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New insights on the Upper Cretaceous pachycormid 'Protosphyraena' gladius (Actinopterygii: Teleostei) from North America
 
SVPCA Conference
 
Platform presentation (20 minutes)
Authors
 
*Matt Friedman
 
 
Anthony Maltese
 
 
Kenshu Shimada
 
Abstract
 
'Protosphyraena’ gladius is an enigmatic pachycormid from the Late Cretaceous of North America, where it is known from the Coniacian-Campanian Niobrara chalks and the Campanian Pierre Shale and Selma Formations. Described remains of this species consist exclusively of pectoral fins, which can exceed one metre in length. Features of these fins link ‘P.gladius to pachycormids (Lambers, 1992), but provide no evidence linking it to other species of 'Protosphyraena'. Newly prepared material of ‘P.’ gladius reveals details of the skull roof, neurocranium, jaws, hyoid and branchial arches, operculogular series, and shoulder girdle. These remains indicate that ‘P.’ gladius cannot be placed within 'Protosphyraena'. Unlike that genus, ‘P.’ gladius is edentulous and lacks anterior extension of the rostrodermethmoid into a prominent rostrum. While ‘P. gladius is not closely related to 'Protosphyraena', it is very similar to two Jurassic pachycormids: Asthenocormus and Leedsichthys (Lambers, 1992). These two taxa appear to have been ram filter-feeders, and one of them–Leedsichthys–reached enormous sizes (Liston & Noè, 2004). ‘P. gladius also displays features consistent with filter feeding, and extends the range of this large-bodied pachycormid clade from the Late Jurassic to the Late Cretaceous. This range extension also fills a conspicuous ecological gap: no large-bodied filter feeders were known previously from the Cretaceous. The apparent extinction of this group of pachycormids at or near the end of the Cretaceous is also intriguing, because it occurs shortly before the earliest records of large-bodied, ram filter-feeding chondrichthyans (rhincodontids, cetorhinids, mobulids) in the earliest Paleogene (Shimada, 2007).
London 2020