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Ptyctodontid Fishes (Vertebrata, Placodermi) from the Late Devonian Gogo Formation, Western Australia, with a Revision of the European Genus Ctenurella 0Rvig, 1960

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Ptyctodontid Fishes (Vertebrata, Placodermi) from the Late Devonian Gogo Formation, Western Australia, with a Revision of the European Genus Ctenurella 0Rvig, 1960 Ptyctodontid fishes (Vertebrata, Placodermi) from the Late Devonian Gogo Formation, Western Australia, with a revision of the European genus Ctenurella 0rvig, 1960 John A. LONG Department of Earth and Planetary Sciences, The Western Australian Museum, Francis Street, Perth, Western Australia, 6000 (Australia) Long J. A. 1997. — Ptyctodontid fishes (Vertebrata, Placodermi) from the Late Devonian Gogo Formation, Western Australia, with a revision of the European genus Ctenurella 0rvlg, 1960. Geodiversitas 19 (3) : 515-555. ABSTRACT A new, almost complete specimen of the ptyctodontid placoderm Campbellodus decipiens Miles et Young, 1977 enables description of the skull toof, trunk shield, visceral skeleton, pelvic girdle, dermal scale cover, and parts of the vertebtal column. A new reconstruction of the head shield of Ctenurella gladbachensis 0rvig, 1960 from Bergisch-Gladbach permits this taxon to be genetically defined from the Gogo species pteviously referred to that genus. The Gogo form is here referred to Austroptyctodus n.g. A new spe­ KEYWORDS cimen of Austroptyctodus gardineri Miles et Young, 1977, together with new Ptyctodontida, observations of Chelyophorus verneuili Agassiz, 1844 and Ctenurella gladba­ Devonian, chensis 0rvig, 1960, shows new information fot the endocranium, the hyoid Placodermi, Gogo, arch and visceral skeleton, identifying the previously identified "metaptery- Australia, goid" elements as paired nasal bones. The large visceral skeleton bone poste­ Austroptyctodus n.g., rior to the jaw joint in ptyctodontids is here identified as an elongated Ctenurella, Chelyophorus. interhyal. RESUME Une nouvelle description du toit crânien, de la cuirasse thoracique, du sque­ lette viscéral, de la ceinture pelvienne, de l'écaillure et de quelques éléments de la colonne vertébtale est proposée à partit d'un nouveau spécimen sub­ complet du ptyctodonte Campbellodus decipiens Miles et Young, 1977. Une nouvelle reconstitution du toit crânien de Ctenurella gladbachensis 0rvig, 1960 (Frasnien de Bergish-Gladbach, Allemagne) permet de redéfinir le genre Ctenurella, en y incluant les formes de Gogo qui y sont rapportées. Un MOTS CLÉS nouveau genre Austroptyctodus est créé. A partir du matériel qui définit Ptyctodontida, Austroptyctodus gardineri, espèce-type du génie, et d'une révision de Devonien, Chelyophorus verneuilli Agassiz, 1844 et de Ctenurella galdbachensis, de nou­ Placodermi, Gogo, velles informations sur l'endocrâne, l'arc hyoïde et le squelette viscéral des Australie, ptyctodontes sont fournies. Ainsi le « métapterygoïde » est interprété comme Austroptyctodus n.g., des os nasaux pairs, de même l'os du squelette viscétal situé en arrière de Ctenurella, Chelyophorus. l'articulation de la mandibule serait un interhyal de forme allongée. GEODIVERSITAS • 1997 • 19(3) Long J. A. INTRODUCTION although the following species have been descri­ bed from relatively complete, well-preserved The ptyctodontid placoderms have for many material of head and trunk armour: Ctenurella years been a problematic and poorly-known gladbachensis (Orvig I960, 1971), Austro- group of extinct fishes. Early workers identified ptyctodus gardineri n.g. (Miles & Young 1977, ptyctodontids only from their characteristic tooth here erected as a new genus), Rhamphodopsis plates and thus allied them to the holocephalans threiplandi and R. trispinatus (Watson 1934, (Pander 1858; Woodward 1891), although when 1938; Miles 1967), Rhynchodus tetrodon the exoskeletal trunk armour was described by (Newberry 1873; Jaekel 1903; Gross 1933; Jaekel (1907) he compared it favourably with the Stensio 1959 ; Miles 1967), Chelyophorus ver- sturgeon Acipenser, an osteichthyan fish. Both nueili (Agassiz 1844; Eichwald 1859; Obrucheva Dollo (1907) and Goodrich (1909) rejected this 1983), and Ptyctodopsis menzeli (Denison 1985). view and argued that they were placoderm fishes. Recent new discoveries of othet relatively com­ Watson (1934) described more complete material plete ptyctodontids have been made in of a new form he called Rhamphodopsis and fur­ North America from the Frasnian Mt. Elden site ther characterised them as placoderm fishes, and in Atizona (Johnson & Elliott, in press) and this view was sttengthened by further discoveries from the Pinicon Range Formation, Iowa of well-preserved specimens (Watson 1938). (Hickerson 1993; work in prep.). Major discoveries of complete, well-preserved The superb three-dimensionally preserved mate­ ptyctodontids from the Bergisch-Gladbach region rial of ptyctodontids from the Frasnian Gogo of Germany described by Orvig (I960, 1962, Formation of Western Australia has provided the 1971, 1980) led him to revive the earlier hypo­ most detailed knowledge of the group to date. thesis of a holocephalan affinity between ptycto­ Miles & Young (1977) described several speci­ dontids and holocephalans, proposing them to be mens of a new species they assigned to the genus ancestral to the holocephalans, an opinion follo­ Ctenurella Orvig, 1960. Two incomplete speci­ wed by Stensio (1963, 1969) and Jarvik (1980). mens were placed in the new genus and species, However, many researchers working with placo­ Campbellodus decipiens. Further observations on derm fishes or chondrichthyans opposed this the structure of the Gogo "Ctenurella" were descri­ view, regarding ptyctodontids as placoderm fishes bed by Gardiner (1984a) and Forey & Gardiner {e.g. Patterson 1965; Stahl 1967; Miles 1967; (1986). New finds of Gogo fishes made during Miles & Young 1977; Denison 1978; Forey & expeditions in 1986-1989 by the author include Gardiner 1986; Young 1986). Today this view is many new arthrodires (Long 1987, 1988a, 1988b, widely held, and the placoderm affinity of ptycto­ 1990b, 1994a, 1995b) as well as two nearly com­ dontids has been borne out by several recent plete, articulated specimens of ptyctodontids, computer analyses of placoderm intetrelation- which belong to the previously described taxa. ships {e.g. Forey & Gardiner 1986; Carr 1991, The aim of this paper was originally to describe 1995; Goujet & Young 1995). this new material of the Gogo ptyctodontids in The problematic position of the group within detail, by comparison with other specimens of the Placodermi has been raised. They have been ptyctodontids, made available for the author to proposed as a primitive sister group to other pla­ study at the Museum national d'Histoire natu- coderms (Miles & Young 1977; Young 1980), as relle. The well-preserved nature of the Gogo spe­ a primitive group more derived than acantho- cimens has permitted new further interpretations thoracids plus rhenanids, but plesiomorphic to of the structure of these other taxa. Comparisons all other placoderms (Forey & Gardiner 1986), with the Bergisch-Gladbach Ctenurella indicated or as a sister taxon to the petalichthyids (Goujet that its skull roof and visceral skeleton could be 1984; Goujet & Young 1995; Carr 1995). reinterpreted. It soon became apparent that this Most of the known ptyctodontid taxa (some species differs in several major features from the forty-seven species, Carr 1995, amended) are Gogo species, and thus a new genus, Austro- based solely on tooth-plates (Denison 1978), ptyctodus n.g., is here erected for the Gogo species. GEODIVERSITAS • 1997 • 19(3) Ptyctodontid fishes from the Late Devonian Gogò Formation DERMAL BONE TERMINOLOGY in some placoderm groups, is always a median IN PTYCTODONTIDS bone lacking sensory-line canals (e.g. as in an- tiatchs, Denison 1978), or maybe represented by The central median bone that bears the X-sha- a series of irregularly-shaped anamestic bones (as ped confluence of the two main dorsal in the thenanid Asterosteus, Stensio 1969, fig 92). sensory-line canals has been previously called the For the other bones in the head shield and cheek centro-nuchal (Orvig 1960), the centro-median of ptyctodontids, papets published since Miles & (Miles 1967), the nuchal (e.g. Miles & Young Young (1977) use a consistant terminology. 1977; Long 1988a) ot the postpineal (Denison However, the latge paited ventral bones in the 1978, 1985; Johnson & Elliott 1996). ttunk shield that have been called either the Confusion over the name of this bone has arisen, anterior ventrolaterals (Gross 1933; Miles 1967) largely due to the supposed ptesence of a small or the interolaterals (Watson 1938; Denison posterior median element in Rhamphodopsis 1978, 1985) tequire discussion. Orvig (1960) which was termed the nuchal. Examination of regarded them as a combination of both ele­ specimens of Rhamphodopsis threiplandi in the ments and termed them the interolateral-anterior collections of the Natutal History Museum, ventrolaterals. The anterior ventrolateral plates in London, and in the Field Museum, Chicago, primitive placoderms, such as petalichthyids shows that the posterior nuchal element is not (Lunaspis, Gross 1961), eatly atthtodites (actino- present in this genus, but was misinterpreted by lepids, phlyctaenaspids, Goujet 1984b), phyllole­ Watson due to the crushed and fractured nature pids (Long 1984b) and Wuttagoonaspis (Ritchie of the Edderton specimens. The area of exposed 1973) are named so because there is also a poste­ bone immediately behind the paired cential rior ventrolateral plate present posterior to them. plates is most likely the crushed occipital ossifica­ All of these forms also bear paired interolatetal tions of the braincase, as this region lacks any plates forming the anterior ventral margin of the ttace of dermal ornamentation on the Edderton shield and meeting
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