A new basal actinopterygian fish from the Middle Devonian Aztec Siltstone of Antarctica

Abstract

A new basal actinopterygian fish, Donnrosenia schaefferi gen. et sp. nov., is described from the Middle Devonian (Givetian) Aztec Siltstone of southern Victoria Land, Antarctica. Donnrosenia gen. nov. is characterized by the large parietals which are of almost equivalent size to the frontals, very small intertemporals, a small accessory operculum situated dorsally to the prominent anterodorsal process of the suboperculum, a deep dentary with anterior flexure, porous ornamentation on the clavicle, an elongate body form with macromeric squamation, an absence of paired fringing fulcra on the fins, and pectoral lepidotrichia which are unsegmented for much of their length. A phylogenetic analysis based on dermal skeletal features of Devonian actinopterygians indicates that Donnrosenia gen. nov. is the sister taxon to Howqualepis from the Middle Devonian of Victoria, Australia, and is embedded within a possible clade containing the actinopterygians from the Gogo Formation, Western Australia. This supports the concept of an endemic radiation of East Gondwanan actinopterygians, and reinforces the already strong biogeographical similarities between the Middle Devonian palaeofaunas of Australia and Antarctica.

A new species of the Devonian actinopterygianMoythomasiafrom Bergisch Gladbach, Germany, and fresh observations onM. durgaringafrom the Gogo Formation of Western Australia

“…The diverse Givetian-Frasnian East Gondwanan actinopterygian fauna (Gardiner, 1984;Long, 1988;Long et al, 2008;Choo, 2009Choo, , 2011Choo et al, 2009 ) and a possible relationship with the Gogo mimiids resolved by Choo (2011) could suggest a Gondwanan origin for Moythomasia, although the genus and forms similar to it are presently unknown in pre-Frasnian Australia. Alternatively, a European origin cannot be ruled out given the presence of the similar Stegotrachelus in Givetian lacustrine deposits of Scotland (Swartz, 2009), although such a north-to-south range expansion would run contrary to other recorded dispersal events.…”

“…Choo-Devonian actinopterygian Moythomasia (e952817-2) Cloutier and Arratia, 2004;Friedman and Blom, 2006;Long et al, 2008;Swartz, 2009). However, the lack of full descriptions of two of the best-preserved species has hampered attempts at understanding early actinopterygian diversity and evolution.…”

“…(M. nitida and M. durgaringa) as sister taxa within an assemblage including Kentuckia, Limnomis, and Cuneognathus. Long et al (2008), with the inclusion of a few additional Devonian taxa, achieved poor resolution above Cheirolepis, with M. nitida recovered within a 'Stegotrachelus-grade assemblage' (along with Krasnoyarichthys and Stegotrachelus) exclusive to M. durgaringa. Swartz (2009) Moythomasia spp.…”

“…Although the skull roofing bones referred to herein as the frontal and parietal are homologous to the sarcopterygian parietal and postparietal, respectively, traditional terminology is used to facilitate easy comparison with the majority of descriptive works on early actinopterygians (Gardiner and Bartram, 1977;Gardiner, 1984;Long, 1988;Taverne, 1997;Daeschler, 2000;Prokofiev, 2002;Friedman and Blom, 2006;Long et al, 2008Choo, 2011). adp, anterodorsal process of suboperculum; an, angular; an.f, anal fin; ano, anterior nasal opening; ap, anterior pit line; br, branchiostegal rays; br.1, first branchiostegal ray; cau.f, caudal fin; c.ful, caudal fulcra; clav, clavicle; clth, cleithrum; den, dentary; dep.f, depressed field of scale; dh, dermohyal; dor.f, dorsal fin; ds, dermosphenotic; ex.1, medial extrascapular; ex.2, lateral extrascapular; f, frontal (sarcopterygian parietal); it, intertemporal; ju, jugal; la, lacrimal; l. gu, lateral gular; man.sc, mandibular sensory canal; m.gu, median gular; mp, middle pit line; mx, maxilla; n, nasal; pa, parietal (sarcopterygian postparietal) ; pcl, postcleithrum; pec.f, pectoral fin; peg, dorsal peg of scale; pel.f, pelvic fin; pinf, pineal foramen; pm, premaxilla; pno, posterior nasal opening; po, postorbital; pop, preoperculum; pp, posterior pit line; psc, presupracleithrum; pt, posttemporal; op, operculum; qj, quadratojugal; r, rostral; rdp, rostrodorsal process of scale; sop, suboperculum; sp, spiracular slit; st, supratemporal; sur, surangular.…”

“…In Kentuckia hlavini (Dunkle, 1964), the intertemporals are longer than the supratemporals, whereas in the remaining Devonian taxa they are considerably shorter. Moythomasia has a complete series of median dorsal scutes extending from the skull to the dorsal fin, as in the Mimiidae (Choo, 2011), Krasnoyarichthys (Prokofiev, 2002), and Stegotrachelus (Swartz, 2009), but unlike Cheirolepis, Kentuckia, Osorioichthys (Taverne, 1997), Tegeolepis, and the Howqualepididae (Long 1988;Long et al, 2008;Choo, 2011). Cuneognathus (Friedman and Blom, 2006) and Limnomis (Daeschler, 2000) lack pelvic fins and have scales lacking dorsal pegs.…”