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The discovery of a living coelacanth specimen in 1938 was remarkable, as this lineage of lobe-finned fish was thought to have become extinct 70 million years ago. The modern coelacanth looks remarkably similar to many of its ancient relatives, and its evolutionary proximity to our own fish ancestors provides a glimpse of the fish that first walked on land. Here we report the genome sequence of the African coelacanth, Latimeria chalumnae. Through a phylogenomic analysis, we conclude that the lungfish, and not the coelacanth, is the closest living relative of tetrapods. Coelacanth protein-coding genes are significantly more slowly evolving than those of tetrapods, unlike other genomic features. Analyses of changes in genes and regulatory elements during the vertebrate adaptation to land highlight genes involved in immunity, nitrogen excretion and the development of fins, tail, ear, eye, brain and olfaction. Functional assays of enhancers involved in the fin-to-limb transition and in the emergence of extra-embryonic tissues show the importance of the coelacanth genome as a blueprint for understanding tetrapod evolution.

The acquisition of terrestrial, limb-based locomotion during tetrapod evolution has remained a subject of debate for more than a century 1 , 2 . Our current understanding of the locomotor transition from water to land is largely based on a few exemplar fossils such as Tiktaalik 3 , Acanthostega 4 , Ichthyostega 5 and Pederpes 6 . However, isolated bony elements may reveal hidden functional diversity, providing a more comprehensive evolutionary perspective 7 . Here we analyse 40 three-dimensionally preserved humeri from extinct tetrapodomorphs that span the fin-to-limb transition and use functionally informed ecological adaptive landscapes 8 – 10 to reconstruct the evolution of terrestrial locomotion. We show that evolutionary changes in the shape of the humerus are driven by ecology and phylogeny and are associated with functional trade-offs related to locomotor performance. Two divergent adaptive landscapes are recovered for aquatic fishes and terrestrial crown tetrapods, each of which is defined by a different combination of functional specializations. Humeri of stem tetrapods share a unique suite of functional adaptations, but do not conform to their own predicted adaptive peak. Instead, humeri of stem tetrapods fall at the base of the crown tetrapod landscape, indicating that the capacity for terrestrial locomotion occurred with the origin of limbs. Our results suggest that stem tetrapods may have used transitional gaits 5 , 11 during the initial stages of land exploration, stabilized by the opposing selective pressures of their amphibious habits. Effective limb-based locomotion did not arise until loss of the ancestral ‘L-shaped’ humerus in the crown group, setting the stage for the diversification of terrestrial tetrapods and the establishment of modern ecological niches 12 , 13 . Analysis of humeri from fossils that span the fin-to-limb transition reveal that the change in the humerus shape is driven by both ecology and phylogeny, and is associated with functional trade-offs related to locomotor performance.

\"Provides comprehensive information on the role hands, feet, arms, and legs play in the body science of humans and animals\"--Provided by the publisher.

New anomalocaridid specimens from the Early Ordovician Fezouata Biota of Morocco show well-preserved trunk anatomy, revealing evidence for the evolution of arthropod limbs. The evolution of arthropod limbs The classic 'Burgess Shales' variety of Cambrian fauna is now known to extend into the Ordovician that begins around 490 million years ago. The anomalocaridids, a diverse group of arthropod-like animals, are familiar as the giant predators of the Cambrian seas. Here Peter Van Roy et al . describe a much younger anomalocaridid from the Ordovician of Morocco, which was a filter-feeder more than two metres long. The new fossils reveal evolutionary relationships with arthropod limbs, in the form of two pairs of swimming flaps on each division of the trunk, the lower pair representing a modified leg and the upper pair representing gills. Exceptionally preserved fossils from the Palaeozoic era provide crucial insights into arthropod evolution, with recent discoveries bringing phylogeny and character homology into sharp focus 1 , 2 , 3 , 4 . Integral to such studies are anomalocaridids, a clade of stem arthropods whose remarkable morphology illuminates early arthropod relationships 5 , 6 and Cambrian ecology 7 , 8 , 9 . Although recent work has focused on the anomalocaridid head 6 , 7 , 8 , 9 , 10 , the nature of their trunk has been debated widely 5 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 . Here we describe new anomalocaridid 17 specimens from the Early Ordovician Fezouata Biota of Morocco 19 , which not only show well-preserved head appendages providing key ecological data, but also elucidate the nature of anomalocaridid trunk flaps, resolving their homology with arthropod trunk limbs. The new material shows that each trunk segment bears a separate dorsal and ventral pair of flaps, with a series of setal blades attached at the base of the dorsal flaps. Comparisons with other stem lineage arthropods 16 , 20 , 21 , 22 indicate that anomalocaridid ventral flaps are homologous with lobopodous walking limbs and the endopod of the euarthropod biramous limb, whereas the dorsal flaps and associated setal blades are homologous with the flaps of gilled lobopodians (for example, Kerygmachela kierkegaardi , Pambdelurion whittingtoni ) and exites of the ‘Cambrian biramous limb’ 23 . This evidence shows that anomalocaridids represent a stage before the fusion of exite and endopod into the ‘Cambrian biramous limb’ 5 , 16 , 23 , confirming their basal placement in the euarthropod stem 4 , 5 , 6 , rather than in the arthropod crown 24 or with cycloneuralian worms 14 . Unlike other anomalocaridids, the Fezouata taxon combines head appendages convergently 9 adapted for filter-feeding with an unprecedented body length exceeding 2 m, indicating a new direction in the feeding ecology of the clade. The evolution of giant filter-feeding anomalocaridids may reflect the establishment of highly developed planktic ecosystems during the Great Ordovician Biodiversification Event 25 .

BackgroundInconsistent nomenclature and anatomical descriptions of regional anesthetic techniques hinder scientific communication and engender confusion; this in turn has implications for research, education and clinical implementation of regional anesthesia. Having produced standardized nomenclature for abdominal wall, paraspinal and chest wall regional anesthetic techniques, we aimed to similarly do so for upper and lower limb peripheral nerve blocks.MethodsWe performed a three-round Delphi international consensus study to generate standardized names and anatomical descriptions of upper and lower limb regional anesthetic techniques. A long list of names and anatomical description of blocks of upper and lower extremities was produced by the members of the steering committee. Subsequently, two rounds of anonymized voting and commenting were followed by a third virtual round table to secure consensus for items that remained outstanding after the first and second rounds. As with previous methodology, strong consensus was defined as ≥75% agreement and weak consensus as 50%–74% agreement.ResultsA total of 94, 91 and 65 collaborators participated in the first, second and third rounds, respectively. We achieved strong consensus for 38 names and 33 anatomical descriptions, and weak consensus for five anatomical descriptions. We agreed on a template for naming peripheral nerve blocks based on the name of the nerve and the anatomical location of the blockade and identified several areas for future research.ConclusionsWe achieved consensus on nomenclature and anatomical descriptions of regional anesthetic techniques for upper and lower limb nerve blocks, and recommend using this framework in clinical and academic practice. This should improve research, teaching and learning of regional anesthesia to eventually improve patient care.

This illustrated book describes how some finned vertebrates acquired limbs, giving rise to more than 25,000 extant terrapod species. Michel Laurin uses paleontological, geological, physiological, and comparative anatomical data to describe this monumental event. Along with discussing the evolutionary pressures that may have led vertebrates onto dry land, the author also shows how extant vertebrates yield clues about the conquest of land and how scientists uncover evolutionary history.--[book cover]

A reduction in the number of digits has evolved many times in tetrapods, particularly in cursorial mammals that travel over deserts and plains, yet the underlying developmental mechanisms have remained elusive. Here we show that digit loss can occur both during early limb patterning and at later post-patterning stages of chondrogenesis. In the ‘odd-toed’ jerboa ( Dipus sagitta ) and horse and the ‘even-toed’ camel, extensive cell death sculpts the tissue around the remaining toes. In contrast, digit loss in the pig is orchestrated by earlier limb patterning mechanisms including downregulation of Ptch1 expression but no increase in cell death. Together these data demonstrate remarkable plasticity in the mechanisms of vertebrate limb evolution and shed light on the complexity of morphological convergence, particularly within the artiodactyl lineage. A study of limb development in multiple mammals reveals that evolutionary digit loss has occured in many different ways—at different stages and by different mechanisms, such as regulation of Shh in initial digit specification events or by removal of digits through cell death. Mechanisms of evolutionary limb loss The basic five-digit limb of tetrapods has been altered many times and in many ways during evolution, usually by the progressive loss of digits. Two papers published in this issue of Nature examine the developmental changes underlying digit reduction in mammals. Javier Lopez-Rios et al . look at cattle, where digits three and four are modified to form hooves; digits two and five are vestigial, and the first digit is lost. The first limb bud is shown to be progressively lost as it develops. The Ptch1 gene, which encodes a receptor for the limb-development morphogen Sonic hedgehog (SHH), is upregulated due to evolutionary alteration of a Ptch1 cis -regulatory module that no longer responds to graded SHH signalling during bovine handplate development. Kimberly Cooper et al . show, using a wide range of mammals, that mechanisms of digit loss vary in different lineages. In creatures as varied as the jerboa and the camel, cell death sculpts the tissue in the emerging limb to leave the remaining toes. In other creatures, such as the pig, digit loss is orchestrated by earlier limb patterning events with no increase in cell death. Taken together these findings demonstrate remarkable plasticity in the mechanisms of limb evolution in hooved mammals and rodents, yet reveal a degree of evolutionary convergence.