Osteology and systematic position of the Eocene salmonid †Eosalmo driftwoodensis Wilson from western North America

Abstract

The fossil salmonid tEosulmo dnzoodensis was originally described from fragmentary specimens. Study of new material of this fossil species confirms that it is a stem-group salmonine, with a mixture of primitive and derived salmonine features in its skull, but with its postcranial skeleton essentially of modern salmonine construction. Two autapomophies define the genus TEosalrno: a long anterodorsal process of the subopercle meeting the dorsal edge of the bone at an angle of about 60°, and a thin dermal basihyal plate apparently lacking teeth. Its salmonine relationship is supported by eight derived features: (1) posterior part of frontal widely expanded above autosphenotic, (2) hyomandibular fossa on pterotic long, (3) posterior part of endopterygoid extending posteriorly and broadly overlapped by both metapterygoid and quadrate, (4) premaxillary process of maxilla extending dorsally at an angle larger than loo, (5) infraorbitals 3 to 5 narrow and covering less than anterior half of hyomandibula, (6) presence of suprapreopercle, (7) anterior end of preopercular canal on horizontal arm distinctly turning to anteroventral corner of preopercle, (8) first uroneural amplified into large fan-shaped stegural, and (9) scales small, with more than two lateral line scales per vertebral centrum. Salmonidae are a monophyletic family defined by at least three synapomorphies: posterior surface of epiotic with sulcus, peg-and-socket connection in caudal skeleton, and tetraploid karyotype. Within the Salmonidae, Thymallinae and Salmoninae form a clade based on features from premaxilla, supramaxilla, anguloarticular, and supraorbital.

Crying wolf, crying foul, or crying shame: alien salmonids and a biodiversity crisis in the southern cool-temperate galaxioid fishes?

“…An area of New Zealand, roughly centred on Rotorua-Taupo in the central North Island, was profoundly influenced by a series of relatively recent, and sometimes huge, volcanic eruptions lasting over ca. 50,000 years, the last major eruption being around 186 A.D. (Wilson and Walker 1985;Froggatt and Lowe 1990;Wilson and Houghton 1993). Substantial impacts on terrestrial biota have been described or postulated, and effects on freshwater biota are equally likely.…”

“…Moreover, the shared evolutionary roots of galaxiids and salmonids must be very ancient, dating back at least to the mid-late Mesozoic. Fossils of recognisable salmonids and osmerids are known back to the upper Cretaceous to early Tertiary times (Romer 1966;Wilson and Williams 1991;Wilson and Li 1999), and even extant species of Oncorhynchus have been found in the Pliocene (Cavender and Miller 1972;Stearley and Smith 1993). Fossil galaxiids resembling extant species are known from the Miocene of New Zealand (McDowall 1976b;McDowall and Pole 1997;Lee et al submitted).…”

Framing the Salmonidae Family Phylogenetic Portrait: A More Complete Picture from Increased Taxon Sampling

“…Based on morphological evidence, it has been suggested that Coregoninae is the sister group to the remainder of Salmonidae [3], [18], a finding that is corroborated by recent molecular investigation of some species of Salmonidae using nearly complete mitochondrial sequence data [14]. However, another recent phylogenetic study using a comprehensive set of nuclear genes suggests that Thymallinae may occupy that position [13], leaving uncertainties on the evolutionary relationship among subfamilies that has been widely accepted for decades.…”

DNA phylogeny supports revised classification of Salmothymus obtusirostris

“…It exhibits a range of morphological particularities (Fig. 1) among which the most evident are the elongated muzzle, small, fleshy mouth and the cranial bone convex in the orbital region (for a detailed morphological description see Karaman, 1927; Janković, 1961; Schöffmann, 1991; Stearley & Smith, 1993; Wilson & Li, 1999).…”