ABSTRACT The nymphal stages of P alaeozoic insects differ significantly in morphology from those of their modern counterparts. Morphological details for some previously reported species have recently been called into question. Palaeozoic insect nymphs are important, however – their study could provide key insights into the evolution of wings, and complete metamorphosis. Here we review past work on these topics and juvenile insects in the fossil record, and then present both novel and previously described nymphs, documented using new imaging methods. Our results demonstrate that some C arboniferous nymphs – those of P alaeodictyopteroidea – possessed movable wing pads and appear to have been able to perform simple flapping flight. It remains unclear whether this feature is ancestral for P terygota or an autapomorphy of P alaeodictyopteroidea. Further characters of nymphal development which were probably in the ground pattern of P terygota can be reconstructed. Wing development was very gradual (archimetaboly). Wing pads did not protrude from the tergum postero‐laterally as in most modern nymphs, but laterally, and had well‐developed venation. The modern orientation of wing pads and the delay of wing development into later developmental stages (condensation) appears to have evolved several times independently within P terygota: in E phemeroptera, O donatoptera, E umetabola, and probably several times within P olyneoptera. Selective pressure appears to have favoured a more pronounced metamorphosis between the last nymphal and adult stage, ultimately reducing exploitation competition between the two. We caution, however, that the results presented herein remain preliminary, and the reconstructed evolutionary scenario contains gaps and uncertainties. Additional comparative data need to be collected. The present study is thus seen as a starting point for this enterprise.
Highlights•A new species of Carboniferous harvestman is described using X-ray microtomography•A total evidence analysis recovers this and a Devonian fossil as stem-Cyphophthalmi•Both are placed in the new fossil suborder Tetrophthalmi subordo nov.•Evo-devo of extant species reveals vestiges of lateral eyes observed in the fossilSummarySuccessfully placing fossils in phylogenies is integral to understanding the tree of life. Crown-group Paleozoic members of the arachnid order Opiliones are indicative of ancient origins and one of the earliest arthropod terrestrialization events [1, 2]. Opiliones epitomize morphological stasis, and all known fossils have been placed within the four extant suborders [3–5]. Here we report a Carboniferous harvestman species, Hastocularis argusgen. nov., sp. nov., reconstructed with microtomography (microCT). Phylogenetic analysis recovers this species, and the Devonian Eophalangium sheari, as members of an extinct harvestman clade. We establish the suborder Tetrophthalmi subordo nov., which bore four eyes, to accommodate H. argus and E. sheari, the latter previously considered to be a phalangid [6–9]. Furthermore, embryonic gene expression in the extant species Phalangium opilio demonstrates vestiges of lateral eye tubercles. These lateral eyes are lost in all crown-group Phalangida, but are observed in both our fossil and outgroup chelicerate orders. These data independently corroborate the diagnosis of two eye pairs in the fossil and demonstrate retention of eyes of separate evolutionary origins in modern harvestmen [10–12]. The discovery of Tetrophthalmi alters molecular divergence time estimates, supporting Carboniferous rather than Devonian diversification for extant suborders and directly impacting inferences of terrestrialization history and biogeography. Multidisciplinary approaches integrating fossil and neontological data increase confidence in phylogenies and elucidate evolutionary history.
Whip scorpions (Thelyphonida) and schizomids (Schizomida) are closely related arachnid orders, whose low species diversity compared to other arachnid groups is reflected in a limited fossil record. Here we investigate two key fossil whip scorpions from the British Middle Coal Measures of Coseley, Staffordshire (late Carboniferous, c. 315 Ma), UK, using X-ray microtomography, and incorporate the taxa into an updated arachnid phylogeny. Geralinura brittanica Pocock, Citation1911 is an unequivocal whip scorpion, whose pedipalps are closer to the modern condition than previously assumed. The trochanter bears a dorsal flange with prodorsal teeth, and the whole pedipalp is rendered subchelate by the presence of at least a patellar apophysis. These results suggest a high degree of stasis in whip scorpions since the late Carboniferous, and the genus Geralinula Scudder, Citation1884 is within the crown-group; i.e. the extant family Thelyphonidae. Proschizomus petrunkevitchi Dunlop and Horrocks, Citation1996 lacks median eyes, a character shared with Schizomida, but unlike schizomids the pedipalp also has patellar and tibial apophyses; albeit with the appendage articulating at an angle of c. 45° rather than articulating horizontally as in living whip scorpions, or vertically as in schizomids. Our phylogeny refutes a previous hypothesis that P. petrunkevitchi is a stem-schizomid, and places it among the whip scorpions instead. However, the species may have branched early from the whip scorpion lineage, and thus its morphology might reflect a plesiomorphic arrangement in which the pedipalps were transitioning from a more leg-like to a fully raptorial and claw-like set of prey-catching appendages.
Abstract T omteluva perturbata gen. et sp. nov. and N asakia thulensis gen. et sp. nov., two new rhynchonelliformean brachiopod taxa, are described from carbonate beds from the lower middle C ambrian ( S eries 3, S tage 5) basinal S tephen F ormation, C anada, and the upper lower C ambrian ( S eries 2, S tage 4) H enson G letscher F ormation, N orth G reenland, respectively. The two taxa are characterized by an unusual coral‐like morphology typified by a high conical ventral valve with an anteriorly curved umbo and a tube‐like structure inside the ventral valve, interpreted as pedicle tube. Both resemble the problematic late middle C ambrian ( D rumian) species A nomalocalyx cawoodi B rock from A ustralia, whose systematic affiliation is controversial. Together, the three genera are interpreted as representatives of a new family of rhynchonelliformean brachiopods, the T omteluvidae fam. nov., which is interpreted as an aberrant or derived taxon within the O rder N aukatida. Convergence between the T omteluvidae and the coralla of small solitary C ambrian coralimorphs, as well as the late P alaeozoic reef‐building richthofenioid brachiopods, might indicate adaptation to a similar life habits and environments. However, their small size (length 4 mm), well‐developed pedicle and perfect morphological symmetry make it more likely that tomteluvids lived attached to frondose algae or sponges, above the seafloor, in a similar fashion to the acrotretoid brachiopods with which they show a high degree of morphological convergence. Morphological features of the pedicle tube of N . thulensis suggest that the tomteluvid pedicle is homologous to that in modern rhynchonelliformean brachiopods. This is the first evidence of the pedicle type within the Naukatida and represents the oldest confirmation of a rhynchonellate pedicle.
This is the dataset for the paper Sherratt et al. 2015 (PNAS, doi: ). Included are the X-ray microtomography (micro-CT) TIFF stacks for the amber encased anole lizard fossils studied. Also included are the morphometric data for the fossil and 100 modern specimens, and the phylogenetic character matrix for the fossils and 181 species (91 morphological characters, 4873 DNA bases). Abstract Whether the structure of ecological communities can exhibit stability over macroevolutionary timescales has long been debated. The similarity of independently evolved Anolis lizard communities on environmentally similar Greater Antillean islands supports the notion that community evolution is deterministic. However, a dearth of Caribbean Anolis fossils—only three have been described to date—has precluded direct investigation of the stability of anole communities through time. Here we report on an additional 17 fossil anoles in Dominican amber dating to 15–20 My before the present. Using data collected primarily by X-ray micro computed tomography (X-ray micro-CT), we demonstrate that the main elements of Hispaniolan anole ecomorphological diversity were in place in the Miocene. Phylogenetic analysis yields results consistent with the hypothesis that the ecomorphs that evolved in the Miocene are members of the same ecomorph clades extant today. The primary axes of ecomorphological diversity in the Hispaniolan anole fauna appear to have changed little between the Miocene and the present, providing evidence for the stability of ecological communities over macroevolutionary timescales.
Abstract Evolutionary inferences require reliable phylogenies. Morphological data have traditionally been analyzed using maximum parsimony, but recent simulation studies have suggested that Bayesian analyses yield more accurate trees. This debate is ongoing, in part, because of ambiguity over modes of morphological evolution and a lack of appropriate models. Here, we investigate phylogenetic methods using two novel simulation models—one in which morphological characters evolve stochastically along lineages and another in which individuals undergo selection. Both models generate character data and lineage splitting simultaneously: the resulting trees are an emergent property, rather than a fixed parameter. Standard consensus methods for Bayesian searches (Mki) yield fewer incorrect nodes and quartets than the standard consensus trees recovered using equal weighting and implied weighting parsimony searches. Distances between the pool of derived trees (most parsimonious or posterior distribution) and the true trees—measured using Robinson-Foulds (RF), subtree prune and regraft (SPR), and tree bisection reconnection (TBR) metrics—demonstrate that this is related to the search strategy and consensus method of each technique. The amount and structure of homoplasy in character data differ between models. Morphological coherence, which has previously not been considered in this context, proves to be a more important factor for phylogenetic accuracy than homoplasy. Selection-based models exhibit relatively lower homoplasy, lower morphological coherence, and higher inaccuracy in inferred trees. Selection is a dominant driver of morphological evolution, but we demonstrate that it has a confounding effect on numerous character properties which are fundamental to phylogenetic inference. We suggest that the current debate should move beyond considerations of parsimony versus Bayesian, toward identifying modes of morphological evolution and using these to build models for probabilistic search methods. [Bayesian; evolution; morphology; parsimony; phylogenetics; selection; simulation.]
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