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Home , Boreosomus, Listracanthus, Paleolimnology, Taphonomy

Journal of Palaeogeography 2013, 2(4): 321-343 DOI: 10.3724/SP.J.1261.2013.00034

Biopalaeogeography and palaeoecology

Taphonomy of Early of the Vega-Phroso Siltstone Member of the Sulphur Mountain Formation near Wapiti , British Columbia, Canada

Karen Anderson, Adam D. Woods* Department of Geological Sciences, California State University, Fullerton, P. O. Box 6850, CA 92834-6850, USA

Abstract The of living in lacustrine environments has been extensively studied in both the laboratory and the record; the taphonomy of marine fishes, however, is poorly known. Triassic marine fishes with heavy ganoid and cosmoid scales, which provided protection from rapid taphonomic loss, offer a means to examine marine fish taphonomy in the fossil record. Four genera of fishes (the ray-finned actinopterygians Albertonia, Bobasatrania, Boreosomus, and the lobe-finned coelacanth (sarcopterygian), Whiteia) from the Wapiti Lake, British Columbia locality of the Lower Triassic Sulphur Mountain Formation were examined in order to gain a better understanding of the taphonomy of fish in marine en- vironments, determine ambient environmental conditions in the region during the Early Trias- sic, and ascertain the and mode of life of the fish. Results indicate that environmental conditions that contributed to the preservation of the fossil fishes of the current study included in deep, quiet waters, which reduced the odds of disarticulation, colder waters un- der higher pressure, which slowed decay and limited postmortem floatation, and waters that were anoxic, which discouraged predators and scavengers. In addition, the thickness of the primitive ganoid and cosmoid scales of the fossil fishes also increased their preservation po- tential. Taphonomic, physiological and environmental indicators suggest that Whiteia, Alber- tonia, and possibly Bobasatrania lived in deep, cold waters near the minimum zone, while Boreosomus lived higher in the water column. While the anatomical and physiological characteristics of modern fishes will likely continue to inhibit marine taphonomy studies, ex- amination of ancient fish, particularly those with ganoid or cosmoid scales, may provide future avenues of research to gain a better understanding of marine fish taphonomy and provide a powerful tool to examine ancient fish behavior and their environment.

Key words taphonomy, fish fossils, fossil fishes, Early Triassic

1 Introduction and background* affect deceased , but also provides a mechanism to reconstruct past depositional environments as well as Taphonomy describes the events that occur to an organ- a means to gain a better understanding of the ecology of ism from to fossilization (Efremov, 1940), and is not organisms prior to their demise (e.g., Behrensmeyer and only an important tool in understanding the processes that Kidwell, 1985; Brett and Baird, 1986; Elder and Smith, 1988; Weigelt, 1989; Fernandez-Jalvo, 1995; Martin-Clo- * Corresponding author. Email: [email protected]. sas and Gomez, 2004; Fürsich et al., 2007; Mapes et al., Received: 2013-07-29 Accepted: 2013-08-28 2010; Histon, 2012; McDonald et al., 2013; Peterson and 322 JOURNAL OF PALAEOGEOGRAPHY Oct. 2013

Bigalke, 2013; Sansom, 2013; Sorensen and Surlyk, 2013). odds that the fish would sink after death and lead to well- Taphonomic studies of fish have typically involved study preserved, articulated specimens (Neuman, 1996). of the decay of modern fish (e.g., Parker, 1970; Britton, 1.1 Geologic background 1988; Weigelt, 1989; Minshall et al., 1991; Hankin and McCanne, 2000; Whitmore, 2003), or the examination of The fish fossils examined for this study were collected fossil fish from ancient lacustrine deposits (e.g., McGrew, from talus shed from multiple fossil horizons that occur in 1975; Elder, 1985; Elder and Smith, 1988; Ferber and the Sulphur Mountain Formation at Ganoid Ridge, near Wells, 1995; Wilson and Barton, 1996; Barton and Wilson, Wapiti Lake, British Columbia, Canada (Figs. 1, 2) (Gib- 2005; Capriles et al., 2008; Malenda et al., 2012; Mancuso, son, 1972). The Sulphur Mountain Formation ranges in 2012). The taphonomy of fish in marine environments is thickness from 225 to 250 meters at Ganoid Ridge, was less well understood, and has been mostly concerned with deposited from the lowermost Triassic to the Middle Tri- the causes of mortality (e.g., Brongersma-Sanders, 1957), assic, and is divided into three Lower Triassic Members: including sudden temperature changes (e.g., Gunter, 1941, (1) The recessive basal Phroso Member, which ranges 1942, 1947), cold shock and hypothermia (e.g., Baugh- from 45-55 m thick, and consists of thin, planar-bedded man, 1947; Gilmore et al., 1978; Donaldson et al., 2008), organic-rich dolomitic silty shale; (2) The Meosin Moun- and low dissolved oxygen levels (e.g., Smith, 1999). One tain Member, which is approximately 12 meters thick, of the few studies to examine post-mortem processes in resistant, and composed of very fine-grained, well-sorted marine fishes was by Schäfer (1972), which documented sandstone that may be current-rippled or planar-laminated; the floatation response due to internal gas production of (3) The Vega Member is approximately 195 meters thick, eight species of deceased marine fishes and the subse- and consists of interbedded calcareous to dolomitic quartz- quent loss of body parts from floating carcasses. Tapho- rich sandstone and organic-rich silty shale (Orchard and nomic analysis of marine fishes in the is Zonneveld, 2009). In addition, the Sulphur Mountain For- limited when compared to those of lacustruine deposits, mation also includes two members, the probably due to a greater likelihood of preservation of fish Whistler Member and the Llama Member (Orchard and remains in relatively low energy lake environments with Zonneveld, 2009). Fossil fish occur at multiple horizons high rates. Taphonomic studies of marine within the Phroso Member and Vega Member at Ganoid fishes include fossils from Cenozoic (Bieńkowska, 2004, Ridge and include at least 17 different taxa of bony fish 2008; Bieńkowska-Wasiluk, 2010; Carnevale et al., 2011; and 4 different taxa of cartilaginous fishes; other fauna in- Asano et al., 2012), Mesozoic (Tintori, 1992; Vullo et al., clude ichthyosaurs, marine reptiles, phyllocarids, brachio- 2009; Chellouche et al., 2012), and Paleozoic-aged rocks pods, bivalves, ammonoids and conodonts (Schaeffer and (Burrow, 1996; Cloutier et al., 2011; Lukševičs et al., Mangus, 1976; Brinkman, 1988; Callaway and Brinkman, 2011; VasiĮkova et al., 2012). Ancient marine fish have 1989; Neuman, 1992; Mutter and Neuman, 2009; Orchard recently been subjected to semi-quantitative taphonomic and Zonneveld, 2009). Much of the Sulphur Mountain analysis, however, the number of such studies is limited Formation at Ganoid Ridge was deposited under quiet, (Bieńkowska-Wasiluk, 2010; Cloutier et al., 2011; Chel- low energy conditions with reduced benthic oxygenation louche et al., 2012). as suggested by the fine-grained nature of the unit, a lack The Early Triassic fossil fishes of Wapiti Lake, Brit- of within the fish-bearing intervals, and the ish Columbia, Canada are ideal for taphonomic study, as excellent preservation of fossil remains, including delicate the specimens are frequently whole and well preserved. dermal denticles of the chondrichthyan (shark) Listracan- Preservation was enhanced by deposition in quiet waters thus (Gibson, 1975; Davies et al., 1997a; Mutter and Neu- with little to no disturbance from ocean currents and suf- man, 2009). Many of the fossil fish specimens from Ga- ficiently low oxygen levels in the surrounding waters that noid Ridge, including those examined for this study, were excluded scavengers (Elder, 1985; Elder and Smith 1988). collected by previous workers from talus; because most Furthermore, Early Triassic marine fishes had heavy ga- fossils are not found in situ, it is difficult to match an indi- noid or cosmoid scales that were not prone to rapid de- vidual fossil to a specific stratigraphic horizon (Neuman, cay, and when coupled with the interlocking arrangement 1992; Mutter and Neuman, 2009), however, most of the of the scales, provided a resistant barrier to environmental fish are early in age (Orchard and Zonneveld, conditions and scavengers (Schäfer, 1972; Weigelt, 1989; 2009), although some -aged fish fossils are also Neuman, 1996). In addition, the heavy scales increased the probably present (Mutter and Neuman, 2009). Karen Anderson and Taphonomy of Early Triassic fish fossils of the Vega-Phroso Adam D. Woods: Siltstone Member of the Sulphur Mountain Formation near Vol. 2 No. 4 Wapiti Lake, British Columbia, Canada 323

Fig. 1 Palaeogeography of the Western Canada Sedimentary Basin during Early Triassic time, and the approximate location of the Wapiti Lake fossil fish locality. Deeper water facies of the Western Canada Sedimentary Basin were deposited under suboxic to anoxic conditions (e.g., Davies, 1997; Davies et al., 1997a, 1997b; Wignall and Twitchett, 2002; Beatty et al., 2008; Zonneveld et al., 2010), which led to the enhanced preservation of Early Triassic fishes from the Wapiti Lake area. Modified from Davies, 1997.

(Neuman, 1992, 1996; Davies et al., 1997b); fossils of 1.2 Lower Triassic fossil fish of Wapiti Lake Albertonia are found in a narrow interval, approximately Four genera of Early Triassic marine fishes that are 30-35 m above the base of the section (Neuman, 1992) represented by numerous, well-preserved, complete speci- (Fig. 2). Albertonia had a deep body, long pectoral fins, mens were selected for the current taphonomic research. and a well-developed caudal fin (Fig. 3);Albertonia was a The four fish genera, each with a distinctive morphology nibbler or grazer based on its weak marginal dentition and that is unlike the other fishes selected for this research, a lack of pharyngeal teeth (Schaeffer and Mangus, 1976; include the ray-finned actinopterygians Albertonia, Boba- Neuman, 1992, 1996). Albertonia was likely a strong, but satrania, and Boreosomus and the coelacanth (sarcoptery- slow swimmer, and lived at moderate depths (Schaeffer gian) Whiteia. Specimens from all four genera consist of and Mangus, 1976; Neuman, 1992). articulated and well-preserved fishes with heavy scales that 1.2.2 Boreosomus are surrounded by a matrix of well-sorted, fine-grained, black siltstone. The scales are well defined on most speci- Boreosomus-bearing beds are located 17-27 m above mens and, in most cases decay has not progressed to the the base of the section at Wapiti Lake (Mutter and Neuman, stage where only the internal structures (i.e., skeleton or 2009), and have been found in association with late Indu- individual bones) are exposed and visible. an (i.e., Dienerian) conodonts (M. Orchard, pers. comm., 2004 in Mutter and Neuman, 2009). Boreosomus has 1.2.1 Albertonia also been collected from Spain (Vía Boada et al., 1977), Albertonia is endemic to British Columbia and Alberta East (Nielsen, 1942), Alaska (Patton and Tail- 324 JOURNAL OF PALAEOGEOGRAPHY Oct. 2013

leur, 1964), China (e.g., Chow and Liu, 1957), (e.g., Stensiö, 1921) and northwestern Madagascar (Bel- tan, 1996). Boreosomus had large eyes and a small, fusi- form body, suggesting it was a generalist swimmer (Fig. 3) (Schaeffer and Mangus, 1976; Neuman, 1996; Barbieri and Martin, 2006). Small conical teeth suggest Boreoso- mus grazed or fed on plankton, detritus, larval fishes, soft , etc. (Schaeffer and Mangus, 1976; Beltan, 1996), probably in the euphotic zone (Beltan, 1996).

1.2.3 Whiteia

Whiteia fossils have been found 17-27 m above the base of the section at Wapiti Lake (Mutter and Neuman, 2009), as well as in Lower Triassic strata from East Green- land (e.g., Stensiö, 1932) and Madagascar (e.g., Moy- Thomas, 1935). Whiteia are a type of coelacanth and are structurally different from the ray-finned actinopterygians (Fig. 3). A distinctive feature is the caudal fin, which has three lobes, consisting of a symmetrical upper and low- er lobe and a separate middle lobe (Moy-Thomas, 1935; Neuman, 1996). In addition, coelacanths have two distinct dorsal fins (ancient actinopterygians had only one- dor sal fin); only the posterior of the two dorsal fins is lobed (Moy-Thomas, 1935). The anterior resembles the ray fins of actinopterygians; the posterior dorsal fin, pectoral fins and pelvic fins are lobed and have a rounded morphology (Moy-Thomas, 1935). The rounded fin struc- ture of Whiteia suggests slow movement, and sculling type locomotion (Forey, 1997; Fricke and Hissmann, 1992). Whiteia likely stalked and lunged at prey (Neuman, 1996); small teeth suggest Whiteia ate small organisms in addi- tion to phytoplankton, algae, and organic detritus (Beltan, 1996).

1.2.4 Bobasatrania

Bobasatrania are found within two stratigraphic hori- zons at Wapiti Lake: from approximately 17-27 m and approximately 120-125 m above the base of the section (Neuman, 1992; Mutter and Neuman, 2009). Bobasatra- nia has also been found in Lower Triassic strata of Idaho (Dunkle, pers. comm., 1974 in Schaeffer and Mangus, 1976), Madagascar (e.g., Lehman et al., 1959), Greenland (e.g., Nielsen, 1952) and Spitzbergen (e.g., Schaeffer and Mangus, 1976). The Wapiti Lake specimens of Bobasa- Fig. 2 Stratigraphy and palaeontology along Ganoid Ridge trania found higher in the section are some of the larg- near Wapiti Lake. Fish fossil-bearing intervals occur from 17-27 est fossil fish specimens found in the assemblage and are m (Boreosomus, Whiteia and Bobasatrania), 30-35 m (Alberto- nia), and 120-125 m (Bobasatrania). Fish fossil intervals from larger than most Bobasatrania found around the world Mutter and Neuman (2009). Stratigraphic section modified from (e.g., Schaeffer and Mangus, 1976), reaching lengths of Orchard and Zonneveld (2009). up to one meter (Neuman, 1996). Smaller fossil specimens Karen Anderson and Taphonomy of Early Triassic fish fossils of the Vega-Phroso Adam D. Woods: Siltstone Member of the Sulphur Mountain Formation near Vol. 2 No. 4 Wapiti Lake, British Columbia, Canada 325

Fig. 3 Fossil fish examined for this study include the ray-finned actinopterygiansAlbertonia , Bobasatrania (modified from Schaeffer and Mangus, 1976), Boreosomus (modified from Nielsen, 1942) and the coelacanth (sarcopterygian) Whiteia.

of Bobasatrania primarily found lower in the section may Palaeontology and the Museum, Edmonton, represent a different species (Neuman, 1996). Alberta, Canada. Of the 379 specimens photographed and Bobasatrania are compressed laterally, resulting in a described for this study, 145 were complete specimens that diamond-shaped morphology (Fig. 3) (Russell, 1951). A could be used for taphonomic analysis. Additional partial well-developed and deeply-forked caudal fin, long fins on specimens were included in the determination of fin tetany the dorsal and ventral parts of the body, and long, fan-like or body tetany when possible. pectoral fins high on the abdomen are indicative of precise Data collected for each specimen included specimen position control coupled with short bursts of speed to catch number (which was assigned by the museum or university prey (Schaeffer and Mangus, 1976; Neuman, 1992, 1996); where the specimen is housed: UALVP for the University Bobasatrania likely lived near the seafloor in quiet waters of Alberta Laboratory for Palaeontology, TMP (Schaeffer and Mangus, 1976; Neuman, 1992, 1996; Bar- for the Royal Tyrrell Museum of Palaeontology), fish ge- bieri and Martin, 2006). Crushing teeth suggest that Boba- nus, geologic age, locality, cirque where the fossil was satrania fed on crustaceans (Neuman, 1992, 1996). Boba- found along Ganoid Ridge (if given), date of collection, satrania did not have pelvic fins (Neuman, 1992, 1996). UTM/field site coordinates (if recorded), standard length of the fish if complete (in millimeters; standard length = 2 Methods the length from the snout to the caudal peduncle), ichno- fabric index of the surrounding (Droser and All available fossil specimens of Albertonia, Bobasa- Bottjer, 1986), and a written description of the preserva- trania, Boreosomus and Whiteia were examined from the tional condition of the fossil. At the time the fossil fishes collections of the Royal Tyrrell Museum of Palaeontology were examined, any disarticulated body parts were identi- in Drumheller, Alberta, Canada, as well as from the collec- fied in a photo (or line drawing) of the fish, along with tions of the University of Alberta Laboratory for Vertebrate a notation of the proximity of the disarticulated part. Be- 326 JOURNAL OF PALAEOGEOGRAPHY Oct. 2013 cause taphonomic ranking required examination of the Previous studies by McGrew (1975), Elder (1985), El- entire fish, only complete specimens were considered; in der and Smith (1988), Wilson and Barton (1996), Whit- the case of broken fossils, partially complete fish fossils more (2003) and Barton and Wilson (2005) have noted that were considered only if the majority of the fish was vis- the skull appears to be the first region of a fish to decay and ible and taphonomic data could be collected. Examination disarticulate; therefore, for the current study, taphonomic of entire fish fossils likely introduced some taphonomic data were normalized to the skull. The degree of decay bias into this study in that not all available fossil material and disarticulation of the skull, or the “skull taphonomic was examined (or collected in the field), and the most dis- stage,” was determined first, and the degree of decay and articulated fossils, and therefore those that underwent the disarticulation of the dorsal fin, anal fin, pectoral fin, pel- greatest degree of decay may have been missed. However, vic fin, caudal fin as well as the degree of preservation of limiting this study to only entire fish fossils is considered the body were determined subsequently. to be the most careful means to determine the sequence of 2.2 Tetany fish decay, as analysis of individual, detached parts (e.g., fins, scales, material within , etc.) would lead to Tetany is a form of severe postmortem muscular con- greater odds of analyzing the same individual fish multiple traction, which is often expressed as an open mouth, ex- times, and introduce what would likely be an even greater panded or fanned and stiffened fins, and, less commonly taphonomic bias. an arched body; tetany is considered to be an indicator of anoxic or hypoxic conditions in aquatic environments, 2.1 Taphonomic model although tetany can also be due to temperature shock or Individual fish fossils examined for this study ranged poisoning by plant toxins (Schaeffer and Mangus, 1976). from extremely well preserved with little alteration of the Skull decay was extensive for the fossil fishes examined fish carcass to varying degrees of distortion, decay and for the current research and therefore it was typically not scattering of elements; therefore, it was important to for- possible to collect data related to whether the mouth was mulate a scale that could be used to semi-quantitatively an- open or closed. The exclusion of data related to the posi- alyze taphonomic loss over a wide range of preservational tion of the jaw is supported by the work of Barton and Wil- stages. Wilson and Barton (1996) developed a taphonomic son (2005) who note that relative tetany was best assessed sequence for lacustrine fossil fishes that utilized a rank- by observing the fins. ing system to examine the differing degrees of decay and 2.2.1 Criteria for determination of tetany of fins disarticulation of fossil fishes; their study served as the ba- sis for the taphonomic stages used in this study. Similar Fin tetany was evaluated based on the presence of at methods of semiquantitatively determining taphonomic least two fossil fins other than the caudal fin; therefore the loss in fishes have been used by multiple other studies entire fish was not necessary for determination of fin teta- (e.g., McGrew, 1975; Elder, 1985; Elder and Smith, 1988; ny. The fins (excluding the caudal fin) were examined and Whitmore, 2003; Barton and Wilson, 2005; Bieńkowska- qualitatively assigned a stage ranging from 1 to 4 (modi- Wasiluk, 2010; Cloutier et al., 2011; Chellouche et al., fied from Barton and Wilson, 2005) based on progressively 2012; Mancuso, 2012). greater angles of extension of the fin away from the body In order to establish a sequence of decay and disarticu- and the expansion and separation of the fin rays, which lation for each examined for this study, color pho- resulted in an increased amount of exposed fin surface area tographs of each complete fish specimen were initially (Table 2). It was necessary for the fins of the fish fossils to placed in a sequence of progressive disarticulation. Next, be in fairly good condition for fin tetany to be determined; the preservational condition of the skull, dorsal fin, pelvic tetany was not determined for those fossils where the fins fin, pectoral fin, anal fin, caudal fin, and the body were in- had detached from the body, exhibited excessive decay, or dependently noted and each was assigned a number based were absent. on a 1 to 5 taphonomic scale, where stage 1 indicated that Tetany data were collected for Albertonia and Whiteia the region of interest was well preserved, and stages 2 because their fins are large and easily ranked. Whiteia has through 4 indicated successive degrees of decay and dis- two dorsal fins; the first dorsal fin is not lobed, but is fan- articulation. Stage 5 represented complete disarticulation, shaped, similar to the dorsal fin of a ray-finned fish. All scattering and loss of skull elements, fins, or scales (in the fins were considered together for both fish genera, and the case of the body) (Table 1). non-lobed first dorsal fin ofWhiteia was not given any spe- Karen Anderson and Taphonomy of Early Triassic fish fossils of the Vega-Phroso Adam D. Woods: Siltstone Member of the Sulphur Mountain Formation near Vol. 2 No. 4 Wapiti Lake, British Columbia, Canada 327

Table 1 Taphonomic ranking system (after Wilson and Barton, 1996)

Dorsal Fin, Pelvic Fina, Skull Caudal Fin Body Pectoral Fina, Anal Fin Fish skull appears complete, unal- The body is in excellent tered and well preserved. Caudal fin is in condition, well pre- Fin is in excellent con- Stage 1 - No excellent condition, served, with no signs of dition, well preserved, decay and disar- All skull elements present and in well preserved, with decay or disarticulation. with no signs of decay ticulation unaltered condition, with no apparent no signs of decay or or disarticulation. evidence of decay or disarticulation disarticulation. Scales present and in of skull. excellent condition. Jaw and cranium present. Fin is in anatomical position. The body has undergone The outline of the skull is appar- The profile of the Stage 2 - Slight little distortion. ent with little evidence of decay or caudal fin has little decay and disar- Fin profile is apparent distortion. evidence of decay or ticulation with little evidence Most or all of the scales distortion. of decay or physical are present. A few skull elements may be scat- distortion. tered or lying adjacent to the body. Skull profile appears deformed or Fin is present and at- Profile of the caudal The body may exhibit distorted. tached. Stage 3 - Mod- fin may be distorted some distortion and may erate decay and and have undergone be bent. Many skull elements are missing, Some distortion and disarticulation minor fragmentation. scattered, and/or dislodged (may still fragmentation of the fin Some scales absent. be in place) or adjacent to the body. is apparent. Skull profile appears deformed or Fin is attached but frag- Profile of the body is Profile of the caudal Stage 4 - Se- distorted. mented or splayed. distorted or bent. fin may be distorted, vere decay and bent, torn or frag- disarticulation Most skull elements missing and/or Fin may be bent or The scales are displaced mented. scattered. twisted. or scattered. Stage 5 - Com- The caudal fin is Complete disarticulation Fin is completely disar- plete decay and Skull profile is unrecognizable. completely disarticu- and loss of scales. ticulated or absent. disarticulation lated or absent. a The paired pelvic fins and pectoral fins are referred in the singular, because individual fossil specimens were lying on their side; therefore only one fin could be observed and described.

Table 2 Stages of tetany for Albertonia and Whiteia fins and Boreosomus body

Stage 1 Stage 2 Stage 3 Stage 4 Degree of Fin Tetany None Slight Moderate Severe One or more fins are raised above the body. One or more fins are Fins lie next to the raised above the body. All of the fins lie next body. One or more fins are splayed. Description to the body (i.e., no ex- One or more fins are tension of the fin). One or more fins are Fins appear stretched and fin rays splayed. slightly splayed. are visibly separated.

Fins may be hyperextended.

Stage 1 Stage 2 Stage 3 Degree of Body Tetany None Moderate Severe The body of the specimen The body exhibits a pronounced curva- No bending, curvature, or has a slight curvature into an Description ture greater than 30°, and often exhibits twisting of the carcass. arc that is no greater than 30° a J- or U-shape. from the horizontal. 328 JOURNAL OF PALAEOGEOGRAPHY Oct. 2013 cial consideration from the lobed fins. Bobasatrania and The standard length of Albertonia examined for this study Boreosomus were not included because the fins ofBobasa- varied from 75 mm to 390 mm. The pectoral, anal, and trania are small and the fins are extended in all specimens. dorsal fins were either extended or pressed against the Boreosomus was not considered for determination of fin body. tetany because the fins were often detached, highly frag- In the early stages of skull decay and disarticulation, mented, or missing. at skull taphonomic stage 2 (n = 3), the caudal fin was the best preserved with all specimens within taphonomic 2.2.2 Postmortem bending of the body: Another possible stage 2 (Figs. 4, 5A; Table 3). The remaining fins and body indicator of tetany were assigned to taphonomic stage 2 (2 specimens) and 3 In addition to fin tetany, tetany may also be expressed by (1 specimen). an arched body or a body bent into a J- or U-shape; arching The largest number of Albertonia specimens (n = 38) of the body has been observed in previous studies of fishes had a skull taphonomic stage of 3. At this taphonomic that have been subjected to hypoxic (low oxygen) or an- stage, the anal fin underwent the greatest degree of tapho- oxic conditions (e.g., Elder, 1985; Elder and Smith, 1988; nomic loss while the body and caudal fin were the better Whitmore, 2003; Barton and Wilson, 2005). Boreosomus, preserved (Figs. 4, 5B; Table 3). The smallest fin, the anal which was not included in the examination of fin tetany fin, exhibited some fragmentation and had a greater degree because of the frequent loss of the fins, was examined for of decay and disarticulation when compared to the dorsal body tetany because the slender, fusiform morphology of or pectoral fins. For the anal fin, 6/38 specimens were clas- the fish is expected to show evidence of body tetany if the sified as taphonomic stage 4, and 9/38 taphonomic stage 5. fish was exposed to detrimental environmental conditions. The remainder of the samples were assigned taphonomic All Boreosomus specimens that were assigned taphonomic stage 1 (2/38), 2 (10/38), or 3 (11/38). The dorsal fin of stages were also visually examined and placed in one of the majority of specimens was ranked at taphonomic stage three stages of body tetany (Table 2). 2 or 3 (13/38 and 14/38, respectively), with most of the remainder at taphonomic stage 4 or 5 (6/38 and 4/38, re- 3 Results spectively). The dorsal fin of a single specimen exhibited no evidence of decay or disarticulation (taphonomic stage 1). The pectoral fin for most specimens was assigned to 3.1 Ichnofabric taphonomic stage 3 (16/38) or 4 (10/38), with the differ- The fossil fishes found within the Vega-Phroso Silt- ence divided between taphonomic stage 1 (1/38), 2 (7/38), stone Member are preserved within fine-grained siltstone or 5 (4/38). The caudal fin of 28/38 of the specimens was that breaks into flat slabs; the varies in color from assessed as taphonomic stage 2 or 3 (17/38 and 11/38, dark brown to dark gray to black (Gibson, 1972, 1975; respectively), with the remainder in taphonomic stage 1 Neuman, 1992, 1996; Davies, 1997; Davies et al., 1997a, (2/38) or 4 (8/38). The body of most specimens was ranked 1997b; Orchard and Zonneveld, 2009). The fine siltstones taphonomic stage 3 (26/38), with the difference divided that surround the four genera of fossil fishes (n = 379) ex- between taphonomic stage 1 (2/38), 2 (5/38) or 4 (5/38). amined for this research have an Ichnofabric Index of 1, As skull decay and disarticulation progressed into implying that the sediments were undisturbed by bioturba- taphonomic stage 4 (n = 29), the dorsal and anal fins of tion (Droser and Bottjer, 1986). several specimens were extremely fragmented and de- tached, but were typically in relative position next to the 3.2 Degree of taphonomic loss body (Figs. 4, 5C; Table 3). The small anal fin continued to All specimens of each of the 4 genera examined for this exhibit the greatest degree of taphonomic loss, with most study underwent some degree of skull decay. Therefore, (9/29, 31%) specimens within taphonomic stage 5. The there were no specimens with a ranking of taphonomic anal fin of the remainder of the specimens was assigned stage 1 for the skull. to taphonomic stage 2 (5/29), 3 (10/29) or 4 (5/29). The dorsal fin exhibited slightly less taphonomic loss than the 3.2.1 Albertonia anal fin with 8/29 and 7/29 within taphonomic stage 4 or A total of 155 specimens of Albertonia were examined 5, respectively. The dorsal fin of the remaining specimens and photographed; of those, 73 specimens (47%) were was assessed as taphonomic stage 2 (4/29) or 3 (10/29). complete and suitable for determining taphonomic stages. The pectoral fin was often extended and sustained some Karen Anderson and Taphonomy of Early Triassic fish fossils of the Vega-Phroso Adam D. Woods: Siltstone Member of the Sulphur Mountain Formation near Vol. 2 No. 4 Wapiti Lake, British Columbia, Canada 329

Fig. 4 Taphonomic data for the 4 genera of marine fishes examined for this study.

decay and disarticulation but was better preserved than the fin, was best preserved with all specimens within tapho- smaller dorsal and anal fins, with 3/29, 13/29, 9/29 and nomic stage 4. The body was also slightly better preserved 4/29 in taphonomic stages 2, 3, 4 and 5, respectively. The than the skull, dorsal fin, pectoral fin, or anal fin at tapho- caudal fin underwent less decay and disarticulation than nomic stage 4. each of the other fins, with 3/29 in taphonomic stage 2, 3.2.2 Boreosomus 10/29 in taphonomic stage 3, and 16/29 in taphonomic stage 4. The body was divided between taphonomic stage Boreosomus had the least number of fossil specimens 3 or 4 (14/29 and 13/29, respectively) for most specimens, for study. A total of 45 specimens of Boreosomus were ex- with the difference in taphonomic stage 2 (2/29). amined and photographed; of those, 18 specimens (40%) During skull taphonomic stage 5 (represented by 3 were complete and suitable for taphonomic analysis. The specimens), the soft tissue of the skull decayed to the point standard length of Boreosomus examined for this study where the skull elements were dissociated and scattered; ranges from 83 mm to 225 mm. Many of the fins (except consequently, the anterior region, which includes the dor- the caudal fin) ofBoreosomus were missing. sal and pectoral fins, also underwent a great deal of de- At the early stages of decay of the skull (skull tapho- cay and disarticulation, with the dorsal and pectoral fins nomic stage 2; n = 3), the dorsal, pelvic, and anal fins were at taphonomic stage 4 (2/3) or taphonomic stage 5 (1/3) not visible in all three specimens; therefore, all fins (ex- (Figs. 4, 5D; Table 3). The specimens were divided be- cluding the caudal fin) were assigned a taphonomic stage tween taphonomic stage 4 (1/3) and 5 (2/3) for the anal fin. of 5 (Figs. 4, 6A; Table 3). The caudal fin was torn in all The posterior region of the specimen, including the caudal three specimens (taphonomic stage 3 or 4; 1/3 and 2/3, re-

Karen Anderson and Taphonomy of Early Triassic fish fossils of the Vega-Phroso Adam D. Woods: Siltstone Member of the Sulphur Mountain Formation near Vol. 2 No. 4 Wapiti Lake, British Columbia, Canada 331

Fig. 6 Decay and disarticulation of Boreosomus. A-Skull taphonomic stage 2. The skull displays very little decay; however, some skull elements are scattered and the underside of the jaw is visible. The dorsal, pelvic, and anal fins of this example are not present; the caudal fin is torn at the lower caudal lobe. The body of this specimen is well defined; however, some scales are missing. Overall taphonomic ranking: Skull (S): 2, Dorsal Fin (DF): 5, Pelvic Fin (PF): 5, Anal Fin (AF): 5, Caudal Fin (CF): 3, Body (B): 2. (Royal Tyr- rell Museum of Palaeontology gallery); B-Skull taphonomic stage 3. The skull of this specimen has undergone some disarticulation, but larger elements appear to be still in place. A large degree of fragmentation is present near the gills, which may be remnants of the dorsal and the pelvic fins of this specimen. The anal fin is not visible, while the caudal fin has been subjected to minor fragmentation or tearing. The body of this fossil is slightly distended, and many scales are missing. Overall taphonomic ranking: S: 3, DF: 4, PF: 4, AF: 5, CF: 3, B: 4. (TMP 1988.98.53); C-At Skull taphonomic stage 4, the skull profile is faint but is apparent; no fins are visible for this specimen except for an outline of the caudal fin. The body is not well preserved, lacks definition, and many scales are missing. Overall taphonomic ranking: S: 4, DF: 5, PF: 5, AF: 5, CF: 4, B: 4. (TMP 1993.120.101); D-Skull taponomic stage 5. This specimen appears to have exploded, with only the caudal fin still intact; skull elements, body, fins, and scales are scattered within the vicinity of the fossil. Overall taphonomic ranking: S: 5, DF: 5, PF: 5, AF: 5, CF: 4, B: 5. (TMP 1995.114.14). 332 JOURNAL OF PALAEOGEOGRAPHY Oct. 2013 spectively). The body was the best preserved, with speci- anterior or the first dorsal fin (which is not lobed) and the mens evenly distributed between taphonomic stage 2, 3, posterior or second (lobed) dorsal fin. In most specimens, and 4. each dorsal fin has a similar degree of decay and disarticu- At skull taphonomic stage 3 (n = 8), the anal fin was not lation; therefore, the two dorsal fins were assigned a single visible on any of the specimens, resulting in the anal fin taphonomic stage ranking. The cosmoid scales for lobe- of all eight specimens ranked taphonomic stage 5 (Figs. finned Whiteia are not as defined and distinctive as those 4, 6B; Table 3). Skull taphonomic stage 3 is the only stage of the ganoid scales for the ray-finned genera examined where pelvic or dorsal fins were observed. The pelvic fin for this study. was fragmented for 2/8 specimens (taphonomic stage 4) At skull stage 2 (n = 3), the body and dorsal fin were and missing from the remainder (6/8) and assigned to the first to show signs of decay (Figs. 4, 7A; Table 3). All taphonomic stage 5. The dorsal fin of 4/8 specimens was specimens (3/3) were ranked at taphonomic stage 2 for the fragmented and classified as taphonomic stage 4. The dor- dorsal fin and body, where the dorsal fin exhibited moder- sal fin was not observed for 3 specimens (taphonomic stage ate decay and the scales on the body were visible, but not 5), while one specimen had a dorsal fin with only moderate well defined. The majority of specimens were assigned to decay and disarticulation (taphonomic stage 3). The caudal taphonomic stage 1 (1/3) or 2 (2/3) for the pelvic, anal, and fin and body are the best preserved aspects ofBoreosomus caudal fins. at skull taphonomic stage 3, however, the body exhibited At skull stage 3 (n = 9), the dorsal fin, anal fin, and some distortion and bending, and the scales were difficult pelvic fin exhibited a slightly greater degree of decay and to see. The caudal fin and body are distributed between disarticulation over the body and caudal fin (Figs. 4, 7B; taphonomic stage 2, 3, or 4, with the majority of speci- Table 3). Over half (5/9, 6/9, 7/9) of the specimens were mens within taphonomic stage 3 (4/8 for the caudal fin and assigned to taphonomic stage 3 for the dorsal fin, anal fin, 5/8 for the body) and the remainder in taphonomic stage 2 and pelvic fin respectively; the remainder of the specimens (2/8) or 3 (2/8) for the caudal fin and taphonomic stage 3 were ranked taphonomic stage 4 for the dorsal fin (4/9), (1/8) or 4 (2/8) for the body. anal fin (3/9), and pelvic fin (2/9). At skull taphonomic At skull taphonomic stage 4 (n = 5), no dorsal, pelvic, or stage 3, the scales were very faint or possibly missing anal fins were visible for Boreosomus, and all specimens from the body for the majority of specimens. As a result were ranked at taphonomic stage 5 for these fins (Figs. 4, the body of most specimens (7/9) were evaluated as tapho- 6C; Table 3). The body and caudal fin were slightly better nomic stage 3; one specimen exhibited less body decay preserved with all samples ranked at taphonomic stage 4: (taphonomic stage 2), and one more decay (taphonomic the body was often distorted, some scales were missing stage 4). The caudal fin was the best-preserved feature at and the caudal fin was fragmented but articulated. skull taphonomic stage 3, with the majority of specimens When the skull and skull elements were completely (8/9) in taphonomic stage 3 and one specimen in tapho- disarticulated and scattered at skull taphonomic stage 5 nomic stage 2. (n = 2), the dorsal, pelvic, and anal fins were absent and At the more advanced stage of skull decay, taphonomic also assigned to taphonomic stage 5 (Figs. 4, 6D; Table stage 4 (n = 9), the fins and body for the majority of speci- 3). At this stage, the body was often bent into a J- or U- mens are also in taphonomic stage 4 (dorsal fin = 8/9; pel- shape, with many scales scattered and missing; the body vic fins = 8/9; anal fin = 5/9; caudal fin = 7/9; body = 5/9) of one specimen was assigned to taphonomic stage 4 and (Figs. 4, 7C; Table 3). The remainder were ranked within one taphonomic stage 5. The caudal fin, while often folded taphonomic stage 3 (2/9 for the caudal fin and body) or or torn, was articulated and the best preserved, with both taphonomic stage 5 (1/9 for the dorsal fin, anal fin and specimens ranked at taphonomic stage 4. body; 2/9 for the caudal fin). Overall, the scales were sel- dom observed and internal structures of the specimens 3.2.3 Whiteia were frequently visible, while the caudal fin was articu- A total number of 107 specimens of Whiteia were ex- lated but fragmented. amined and photographed; of those, 23 specimens (22%) There were two specimens at taphonomic stage 5 for were complete and suitable for determining taphonomic the skull, where the skull had undergone extensive disar- stages. The standard length of Whiteia examined for this ticulation (Figs. 4, 7D; Table 3). The body also underwent study ranges from 70 mm to 490 mm. In contrast to the significant , with scales scattered (tapho- other three genera, coelacanths have two dorsal fins: the nomic stage 5 for both specimens). The anal, pelvic, and Karen Anderson and Taphonomy of Early Triassic fish fossils of the Vega-Phroso Adam D. Woods: Siltstone Member of the Sulphur Mountain Formation near Vol. 2 No. 4 Wapiti Lake, British Columbia, Canada 333

Fig. 7 Decay and disarticulation of Whiteia. A-Skull taphonomic stage 2. Some skull decay is evident; however, the skull has a well-defined profile. All fins are fairly well preserved; in addition, the caudal fin exhibits a detailed tassel. The body of this specimen has undergone very little decay and scales are visible. Overall taphonomic ranking: Skull (S): 2, Dorsal Fin (DF): 2, Pelvic Fin (PF): 2, Anal Fin (AF): 2, Caudal Fin (CF): 2, Body (B): 2. (UALVP 24130); B-Skull taphonomic stage 3. The skull has undergone minor decay and some smaller skull elements have been scattered. The body of this specimen is fairly well preserved; the fins have some fragmentation and are splayed. The caudal fin is present, but has undergone some decay. Overall taphonomic ranking: S: 3, DF: 3, PF: 3, AF: 3, CF: 3, B: 2. (TMP 1984.42.6); C-Skull taphonomic stage 4. The skull of this specimen is distorted, and decay has caused some skull elements to migrate. In this example, the dorsal, pelvic, and anal fins are fragmented and appear to be in relative position but are not attached to the body; the caudal fin is also fragmented and the tassel is missing. The upper body of this specimen is not visible; however, no individual scales or elements are within close proximity to the specimen. Ovearll taphonomic ranking: S: 4, DF: 4, PF: 4, AF: 4, CF: 4, B: 4. (TMP 1995.42.135); D-Skull taphonomic stage 5. A significant amount of decay and disarticulation has taken place in this specimen; several structures including the caudal fin, pelvic fin, and anal fin are present and are mostly likely in relative position; however, the remainder of the fish carcass has been scattered. Overall taphonomic ranking: S: 5, DF: 5, PF: 3, AF: 3, CF: 3, B: 5. (TMP 1993.120.127). 334 JOURNAL OF PALAEOGEOGRAPHY Oct. 2013 caudal fins were split between taphonomic stage 3 (1/2) or 4 (4/10). 4 (1/2) and were better preserved than the dorsal fin (1/2 in At skull taphonomic stage 4 (n = 19), the skull experi- taphonomic stage 4 and 1/2 in taphonomic stage 5). enced significantly more decay, with skull elements scat- tered (Figs. 4, 8C; Table 3). The dorsal and anal fins, which are very small fins, are fragmented and fin rays are often 3.2.4 Bobasatrania difficult to see. The majority of specimens were within Taphonomic stages for Bobasatrania were assigned taphonomic stage 5 (12/19) for the dorsal fin, with the re- for the skull, body, caudal fin, dorsal fin and anal fin; this mainder in taphonomic stage 2 (1/19), 3 (3/19) or 4 (3/19). genus does not have pelvic fins, therefore, determination Most specimens were ranked within taphonomic stage 4 of taphonomic stages was slightly different than that for (9/19) or 5 (6/19) for the anal fin, with the remainder in the other three genera. The pectoral fin, located behind the taphonomic stage 2 (1/19) or 3 (3/19). The body and cau- gills, is fairly long and extends past the caudal peduncle, dal fin were assigned taphonomic stage 4 (13/19 for the but was also not included in this study because it was often body and 11/19 for the caudal fin); the body of the remain- pressed flat against the body and obscured by the scales; der of the specimens are ranked within taphonomic stage the other fins were positioned within the surrounding sedi- 2 (1/19) or 3 (5/19), while the caudal fin for the remain- ment, which provided greater contrast. ing specimens occur within taphonomic stage 2 (2/19), 3 A total of 72 specimens of Bobasatrania were exam- (5/19), or 5 (1/19). ined and photographed; of those, 32 specimens (44%) Skull taphonomic stage 5, with only one specimen, fol- were complete and suitable for determining taphonomic lowed the pattern of previous stages: the small dorsal and stages. Standard length determined by this study ranges anal fins exhibit extensive decay and disarticulation and from 57 mm to 255 mm, however, larger, incomplete spec- were assigned taphonomic stage 5 (Figs. 4, 8D; Table 3). imens not included in the taphonomic data for this research The body and caudal fin are the best preserved, although reached a projected standard length of 570 mm to 1075 they still underwent a great deal of decay and disarticula- mm (in most cases the skull of the larger specimens was tion and are assessed as taphonomic stage 4. At this skull missing), and demonstrate the large size of some Early Tri- stage, many scales are missing from the body and the pro- assic fishes in the region. The dorsal and anal fins ofBoba- file of the body is distorted; nevertheless, the caudal fin satrania are very small and appear extended at all times; and body exhibit a lesser amount of decay and disarticula- Bobasatrania also had numerous fin rays along the margin tion, with each assigned to taphonomic stage 4. of the body (Fig. 3D). 3.2.5 Fin tetany of Albertonia and Whiteia Only two specimens were assigned taphonomic stage 2 for the skull. At this stage, the dorsal and anal fins were All (n = 67) specimens of Albertonia exhibited tetany the best preserved with both specimens within taphonomic of the fins (Table 4); there were no specimens at fin tetany stage 1 (Figs. 4, 8A; Table 3). The specimens were split stage 1. The vast majority (61/67) of the specimens were between taphonomic stage 1 and 2 for the body; some of ranked at fin tetany stage 4, severe tetany, where all fins the scales were missing from one specimen. The caudal fin were extended and the fin rays were clearly separated (Fig. was also divided between taphonomic stage 1 and 3; the 9). Five specimens displayed moderate fin tetany at fin caudal fin of one specimen was fragmented. tetany stage 3, where one or more of the fins were raised As skull decay progressed to skull stage 3 (n = 10), above the body and fin rays were splayed. One specimen the anal fin exhibited the most decay and disarticulation, showed signs of slight tetany, fin tetany stage 2, where the with the majority of specimens within taphonomic stage 5 fins were splayed but not raised above the body. (3/10), and the remainder in taphonomic stage 3 (3/10) or 4 All specimens (n = 32) of Whiteia exhibited tetany of (4/10) (Figs. 4, 8B; Table 3). The dorsal fin was distributed the fins (Table 4). There were no specimens at FinTet- between taphonomic stage 2, 3, 4 and 5 (2/10, 3/10, 1/10 any Stage 1. Over half (18/32) of the specimens exhib- and 4/10, respectively). At this stage, the body appears to ited moderate tetany at fin tetany stage 3, where one or have lost more scales and the body profile is increasingly more fins were raised above the body and splayed (Fig. distorted, with more than half (6/10) of the specimens 10). Nine specimens displayed severe fin tetany, fin tetany within taphonomic stage 4 and the remainder (4/10) within stage 4, where the fins were extended away from the body taphonomic stage 3. Overall, the caudal fin appeared to be and fully stretched. Five specimens showed signs of slight the best-preserved region, at taphonomic stage 3 (6/10) or tetany; the fins were positioned next to the body with one Karen Anderson and Taphonomy of Early Triassic fish fossils of the Vega-Phroso Adam D. Woods: Siltstone Member of the Sulphur Mountain Formation near Vol. 2 No. 4 Wapiti Lake, British Columbia, Canada 335

Fig. 8 Decay and disarticulation of Bobasatrania. A-Skull taphonomic stage 2. The skull of this larger specimen is well preserved and exhibits very little distortion and very few elements are missing. The mouth appears to be open, and may possibly be an indication of tetany (Elder, 1985). All fins are well preserved in this specimen as are the fin rays on the posterior margin of the body. The body is well defined and scales appear to be intact. Standard length: 176 mm. Taphonomic ranking: S: 2, DF: 1, AF: 1, CF: 1, B: 1. (UALVP 17942); B-Skull taphonomic stage 3. This small specimen has a fairly well-preserved skull with some skull elements scattered. This example differs from other specimens because the pectoral fin is visible. The remaining fins are visible and in fairly good condition; however, the caudal fin is torn and fragmented on the upper lobe of the fin. Many scales appear to have sloughed off the body. Stand- ard length: 115 mm. Taphonomic ranking: S: 3, DF: 2, AF: 3, CF: 3, B: 3. (UALVP 46939); C-Bobasatrania skull stage 4. The skull exhibits severe disarticulation, with many larger and heavier elements scattered and lying next to the fossil. Unlike most specimens for this research, the pectoral fin is visible on this specimen. The dorsal, anal, and caudal fins of this example are fairly well preserved; the body is slightly distended and some scales appear to be missing. Standard length: 255 mm. Taphonomic ranking: S: 4, DF: 3, AF: 3, CF: 3, B: 3. (UALVP 43674; previous number UALVP 46509); D-Skull taphonomic stage 5. This specimen exhibits significant decay and disarticulation. The skull and skull elements have scattered. The dorsal, pelvic and anal fins are absent while the caudal fin consists of a remnant of the upper lobe. The body demonstrates major decay, with little or no definition, and many scales are missing. Standard length: 100 mm. Taphonomic ranking: S: 5, DF: 5, AF: 5, CF: 4, B: 4. (TMP 1995.120.22).

or more fins slightly splayed (fin tetany stage 2). All 18 specimens of Boreosomus examined for taphonom- ic stages were also examined to determine the orientation 3.2.6 Body tetany of Boreosomus of the body (Table 4). The majority of Boreosomus speci- Many of the fossils of Boreosomus exhibit an arched mens (11/18) were flat-lying and did not exhibit arching, body that forms a J- or U-shape, a common characteristic or bending of the body, while the remaining seven speci- of floatation or, less commonly, due to tetany of the body. mens exhibited bending, arching, or twisting of the body 336 JOURNAL OF PALAEOGEOGRAPHY Oct. 2013

Fig. 9 Stages of fin tetany for Albertonia. A-Fin tetany stage 2 (slight). All of the fins lie next to the body and are slightly splayed. (TMP 1990.120.5); B-Fin tetany stage 3 (moderate). The dorsal and pectoral fins are raised above the body and are slightly splayed. (TMP 1990.120.12); C-Fin tetany stage 4 (severe). All fins are extended away from the body and fin rays are separated. The dorsal fin, at a nearly 90° angle from the body, is also splayed. (TMP 1990.120.15). Karen Anderson and Taphonomy of Early Triassic fish fossils of the Vega-Phroso Adam D. Woods: Siltstone Member of the Sulphur Mountain Formation near Vol. 2 No. 4 Wapiti Lake, British Columbia, Canada 337

Fig. 10 Stages of fin tetany forWhiteia . A-Fin tetany stage 2 (slight). The fins of this specimen are slightly splayed but not extended away from the body. (TMP 1984.24.6); B-Fin tetany stage 3 (moderate). This specimen exhibits fin tetany; all fins, except the first dorsal fin, are extended away from the body. (UALVP 24130); C-Fin tetany stage 4 (severe).

Table 4 Tetany results Fin tetany:

Fin tetany stage 1 Fin tetany stage 2 Fin tetany stage 3 Fin tetany stage 4 Number of specimens (none) (slight) (moderate) (severe) Albertonia 67 0 1 5 61 Whiteia 32 0 5 18 9

Body tetany (Boreosomus):

Skull stage 1 Skull stage 2 Skull stage 3 Skull stage 4 Skull stage 5 Number of specimens 0 3 8 5 2 Body bent in in a J- or U-shape 0 3 2 1 1 No bending of body 0 0 6 4 1

Karen Anderson and Taphonomy of Early Triassic fish fossils of the Vega-Phroso Adam D. Woods: Siltstone Member of the Sulphur Mountain Formation near Vol. 2 No. 4 Wapiti Lake, British Columbia, Canada 339

Smith, 1988; Wilson and Barton, 1996; Whitmore, 2003; implies that Albertonia perished in deep, oxygen-depleted Barton and Wilson, 2005). As the body and fins decayed, waters, and probably lived near the oxygen minimum zone the skull underwent further decomposition, eventually re- (OMZ). sulting in scattering of some of the skull elements and dis- 5.2 Boreosomus tortion of the profile of the skull. The caudal fin was typi- cally the last region to decay and was still intact even in The fusiform shape of Boreosomus suggests the fish was those specimens where the body had apparently exploded a generalist swimmer that lived higher in the water col- from the buildup of decay gases. umn than Albertonia, Bobsatrania and Whiteia (Schaeffer The decay and disarticulation of the dorsal and ven- and Mangus, 1976; Beltan, 1996; Neuman, 1996; Barbieri tral fins was controlled by the degree of decomposition of and Martin, 2006), and took longer to reach the seafloor the body and abdomen, as well as the size, structure and following death. Many specimens of Boreosomus (39%) shape of the fins. Small fins underwent decay, tearing, and exhibit a body that is bent into a J- or U-shape (Fig. 11), fragmentation more rapidly than larger fins. Laboratory which may due to tetany or postmortem floatation; the experiments conducted by Whitmore (2003) demonstrate fins of Boreosomus that are preserved are not extended or that fins are a sensitive indicator of postmortem floatation: stretched, as would be expected from tetany, and the num- fins are more likely to lose rigidity, droop, and decay as a ber of specimens exhibiting bending would be expected response to the length of time the fish floated (Whitmore, to be in the majority if exposure to persistent anoxic con- 2003). The caudal fin was typically the last region to de- ditions were responsible Boreosomus mortality (Elder, compose, probably because the caudal fin had a strong 1985; Ferber and Wells, 1995; Whitmore, 2003; Barton muscle attachment to the body over a larger area than that and Wilson, 2005; Faux and Padian, 2007; Chellouche et for the other fins and the caudal fin was not located near al., 2012). Furthermore, many fins (excluding the caudal any large cavities (e.g., oral or abdominal cavities) where fin) were missing completely, suggesting rapid decay and bacteria could easily infiltrate. fragmentation in oxygenated waters (Whitmore, 2003). The body was better preserved than most of the fins; Therefore, arching of the body of Boreosomus is thought none of the fishes examined for this study had decayed to to be due to floatation, not tetany. Full floatation of the the extent where only the skeleton or scattered bones were carcass would have likely led to widespread scattering of present. The sturdy ganoid and cosmoid scales were prob- the remains of Boreosomus (Schäfer, 1972); therefore, it ably the most important factor in the high degree of preser- seems likely that only the upper body and skull were lifted vation of the external features of the body; rapid burial also as decay gas built up, and the fish fell to the seafloor with probably played an important role. The specimens exam- a twisted or arched orientation as gas escaped from the ined for this study were often better preserved than fossil carcass. The heavy ganoid scales prevented the fish cara- fishes from other studies where skeletal remains were the cass from becoming positively buoyant, and led instead to only structures available for study (e.g., McGrew, 1975; a slow descent to the bottom; interlocking ganoid scales Elder, 1985). The ganoid and cosmoid fish of Wapiti Lake also prevented disarticulation during descent to the sea- therefore provide a useful means to examine the taphono- floor (Neuman, 1996). my marine fish, with the caveat that the heavy, armor-like 5.3 Whiteia structure of the scales likely led to better preservation than might be expected otherwise. Whiteia is the only genera examined for this study with a living relative; therefore, predictions can be made about 5 of Early Triassic fishes Whiteia through examination of the modern coelacanth, Latimeria chalumnae, which is not significantly different with respect to outward appearance from Whiteia. Ob- 5.1 Albertonia servations of Latimeria from submersibles demonstrates Albertonia was a grazer (Schaeffer and Mangus, 1976; a passive lifestyle hovering above the seafloor in deep Neuman, 1992, 1996) that lived at moderate depths ocean waters (e.g., Fricke and Hissmann, 1992). Latimeria (Schaeffer and Mangus, 1976; Neuman, 1992). Severe commonly inhabits the subphotic zone with little current tetany of the fins, well-preserved scales, fins, and gills, and activity, low oxygen concentrations, and cold waters with a lack of evidence for postmortem flotation (i.e., no evi- temperatures that range from 15℃ to 19℃ (Hughes and dence of the body bending or arching into a J- or U-shape), Itazawa, 1972; Fricke and Hissmann, 1990, 2000; Fricke 340 JOURNAL OF PALAEOGEOGRAPHY Oct. 2013 et al., 1991; Forey, 1997; Hissmann et al., 2000). Hughes Sulphur Mountain Formation, in British Columbia, Cana- and Itazawa (1972) conducted experiments on the blood of da. The diverse community of fishes and other organisms, Latimeria and found that oxygen saturation for Latimeria including marine reptiles, ichthyosaurs, phyllocarids, bra- is dependent on low temperatures; the oxygen dissociation chiopods, bivalves, ammonoids and conodonts was likely curve of Latimeria blood shows a higher affinity for oxy- a good representation of the organisms living in the region gen at 15℃ than at 28℃, which suggests that it is well- at the time. The following conclusions are made concern- adapted to living under deep, cold waters with reduced ox- ing these fossil fishes and their taphonomy: ygen levels. Latimeria has also been observed migrating to 1) Each of the genera examined for this study sustained depths of 200 m to 400 m (to temperatures as low as 12℃) some level of decay and disarticulation that was initiated to feed and to avoid predators (Hissmann et al., 2000). El- within the skull and progressed from the anterior to the der (1985) proposed that 15℃ is the threshold tempera- posterior region of the fish fossil; this phenomenon has ture for floatation of a fish carcass; 15℃ is the same water been documented by many other studies (McGrew, 1975; temperature that Latimeria inhabits today (Hissmann et Elder, 1985; Elder and Smith, 1988; Wilson and Barton, al., 2000). Like Latimeria, Whiteia most likely also inhab- 1996; Whitmore, 2003; Barton and Wilson, 2005). ited deep, cold waters near the OMZ, based on morpho- 2) The lifestyle and niche that each of the four genera logic similarities between the two fish genera, as well as occupied was an important factor in determining the lev- the fine-grained, organic-rich sediments, undisturbed by el of preservation. Those fishes living close to the OMZ bioturbation, that surround the Whiteia fossils from Wapiti (Albertonia, Whiteia and Bobasatrania) had a shorter Lake (Neuman, 1992; Davies et al., 1997a). The OMZ, a distance from death to burial and were better preserved, stable environment with minimal water currents and cool which is supported by taphonomic and tetany data. Alter- temperatures, was also an optimal environment for fossil natively, those fishes living farther from the OMZ, most preservation that would minimize floatation and transport likely in warmer, oxygenated waters, underwent greater of a carcass, as well as discourage scavengers and preda- taphonomic loss: indeed, Boreosomus exhibits ample evi- tors. dence of arched bodies due to postmortem floatation, more fin fragmentation, and greater degree of taphonomic loss 5.4 Bobasatrania than Albertonia, Whiteia and Bobasatrania, which lived Bobasatrania was a large fish with a deep, laterally closer to the OMZ. compressed body that was well suited to a lifestyle in 3) The four fish genera are well preserved because they relatively still and quiet waters (Russell, 1951; Schaeffer were deposited in deep, cold waters under anoxic condi- and Mangus, 1976; Neuman, 1992, 1996). Their crushing tions. These results support previous studies that suggest teeth suggest they fed on small, slow moving, hard-shelled that widespread bottom water anoxia persisted in the re- animals and most likely pursued a lifestyle of limited ac- gion during the Early Triassic (e.g., Davies, 1997; Davies tivity, grazing in quiet waters near the seafloor (Neuman, et al., 1997a, 1997b; Wignall and Twitchett, 2002; Beatty 1992, 1996). Bobasatrania also had well-developed and et al., 2008; Zonneveld et al., 2010). thick ganoid scales, which more than likely made Boba- 4) The four fish genera are also well-preserved because satrania a fairly heavy fish. If Bobasatrania ventured into of the dermal covering of the fish; the ganoid scales for deeper, suboxic waters the combination of oxygen-deplet- Albertonia, Bobasatrania and Boreosomus, and cosmoid ed waters and the weight of the heavy ganoid scales may scales for Whiteia provided a protective outer covering have made it difficult for the fish to escape. Overall, the that limited the amount of disarticulation and scattering well-preserved nature of Bobasatrania coupled with an and increased the preservation potential of fish that pos- interpreted lifestyle in deep, quiet waters (Russell, 1951; sessed these scales. Therefore, the results of this study are Schaeffer and Mangus, 1976; Neuman, 1992, 1996), sug- somewhat constrained to fish with similar tough, outer der- gests that it also lived near the OMZ. mal coverings that limited decay and disarticulation of the fish, however, the comparable sequence of head to tail de- 6 Conclusions cay between this study and other studies (McGrew, 1975; Elder, 1985; Elder and Smith, 1988; Wilson and Barton, The current study examined four genera of well-pre- 1996; Whitmore, 2003; Barton and Wilson, 2005) is sig- served, Early Triassic fossil marine fishes from the Wapiti nificant, as is the similarity with respect to the early loss of Lake locality of the Vega-Phroso Siltstone Member of the fins other than the caudal fin (Whitmore, 2003). Therefore Karen Anderson and Taphonomy of Early Triassic fish fossils of the Vega-Phroso Adam D. Woods: Siltstone Member of the Sulphur Mountain Formation near Vol. 2 No. 4 Wapiti Lake, British Columbia, Canada 341 this study has applications beyond ganoid and cosmoid Bieńkowska, M., 2004. Taphonomy of ichthyofauna from an Oligo- fishes in that it suggests that the taphonomic processes act- cene sequence (Tylawa Limestones horizon) of the Outer Car- ing on lacustrine and marine fish are similar with respect pathians, Poland. Geological Quarterly, 48: 181-192. to decay and disarticulation, and suggests that many of the Bieńkowska, M., 2008. Captivating examples of fish- observations about lacustrine fish taphonomy are also ap- taphocoenoses from the Polish Outer Carpathians. In: Krem- paská, Z., (ed). 6th Meeting of the European Association of Ver- plicable to marine fish. tebrate Palaeontologists. Spišská Nová Ves - Slovak Republic, Fricke and Hissmann (2000) suggest that the radiation 17-21. of modern actinopterygian fishes forced coelacanths of the Bieńkowska-Wasiluk, M., 2010. 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