Draft New records from Banks Island expand the diversity of Eocene fishes from Canada ’ s western Arctic Greenhouse

Journal: Arctic Science Manuscript ID AS-2017-0007.R1 Manuscript Type: Article Date Submitted by the Author: 22-May-2017 Complete List of Authors: Gottfried, Michael; Michigan State University, Earth and Environmental Sciences Eberle, Jaelyn; University of Colorado Boulder, Geological Sciences and Museum of Natural History Keyword: Eocene, Arctic, Greenhouse, fishes, paleoenvironment Is the invited manuscript for consideration in a Special Issue?: N/A


Introduction
The discovery over the past several decades of a wide range of late early to middle Eocene [~50-53 Ma] vertebrates from the Canadian Arctic has been instrumental to developing the concept of the 'Greenhouse Earth' interval, during which global temperatures were significantly higher than at present and the Arctic experienced mild temperate conditions with above-freezing winters (Dawson et al. 1976, Estes andHutchison 1980).A host of vertebrates, including fishes, turtles, lizards, alligators, and a diverse mammalian fauna that includes tapirs, primates, and the hippo-like Coryphodon, have been recovered from Ellesmere Island, from non-marine sediments of the lower-middle Eocene Margaret Formation of the Eureka Sound Group (Eberle and Greenwood 2012, and references therein).
Banks Island, at the far western edge of the Canadian Arctic archipelago ca.1,100 km west of Ellesmere (Fig. 1), also preserves a significant Eocene Greenhouse assemblage, but one that complements and augments the finds from Ellesmere in that it is more marineinfluenced and samples a less terrestrial paleoenvironment (Padilla et al. 2014, Eberle et al. 2014).Eberle et al.'s recent (2014) report documented bony fish (the gar Atractosteus, possible amiid, esocids, and indeterminate teleosts) and crocodyliform ( a single eusuchian centrum) fossils, and Padilla et al. (2014) described the chondrichthyan fauna, which is notable for its relatively low diversity but very high numbers of teeth of the Sand-tiger sharks (Carcharias and

Striatolamia macrota).
Here we further expand the Eocene fish fauna from Banks Island, including an unambiguous and more informative record for amiids (Amia sp.), and a large sample of teeth of the 'scombroid' teleost Eutrichiurides.These discoveries were made from strata of the lowermiddle Eocene Cyclic Member of the Eureka Sound Formation, at sites near the Eames River within the northern part of Aulavik National Park on northern Banks Island (Fig. 1).The new D r a f t finds definitively expand the range of amiids to the western edge of the Canadian Arctic during the Greenhouse interval, and add a distinctive new predatory teleost to the Arctic that is otherwise known from a range of lower latitude Eocene sites.Identifications were made on the basis of comparisons with specimens at the Natural History Museum (London) (NHM) and the Field Museum of Natural History (FMNH), Chicago, as well as collections held at UCM and MSUM.Terminology for amiid specimens follows Grande and Bemis 1998.We note that additional Eocene fish specimens from Banks Island have been collected that are not included in this report; our focus here is on the diagnostic and most informative material from Banks Island that has not previously been described.Nomenclature and classification follows Betancur-R. et al. 2013.

Geologic Setting and Age
The fossils described below were collected over the course of three field seasons (2004,2010,2012)  The Eocene vertebrate-bearing strata are assigned to the Cyclic Member of the Eureka Sound Formation (Eberle et al. 2014, Padilla et al. 2014, Miall 1979).The Cyclic Member consists of coarsening-upward cycles of shale, silt, unconsolidated sand, paleosol, and lignitic coal, interpreted as a deltaic sequence in a marginal marine setting (Miall 1979).The unit preserves abundant shark teeth, bivalves, the trace fossil Ophiomorpha (interpreted as a thalassinidean shrimp burrow and generally indicative of a shallow-water, moderately high energy, coastal marine environment, according to Frey et al. 1978).Rare marine microfossils (foraminiferans and radiolarians) have also been documented from the Cyclic Member (Miall 1979).The fossils described here were recovered as float, alongside hundreds of shark teeth, on unconsolidated sands in the Cyclic Member.This was supplemented by dry screening to recover smaller specimens (primarily small shark teeth).
The Eocene age for these fossil localities is based on pollen samples initially analyzed by Hopkins (1974Hopkins ( , 1975) ) and reported by Miall (1979).Re-analysis of four pollen samples collected near the Eames River by Sweet (2012) (discussed in Padilla et al. 2014) suggest that the localities are late early to middle Eocene in age and spanned the early Eocene Climate Optimum, based on species richness and the abundance of Caryapollenites spp., Ericipites, Intratriporopollenites (Tilia), Nyssapollenites sp., and Quercoidites (oak) pollen.Presence of Pistillipollenites suggests a probable minimum age of middle Eocene for the samples, while the absence of Aquilapollenites tumanganicus Bolotnikova and closely allied species, infrequent occurrences of Momipites spp., and the richness of the angiosperm component of the assemblages precludes an earliest Eocene age (Padilla et al., 2014).

D r a f t
Early -middle Eocene Arctic climate was characterized by warm wet summers and mild winters.Estimates of early -middle Eocene Arctic mean annual temperature (MAT) range from 8 -15˚C, summers probably reached 19 -25˚C, and winters were above freezing (Eberle et al. 2010, Eberle andGreenwood 2012).Based upon carbon isotope analysis of mummified wood from the Cyclic Member near Muskox River on northern Banks Island, Schubert et al. (2012) concluded that the Eocene forests on northern Banks experienced three times more precipitation during summer than winter, a seasonal pattern analogous to today's temperate forests of eastern Asia.Mild coastal marine temperatures are supported by presence of the Sand-tiger shark genera Striatolamia, Carcharias, and Odontaspis, whose living relatives inhabit temperate and tropical waters around the world, and the ray Myliobatis, whose present-day distribution is restricted to tropical and warm-temperate seas (Padilla et al. 2014 and references therein).In addition to being warm, the shallow coastal waters of the Eocene Arctic Ocean were brackish, as indicated by oxygen isotope analysis of shark teeth from the Cyclic Member (Kim et al. 2014).This is consistent with paleogeographic reconstructions of a largely isolated Arctic Ocean during the early -middle Eocene Greenhouse and an intensified hydrologic cycle with precipitation exceeding evaporation (Pagani et al. 2006) Description.CMN 57523 (Fig. 2) is a nearly complete large lateral line scale preserved on the internal surface of a small sideritic nodule that has split open to reveal the fossil.The subrectangular scale is slightly rounded at the anterior and posterior corners, slightly deeper anteriorly, and measures 36 mm in anterior-posterior length as preserved, and 31 mm where it is deepest from the dorsal to ventral edges of the scale.The lateral line can clearly be seen as an open canal that penetrates the mid-region of the scale.The posterior edge of the scale bears a small, ovoid thickened area that is ornamented with raised anastomosing ridges and shallow sunken troughs, representing the free-field area of the scale that would have been externally exposed when the scale was is in position along the body.The anterior overlapped area of the scale is extensive and thin, and bears very fine sub-parallel ridges that subtly diverge as they pass along the surface of the scale towards the slightly deeper anterior edge.

D r a f t
This scale is strikingly similar to lateral line scales of the extant species Amia calva (see Grande and Bemis 1998, Figure 92, p. 147), although the extant species has lateral line scales that are slightly more anterior-posteriorly elongated in proportion.Those authors illustrate (their  Arambourg 1952, Casier 1944, Cvancara and Hoganson 1993, Dutheil et al. 2006, Kemp et al. 1990, Kumar et al. 2007, Merle et al. 2002, Monsch 2004, Pickford 1987].Teeth assigned to this taxon from the Eocene of Banks Island range in size from ca. 10 to 25 mm in length, are narrowly elongate and sharply pointed when well-preserved, erect to shallowly posteriorly recurved, and conical in cross-section.The outer surfaces of the teeth bear very fine longitudinal striations and show subtle lateral banding that gives the teeth the appearance of varying from darker to lighter zones along the length of the teeth.The apices of the teeth characteristically bear a slightly expanded translucent cap that in close view has the appearance of a small expanded spear point or arrowhead positioned on the apex of the tooth (see Fig. 3).Teeth that are well-preserved at their base show an expanded area of bone that marks the site of attachment to the jaw.The largest teeth of this taxon are interpreted to be premaxillary fangs (Monsch 2004).The Banks Island teeth are fully consistent with Monsch's (2004) description of Eutrichiurides teeth as diagnostic at the generic level based on being comparatively large, semi-conical, elongate to stoutly erect, with small slightly expanded caps at their apices, and not as laterally compressed as the otherwise similar teeth of the related trichiurins.

Discussion
The scales of Amia establish that amiid fishes were present at the far western edge of the Canadian Arctic in the Eocene, a further expansion of their previously known range from the eastern Canadian Arctic (Estes andHutchison 1980, Eberle andGreenwood 2012) and reassuring given the uncertainty over an earlier account (Eberle et al. 2014) that tentatively identified amiids on Banks Island based on less diagnostic material.The strikingly large lateral line scale indicates that these fish were not only present at this far northern latitude, but likely grew to a size significantly larger than extant Amia calva.Ray (1960) and Van Voorhies (1996) maintained that ectotherms, including freshwater fishes, follow Bergmann's Rule (Bergmann 1847, Mayr 1956) in which species at higher latitudes exhibit larger body size than their lower latitude close relatives.Belk and Houston (2002), however, convincingly argued against this in their study, which included a large sample size of representatives of 18 relatively large-bodied northern hemisphere fish species -they concluded that North American freshwater fishes in general do not follow Bergmann's Rule (although Amia was not included in their analysis).
It is not surprising that amiids would thrive in the paleoenvironment interpreted for Banks Island -relatively warm winters above freezing, and in a marginal marine setting with low salinity (Kim et al. 2014).Amiids are known to be tolerant of poorly oxygenated conditions and are capable of air-breathing and even aestivation (Grande and Bemis 1998) and so would have been well suited to survive a variety of climatic conditions during the Eocene Greenhouse interval.It can be reasonably assumed that an amiid well in excess of one meter in length would have been a formidable predator in the Eocene Arctic ecosystem, as living bowfins are voracious predators that consume a variety of prey.
The identification of Eutrichiurides in the Arctic Eocene is a bigger surprise, as previous records of this taxon are from much lower latitude sites in the United Kingdom, central Europe, D r a f t India, Africa, and the USA.The recovery of several dozen teeth of this taxon on Banks Island suggests that it was a regular element of the fauna and not an accidental or sporadic visitor.
Eocene paleogeographic reconstructions, e.g.those of Blakey (see Fig. 3  Eutrichiurides may indicate some level of previously unrecognized regional faunal differentiation in Arctic Eocene Greenhouse fishes.Among the fishes now known from the Arctic Eocene, the only Recent survivors above the Arctic Circle are the esocids (pikes and their allies), which occur on Banks and Ellesmere islands in the Eocene (see Eberle et al. 2014), and today have a Holarctic distribution at latitudes as high as 74 degrees.Osteoglossomorphs are also known from the North American Arctic, but so far have only been reported from Late Cretaceous deposits there (e,g, Grande, 1986).
fossils were collected on Banks Island in 2002, 2010, and 2012.All required permits were obtained from the Parks Canada, Western Arctic Field Unit, the authority for research activities in Aulavik National Park.Fossils are curated in the collections of the Canadian Museum of Nature (CMN) in Ottawa, Canada, and loaned to the University of Colorado Museum of Natural History (UCM) and Michigan State University Museum (MSUM) for study.
. The Banks Island biota would have experienced months of continuous daylight during the summer and continuous darkness during the polar winter, as the Eocene paleolatitude of the Eames River localities was approximately 76˚ N (GEOMAR 2011) and well within the Arctic Circle.Referred specimens.CMN 57523 (lateral line scale) (Fig. 2), CMN 57514 (scale), Locality and horizon.Aulavik National Park, northern Banks Island, NWT, Canada; Cyclic Member, Eureka Sound Formation, late early -middle Eocene.

Fig
Fig. 92c) a lateral line scale from a 'large individual' that measured 60.8 cm in standard length (SL); the scale measures 17 mm in length, and according to the relation between SL:Total Length [TL] in Amia calva, that would correspond to a fish with a TL of approximately 71 cm [in Amia TL = SL(1.169);fishbase.org,accessed January 23, 2017].Assuming similar proportionsin the Banks Island Amia, a lateral line scale with a length of 36 mm would correspond to a fish of approximately 1.4 meters in TL, a length that would exceed the recorded maximum TL of 1.07 meters for extant Amia calva(Page and Burr 1991).
in Eberle and   Greenwood 2012), show an open Turgai Strait connecting the Arctic Ocean with the Atlantic,and possibly an open Eocene channel between Greenland and Europe.Either or both could have served as dispersal corridors for biotic interchange between the Arctic Ocean and Europe, India, and Africa, although caution is warranted on the basis of this one taxon.Eutrichiurides is a distinct new addition to the Arctic Eocene, and to date has not been reported from the Eocene of Ellesmere Island, which has gars, amiids, and pikes in common with Banks Island.As such,