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The family Zoroasteridae is a clade of extant sea stars found exclusively in deep marine environments (i.e. bathyal environments deeper than 200 m). In the fossil record, seven species have been compared and/or assigned to the Zoroasteridae, on a time span ranging from the Middle Jurassic to the Miocene. This study describes a new taxon, Viridisaster guerangeri gen. et sp. nov., from the Cenomanian of Le Mans (Sarthe, France) and reappraises two Mesozoic species, the Jurassic Terminaster cancriformis and the Early Cretaceous Protothyraster priscus. To test the relationships of the putative fossil zoroasterids with modern taxa, a phylogenetic analysis was performed combining six of the best-known fossil species and 29 forcipulatacean species, including four Zoroasteridae. Many of the characters that define the extant Zoroasteridae do not appear in the fossil record before the Cenozoic. The family name is maintained for the crown group only. The family Terminasteridae, that accounted for the genera Terminaster and Alkaidia, is found paraphyletic and is rejected here. The order Zorocallida, initially erected for the family Zoroasteridae only, is redefined as the sister clade to the Forcipulatida that includes the crown-group Zoroasteridae and its stem relatives. Mesozoic Zorocallida are small in size compared to the Cenozoic Zorocallida, and they express morphological characters that are typical of juvenile Zoroasteridae; thus, the emergence of modern forms is likely associated with peramorphic evolution. The palaeoecology of the Zoroasteridae and their restriction to deep-sea environments after the Eocene is discussed. [ABSTRACT FROM AUTHOR]

The phylogenetic history of rudist bivalves is reviewed using a cladistic analysis based on 41 morphological shell characters and a new topology is proposed. A novel approach to rudist comparative anatomy has enabled the mapping of homologous zones. We highlight that 'pallial canals' can be homologous to four specific cavities that have merged during rudist evolution. The characters of the myophores and muscle insertions have also been reappraised using a hierarchical scheme. We formalize, for the first time, the complex diversification of rudist myophores by constructing tree-like characters that can contain up to six informative states for each of the four myophores. All characters have been coded as independent features. This has enabled the identification of different evolutionary rates of change between left and right valves and allows the recognition of the various morphoanatomic responses of one valve to the structural changes of the other. All characters have been coded in hierarchies and analysed in three-taxon analysis. Taxonomic sampling composed of two species per family allows an exhaustive monophyly test of all families of the suborder Hippuritidina. Only the families Polyconitidae, Plagioptychidae, Radiolitidae and Hippuritidae are found to be monophyletic. The two superfamilies are both found to be polyphyletic. The Hippuritidae is found to be the sister group of the Radiolitidae. Pachytraga is found as the sister group of all the rudists with pallial canals except Sellaea. Two evolutionary radiations in rudists are dated, using the cladistic concept of temporal hierarchy, to the Hauterivian + and the Albian+. [ABSTRACT FROM AUTHOR]

We describe Superstesaster promissor gen. et sp. nov., a starfish from the Smithian (Early Triassic) of Utah (USA) that fills a major gap in the fossil record of the Asteroidea. The post-Palaeozoic crown group Asteroidea are distinct from any of the diverse Palaeozoic forms. However, current understanding of the Palaeozoic-Mesozoic transition is blurred by a large gap in the fossil record between the Early Permian and the Middle Triassic. Building on the newly described taxon, a phylogenetic analysis investigates the relationships between Palaeozoic and Mesozoic Asteroidea. Including 30 species and 70 morphological characters, it is the most comprehensive phylogeny produced for fossil starfishes so far. Relationships among Palaeozoic forms remain poorly resolved, but their position in the tree is grossly consistent with stratigraphy. The tree topology implies the appearance of a wide range of morphologies during the Ordovician, a bottleneck during the end-Devonian events, and a second diversification during the Carboniferous, before a diversity decline at the end of the Permian. Superstesaster promissor nests above Palaeozoic taxa and appears as the sister group to the post-Palaeozoic Asteroidea. It represents the first record of a member of the stem group in the Mesozoic, and it likely reflects the ancestral morphology of the crown group. S. promissor shares with the crown group typical ambulacral and adambulacral plate shape and articulation. Phylogenetic relationships within the crown group remain poorly resolved, although three clades are consistent with molecular and morphological phylogenies available for extant forms: Valvatacea (Comptoniaster, Pentasteria, Advenaster, Noviaster), Forcipulatacea (Germanasterias, Argoviaster) and Velatida (Tropidaster, Protremaster). A Triassic and Jurassic radiation of the crown group is confirmed. Most Triassic and Jurassic forms do not share all synapomorphies with extant clades and usually represent separate clades or stem members of modern clades rather than true members of modern families. [ABSTRACT FROM AUTHOR]