David Legg | University of Oxford (original) (raw)

Papers by David Legg

Bookmarks Related papers MentionsView impact

Utahcaris orion Conway Morris & Robison, 1988, from the lower middle Cambrian (Series 3, Stage 5)... more Utahcaris orion Conway Morris & Robison, 1988, from the lower middle Cambrian (Series 3, Stage 5) Spence Shale Member situated in Utah, USA, is redescribed based on a restudy of the original material. Newly recognized features , including ventral lateral eyes, trunk appendages, and a bulbous cephalic shield with subtriangular extension, reinforce similarities with Sanctacaris uncata from the middle Cambrian Burgess Shale. Both are assigned to the new family, Sanctacarididae. Sanctacaridids represent the oldest chelicer-ates. Their ecology and that of their nearest non-chelicerate relatives indicate that Chelicerata were plesiomorphically predatory.

Bookmarks Related papers MentionsView impact

Exceptional preservation of non-biomineralized arthropods, sponges and vermiform taxa occurs in t... more Exceptional preservation of non-biomineralized arthropods, sponges and vermiform taxa occurs in the Darriwilian (Middle Ordovician) Llanfallteg Formation of South Wales, UK. The assemblage contains elements typical of Ordovician communities juxtaposed with those more commonly associated with Cambrian Konservat-Lagerstätten. This assemblage is
preserved in rocks of a deep-marine succession dominated by fine-grained siliciclastic and volcaniclastic density-current
deposits. Non-biomineralized taxa of Cambrian aspect are preserved as pyritized carbonaceous compressions on the spectrum of Burgess Shale-type preservation. Trilobites with phosphatized digestive structures have also been recovered. The assemblage of the Llanfallteg Formation Konservat-Lagerstätte demonstrates that some Burgess Shale-type faunal elements survived into the Middle Ordovician within cool, deep-water refugia in the Welsh Basin, offshore from communities dominated by typical Ordovician taxa.

Bookmarks Related papers MentionsView impact

The Middle Ordovician Llanfalteg Formation has yielded remains of soft-bodied organisms previousl... more The Middle Ordovician Llanfalteg Formation has yielded remains of soft-bodied organisms previously known only from Cambrian Burgess Shale-type deposits. Here a new arthropod, Etania howellsorum gen. et sp. nov. is described, characterised by a semi-circular cephalon, clusters of spinose endites on the endopod, and exopods with ovoid distal lobes. These characters are consistent with xenopod affinities, a clade otherwise known exclusively from the Cambrian. The discovery of E. howellsorum demonstrates that a number of Burgess Shale-type taxa, including xenopods survived past the Cambrian, albeit within a restricted environment, and may have been outcompeted during the Great Ordovician Biodiversification Event (GOBE).

Bookmarks Related papers MentionsView impact

The morphology of the arthropod Sanctacaris uncata, from the Middle Cambrian Burgess Shale of Can... more The morphology of the arthropod Sanctacaris uncata, from the Middle Cambrian Burgess Shale of Canada, is reinterpreted based on a restudy of previously described material. Although originally considered a chelicerate-like arthropod, these affinities were dismissed based primarily on interpretations of the anterior appendages, and hypotheses which considered the megacheirans (“great-appendage” arthropods as putative ancestors of chelicerates. The similarities between megacheirans and chelicerates appear to be overstated however, and this study instead reaffirms the identity of putative chelicerate feature in Sanctacaris uncata and similar arthropods such as Sidneyia and Emeraldella, both also from the Middle Cambrian Burgess Shale. Newly interpreted features, including the presence of pediform exites, multi-partite trunk exopods, and a trunk differentiated into an anterior limb-bearing area and a differentiated posterior limb-less abdomen, were coded into an extensive phylogenetic data set of fossil and Recent arthropods. In all analyses Sanctacaris resolved as the basal-most member of total-group Euchelicerata (the least inclusive group including horseshoe crabs and arachnids but not pycnogonids), thus making it the oldest chelicerate in the fossil record. The vicissicaudates (including Sidneyia, Emeraldella, aglaspidids, and cheloniellids – all of which have previously been allied to chelicerates) resolved as sister-taxon to crown-group Chelicerata. This topology indicates that many purported chelicerate features, such as lamellar gills, and a differentiated posterior abdomen evolved sequentially in the chelicerate stem-lineage.

Bookmarks Related papers MentionsView impact

A new arthropod, Enalikter asphon gen. et sp. nov., is described from the Silurian (Wenlock Serie... more A new arthropod, Enalikter asphon gen. et sp. nov., is described from the Silurian (Wenlock Series) Herefordshire Lagerstatte of the UK. It belongs to the Megacheira (=short-great-appendage group), which is recognized here, from the first time, in strata younger than mid-Cambrian age. Discovery of this new Silurian taxon allows us to identify a Devonian megacheiran representative, Bundebachiellus giganteus from the Hunsruck Slate of Germany. The phylogenetic position of megacheirans is controversial: they have been interpreted as stem chelicerates, or stem euarthropods, but when Enalikter and Bundenbachiellus to the most comprehensive morphological dataset available, a stem euarthropod position is supported, it falls in the sister clade to the crown-group euarthropods, and it provides new insights surrounding the origin and early evolution of the euarthropods. Recognition of Enalikter and Bundenbachiellus as megacheirans indicates that this major arthropod group survived for nearly 100 Myr beyond the mid-Cambrian.

Bookmarks Related papers MentionsView impact

The morphology of two new bivalved arthropods, Loricicaris spinocaudatus gen. et sp. nov. and Ner... more The morphology of two new bivalved arthropods, Loricicaris spinocaudatus gen. et sp. nov. and Nereocaris briggsi sp. nov. from the Middle Cambrian (Series 3, Stage 5) Burgess Shale Formation (Collins Quarry locality on Mount Stephen, Yoho National Park, British Columbia, Canada), are described. The material was originally assigned to the genus Branchiocaris but exhibits distinctive character combinations meriting its assignment to other taxa. Loricicaris spinocaudatus possesses an elongate and spinose abdomen comparable to the contemporaneous Perspicaris and Canadaspis, as well as chelate second head appendages and sub-triangular exopods, comparable to Branchiocaris. Nereocaris briggsi possesses a laterally compressed carapace, elongate and delicate appendages and a medial eye located between a pair of lateral eyes on a rhomboidal eye stalk. Although undoubtedly congeneric with Nereocaris exilis from a slightly younger horizon of the Burgess Shale Formation, N. briggsi differs in overall proportions and segment number, warranting assignment to a new species. The newly described taxa were coded into an extensive cladistic analysis of 755 characters, and 312 extinct and extant panarthropods, including a variety of Cambrian bivalved arthropods from both the Burgess Shale and the Chengjiang Lagerstätten. Cambrian bivalved arthropods consistently resolved as a paraphyletic assemblage at the base of Arthropoda. Important innovations in arthropod history such as the specialization of the deutocerebral head appendages and a shift from a nekton-benthic deposit feeding habit to a benthic scavenging/predatory habit, the symplesiomorphic feeding condition of Euarthropoda (crown-group arthropods), were found to have occurred among basal bivalved arthropods.

Bookmarks Related papers MentionsView impact

Cambrian lobopodians have attracted much attention in that they are considered to have close affi... more Cambrian lobopodians have attracted much attention in that they are considered to have close affinities with the origin of arthropods, and recent studies agree that they sample the stem-groups of both Arthropoda and Onychophora. A new lobopodian species, Diania cactiformis Liu et al., 2011, was recently reported from the Chengjiang Lagerstätte (south-west China; Cambrian Series 2). This animal was interpreted as bearing arthropod-like articulated appendages and was resolved as the sister taxon to Arthropoda in a cladistic analysis. A reanalysis of the published dataset did not reproduce the phylogenetic placement of D. cactiformis, and the interpretation of its appendage morphology is controversial. New observations on D. cactiformis are made using newly collected material, rejecting the evidence for sclerotized, segmented and articulated appendages; instead the appendages compare more closely to lobopods. The criteria for defining arthropodized appendages are further discussed through comparative studies among fossil lobopodians, anomalocaridids and arthropods. Our study challenges the previous description of anteroposterior orientation, terminal claws and trunk tagmosis as expressed by differentiated anterior and posterior appendages. A synthesis of four recent datasets for lobopodians and stem-group arthropods is used to revisit the phylogeny of stem arthropods. Irrespective of how characters are weighted, D. cactiformis is resolved at a much more basal position to arthropods, indicating that the morphology of this animal's appendages does not fundamentally inform on the evolution of arthropodization.

Bookmarks Related papers MentionsView impact

"Phylogenomics reconstructs an arthropod tree in which a monophyletic Arthropoda splits into Pycn... more "Phylogenomics reconstructs an arthropod tree in which a monophyletic Arthropoda splits into Pycnogonida + Euchelicerata and Myriapoda + Pancrustacea. The same chelicerate–mandibulate groups are retrieved with morphological data sets, including those encompassing most taxa known from Palaeozoic Konservat-Lagerst€atten. With respect to the interrelationships of the three extant clades of Panarthropoda, a sister group relationship between Onychophora and Arthropoda is endorsed by transcriptomics and microRNAs, although this hypothesis forces homoplasy in characters of the segmental ganglia that are shared by tardigrades and arthropods. Cambrian lobopodians, dinocaridids, bivalved arthropods and fuxianhuiids document the successive appearance of characteristic arthropod features in the stem lineage of Euarthropoda (crown-group arthropods). Molecular dating suggests that arthropods had their origin and
initial diversification in the Ediacaran, but no convincing palaeontological evidence for Panarthropoda is available until
the earliest Cambrian."

Bookmarks Related papers MentionsView impact

The interrelationships of the major extant arthropod groups are equivocal with various conflictin... more The interrelationships of the major extant arthropod groups are equivocal with various conflicting hypotheses being proposed. Recent large-scale molecular analyses have produced partly equivocal, sometimes novel and often surprising hypotheses of relationships. Some proposed relationships, such as a sister-taxon relationship between chelicerates and myriapods, seemingly lacked morphological support, thus prompting a reevaluation of character homologies and a search for potential synapomorphies. Despite this the novel molecular clades remain elusive in large-scale morphological phylogenies, which tend to favor “traditional” groupings. The causes of this phenomenon are poorly understood. Here we present a comprehensive phylogeny of 307 edysozoans (96 extant, 211 extinct) representing all major panarthropod groups and two cycloneuralian outgroups and utilizing data from morphology, development, behavior and gene-order. We recovered strong support for the inclusion of hexapods within a paraphyletic Crustacea as sister-taxon to remipedes and the Silurian crustaceomorph Tanazios. A remipede-hexapod relationship is consistent with recent molecular analyses but had not been previously recovered in a morphological phylogenetic analysis. This relationship is shown to be the consequence of the inclusion of fossil data within our analysis, reducing the effect of long-branch attraction between extant myriapods and hexapods resulting from convergent adaptations to terrestrialisation. Fossil evidence also indicates that the arthropods have an extensive and diverse stem-group which demonstrates the gradual acquisition of typical arthropod features. The diversity of this long stem serves to better polarize characters within Euarthropoda thus providing a better picture of basal arthropod features and reducing the effects of long-branch attraction amongst extant arthropod clades.

Bookmarks Related papers MentionsView impact

We present a comprehensive cladistic analysis, including 10 genera of aglaspidids sensu stricto, ... more We present a comprehensive cladistic analysis, including 10 genera of aglaspidids sensu stricto, 6 aglaspidid-like arthropods and 42 Palaeozoic arthropod taxa. The results of this work provide a much clearer picture of the phylogenetic relationships among Lower Palaeozoic artiopodans.

Bookmarks Related papers MentionsView impact

The mid-Silurian Wenlock Series Herefordshire Lagerstätte preserves invertebrates in three-dimens... more The mid-Silurian Wenlock Series Herefordshire Lagerstätte preserves invertebrates in three-dimensions as calcitic void in-fills in carbonate nodules within a volcaniclastic horizon. A new arthropod from this fauna belongs to the ‘short great appendage’ (megacheiran) group. Phylogenetic analysis, based on the most detailed panarthropod character matrix yet assembled, recovers the new Herefordshire genus with other short great appendage genera in a clade that is the most derived of the euarthropod stem. It thus provides new insights into the nature of this stem and the morphology of immediately pre-crown group forms; its phylogenetic position, as well as that of other short great appendage genera, contrasts with the position of this group as determined in many other studies, in which they have been considered to be part of the chelicerate stem lineage; and the new genus represents the first identification of a short great appendage form in strata younger than mid-Cambrian in age.

Bookmarks Related papers MentionsView impact

Furca bohemica Fritsch, 1908 is one of the most unusual arthropod from the Letná Formation (Czech... more Furca bohemica Fritsch, 1908 is one of the most unusual arthropod from the Letná Formation (Czech Republic). Stratigraphy, taphonomy as well as phylogenetic affinities and its comparison to its marrellomorphs relatives is studied.

Bookmarks Related papers MentionsView impact

A remarkable new horseshoe crab from the the mid-Silurian of Herefordshire (~425 Myr) preserves b... more A remarkable new horseshoe crab from the the mid-Silurian of Herefordshire (~425 Myr) preserves biramous limbs in the prosoma that can be homologized with those of living Limulus. The fossil shows that a true biramous limb evolved in chelicerates as well as in crustaceans, in contrast to the endopod with exite present in trilobites. The evidence of the new fossil supports models for the origin of the limb morphology of living horseshoe crabs through loss of gene expression.

Bookmarks Related papers MentionsView impact

Bivalved arthropods are a common constituent of many early Palaeozoic Konservat Lagerstätten; des... more Bivalved arthropods are a common constituent of many early Palaeozoic Konservat Lagerstätten; despite their ubiquity in such sites of exceptional preservation, however, their soft-parts are rarely well preserved. This has made determining their affinities difficult. Often considered relatives of crustaceans due to their carapace morphology, their limb morphology is at odds with this interpretation. Common crustacean features identified in these taxa, including two pairs of antenna and gnathobasic mandibles are actually absent. Recent discoveries from the Burgess Shale (Cambrian, Stage 5) and Chengjiang biota (Cambrian, Stage 3) have provided a wealth of new information regarding the anatomy of these arthropods and indicate they play a key role in understanding some of the fundamental questions in arthropod palaeobiology such as the acquisition of key “arthropod” characteristics in the euarthropod stem-lineage including biramy and head-limb specialisation. They also help to resolve issues regarding the segmental nature of early arthropod appendages. Specifically a number of these arthropods have been shown to possess both frontal antennae and “great-appendages” and calls into question the homology of the “greatappendage” with the appendages of extant arthropods. If homologous then the antenna of such taxa would be considered protocerebral and therefore unique amongst arthropods. The implications of this are discussed.

Bookmarks Related papers MentionsView impact

Whilst progress has been made in recovering a stable lower euarthropod stem group, basal stem gro... more Whilst progress has been made in recovering a stable lower euarthropod stem group, basal stem groups systematics within the euarthropod crown remain problematic. Current concepts include an expanded ‘Antennata’ encompassing the mostly Cambrian arthropods possessing a single antenna. The stem group of the Chelicerata, conversely, is poorly populated, with no universally agreed members before the appearance of chasmataspid trace fossils towards the end of the Cambrian. In short, the older consensus about the ‘Arachnomorpha’ whereby trilobites and their allies were considered to be related to chelicerates has thoroughly broken down. A hypothesis in which the ‘great appendage’ arthropods were considered stem-group chelicerates based on their chelicera-like frontal appendages has in its stead gained considerable support. However, this reconstruction pays insufficient attention to older ideas of stem-group chelicerates possessing an antenniform, not cheliceriform first appendage. When the ‘xenopod’ taxa such as Sidneyia and Emeraldella are included in the analysis, an antennate first appendage is recovered as a chelicerate and thus euarthropod plesiomorphy. This reconstruction has significant implications for both the composition of the stems of the pancrustaceans and euarthropods more generally, as well as raising the old problem of functional transitions within arthropod frontal appendages once more.

Bookmarks Related papers MentionsView impact

Cambrian lobopodians have attracted much attention in that they are considered to have close affi... more Cambrian lobopodians have attracted much attention in that they are considered to have close affinities with the origin of arthropods. A new lobopodian species, Diania cactiformis Liu et al. 2011, was recently reported from the Chengjiang Lagerstätte. The authors suggested that this animal bears arthropod-like appendages and resolved D. cactiformis as sister-taxon to Arthropoda in their cladistic analysis. However, a reanalysis of the published dataset does not reproduce the phylogenetic placement of D. cactiformis. In our study, new observations on D. cactiformis are made using newly collected material, which rejects the existence of unequivocal evidence for arthropod-like articulated appendages. The criteria for defining arthropodized appendages are further discussed through comparative studies
among fossil lobopodians, anomalocaridids and arthropods. Our study also challenges the previous description of antero-posterior orientation, terminal claws and trunk tagmosis. A synthesis of recent datasets for lobopodians and stem-group arthropods is used to revisit the phylogeny of stem arthropods. Irrespective of how characters are weighted, D. cactiformis is resolved at a much more basal position to arthropods, and is actually one of the most basal Cambrian lobopodians, indicating that the morphology of this animal’s appendages does not fundamentally inform on the evolution of arthropodization.

Bookmarks Related papers MentionsView impact

With over 1,000,000 described species, arthropods are the dominant phylum on Earth today. The in... more With over 1,000,000 described species, arthropods are the dominant phylum on Earth today. The interrelationships between their constituent clades (subphyla) remain poorly understood however, with conflicts arising between different molecular and morphological data sources. The position of the pycnogonids (sea spiders) is particularly problematic, some analyses allying them to euchelicerates (horseshoe crabs and arachnids) and others placing them as sister-taxon to all other extant arthropods. This problem is largely the result of an uncertain root position rather than topological conflicts per se; phylogenetic analyses incorporating stem-group euarthropod taxa have the potential to resolve these issues. Cambrian lagerstätten contain many candidate stem-group arthropods, supplemented here by two new exceptionally-preserved taxa from the Cambrian of British Columbia: an elongate ‘great-appendage arthropod’ with multipodomerous trunk limbs; and a bivalved form lacking distinct tergal pleurae, a feature previously considered diagnostic of extant arthropods. A comprehensive phylogenetic analysis was undertaken incorporating these and many other fossil and Recent arthropods; this resolved the stemlineage (including the new taxa) in some detail, documenting many steps in the sequential acquisition of euarthropod characters. Pycnogonids resolved as sister-taxon to other euarthropods, implying that their chelicerate-like characters (e.g. chelate first appendage) are plesiomorphies rather than synapomorphies for euchelicerates.

Bookmarks Related papers MentionsView impact

Arthropods are a diverse group of animals including spiders, scorpions, centipedes, millipedes, i... more Arthropods are a diverse group of animals including spiders, scorpions, centipedes, millipedes, insects and crustaceans. With over 1,000,000 described species they outnumber all other extant (living) phyla combined, and have been the dominant contributor to species diversity for the last 520 million years. They are also commonly used as model organisms for evolutionary studies. Despite all this, we understand very little about their actual relationships, either to each other or other animal groups. Nearly every possible arrangement of the arthropod subgroups has been proposed and each is largely dependent on the type of evidence used, i.e. morphological vs. molecular (DNA) data. Recently a ―total evidence‖ approach has been utilised which includes all available data, including information from extant and extinct species. Fossil data has been shown to be of particular importance in
phylogenetic studies as they tend to resolve major character conflicts created by extant taxa and provide a ―snapshot‖ of evolution. The aim of this talk is to provide an overview of recent works attempting to resolve arthropod interrelations and will demonstrate the importance of fossil data for
resolving this issue.

Bookmarks Related papers MentionsView impact

The marrellomorphs are a small group of Palaeozoic arthropods noted for their aberrant morphology... more The marrellomorphs are a small group of Palaeozoic arthropods noted for their aberrant morphology, which has precluded resolution of their phylogenetic position. Marrellomorpha includes two clades, the marrellids and the acerostracans, allied by the shared possession of numerous (>25) trunk somites with appendages that reduce in size posteriorly. The marrellids are characterised by the possession of extensive anteriolateral head spines and typified by the Burgess Shale taxon Marrella; the acerostracans are characterised by the possession of a dorsal ―shield‖ that covers their entire body and appendages. Recent work on marrellomorph anatomy, including descriptions of unpublished material, has augmented our understanding of the morphology of the group, and enabled us to identify potential homologies with other arthropod taxa. A cladistic analysis was undertaken including all currently recognised marrellomorphs and a variety of extinct and extant arthropods. Preliminary results indicate that the marrellomorphs are monophyletic that includes: marrellids; acerostracans; and ―skaniids‖, a paraphyletic group of Cambrian arthropods that, like the acerostracans, possess a dorsal ―shield‖. This analysis also indicates that the marrellomorphs form part of a stem-mandibulate lineage that includes megacheirans, trilobites and various ―orsten‖ taxa.

Bookmarks Related papers MentionsView impact

Arthropod tagmosis is the differentiation of segments along the anterior/posterior axis, producin... more Arthropod tagmosis is the differentiation of segments along the anterior/posterior axis, producing appendages specialized for sensation, feeding, and locomotion. Characters relating to segment and limb number and morphology are important in constructing phylogenies that include fossil taxa. Chelicerates are a diverse group, including the extant spiders, mites, harvestmen, scorpions, xiphosurans, and the extinct trigonotarbids, eurypterids, chasmataspids, and synziphosurans. The extant pygnogonids (sea spiders) may also belong to this group. The chelicerate body is divided into two major tagmata: prosoma and opisthosoma. There is variation, however, within this bauplan (e.g. number of segments in a limb, fusion of dorsal tergites). Developmentally, patterns of tagmosis are associated with changes in the expression of Hox genes, segment polarity genes, and limb gap genes. The distribution of extant taxa for which Hox expression patterns are known is sparse. Therefore, we studied morphological traits for which the developmental basis is understood in extant chelicerates. We constructed a new phylogeny for chelicerates from over 400 morphological characters. Representative extant taxa with sequence or developmental gene expression data were included, as well as fossils with unique patterns of tagmosis or other morphological traits. Using this morphological topology, ancestral character states were inferred. Results under different models of character evolution (parsimony, likelihood, Bayesian) are compared.

Bookmarks Related papers MentionsView impact

Arthropod tagmosis is the differentiation of segments along the anterior/posterior axis, producin... more Arthropod tagmosis is the differentiation of segments along the anterior/posterior axis, producing appendages specialized for sensation, feeding, and locomotion. Characters relating to segment and limb number and morphology are important in constructing phylogenies that include fossil taxa. Chelicerates are a diverse group, including the extant spiders, mites, harvestmen, scorpions, xiphosurans, and the extinct trigonotarbids, eurypterids, chasmataspids, and synziphosurans. The extant pygnogonids (sea spiders) may also belong to this group. The chelicerate body is divided into two major tagmata: prosoma and opisthosoma. There is variation, however, within this bauplan (e.g., number of segments in a limb, fusion of dorsal tergites). Developmentally, patterns of tagmosis are associated with changes in the expression of Hox genes. The distribution of extant taxa for which Hox expression patterns are known is sparse. Therefore, we studied
morphological traits for which the developmental basis is understood in extant chelicerates. We constructed a new phylogeny for chelicerates from over 400 morphological characters. Representative extant taxa with sequence or developmental gene expression data were included, as well as fossils with unique patterns of tagmosis or other morphological traits. Using this morphological topology, ancestral character states were inferred. Results under different models of character evolution (parsimony, likelihood, Bayesian) are compared.

Bookmarks Related papers MentionsView impact

With over 1,000,000 currently recognised species, arthropods are the most speciose phylum on Eart... more With over 1,000,000 currently recognised species, arthropods are the most speciose phylum on Earth. Four distinct major extant clades are recognised: Chelicerata (spiders, scorpions, ticks), Myriapoda (centipedes and millipedes), Hexapoda (insects), and Crustacea (crabs, ostracods, brine shrimp, etc). Although the monophyly of these clades is often well supported, their relationships to each other are hotly debated – with nearly every conceivable grouping proposed. In morphological analyses, the main problem is identifying homologous structures amongst the different clades. New evidence from molecular and fossil data is helping to resolve these problems and establish a consensus. The importance of these techniques for determining patterns of arthropod head segmentation is given as a case study and highlighted as an area for future research.

Bookmarks Related papers MentionsView impact

A restudy of the scorpion fauna of Glencartholm (Lower Carboniferous, Viséan), in Scotland, has r... more A restudy of the scorpion fauna of Glencartholm (Lower Carboniferous, Viséan), in Scotland, has revealed that many previously described species are invalid: most taxa represent ontogentic stages of a single taxon, Archaeoctonus glaber (Peach, 1882). A new phylogeny of Palaeozoic scorpions indicates that the same sequences of changes that occur throughout A. glaber’s ontogeny also occur throughout Palaeozoic scorpion evolution, i.e. ontogeny recapitulates phylogeny. In particular, abdominal plate morphology, an important taxobase in many previous classifications, varies considerably with ontogeny, and is therefore useful for determining the age of fossil scorpions. Regression analysis indicates that many aspects of the anatomy of A. glaber grew isometrically. Isometric scaling indicates that the largest specimen represents the ninth moult and may have grown to a length of over 510 mm.

Bookmarks Related papers MentionsView impact

Acanthoscorpio mucronatus Kjellesvig-Waering was one of three species of fossil scorpion describe... more Acanthoscorpio mucronatus Kjellesvig-Waering was one of three species of fossil scorpion described from the Lower Devonian (Pragian?), Beartooth Butte Formation (Wyoming). A restudy of the only known specimen has revealed this taxon to be a juvenile eurypterid. Previously unrecogonised features supporting this placement include a Dolichopterus-type swimming paddle and a type-A genital appendage. The overall size of the individual, limb proportions and eye placement indicate this specimen is a juvenile. Only two species of eurypterid have previously been described from the Beartooth Butte Formation: Strobilopterus princetonii (Ruedemann) and Jaekelopterus (?) howelli (Kjellesvig-Waering and Størmer). A. mucronatus is considered an early instar of S. princetonii based on swimming paddle morphology and allometric growth estimates. A. mucronatus is a junior synonym of S. princetonii and is thus suppressed under Article 23.1 of the ICZN.
A. mucronatus has previously been assigned to Mesoscorpionina, a clade of terrestrial scorpions. Its reassignment thus has implications for the understanding of scorpion systematics and terrestrialisation. A reanalysis of Jeram’s (1998) data matrix was undertaken with A. mucronatus removed. Greater levels of support were found and Mesoscorpionina became paraphyletic with regards to crown-group scorpions. Other problematic scorpion taxa are briefly discussed in this context.

Bookmarks Related papers MentionsView impact