ABSTRACT
The original diagnosis of the genus Microceratina Swanson is re-examined with the aim of elucidating the evolutionary history of this living and fossil genus. The different systematic placements of this genus in one of three alternative suprageneric taxa, family Bythocytheridae Sars, family Cytheruridae G.W. Müller (subfamily Eucytherurinae Puri, emend. Maddocks & Steineck) and/or family Loxoconchidae Sars are reviewed. We provide details of a special type of tiny pores, named Loophole Sieve-type Pore Canals, and show how their morphology and position on the valve differ from the typical Sieve-type Pore Canals present in other superfamily Cytheroidea groups, especially members of the Loxoconchidae. A comparative analysis of the valve ornamentation, especially the structure of the anterior peripheral area, and posterior margin morphology, between selected taxa of the three subfamilies of the Cytheruridae (Cytherurinae, Cytheropterinae, Eucytherurinae) demonstrates that Microceratina species belong to a special phylogenetic lineage of Eucytherurinae, which differs from another lineage represented by the genus Xylocythere Maddocks & Steineck. This proposal is strengthened by examination of the limb traits of Microceratina martensi Namiotko et al., currently the only living species of the genus for which both valves and limbs are described; the description is extended herein. Key diagnostic traits of the genus Microceratina are presented, a new Early Jurassic age species is described, and two new combinations are proposed. The homeomorphic valve shapes of M. andreui sp. nov., M. amfibola and ?S. rectum (Loxoconchidae) support the value of the approach adopted herein: analysis of subtle morphological details with high-resolution microscopy.
Subject(s)
Crustacea , Fossils , Animals , Phylogeny , Microscopy , PhenotypeABSTRACT
Type material of 10 genera, one subgenus, 110 species and 28 subspecies described by Wicher (1959), Krmmelbein (1961, 1962, 1963, 1964a,b, 1965a,b), Krmmelbein Weber (1971) and Bate (1972, 1994) are re-illustrated using optical digital technology in order to provide a standard reference for future systematic work and its biostratigraphical and palaeoenvironmental application. The genera are: Brasacypris, Coriacina, Hourcqia, Ilhasina, Looneyellopsis, Pattersoncypris, Petrobrasia, Reconcavona, Salvadoriella, and Tucanocypris, and subgenus Cypridea (Sebastianites).
Subject(s)
Crustacea , Animals , BrazilABSTRACT
Owing to the assumed lack of deep-sea macrofossils older than the Late Cretaceous, very little is known about the geological history of deep-sea communities, and most inference-based hypotheses argue for repeated recolonizations of the deep sea from shelf habitats following major palaeoceanographic perturbations. We present a fossil deep-sea assemblage of echinoderms, gastropods, brachiopods and ostracods, from the Early Jurassic of the Glasenbach Gorge, Austria, which includes the oldest known representatives of a number of extant deep-sea groups, and thus implies that in situ diversification, in contrast to immigration from shelf habitats, played a much greater role in shaping modern deep-sea biodiversity than previously thought. A comparison with coeval shelf assemblages reveals that, at least in some of the analysed groups, significantly more extant families/superfamilies have endured in the deep sea since the Early Jurassic than in the shelf seas, which suggests that deep-sea biota are more resilient against extinction than shallow-water ones. In addition, a number of extant deep-sea families/superfamilies found in the Glasenbach assemblage lack post-Jurassic shelf occurrences, implying that if there was a complete extinction of the deep-sea fauna followed by replacement from the shelf, it must have happened before the Late Jurassic.
