Dapedium sp. from the Toarcian (Lower Jurassic) urkut Manganese Ore Formation (Bakony Mts., Hungary) and an overview of diversity of dapediiform fishes

摘要

Dapediidae are a characteristic group of deep-bodied Mesozoic actinopterygian fishes with a moderate diversity at genus- and species-level. Here, we add a new occurrence to their patchy fossil record and describe in detail a nearly complete dapediid specimen from the pelagic deposit of the Toarcian urkut Manganese Ore Formation in the Transdanubian Range of Hungary. The preserved characters represent nearly all anatomically important body parts and allow assignment to Dapedium and comparison with other dapediid genera. This is the first reported occurrence of the order in Hungary and the Carpathian Basin that extends the known geographical range of the genus to the Mediterranean (western Tethyan) Jurassic. A review of the temporal distribution of published occurrences of dapediids permits speculation that the disappearance of exclusively Late Triassic genera, coincident with the end-Triassic extinction event, was likely related to their specialised feeding strategies and light or incomplete squamation. Multiple environmental crises (warming, acidification and anoxia) severely affected reefal habitats and favoured the survival of the generalist-durophagous Dapedium. The urkut specimen adds important data to the Early Jurassic, particularly Toarcian Lagerstatte-dominated fossil record of dapediids. In contrast to the end-Triassic, the Toarcian oceanic anoxic event did not lead to genus extinction among dapediids, possibly prevented by adaptations evolved during the preceding and similarly multi-stressor event. Continuing studies of Mesozoic fish specimens in Hungarian collections may provide new records and insights into other groups as well.