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A Fork-Tailed Coelacanth, Rebellatrix Divaricerca, Gen. Et Sp. Nov

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A Fork-Tailed Coelacanth, Rebellatrix Divaricerca, Gen. Et Sp. Nov This article was downloaded by: [114.79.54.1] On: 09 May 2012, At: 04:42 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Journal of Vertebrate Paleontology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/ujvp20 A fork-tailed coelacanth, Rebellatrix divaricerca, gen. et sp. nov. (Actinistia, Rebellatricidae, fam. nov.), from the Lower Triassic of Western Canada Andrew J. Wendruff a b & Mark V. H. Wilson a a Department of Biological Sciences and Laboratory for Vertebrate Paleontology, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada b School of Earth Sciences, 125 South Oval Mall, The Ohio State University, Columbus, Ohio, 43210, U.S.A. Available online: 03 May 2012 To cite this article: Andrew J. Wendruff & Mark V. H. Wilson (2012): A fork-tailed coelacanth, Rebellatrix divaricerca, gen. et sp. nov. (Actinistia, Rebellatricidae, fam. nov.), from the Lower Triassic of Western Canada, Journal of Vertebrate Paleontology, 32:3, 499-511 To link to this article: http://dx.doi.org/10.1080/02724634.2012.657317 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Journal of Vertebrate Paleontology 32(3):499–511, May 2012 © 2012 by the Society of Vertebrate Paleontology FEATURED ARTICLE A FORK-TAILED COELACANTH, REBELLATRIX DIVARICERCA, GEN. ET SP. NOV. (ACTINISTIA, REBELLATRICIDAE, FAM. NOV.), FROM THE LOWER TRIASSIC OF WESTERN CANADA ∗ ANDREW J. WENDRUFF ,† andMARKV.H.WILSON Department of Biological Sciences and Laboratory for Vertebrate Paleontology, University of Alberta, Edmonton, Alberta T6G 2E9, Canada, [email protected] ABSTRACT—An unusual fork-tailed coelacanth from the Lower Triassic Sulphur Mountain Formation of British Columbia, Canada, marks the first considerable departure in actinistian body form since the Mississippian Period. Rebellatrix divaricerca, gen. et sp. nov., is unique among coelacanths in its possession of a bifurcated caudal fin, reduced segmentation of fin rays, and fusion of caudal fin elements. Parsimony analysis of a character-taxon matrix of 109 characters and 29 taxa recovered R. divaricerca as sister taxon to Latimerioidei. The family Rebellatricidae is erected to include only R. divaricerca. This novel body shape of the new coelacanth raises questions about the idea that coelacanths were morphologically static following the Mississippian. Rebellatrix divaricerca also emphasizes the morphological diversity of coelacanths during the Early Triassic, a time when species diversity of coelacanths was also highest. The slender, fork-tailed body form suggests fast swimming and an active lifestyle, unique among known fossil and extant coelacanths. INTRODUCTION ciated elements of R. divaricerca, sp. nov., show that coelacanths were likely still capable of great anatomical change. By adding Coelacanths are traditionally thought of as an evolutionarily to the ever-growing record of anatomical diversity seen in fossil conservative group of sarcopterygian fishes that have changed coelacanths, it further supports the idea that coelacanths are not little over geological time (Huxley, 1861, 1935; Schaeffer, 1948, as morphologically conservative as widely believed. 1952; Moy-Thomas and Miles, 1971; Jarvik, 1980; Forey, 1984; Lund and Lund, 1985; Schultze, 1987; Balon et al., 1988 Cloutier, GEOLOGY 1991; Schultze, 2004). However, early in their evolutionary his- tory, they exhibit a wide array of caudal fin forms, from tapering Coelacanths have been known from the Lower Triassic of to heterocercal (Schultze, 1973; Forey, 1998; Long, 1999; Fried- Western Canada since 1916, when Lambe described a partial man and Coates, 2006). After the Mississippian, they are believed specimen as belonging to the genus Coelacanthus Agassiz, 1839. to have been morphologically static (Schaeffer, 1948, 1952; Moy- Since that time, a more productive locality, commonly referred to Thomas and Miles, 1971; Lund and Lund, 1985; Schultze, 1987; as Wapiti Lake or more precisely Ganoid Ridge and occurring in Cloutier, 1991; Schultze, 2004), adhering closely to a body plan the Sulphur Mountain Formation, was found in British Columbia within and around the area of what is now Wapiti Lake Provin- Downloaded by [114.79.54.1] at 04:42 09 May 2012 comparable to that of the extant coelacanth Latimeria Smith, 1939. A number of authors have suggested that peak species di- cial Park (Laudon, 1949; Callaway and Brinkman, 1989; Neuman, versity of coelacanths occurred in the Early Triassic (Schaeffer, 1992; Neuman and Mutter, 2005). A preliminary description of 1948, 1952; Forey, 1984, 1988; Cloutier, 1991; Cloutier and Forey, the fossil fishes by Schaeffer and Mangus (1976) included a brief 1991; Forey, 1991, 1998); however, there is disagreement over the synopsis of the coelacanths, attributing them to an undescribed implications of this peak. Schaeffer (1952) argued that despite species of Whiteia (Moy-Thomas, 1935). coelacanth species peaking in the Lower Triassic, the group dis- The Sulphur Mountain Formation consists of (from lowest in played little morphological disparity at that time, whereas Forey stratigraphic succession to highest) the Vega, Meosin, Phroso, (1988) argued that morphological diversity peaked along with Whistler, and Llama members (Gibson, 1975; Orchard and Zon- species diversity in the Early Triassic. Forey (1988) asserted that neveld, 2009). The formation spans the Lower to Middle Trias- arguments to the contrary might have been biased by compari- sic and sits on a Permian unconformity (McGugan and Rapson- son with the large early deviations in Devonian to Mississippian McGugan, 1976; Neuman, 1992). The majority of the fossils have forms. not been collected in situ, but rather were found along scree Here we describe the first major divergence in coelacanth body slopes well below the exposures, causing problems for determin- form since the time of the Mississippian coelacanth Allenypterus ing the exact fossil-producing beds and the exact age of the fos- Melton, 1969, from the Bear Gulch limestone of Montana. Rebel- siliferous horizons. Additionally, most of the fossils collected are latrix divaricerca, gen. et sp. nov., is the first morphologically di- fragmentary. vergent body form consistent with Forey’s (1988, 1998:245) claim Neuman (1992) noted that there are at least three fossil- that the highest number of species is correlated with the highest producing layers within the Sulphur Mountain Formation in rate of morphological change. The unusual caudal fin and asso- Wapiti Lake Provincial Park. The main fossil bed is approxi- mately 30 to 70 m above the Permian unconformity and produces the majority of the fossil fishes, including the coelacanths from *Corresponding author. †Current address: School of Earth Sciences, this study. These specimens are from the Vega-Phroso Member 125 South Oval Mall, The Ohio State University, Columbus, Ohio 43210, (Meosin Member not present), and are preserved in a dark-grey U.S.A. E-mail: [email protected] to brownish-grey calcareous siltstone (Gibson, 1968; Neuman, 499 500 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 32, NO. 3, 2012 1992) (for detailed accounts of the geology, see Neuman, 1992; Holotype—PRPRC 2006.10.001, a nearly complete and articu- Neuman and Mutter, 2005; Orchard and Zenneveld, 2009). lated specimen, missing the pectoral and pelvic fins and much of The specimens described here were collected from skree slopes the skull, the caudal margin being truncated at the end of the within several different cirques along the Ganoid Ridge. The block (Fig. 1), length 54 cm, collected in 2006 outside Wapiti preservation of the fossils is such that they appear at first glance Lake Provincial Park by members of the collecting party from to be well preserved but upon closer inspection the bone detail is the PRPRC. poor. The age of the Sulphur Mountain Formation has been de- Paratypes—PRPRC 2004.10.001, consisting of the posterior termined to be Griesbachian to Ladinian (Lower to Middle Tri- half of the skeleton from pelvic fin to caudal fin (Fig. 2), length assic) based on conodont and ammonoid biostratigraphic zona- 69 cm, collected by a private collector in the 1950s in the vicin- tion (Orchard and Zonneveld, 2009). The most productive cirque ity of Wapiti Lake Provincial Park and recently donated to the withintheparkisreferredtoasCirqueC(mapinCallawayand PRPRC—no other information available; PRPRC 2007.11.108, Brinkman, 1989:fig. 1; Orchard and Zonneveld, 2009:fig. 1) where consisting of the posterior half of the skeleton from the pelvic TMP 1989.138.33 was found. The age of the fossils recovered girdle to the
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