Article: Taxonomy, evolution, and functional morphology of southern Australian Tertiary hemiasterid echinoids

Eight species of hemiasterid echinoids, assigned to the genera Hemiaster (Bolbaster) and Psephoaster gen. nov., are described from Late Eocene to Middle Miocene strata of southern Australia. Seven of the species are new: the Late Eocene H. (B.) subidus, the Early Oligocene H. (B.) dolosus, the Early Miocene H. (JB.) verecundus, the Middle Miocene H. (B.) callidus, the Late Eocene P. lissos, the Late Oligocene P. apokryphos and the Early Miocene P. klydonos. A neotype is selected for H. (B.) planedeclivis Gregory, 1890. The five species of H. (Bolbaster) are considered to have formed a single evolutionary lineage, as are the three species of Psephoaster. Directional trends in many morphological features in these two lineages are interpreted as reflecting both paedomorphosis and peramorphosis. The sediments in which the echinoids lived became progressively finer-grained from the Eocene to the Miocene and the morphological changes in the two lineages are considered to reflect adaptations by descendant morphotypes to the occupation of finer-grained sediments. Many of the morphological changes are common to both lineages. Species of Psephoaster are considered to have been shallow burrowers, while species of H. (Bolbaster) are interpreted as having burrowed more deeply in the sediment.