration of HIV infection [1 month to >10 years]). The mean window period (average time individuals appear positive for a given algorithm) and performance in estimating an incidence estimate (in terms of bias and variance) of these MAAs were evaluated in three simulated epidemic scenarios (stable, emerging and waning). The power of different test methods to detect a 35% reduction in incidence in the matched communities of Project Accept was also assessed. A MAA was identified that included BED-CEIA, the avidity assay, CD4 cell count, and viral load that had a window period of 259 days, accurately estimated HIV incidence in all three epidemic settings and provided sufficient power to detect an intervention effect in Project Accept. Conclusions In a Southern African setting, HIV incidence estimates and intervention effects can be accurately estimated from cross-sectional surveys using a MAA. The improved accuracy in cross-sectional incidence testing that a MAA provides is a powerful tool for HIV surveillance and program evaluation

Pembuatan Kulit Atasan Sepatu Bebas Krom

The purpose of this study was to obtain the process formulation for leather tanning in manufacturing chrome-free upper leather. The tanning process used vegetable tanning material (mimosa), syntan, and combination of vegetable-syntan. The leather were prepared using 25, 30, and 35% of mimosa, 10, 15, and 20% of syntan, and 15:10; 15:15; and 20%:15% of mimosa:syntan. Chrome tanning material 6% was used as control. Based from the results of physical testing according to SNI 0234:2009, the resulting leather met the quality requirements for shoe upper leather. Tanning process with 20% syntan gave the best result