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(Osteichthyes: Coelacanthiformes) from the Middle Devonian of Southeastern Australia

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(Osteichthyes: Coelacanthiformes) from the Middle Devonian of Southeastern Australia Records of the Western Australum Museulll Supplement No. 57: 37-53 (1999). A new genus of fossil coelacanth (Osteichthyes: Coelacanthiformes) from the Middle Devonian of southeastern Australia John A. Long Western Australian Museum, Francis St, Perth, WA 6000; email: [email protected] Abstract A new primitive coelacanth Gavinia syntrips gen. et sp. nov., is described from the upper Middle Devonian Mt Howitt site, central Victoria. The genus is based on a partial skull, complete caudal fin and distal section of trunk and median fins, some isolated scales, and indeterminate remains. It is regarded as the most primitive member of the Coelacanthiformes because it has a very long dentary bone, approximately 36% of the lower jaw length, a relatively elongate cheek region, and coarsely omamented scales. It retains the basic coelacanthiform synapomorphies of having a tandem double lower jaw joint; broad-headed, short hyomandibular; large, deep operculum; and a rostraI organ denoted by the large pore system in the snout bones. Isolated coelacanth remains from the Pambula River site, New South Wales, are also referred to Gavinia sp. indet. A provisional phylogenetic analysis places Gavinia as the plesiomorphic sister taxon to all other Coelacanthiformes (Actinistia), and this suggests a possible origin for the c1ade in eastern Gondwana. INTRODUCTION and this material is currently under study by Or The Mt Howitt fauna, from central Victoria Alex Ritchie. (Figure 1), contains a diverse assemblage of fishes The Mt Howitt fauna also contains several preserved in finely-laminated black lacustrine primitive teleostomes, namely the acanthodians shales of the Avon River Group. The depositional Culmacanthus stewarti Long, 1983b and environment has been interpreted as part of an Howittacanthus kentoni Long, 1986, and the intramontane basinal setting in which lakes were palaeoniscoid Howqualepis rostridens Long, 1988. periodically formed by damming of the high energy Sarcopterygians are represented by the fleurantiid drainage system by acid lava flows and ignimbritic lungfishes Howidipterus donnae Long, 1992 and eruptions (Long 1982). The fish fauna is well­ Barwickia downunda Long, 1992 (Long 1993), and the preserved, represented by mostly complete osteolepiforms Marsdenichthys longioccipitus Long, individuals in all stages of growth, indicating that 1985 and Beelarongia patrichae Long, 1987, plus the mass kill was most likely a randomly generated, new coelacanthiform described herein. but geologically regular event. Marsdenichthys was first referred to the The fauna is dominated by several species of Tristichopteridae (= Eusthenopteridae) by Long placoderms. Long (1983a) and Long and Werdelin (1985) but since then new material has been found (1986) described three species of the antiarch that has been studied by the author and Or Oleg Bothriolepis from the Mt Howitt sites (B. Lebedev, from the Palaeontological Institute of gippslandiensis, B. cullodenensis, B. fergllsoni) and a Moscow. We now regard it as possibly a primitive fourth species (B. bindareei) from a nearby road member of the family Rhizodopsidae, due to its cutting. Long (1984) described two species of the intricate scale ornamentation. Beelarongia has been phyllolepid arthrodire Austrophyllolepis (A. ritchiei referred to the new family Canowindridae by and A. YOlwgi). I consider now that there may only Young et al. (1992). In addition, a glyptolepid be one species of phyllolepid present, as porolepiform may also be present in the fauna, deformation of the strata can account for the based on isolated scales and a partial body showing distortion of plate measurements that separate the a long, lobed pectoral fin and broad cleithrum. two originally named species. However, despite However, as the scales of this form are easily this, there are still three distinct species of distinguished from those of Gavinia gen. nov., the Bothriolepis present in the Mt Howitt faunas: the isolated tail described herein is clearly attributed to low-erested B. gippslandiensis, the high-crested B. Gavinia gen. novo rather than the glyptolepid. The cllllodenensis and the non-crested B. fergllsoni. Only sarcopterygian fauna present at Mt Howitt is one species of Groenlandaspis appears to be present, entirely endemic at the generic leveL 38 I.A. Long N i fossil fish sites , . Victoria D Early Carboniferous ~sediments Middle-Late Devonian Dvolcanics k<d sediments 30 km VICTORIA Figure 1 Locality map showing Mt Howitt in its geological setting. In addition to the articulated coelacanth remains group, as the vitally important features of early of Gavinia gen. novo from Mt Howitt, an isolated coelacanths are related to their cranial proportions, bone and scale of a similar coelacanth is described such as the relative size of lower jaw bones to total from the Pambula River site, of probable early­ jaw length, skull table bones and proportions, and middle Givetian age, estimated to be slightly older cheek length, as will be shown in the discussion than the Mt Howitt site by correlation with the below. A newly discovered coelacanth from the Aztec Siltstone fauna of Antarctica (Young 1983, Late Givetian Gauja Formation of Latvia is currently 1993; Turner 1997). under study by Or Per Ahlberg, and Or Ervins Coelacanths are known from few other Oevonian Luksevics and colleagues. Known from well­ deposits, all of which fall within the latest Givetian preserved three-dimensional material, it is said to to Famennian age range. Cloutier (1991) reviewed be of similar primitive organization to Migllashaia, Palaeozoic coelacanth occurrences and recognized a but further comparisons with the new material number of synapomorphies that define the group. described herein must wait until the Latvian genus Figure 2 shows all the major occurrences of is fully described (P.E. Ahlberg pers. comm. 1998). Oevonian coelacanths in order of age (except for Thus, the earliest coelacanths which offer useful some of the indeterminate forms noted by Cloutier). information on the nature of the primitive members The coelacanth most often cited in the recent of the group are Migllashaia bllreaui Schultze, 1973 literature as being the oldest member of the group from the Frasnian Escuminac Formation of Canada, is Euporosteus eifeliensis ]aeckel, 1927, from the Diplocercides spp. Stensio, 1937 and Nesides? Crinoidmergel of Germany, now considered to be heiligenstockiensis lessen, 1966, from the Upper late Givetian in age (Schultze 1993; Schultze and Frasnian of Germany and the Middle Frasnian of Cloutier 1996). This specimen is represented by a Iran (Janvier and Martin 1979). The new form single ethmosphenoid, which gives no clear described from Mt Howitt is either a contemporary indication of its degree of plesiomorphy within the of, or older than, the previously oldest known New Devonian coelacanth from southeastern Australia 39 Gondwana Euramerlca Z c: I gen. Indet. Chagrlnla ea South Africa et -c: I United States - c: Z Cl) 0 E > ea W u. C Dlplocercldes spp., c: Nesldes W ea Germany I- -c: et (I) ..J ea I Dlplocercldes ... Iran U. Mlguashala Canada > c: (Mt Howitt) Euporosteus W ea Germany C - GavlnJa gen. novo I Cl) Australia -> C - I (Pambula River) -:E " Figure 2 Distribution of Devonian coelacanths in time and space. Sources: Stensi6 (1937), Jessen (1966), Janvier and Martin (1979), Cloutier (1991), Anderson et al. (1994) and Cess and Hiller (1995). coelacanthiform, Euporosteus eifeliensis, yet despite Mt Howitt fauna is seen by the close phylogenetic its relative incompleteness, it can be argued that it relationship between the Bothriolepis species (Young is more primitive than any of the other Late 1988; Johanson and Young this volume), the Devonian taxa. presence of the endemic acanthodian genus Clllmacanthus (Long 1983b; Young 1989), and the possible presence of Austrophyllolepis and THE AGE OF THE MT HOWITT FAUNA Howidipterus in both faunas. The age of the Mt Howitt fauna is placed as late Overall these data suggest that the Mt Howitt Givetian by Young (1993), on the basis of its fauna is, at youngest, late Givetian, making it stratigraphic position low in the order of fish­ approximately contemporaneous with the German bearing sites in the central Victorian sequence, and site containing Euporosteus; or, maybe older, from its correlation with the Taggerty site on the perhaps lower or middle Givetian. This would basis of both containing B. gippslandiensis and imply a slightly older age for the base of the Aztec Allstrophyllolepis sp. The Taggerty site has a Silstone than first proposed by Young (1988), and radiometric date on a rhyolite above the fish­ correlations between the base of this unit and the bearing horizon of 367 ± 2 Myr, giving a minimum Hatchery Creek Conglomerate in New South Wales age of early Frasnian (Williams et al. 1982). The Mt (Eifelian age: Young and Gorter 1981; Young 1993; Howitt site can also be closely correlated with the Turner 1997) would not seem unreasonable, given Freestone Creek faunas of east Gippsland, on the the presence in both faunas of similar thelodonts basis of Bothriolepis cllllodenensis, Culmaclmthlls (Turinia antarctica Turner and Young, 1994, TlIrinia stewarti, and Allstrophyllolepis sp. Furthermore, the sp. cf. T. hlltkensis), primitive osteolepiforms recent studies on late Devonian fish sites in New (Beelanmgia patrichae and 'Gyroptyclzills' allstralis South Wales (Young this volume) also corroborate Young and Gorter, 1981), primitive asterolepidoid an older age for the Mt Howitt
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