The archaeocidarids comprise the most derived stem group echinoids and have long been regarded as closely related to the crown group. The fossil record of echinoids in the Palaeozoic is, however, poor, so details surrounding the initial divergence of crown group echinoids are not well constrained. In order to better understand the phylogenetic relationships of the most derived stem group and most basal crown group echinoids, a phylogenetic analysis was undertaken of the Archaeocidaridae, including the genera Nortonechinus, Devonocidaris, Lepidocidaris, Polytaxicidaris and Archaeocidaris and the Palaeozoic miocidarid cidaroids from the genus Eotiaris. We found that Archaeocidaris appears to be paraphyletic with respect to crown group echinoids. Furthermore, we mapped character evolution along our phylogeny and found that the diversification of archaeocidarids and miocidarids may be linked to large-scale macroecological changes taking place in the late Palaeozoic, including increasing predation pressure and echinoid encrustation by epibionts. We compared the stratigraphical distribution of archaeocidarid and miocidarid occurrences to our resulting phylogenies, and found that the fit of our cladograms to the stratigraphic record of archaeocidarid occurrences is worse than other echinoid groups, supporting the idea that the imbricate plated archaeocidarids have a poor fossil record. In the course of carrying out these analyses, we also felt it necessary to describe a new species of Archaeocidaris, Archaeocidaris ivanovi sp. nov. We also provide novel descriptions and interpretations for Devonocidaris primaevus, Archaeocidaris brownwoodensis, Archaeocidaris apheles and revise the synonymy of Archaeocidaris legrandensis and ?Eotiaris meurevillensis, which may be a crown group echinoid.

From the Middle Jurassic to the Early Cretaceous, metriorhynchid crocodylomorphs inhabited marine ecosystems across the European archipelago. Unfortunately, European metriorhynchids are only well known from Germany, France, and the UK, with the Eastern European fossil record being especially poor. This hinders our understanding of metriorhynchid biodiversity across these continuous seaways, and our ability to investigate provincialism. Here we describe eleven isolated tooth crowns and six vertebrae referable to Metriorhynchidae from the Callovian, Oxfordian, Volgian (Tithonian), and Ryazanian (Berriasian) or Valanginian of European Russia. We also describe an indeterminate thalattosuchian tooth from the lower Bajocian of the Volgograd Oblast, the first discovery of a marine reptile from the Bajocian strata of European Russia. These rare fossils, along with previous reports of Russian thalattosuchians, indicate that thalattosuchians have been common in the Middle Russian Sea since it was formed. Palaeolatitude calculations for worldwide metriorhynchid-bearing localities demonstrate that the occurrences in European Russia are the most northern, located mainly between 44–50 degrees north. However, metriorhynchids appear to be rare at these palaeolatitudes, and are absent from palaeolatitudes higher than 50°. These observations support the hypothesis that metriorhynchids evolved an elevated metabolism but were not endo-homeothermic, especially as endo-homeothermic marine reptiles (ichthyosaurs and plesiosaurs) remained abundant at much higher palaeolatitudes.

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During the Carboniferous, crinoids were commonly so abundant that their skeletal ossicles formed limestones termed encrinites. Major evolutionary changes occurred within the Camerata and Articuliformes, as the former were displaced by the latter as the dominant clade. Both the Mississippian and the Pennsylvanian subperiods started with high evolutionary rates and ended with low evolutionary rates associated with glaciation. Although not typically used for biostratigraphy, crown-based crinoid genera can be used as biostratigraphic indicators for Carboniferous stages. Palaeozoic crinoid biodiversity reached its maximum during the Carboniferous, from which there are numerous well-documented localities with high biodiversity. Faunas from the palaeobiogeographic regions of Laurussia, Palaeo-Tethys, and Gondwana are reviewed. For Mississippian crinoids, 37 genera are designated as biostratigraphically useful; and for the Pennsylvanian, 44 genera are identified. Recognition of the utility of these genera for biostratigraphy is important for dating crinoid deposits, which may be devoid of other biostratigraphically useful fossils; and add to our overall ability to delineate the temporal resolution of life on Earth.