ZoologicalJournal ofthe Linnean Sociep (1999), 125: 279-31 I. With 9 figures Article ID: zjls.1997.0166, available online at http://www.idealibrary.com on 10 Ehl

Osteology and systematic position of the Eocene salmonid TEosalmo dr@woodensis Wilson &om western North America

MARK V.H. WILSON1*AND GUO-QING LI1"

I Laboratory for Ertebrate Paleontology, Department of Biological Sciences, Universig of Alberta, Edmonton, Alberta T6G 2E9, Canada Institute of Vertebrate Paleontology and Paleoanthropology, Academia Sinica, rl 0. Box 643, Beging 100044, China

Received May 1996; acceptedfor Publication April 1997

The fossil salmonid tEosulmo dnzoodensis was originally described from fragmentary speci- mens. 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.

0 1999 The Linnean Society of London

ADDITIONAL KEY WORDS:-Eocene ~ tEosulmo ~ North America ~ osteology phylogeny - stem-group salmonine.

CONTENTS

Introduction ...... 280 Methods and material ...... 281 Methods ...... 281 Materials ...... 282 Abbreviations ...... 282

* Corresponding author: E-mail: [email protected] 279 0024-4082/99/030279 + 33 $30.00/0 0 1999 The Linnean Society of London 280 M. V. H. WILSON AND C.-Q. IJ

Systematic description ...... 283 Genus TEosalmo Wilson, 1977 ...... 283 TEosalmo dn@ooodensis Wilson, 1977 ...... 2 84 Description ...... 2 84 Discussion ...... 2 99 New evidence on the ostcology of tEosalmo ...... 303 Autapomorphies of tEosalmo ...... 303 Synapomorphies of Salmonidae ...... 304 Interrelationships among three subfamilies of Salmonidae ...... 304 Phylogeny ofthe subfamily Salmoninae ...... 305 Conclusions ...... 307 Acknowledgements ...... 307 References ...... 307 Appendix ...... 310

INTRODUC‘I’ION

Salmonids are euteleostean fishes that have high value in commercial and sport fisheries (Wu & Wu, 1992; Nelson, 1994). They have long been interesting to ichthyologists not only because of their great economic significance but also because of their problematic phylogenetic relationships (see Sanford, 1990), their ecological adaptations including anadromous habits (Stearley, 1992), and their geographic distributions. Numerous systematic studies have been done on the family since 1960, including treatments of morphology (e.g. Norden, 196 1 ; Vladykov, 1962, 1963; Kolyushev, 197 1; Shaposhnikova, 1968, 197 1, 1975; Gorshkov et al., 1979; Cavender, 1980; Behnke, 1980; Williams, 1987; HolGk et al., 1988; Smith & Stearley, 1989; Sanford, 1990; Stearley, 1990; Stearley & Smith, 1993; Burnham-Curtis & Smith, 1994), karyology (e.g. Booke, 1968; Hartley, 1987; Phillips, Pleyte & Ihssen, 1989; Phillips, Van Ert & Pleyte, 1989), allozymes (e.g. Tsuyuki & Roberts, 1966; Utter, Allendorf & Hodgins, 1973; Johnson, 1980), ontogeny (e.g. Balon, 1980; Pavlov, 1980; Kendall & Behnke, 1984), and DNA sequences (e.g. Berg & Ferris, 1984; Skurikhina, Tugarina & Mednikov, 1986; Thomas, Withler & Beckenbach, 1986; Grewe, Billington, & Hebert, 1990; Partti-Pellinen et al., 1991; Phillips & Pleyte, 1991). However, these studies have not yet removed all the uncertainties about the phylogeny of this group, particularly those related to its origin and early evolution. Wilson (1974, 1977) described what is still regarded as the oldest known fossil salmonid, in the genus TEosalmo, based on specimens from Eocene lacustrine rocks at a locality near Smithers, British Columbia, Canada. f.Eosalmo has since been found in the Eocene near Princeton, British Columbia (Wilson, 199610) and near Republic, Washington, USA (Wilson, 1996a). This fossil salmonid was originally thought to be morphologically intermediate between extant thymallines and sal- monines (Wilson, 1977). Recently, Stearley & Smith (1993) reconstructed the phylogeny of Salmonidae based on a cladistic analyses of 1 19 characters, presenting a cladogram suggesting that TEosalmo is the sister group to the Salmoninae. This suggestion, though generally in agreement with the ideas of Wilson (1977), was vulnerable to criticism because 41 of the 1 19 characters used in Stearley and Smith’s analyses were not available (i.e. ‘missing data’) for TEosalmo. This paper summarizes new information on the osteology of TEosalmo based on a review of the previously described specimens together with new materials from western North America. It also documents several synapomorphies for the genus OSTEOLOGY AND PHYLOGENY OF tEOSAW.IO 28 1 fEosalmo, and uses these data to place the fossil species within the phylogeny of the Salmonidae.

METHODS AND MATERIAL

Methods

Terms used for general description follow Wilson (1977), Rojo (199 l), and Stearley & Smith (1993). For caudal skeleton, terms mainly follow Arratia (199 l), and Arratia & Schultze (1992). Numerical phylogenetics programs (PAUP 3.1.1, Swofford, 1993; and MacClade 3.04, Maddison & Maddison, 1992) were used in carrying out cladistic analyses of character states for reconstruction of the phylogeny. Characters used for cladistic analysis are mainly those from the skeletal system that are observable in both fossil and Recent specimens. All of the characters are unordered and equally weighted in our analyses. Each of the states of a given character is placed in square brackets following the number representing the character (e.g. 10[1] is character state 1 of character 10). Missing data are coded by question marks in the data matrix. There remains considerable controversy over the question of the phylogenetic position of the Salmonidae within the Teleostei. Williams (1 987) presented evidence favouring a sister group relationship of salmonids with esocoids; however, Johnson and Patterson (1 996) reviewed recent studies and advocated a sister group relationship of salmonoids (coregonids + salmonids) with osmeroids (including galaxioids); salmonoids + osmeroids in turn were held to be the sister group of argentinoids. Wilson and Williams (1992) and Johnson and Patterson (1996) agree that Hypomesus is the most primitive extant osmerid. In this paper, we have used data for Hypomesus, the esocoid Novumbra, and the argentinoid Algentina as out-group taxa to root the cladogram and thereby establish the polarity of character-state transformations within the Salmonidae. In addition to tEosalmo dnjhooodensis, five other fossil species have been included in the subfamily Salmoninae. They are (1) tRhabdofario lacustris (Cope, 1870) from the Miocene to Pliocene of Idaho and Oregon (see Kimmel, 1975; Smith, 1975, 1981; Smith et al., 1982), (2) tSmilodonichthys rastrosus (Cavender & Miller, 1972) from the Miocene to Pliocene of Oregon and California (also see Barnes, McLeod & Raschke, 1985), (3) tSalmo cyniclope (La Rivers, 1964) from the Miocene of Nevada, (4) tSalmo australis (Cavender & Miller, 1982) from the Pliocene of southwestern Mexico, and (5) a fossil from eastern Asia referred by Sytchevskaya (1986) to tEosalmo. Too little is known about the fifth fossil for inclusion in this study. The other four fossil species were recently referred to the genus Oncorhynchus (see Kendall, 1988; Stearley & Smith, 1993; Nelson, 1994). Therefore, the generic names f Rhabdofario and tSmilodonichthys are considered to be synonymous with Oncorhynchus. Comparative Recent fishes consist of dried skeletons, specimens fixed in formalin and preserved in alcohol or cleared and stained with alizarin. Data for measurements and counts made following Hubbs and Lagler (1964) are from the more complete fossil specimens and from the Recent fishes. Taxa marked with daggers ‘7’ preceding their names are exclusively known as fossils. 282 M. V. H. WILSON AND G.-Q LI Materials

In addition to those tEosalmo specimens listed in the systematic section, the following materials were used in this study for comparison and for checking information in the literature. Alizarin prepared extant specimens: Novumbra hubbsi, specimens listed in Wilson and Veilleux (1982); Aqentina silus, UAMZ 1397, Chanos chanos, UAMZ 3523; Hypomesuspretiosus UAMZ 874 and 35 15; Coregonus clupeafomis, UAMZ 155 1; Prosopium williamsi, UAMZ 524; nymallus arcticus, UAMZ 3425; Salvelinusfontinalis, UAMZ 3349; Salmo trutta, UAMZ 1630 and 2066; Oncorhynchus nerka, UAMZ 2063; Oncorhynchus keta, UAMZ 2338. Prepared dry skeletons: Esox lucius, UAMZ 4875 and 4878; Coregonus clupeafomis, UAMZ 6829; Salmo trutta, UAMZ 6324.

Abbreviations

Institutional FMNH Field Museum of Natural UALVP Laboratory for Vertebrate History, Chicago, USA Paleontology, Department of ROM Royal Ontario Museum, Biological Sciences, University of Toronto, Canada Alberta, Edmonton, Canada TBMW Thomas Burke Memorial UAMZ Museum of Zoology, Department Washington State Museum, of Biological Sciences, University Seattle, USA of Alberta, Edmonton, Canada

Anatomical angart angulo-articular npu2 to npu4 neural spines on 2nd to ao antorbital 4th preurals asp autosphenotic OP opercle den dentary Pa parietal dmes dermethmoid Ph parhypural dSP dermosphenotic Pal palatine ecP ectopterygoid Pmx premaxilla enP endopterygoid POP preopercle epl-3 1st to 3rd epurals Pto dermopterotic ePo epiotic pul to pu4 1st to 4th preurals fr frontal qa quadrate hl to h6 1st to 6th hypurals rart retroarticular hm hyomandibula sm symplectic hpu2 to hpu4 haemal spines on 2nd to smx supramaxilla 4th preurals so supraorbital iol to io5 1st to 5th infraorbitals SOC supraoccipital iop interopercle SOP subopercle meP metapterygoid ul to u2 1st to 2nd urals mx maxilla unl to un3 1st to 3rd uroneurals na nasal OSTEOLOGY AND PHYLOGENY OF tEOSALhlO 283 Measurements AFBL anal fin base length HL head length BD body depth PAL preanal length CPD caudal peduncle depth PDL predorsal length C PL caudal peduncle length PPL prepectoral length DFBL dorsal fin base length PVL prepelvic length FL fork length SL standard length HD head depth TL total length

Meristics AFR principal anal fin rays H hypurals AP anal pterygiophores PFR pectoral fin rays BR branchiostegals PCV precaudal vertebrae CFR principal caudal fin rays SN supraneurals CV caudal vertebrae TV total vertebrae DFR principal dorsal fin rays UN uroneurals DP dorsal pterygiophores VFR pelvic fin rays EP epurals

SYSTEMATIC DESCRIPTION

Division Teleostei Muller, 1846 Subdivision Euteleostei Greenwood et al., 1966 Order Salmoniformes sensu Nelson, 1994 Family Salmonidae sensu Nelson, 1994 Subfamily Salmoninae sensu Nelson, 1994

Diagnosis (osteological characters on&). Salmonids differing from Coregoninae and Thy- mallinae in the following derived features: posterior part of frontal widely expanded above autosphenotic, hyomandibular fossa on pterotic particularly long, posterior part of endopterygoid extending posteriorly and broadly overlapped by both me- tapterygoid and quadrate, premaxillary process of maxilla extending dorsally at an angle larger than loo, postorbitals (io3 to io5) short and covering less than anterior half of hyomandibula, presence of suprapreopercle, anterior end of preopercular canal on horizontal arm distinctly turning to anteroventral corner of preopercle, first uroneural amplified into a large fan-shaped stegural, and scales small with more than two lateral line scales per vertebral centrum.

Genus TEosalmo Wilson, 1977

Diagnosis. As for the type and only species. 284 M. V. H. WILSON AND G.-Q, LI TEosalmo dnjwoodensis Wilson, 1977 Figs 1-8

Emended diagnosis: An Eocene species of Salmoninae different from all extant members of Salmoninae in having a subopercle with a long anterodorsal process that meets the dorsal edge of the bone at an angle of about 60°, and a broad and toothless basihyal tooth plate. It differs from all the extant salmonines also in the following plesiomorphic features: frontal posteriorly not included as part of the floor of the temporal fossa, parietal directly posterior to the frontal and incompletely separated by the supraoccipital, premaxillary process of palatine with small or no posterior crest, and flat extrascapulars. The species shares three derived features with the extant species of Hucho, Saluelinus, Salnzo, and Oncorhynchus: (1) foramen for anterior branch of trigemino-facial nerve on anterolateral margin of prootic, (2) anterior emargination of the orbitosphenoid, and (3) metapterygoid dorsal to quadrate and symplectic with minimal contact with symplectic. Hologpe. ROM 11 178a-b, an almost complete fish in part and counterpart with SL of 307 mm. Referred specimens. UALVP 13482, a nearly complete impression of a fish with SL of at least 390 mm. UALVP 12326, a nearly complete fish with SL of 146 mm. UALVP 27138, impression of a fish skull with a HD about 75 mm. UALVP 12327 and 14919, two specimens with only the postcranial part preserved. UALVP 13464 and 17739, two tails. UALVP 13409 (cast of ROM 1 1 172), 13410 (cast of ROM 1 1 174b), and 1341 1 (cast of ROM 1 1174a), three specimens with only the anterior part preserved. UALVP 12332, disarticulated bones from skull, in part and counterpart. UALVP 31758, cast of complete fish in the collection of Miguasha Museum of Natural History. FMNH PF13561, 14250-14253, five incomplete to nearly complete specimens in the collection of the Field Museum of Natural History, and TBMW 73756, 82176, and 82489, incomplete specimens in the collection of the Thomas Burke Memorial Washington State Museum. Localities. (1) UALVP Locality No 60, Driftwood Creek, British Columbia ( = type locality), specimens include UALVP 12326-12327, 12332, 13408-1341 1, 13449, 13464, 14919, 17739, 27138; and FMNH PF13561, 14250-14253. (2) UALVP Locality No. 178, China Creek, British Columbia, one complete specimen (UALVP 13482). (3) UALVP Locality No. 777, Republic, Washington, USA, three incomplete specimens (TBMW 73756, 82 176, and 82489). Horizon. Driftwood Creek Formation (specimens from UALVP Locality No 60), Allenby Formation (specimens from UALVP Locality No. 178), and Klondike Mountain Formation (specimens from UALVP Locality No. 777), all middle Eocene in age.

Description

BO~shape Although we have only a few articulated and relatively complete specimens, all of them suggest an elongate, fusiform, and lateral compressed body shape, similar z3 U

FiLgure 1. tEosulmo driftwoodemis, specimen in the Miguasha Museum of Natural History, the most complete and largest specimen known, showing the body shape, the distribution and shape of fins, and the vertebral column. Scale bar = 10 cm. 286 M. V. H. WILSON AND G.-Q LI

Figure 2. Restoration of the skull roof of tEosalmo drzzoodensis based on UALVP 13482a.

to that of the extant salmonids; as well, the fins are positioned as in the extant genera (Fig. 1).

Measurements (in mm) UALVP 12326: SL = 145, BD = -33, HL = -37, HD = -21, PPL = 41, PVL = 80, PDL = 62, PAL = 113, CPL = 25, CPD = 13, DFBL = 19, AFBL = 15. UALVP 31758: TL = 420, FL = 397, SL = 360, BD = 80, HL = 90, HD = -70, PPL = 97, PVL = 185, PDL = 158, PAL = 285, CPL = 62, CPD = 35, DFBL = 49, AFBL = 38.

Meristics UALVP 12326: BR = -9, TV = 57 (33 PCV + 24 CV), SN = N 13, PFR = 13, VFR = 10, DFR = 11, DP = 13, AFR = 11, AP = 13, CFR N 19, H = 5+, UN = 1+, EP = l+. UALVP 13482: TV = 57 (34 PCV + 23 CV), SN = - 11, PFR = ?, VFR = -9, DFR = 12, DP = 12, AFR = 12, AP = 12, CFR = 19 (i+8+9+i), H = 6, UN = 3, and EP = 3. UALVP 31758: BR = 11, TV = 54 (32 PCV + 22 CV), SN = 12, PFR = 13, VFR = 8, DFR = 11, DP = 12, AFR = 11, AP = 12, CFR = 19 (i+8+9+i), H = 6, UN = 3, and EP = 3.

Neurocranium and skull ro@ This region was studied in UALVP 13482a by casting the natural impression in the rock. The supraoccipital is more or less rectangular in outline and convex dorsally with a prominent occipital crest. Unlike that in the extant salmonids, which completely and widely separates the two parietals, it separates only the posterior half of the parietals (Fig. 2). Each parietal is somewhat trapezoidal in shape, with a posterolateral process similar to that of the extant Coregonus. OSTEOLOGY AND PHYLOGENY OF tEOSAM0 287

Figure 3. tEosalmo dnjuoodensis, photos of two black latex casts dusted with ammonium chloride, showing the cranial skeleton preserved on UALVP 13482a (A) and 1348215 (B). Scale bars = 1Omm. 288 M. V. H. WILSON AND G.-Q LI

Figure 4. tEosalmo dnftreodensis, some disarticulated bones of UALVP 12332. A, interopercle; B, frontal; C, suhopercle; and D, parasphenoid. A was based on UALVP 12332a, anterior to right; B to D were based on its counterpart UALVP 12332b, anterior to left.

idp

Figure 5. Opercular series of tEosalrno dnjwoodensis, based on UALVP 27 138. OSTEOLOGY AND PHYLOGENY OF tEOSALMO 289

B .^I

den Figure 6. TEosalmo dn$eJoodmsis. A, bones in the circumorbital series; B, lower and upper jaws, drawn from UALVP 13482a.

The frontal is subtriangular with internal angles of 30" anteriorly, 60' postero- dorsally, and about 90" laterally. It is anteriorly tapered, with a straight medial edge marking the suture between the two frontals, and a greatest width at about the midlength of the bone. In outline this bone is more similar to that of Sulmo than it is to that of other genera in the Salmonidae (Figs 2 and 4B). The supraorbital canal runs in a bony tube from the area posterior to the lateral corner about half way to the midline, then bends anteriorly and nearly parallels the midline (UALVP 12326, 13482a, and 27 138). A short posterior branch of the canal is visible in all the well- preserved frontals. At least four pores can be counted along the anterior branch of the canal, which ends in the margin of the frontal lateral to the pointed anterior end of the bone. The nasal is slender and tubular but not curved. It lies immediately anterior to the anterior end of the bony tube of the supraorbital canal in the frontal (UALVP 13482a). A displaced nasal is also seen on UALVP 12326. No complete dermethmoid (Stearley & Smith, 1993) (= supraethmoid, Norden, 1961; Wilson, 1977; Cavender, 1980) is preserved in any specimen. However, an impression of this bone on UALVP 12326 confirms the description of the bone given by Wilson (1977), which is more or less similar to that of irymullus (see Stearley 290 hl. V. H. WILSON AND G.-Q. L1

Fi

I I I hpu4 ph hpu2 hpu3

Figure 8. Restoration of the caudal skeleton of tEosalmo dnfimderirir, based on UALVP 12327

& Smith, 1993, p. 1 1, fig. 3-a) in having a triangular anterior portion and a notched posterior portion. The temporal region is partly seen on UALVP 13482. The pterotic is somewhat triangular and dorsally contacts the parietal. The epiotic is irregular in shape, taking a position lateral to the supraoccipital, and posterior to the pterotic and parietal. These three bones border a prominent temporal fossa that is positionally similar to the ‘temporal fenestra’ in hiodontids (Osteoglossomorpha) (see Li, 1994; Li & Wilson, 1996). A temporal fossa is also present in extant salmonids (e.g. Sulmo truttu, UAMZ 6324). A broad and wide, flat bone bearing a branched canal is present at the rear of the skull of UALVP 13482, although it is not complete in outline. This bone may represent the possibly median element (extrascapular) which was described by Wilson (1974, 1977) as in nymallus. Unfortunately, whether or not there is a median extrascapular could not be determined with confidence in the present study. Extrascapulars in coregonines and thymallines are broad, but those of extant salmonines are reduced to narrow tubular bones. A complete impression of the parasphenoid is preserved on UALVP 12332b (Fig. 4D). As in all other salmonids, it is stout, longitudinally grooved, devoid of teeth on the ventral side, and slightly curved with a shallow ascending arm. In lateral view, the orbital arm is tapered anteriorly and much longer than the handle-like occipital arm, which does not deepen posteriorly. A nearly complete sword-shaped impression of the dorsal side of the parasphenoid is preserved on UALVP 13482b. 292 M. V. H. WILSON AND G.-Q L1 An impression of the vomer is visible on UALVP 27138 and resembles that in Salmo in having teeth distributed all along its ventral side. This bone has been considered to be taxonomically significant in previous studies (see Kolyushev, 197 1 ; Shaposhnikova, 1975; Cavender, 1980; Stearley & Smith, 1993).

Opercular series A complete opercular series is preserved on FMNH PF14253 and UALVP 31758, and portions of it in other specimens. The preopercle is curved, and more similar to that of Salmo (e.g. UAMZ 6324) than other genera of Salmonidae, with a concave anterior edge and a convex posterior edge. The vertical arm tapers slightly, and is about twice as long as the horizontal arm. The two arms meet at an angle of approximately 115" (Figs 5 and 7A). The preopercular sensory canal descends the anterior margin of the vertical arm, bends forward at the angle, and then curves ventrally to meet the anteroventral edge of the bone just behind the anterior tip. The canal gives off four branches along the horizontal arm and at least two branches on the lower part of the vertical arm; all branches are markedly curved posterodorsally. As in extant Salmo, a narrow and tubular suprapreopercle is also present (see FMNH PF 14253, UALVP 13410 and 1341 1). The opercle (FMNH PF 14253, UALVP 13409-13410,13482,27138, and 31758) is narrower dorsally than ventrally, with a straight anterior edge deeper than its prominent convex posterior edge. The straight anterior edge meets the somewhat serrate ventral edge to form an anteroventral corner at an angle of about 60" (Figs 5 and 7A). The anterior part of the dorsal edge makes a prominent anterodorsal notch (UALVP 13482). The subopercle is recoverable on FMNH PF 14253, UALVP 13482 and 31758. A complete impression of this bone is also preserved on UALVP 1233213 (Fig. 4C). It is of typical salmonid shape with a prominent anterodorsal process and a deep main body. The main difference is that the anterodorsal process is posterodorsally directed, and meets the dorsal edge of the subopercle at an angle of about 60" that fits the anteroventral corner of the opercle (UALVP 13482). However, in all other salmonids the anterodorsal process of the subopercle is almost at a right angle to the bone. As in Thymallus, the interopercle (UALVP 12332 and 31758) is triangular with an acute anterior internal corner of about 35". The ventral edge is convex; it meets a slightly concave posterior edge in a posteroventral corner of about 70". The dorsal edge is slightly convex anteriorly where it meets the upward-curving ventral edge in a point (Fig. 4A).

Circumorbital region The circumorbital series consists of eight bones, including a single supraorbital (UALVP 13482a and its cast), an antorbital (UALVP 12326 and 31758), five infraorbitals, and a dermosphenotic (UALVP 12326, 13482a, and 3 1758) (see Fig. 6A). The supraorbital is narrow, elongate, and somewhat fusiform; it is contained in a shallow emargination of the anterolateral edge of the frontal. The antorbital is shaped like a curved teardrop: broader and slightly thicker posterodorsally, pointed anteroventrally, and with a concave dorsal edge. OSTEOLOGY AND PHYLOGENY OF tEOSAIM0 293

The first infraorbital (= lachrymal in Wilson, 1974 and 1977) as well as its impression is well preserved on FMNH PF 14253, UALVP 27138 and 31758. It resembles that of Brachymystax and Salmo in both shape and the way in which the infraorbital sensory canal curves around near the anteroventral margin, giving off at least five short branches (Fig. 6A). Posteriorly it is gradually tapered with a narrow posterior end where it receives the sensory canal from the second infraorbital. The second infraorbital is narrow and elongate, posteriorly slightly deeper than anteriorly, and bears two short, ventrally directed canal branches in addition to the main sensory canal running through the middle of the bone (see the cast of UALVP 13482a and 3 1758). Infraorbital 3 is almost identical to that of Salmo (Fig. 6A) with a somewhat pointed anterior end and a somewhat squared posterior end. Its convex ventral edge does not extend to the level of the dorsal edge of the quadrate. As in Salmo, the curved infraorbital sensory canal running through the bone gives off two branches, of which the anterior one is anteroventrally directed, and the posterior one posteroventrally directed (FMNH PF14253 and UALVP 13482a). Infraorbital 4 is somewhat trapezoidal, deeper posteriorly than anteriorly, and not fused with infraorbital 5. The infraorbital sensory canal also gives off two branches, which are posteroventrally directed. Infraorbital 5 is similarly somewhat trapezoidal but distinctly shorter than io4. The infraorbital sensory canal gives off only one posteriorly directed branch. On all five infraorbitals, the infraorbital sensory canal runs in a tube near the middle of each element. A somewhat triangular dermosphenotic bearing the branched sensory canal is visible on UALVP 13482a. This bone dorsally contacts the posterolateral edge of the frontal immediately behind the latter’s posterolateral corner, and posteriorly contacts the anterior edge of the pterotic.

Jaws The lower and upper jaws are best preserved in UALVP 12326, 13482, 27138, and 31758 (Fig 3A and 6B). The upper part of the mouth cleft is bordered mainly by the maxilla, which is elongate and slightly deeper posteriorly than anteriorly. The anterior end of the maxilla is slightly tapered and bends mesially to form a knob-shaped process (= premaxillary process in Stearley & Smith, 1993) which is supposed to fit the dorsomesial notch on the premaxilla, as in other salmonines. This knob-shaped process extends dorsally at an angle (larger than 10’) to the main axis of the bone. The posterior end of the maxilla is turned slightly posterodorsally with a smooth and rounded margin. Sharp conical teeth are developed all along the oral margin of the bone. As in all salmonids, a slender, anteriorly tapered supramaxilla is present posterodorsal to the maxilla. As in nymallus, the premaxilla (UALVP 12326 and 1341 1) is triangular with a well-developed ascending process located in the middle of the dorsal margin. Its oral margin bears at least eight sharp, conical teeth (about 10 on UALVP 1341 1) that are stouter than those on the oral margin of the maxilla. All the teeth on the premaxilla and maxilla are slightly curved posteriorly. The lower jaw (UALVP 13482a and 31758) consists of the dentary, angular, articular, and retroarticular. The dentary, which forms about the anterior half of the mandible, is deeper posteriorly than anteriorly, with a knob-shaped anterior end 294 M. V. H. WILSON AND G.-Q I,I and a deeply notched posterior end. Its oral margin hears strong teeth and rises suddenly immediately behind the mouth corner to form a high coronoid process (Fig. 6B), similar to that in Ihymallus. The mandibular sensory canal runs in a bony tube along the ventral margin. A mesial view of the dentary is also seen on the cast of UALVP13482a, where it has a deep, posteriorly widely open groove. The angular, which forms about the posterior half of the mandible, appears to have fused with the articular to form a compound angulo-articular similar to that in other salmonids. This bone inserts in the deep triangular notch of the dentary and carries a spacious and curved articulation facet for the quadrate. Unlike in Salmo, this bone bears no prominent anterodorsally directed dorsal process and no postarticular process (Fig. 6B). The retroarticular is small, irregular in shape, and located posteroventral to the angulo-articular.

Palatopterygo-quadrate arch An impression of the palatine is preserved on UALVP 12332 and 13482. It is similar to that in Hucho (see Stearley & Smith, 1993) and Salmo (e.g. UAMZ 6324) in having a posteriorly sharply tapering lateral view. Sharp conical teeth are present along the oral surface of the bone (UALVP 13482a). However, it lacks a prominent dorsal lamina seen in extant salmonines. The ectopterygoid is slender, with a pointed anterior tip, which joins the dorsal side of the tapered posterior end of the palatine, and a curved posterior part, which fits the anteroventral margin of the quadrate (UALVP 13482a). An impression of the left endopterygoid is completely preserved on UALVP 12332a. This hone has a straight labial margin and an acute anterior extension. The mesial edge of the bone is suddenly convex immediately behind the acute anterior extension, ending in a slightly concave posterodorsal edge. The posterior part of the endopterygoid appears to be overlapped by both the metapterygoid and quadrate, and is more or less square with a slightly concave posterior edge; on its surface it bears an arched crest that extends from the labial margin. The greatest width of this hone is about half the length. As in extant salmonines, growth lines are also visible on this hone. No complete metapterygoid is seen on any of the specimens. Judging from the ventral margin preserved on UALVP 13482A (Fig. 3A), this bone is dorsal to the quadrate and symplectic with minimal contact with the symplectic. The quadrate is completely seen on FMNH PF14253 and UALVP 13482a (Fig. 3A). It is similar in shape to that of all other salmonids. A deep notch divides the bone into a wide fan-shaped anterior limb and a needle-like posterior limb that extends only as far as the dorsal edge of the fan-like anterior limb. In the notch of the quadrate fits a rod-like symplectic that is pointed anteroventrally and distinctly thickened posterodorsally. As in extant salmonines, the dorsal end of the symplectic apparently just fails to contact the ventral end of the hyomandibula (Fig. 3A).

Hyoid arch The hyomandibula on UALVP 1341 1, 13482a (Fig. 3A), and 27138 (Fig. 7A) seems to be intermediate in shape between those of Brachyrnystax and Salmo in having a large triangular dorsal portion, a ridged vertical (ventral) ramus, and a short handle-like opercular process. The dorsal margin of the dorsal portion, which joins the ventral side of the pterotic and autosphenotic, is straight or only slightly curved. OSTEOLOGY AND PHYLOGENY OF tEOSAMO 295 The ridged vertical ramus is slightly curved and anteroventrally directed with its ventral end just failing to contact the dorsal end of the symplectic. The ridge on the lateral side of the bone extends from the anterodorsal corner of the triangular dorsal portion to the level of the opercular process and then bends anteroventrally at an angle of approximately 1 10' (UALVP 13482 and 27 139). This strongly angular ridge delineates a somewhat rectangular anterior portion that is much thinner than the other parts of the hyomandibula (UALVP 1341 1 and 27139). The epihyal (= posterohyal or dorsal ceratohyal, see Rojo, 1991), as seen on FMNH PF1356 1 and UALVP 13410 and 134 1 1, is nearly identical to that of extant salmonids in having a subtriangular outline that is deeper anteriorly than posteriorly, with a straight (or only slightly concave) anterodorsal edge, a rounded posterior edge, and a straight anteroventral edge that joins with the posterior edge of the ceratohyal. As in other salmonids, a narrow groove is also developed on its lateral side near the anterodorsal margin of the bone. This groove starts from the posterior 1/5 of the epihyal and runs anteriorly through the bone in parallel with the anterodorsal edge. The ceratohyal seen on FMNH PF1356 1, UALVP 1341 1 and 14262 (impression of the mesial view of the right ceratohyal) is similarly shaped to that of other salmonids, deeper posteriorly than anteriorly, with a somewhat trapezoidal posterior portion; its ventral edge is more strongly concave than its dorsal edge. A lateral view of the left ceratohyal partly exposed on UALVP 13482a and 27 138 suggests that the dorsal part of the bone is also distinctly grooved (Fig. 7A). The anterior end of the ceratohyal contacts two small irregularly shaped bones: the dorsal and ventral hypohyals (UALVP 12326). Impressions of these may also be seen on UALVP 27 138, where they are disarticulated and displaced ventral to the posterior part of the angulo-articular of the specimen. An impression of the basihyal ( = glossohyal) is well preserved on UALVP 27 138 (Fig. 7A) and partly seen on FMNH PF13561. This irregularly shaped bone bears a flat, thin, and toothless dermal plate, unlike that of any other salmonids, though those of coregonines and thymallines are flat and only weakly toothed. The urohyal (UALVP 12332 and 14262) is similarly shaped to that of other salmonids with a rod-like anterior end. The dorsal margin of the bone extends symmetrically on both sides to form a pair of narrow wings.

Branchial arches Disarticulated branchial arches are seen on FMNH PF1356 1. A basibranchial plate is definitely present, with its posterior end contacting the rectangular right and left hypobranchials. There are about 10 (UALVP 12326) to 1 1 (UALVP 27 138 and 3 1758) pairs of branchiostegals; all of them are curved and spathiform with the anterior ones considerably narrower than the posterior ones. The posteriormost three to four branchiostegals are broadened anteriorly to form an almost rectangular anterior end with clupeoid projection (McAllister, 1968), whereas all the others are distinctly narrower at their anterior ends; they meet the ventrolateral margin of the ceratohyal with a knob-like projection.

Vutebral column In total, six nearly complete specimens have been found since Wilson (1974, 1977) named TEosalmo. Two of them are in the UALVP collection, the third (Fig. 296 hl. V. H. WILSON AND G.-Q. LI 1) is in the collection of the Miguasha Museum of Natural History (a cast is UALVP 3 1758), and three incompletely prepared specimens are in the FMNH. A count of both the centra and the neural and haemal spines of the first three specimens suggests that tEosalmo has 54-57 vertebral centra (more than Wilson had reported in 1977), ofwhich 32 (UALVP 31758) to 33 (UALVP 12326) or 34 (UALVP 13482) are precaudals, including the first three or four that are anterior to the cleithrum and bear neural spines but no ribs, and 22 (UALVP 3 1758) to 23 (UALVP 13482) or 24 (UALVP 12323) are caudals including the two strongly upturned urals. Centra anterior to the dorsal fin are slightly deeper than long, while centra behind the dorsal fin are slightly longer than deep. All the centra but the last two urals are horizontally ridged and pitted; in general three to four ridges are found on the precaudals and four to five on the caudals except for the last two urals. Each of the caudal vertebrae has small pre- and post-zygapophyses dorsally and ventrally. The neural arches on the last six precaudals and all the caudals anterior to the first preural are fused with the centra; the left and right halves of the arches and their bilaterally opposite neural spines are also fused with each other. Some 30 (UALVP 13482 and UALVP 31758) or 31 (UALVP 12326) pairs of slender and curved ribs are present. The extent of ribs differs in young individuals (e.g., UALVP 12326) from that in adult (large) ones (e.g. UALVP 13482 and 3 1758). In young individuals, they extend from each of the precaudals bearing ribs to near the ventral wall of the abdominal cavity, while in the adult (large) individuals, they reach to the level of approximately 2/3 (anterior to the pelvic fins) to 1/2 (behind the pelvic fins) of the lateral abdominal walls (see UALVP 31758). As in the extant salmonids, there are about 13 supraneurals anterior to the dorsal fin origin. The proximal ends of these sigmoid elements overlap the neural spines of the precaudal centra. Fine epineurals are also present on all but the last two (UALVP 12326 and 3 1758) or three (UALVP 13482) precaudal centra. They extend posteriorly (or somewhat posterodorsally) from beside the anterodorsal side of the base of the neural arches. Needle-like and posteroventrally directed haemal spines on the caudal vertebrae anterior to the fifth preural are proximally fused with the centra, with their distal tips extending only to the dorsal 113 of the hypaxial region; therefore, they do not overlap the proximal tips of the anal pterygiphores.

Caudal skeleton At present, we have seven new specimens preserved with the impression of the caudal skeleton (UALVP 12326, 12327, 13464, 13482, 14919, 17739, and 31758); of these, the impressions on UALVP 12327 and 13482 are particularly well preserved. Structurally, the caudal skeleton is almost identical to that of extant Salmo (Figs 7B and 8). The caudal vertebrae supporting the caudal fin consist of two urals and four preurals, of which the first preural and the two urals are strongly upturned. The first ural is longer than deep and superficially pitted; the second is conical in shape. There are also six hypurals arranged in the same way and similarly shaped to those of the extant salmonines. The first hypural (hl) is the largest and distally much deeper than proximally to form a triangular posterior portion with a posterior edge ventrally slightly convex but dorsally concave. The proximal part is strongly contracted to form a knob-like head that mainly joins the first ural (Fig. 8). The OSTEOLOGY AND PHYLOGENY OF tEOSALMO 297 second hypural (h2) is elongate and posteriorly more or less rectangular with a length about 0.6 times that of the first hypural (same proportion as that of extant Salmo). Its proximal part is also contracted (but not as much as that of the first hypural) to form a stout head articulating with the upper part of the first ural. These two lower hypurals appear to have fused with each other at mid-length; they together support the lower lobe of the caudal fin. The upper hypurals consist of four elements that are arranged in the same pattern as those in extant salmonines, with the third and fourth hypurals directly articulating with the second ural. The third hypural (h3) is almost equally as long as h2 but distally much deeper than proximally to form a triangular main body. The fourth hypural (h4) is also distally much deeper than proximally. It is slightly shorter than h3, and has a slightly concave ventral margin and a distinctly convex dorsal margin. The fifth hypural (h5) is rod-like; the sixth (h6) is slender and the smallest of the set. Hypurals 3-6 support the upper lobe of the caudal fin. As in extant salmonids, the posterior margin of the hypural complex forms a vertical line (e.g. UALVP 12327). The parhypural articulating with the first preural centrum is proximally strongly ridged with a knob-like articulation with pul; its distal part is not distinctly deeper than the proximal part and is oar-shaped. The haemal spines on pu2 and pu4 are rod-like, while the haemal spine on pu3 is oar-shaped distally with a concave lateral surface. The peg-and-socket mechanism (Cavender, 1970) is visible on the parhypural and the preceding three haemal spines (see Fig. 8). These four haemal spines together with the two lower hypurals (hl and h2) support the lower lobe of the caudal fin. Three uroneurals are present (as in other salmonines). The first uroneural (unl) is located dorsal to pul and the two urals, with its anterior tip overlapping the posterodorsal margin of pu2. This element forms a large stegural (see Rojo, 1991) that bears a very large fan-shaped and marginally serrated anterodorsal extension (Fig. 8). The second uroneural (un2) is small and proximally tapered to insert between the posterodorsal tip of un 1 and the third epural (ep3). The third uroneural is the smallest, and is far posterodorsal to the caudal skeleton, articulating directly with the caudal fin base. Three stout epurals are present in the space between un2 and the lengthened neural spine of pu2, with their anterior ends just reaching the serrated posterior edge of the fan-shaped anterodorsal extension of the first uroneural. Although all the neural spines on pu2 to pu5 are lengthened and distally more or less oar-shaped; only the neural spines on pu2 and pu3 take part in the support of the upper lobe of the caudal fin together with the upper hypurals, uroneurals, and epurals. The peg-and-socket mechanism is seen on the proximal part, im- mediately behind the articulation head, of the neural spines of pu2 to pu5.

Girdles and pairedjns Incomplete cleithra seen on UALVP 13482 and 27 138 have a broad anteroventral portion and a relatively short vertical portion, similar to those in extant salmonids in shape. The supracleithrum is leaf-shaped, dorsally distinctly tapered, and dorsally articulates with a spade-like posttemporal, which is completely seen on UALVP 27138. This bone is moderately convex anteroventrally and has a notched ventral margin, with the notch just fitting the tapered dorsal end of the supracleithrum (Fig. 298 M. V. H. WIISON AND C.-Q LI 7A). The coracoid is also similarly shaped to that in other salmonids (UALVP 12326). There appear also three postcleithra (UALVP 13482 and 27 138), of which the ventral one (3rd postcleithrum) is slender and sigmoid (UALVP 27 138). The pectoral fins contain at least 13 and as many as 16 rays (e.g. UALVP 12326 and 3 1758), of which the first is the longest and distally segmented but unbranched; all the others are distally both branched and segmented. The pelvic girdle consists of two stout innominata (UALVP 12326, 12327, and 31758), which are anteriorly tapered but posteriorly greatly enlarged to form a strong knob that articulates with the pelvic fin base. The pelvic fins contain nine (UALVP 12327) to 11 (UALVP 12326) rays with the first one distally segmented but unbranched. The distance between the origins of the pelvic and pectoral fins is approximately as far as that between the origins of the pelvic and anal fins (see UALVP 12326 and 31758).

Dorsal and analjins The dorsal fin is typically triangular in lateral view. It contains 10 (UALVP 3 1758) to 11 (UALVP 12326) principal rays plus two or three short procurrent rays. The first principal dorsal fin ray is distally unbranched; the others are branched with the last one double. The origin of the dorsal fin is anterior to the pelvic fin by at least six precaudal vertebrae. Thirteen slender dorsal pterygiophores are present on both UALVP 12326 and 3 1758. They decrease in length posteriorly. The ratio of dorsal- fin-base length to standard length is 0.13 on both specimens, slightly less than that (0.16) described for the holotype (Wilson, 1977). An adipose fin was probably present but not definitely preserved on any specimen. Its likely location is indicated by a slight bulge in the dorsal body margin of UALVP 12326, dorsal to the anal fin (Wilson & Williams, 1992, fig. 2). The anal fin has a prominent rounded distal margin in adults (Fig. 1). It consists of 10 (UALVP 31758) to 11 (UALVP 12326 and 13482) principal rays plus three or four accessory rays. The first principal anal fin ray is distally unbranched but segmented; the others are distally branched as well as segmented with the last one double. They are supported by 13 needle-like anal pterygiophores, which are distally knob-shaped and posteriorly decrease in length. The first two anal pterygiophores lie very close to each other with their pointed proximal ends opposite the space between the second and the third caudal vertebrae. The proximal ends of the anal pterygiophores do not overlap the distal ends of the haemal spines. The ratio of anal-fin-base length to standard length is 0.10 (UALVP 12326) to 0.11 (UALVP 3 1758).

CaudalJin Even in the largest specimens (Fig. 1) the caudal fin is emarginate, with the tips of the dorsal and ventral lobes and the apex of the fork rounded in outline. There are 17 branched principal caudal fin rays, nine in the upper lobe and eight in the lower lobe. Some 14 anteriorly shorter upper and lower procurrent rays are present anterior to unbranched dorsal and ventral principal caudal fin rays, with the anteriormost reaching as far as the distal ends of the neural spine of pu3 and the haemal spine of pu4 respectively. OSTEOLOGY AND PHYLOGENY OF tEOSilLMO 299 Scales The scales (seen on the caudal region of the cast of UALVP 13482b) are small, slightly deeper than long, and more or less square in outline, with nearly centrally located foci but no radii in either the apical (posterior) or basal (anterior) fields, as in the extant salmonines. The apicolateral corners are more developed than the laterobasal corners. The apical area is deeper than the basal area and the apical margin is broadly rounded. The basal area has a scalloped basal margin. Circuli (= scale ridges) in the apical field are more widely spaced than in the basal field, following wavy paths. As in the extant salmonines, there are more than two lateral line scales per vertebral centrum (Wilson, 1977). No scales have been seen on any skull bone.

DISCUSSION

When Wilson (1977) described TEosalmo dnfboodensis, it was said to be the most primitive known salmonine, close to the ancestry of all living salmon, trout, and char. More recently, Wilson and Williams (1992) argued that tEosalmo’s anatomy suggests earlier evolution of post-cranial adaptations than of most cranial adaptations in Salmoninae. Stearley (1992) and Stearley & Smith (1 993) discussed phylogeny and evolution of anadromy in the Salmonidae and concluded that tEosalmo is the sister group to all extant Salmoninae, based on partial data for tEosalmo included in a cladistic analysis. However, they found no unique characters for the genus 7Eosalmo. The greatest weakness of earlier interpretations of the phylogenetic position of tEosalmo was the incomplete information available about the osteology of tE. d$?boodensk. New specimens described in this paper allow a much more complete treatment of its osteology, and a more complete understanding of its phylogenetic position within the family. Study of the new specimens also allows determination, for the first time, of states for numerous characters used by Stearley & Smith (1993) but coded as missing for tEosalmo, as well as several characters not previously used. In total, 54 characters and their states distributed in 16 taxa (genera) were examined (Table 1). A cladistic analysis of these characters with PAUP 3.1.1 and MacClade 3.04 resulted in four equally short trees of 99 steps. The four trees differ in relative position of Acantholingua, as well as in whether Hypomesus or ATentina is the most closely related outgroup. However, most details of the four trees are identical, including the character states suggested to be synapomorphies of Salmonidae. The strict and majority-rule consensus trees are the same, having a trichotomy between Argentina, Hypomesus, and Salmonidae, and another trichotomy between Acantholingua, Salmothymus + Pla&salmo, and Hucho + Salvelinus + Salmo + Oncorhynchus. Detailed relationships of tEosalmo agree with those proposed by Wilson (1977, 1992) and by Stearley & Smith (1993) except that several derived character states now separate tEosalmo from the lineage leading to extant salmonines (Fig. 9), for the first time providing autapomorphies for the genus TEosalmo. Figure 9 shows derived character states optimized onto one of the four shortest trees (the one with Hypomesus as sister group to Salmonidae, and with Acantholingua outside the Salmothymus + Pla&saLmo clade).

OSTEOLOGY AND PHYLOGENY OF tEOsALnlO 30 1

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I81.1.2 - 81.1.1 0 81.1.0 I Figure 9. One of the four shortest trees generated by MacClade 3.04 and PAUP 3.1.1, based on data in Fig. 9, showing the phylogeny of Salmonidae, with only unambiguous changes mapped on the tree. Autapomorphies are not included. Branch lengths are proportional to number of unambiguous changes. Note that tEosalmo takes the position of stem-group salmonine. In this tree Hypomesus is the closest out-group taxon to Salmonidae, and Acantholingua is discriminated from Salmothymus, Plagsalmo, Hucho, Salvelinus, Salmo, and Oncorhynchus because it does not share 39[1] with these genera. In other, equally short arrangements, Acantholingua is the sister group of Salmothymus + Plagsalmo, and Argentina is the closest out-group taxon to Salmonidae (though the number of relevant characters included in this study is small). In the strict consensus tree, Acantholingua is placed in a trichotomy with the clade consisting of Salmothymus and Plapsalmo and the clade containing Hucho, Saluelinus, Salmo, and Oncorhynchus. OSTEOLOGY AND PHYLOGENY OF tEOSAW/IO 303

New evidence on the osteology uftEosalmo

Our study yields the following new osteological features for tEosulmo. 4[1] Ethmoid absent. 6[0] Frontal posteriorly not included as part of the floor of the temporal fossa. 7 [ 11 Posterolateral part of frontal above autosphenotic widely expanded laterally, covering all or most of autosphenotic. 16[ 11 Anterior emargination of orbitosphenoid absent. 19[0] Anterior extension of vomer in breeding males not present. This judgment is based on examination of all the presumably mature specimens that are preserved with vomers. 22[ 11 Posterior part of endopterygoid extended posteriorly and overlapped by both metapterygoid and quadrate. 35[1] Retroarticular sutured with the anguloarticular at an angle larger than 45" (Fig. 6B). 38[ 13 Suprapreopercle present. 43 [ 11 Basihyal tooth plate toothless. 53[0] Lateral line scales roughly circular. These character states, which mostly coded with question marks in previous publications (e.g. Stearley & Smith, 1993) are important for understanding the relationships of tEosalmo in the Salmonidae. In addition, we have a revised interpretation of the following character states: 20[1] The position of the metapterygoid was considered to be between the quadrate and symplectic and in broad contact with the symplectic (see Stearley & Smith, 1993).Judging from the cranial skeleton preserved on UALVP 13482a, this element is dorsal to the quadrate and symplectic with minimal (or no) contact with symplectic (Fig. 3A). 27 [ 11 Smith & Stearley (1989) noticed the variation of the premaxillary process of the maxilla in extant salmonids. They later coded this character as '0' for fEosalmo, that is, the premaxillary process of maxilla in tEosalmo extends dorsally in an angle less than 10" from the main axis of the maxilla (see Stearley & Smith, 1993: ch. 53). We found that the process in fEosalmo extends dorsally at an angle somewhat larger than 10". 37[1] The posterior infraorbitals have two states in Salmonidae (see Smith & Stearley, 1989; Stearley & Smith, 1993). In Coregoninae and Thymallinae, they are broad, covering most of the hyomandibular (37 [O]), whereas in Salmoninae including fEosalmo (Fig. 6A), they are relatively narrower than those in Coregoninae and Thymallinae, covering less than half the hyomandibular. 46[1] Branchiostegals number from 10 to 13 in most salmonines (pers. observ.; also see Stearley & Smith, 1993). fEosalmo has 10 to 11 branchiostegals. The new information confirms that fEusalmo has a mixture of primitive and derived features in its cranial skeleton (Wilson & Williams, 1992).

Autupomoqhies off Eosalmo

Two unique autapomorphies (not included in the cladistic analysis) were also discovered for tEosulmo: (1) Long anterodorsal process meets dorsal edge of subopercle at angle of about 304 M. V. H. WILSON AND G.-Q. LI

60’ and fits anteroventral corner of opercle (Fig. 4C). A subopercle with an anterodorsal process is present in all Salmoniformes as well as in Esociformes (pers. observ.) but is usually either dorsally or slightly posterodorsally directed (as in most salmonids). (2) Basihyal tooth plate broad, flat, thin, and toothless. In Coregoninae and Thymallinae the basihyal tooth plate is flat but relatively narrow with small median teeth; when the teeth on the perimeter are present, they are not enlarged. All salmonines except tEosalmo have a basihyal tooth plate with stout teeth around the perimeter (also see Stearley & Smith, 1993). Lack of teeth on the basihyal of tEosalmo raises questions about its feeding habits; unfortunately, these cannot yet be answered by available fossil evidence. In addition, the analysis suggests three homoplasious derived features for tEosalmo: 14[11 foramen for anterior branch of trigemino-facial nerve on anterolateral margin of prootic; 20[1] metapterygoid dorsal to quadrate and symplectic with minimal contact with symplectic; and 35[1] retroarticular suture at an angle higher than 45”. Of these, the first two are shared with Hucho, Saluelinus, Salmo, and Oncorhynchus, and the third with Salvelinus, Salmo, and Oncorhynchus (Fig.9). Together, the three homoplasious derived character states and the two autapomorphies strongly support the validity of the genus tEosalmo.

Synapomorphies of Salmonidae

Stearley & Smith (1993: tab. 2) defined the monophyly of Salmonidae based on 10 features; four of them were considered to be uniquely present in the family. Although 54[1] ‘tetraploid karyotype’ is not testable in fossils, our study confirms that two of the osteological features are present in tEosalmo, and therefore remain as synapomorphies for all Salmonidae. They are 13[ 11 posterior surface of epiotic with sulcus; and 46[1] peg-and-socket mechanism in caudal skeleton (Figs 7B and 8).

Interrelationships among three subfamilies of Salmonidae

Since Greenwood et al. (1966), it has been commonly accepted that the Salmonidae consist of Coregoninae, Thymallinae, and Salmoninae (see Behnke, 1972; Nelson, 1994), although some authors divide the family into two (Coregonidae and Sal- monidae, the lattcr including Thymallinae and Salmoninae) (Johnson & Patterson, 1996). According to Norden (1961), Stearley & Smith (1993), and Nelson (1994), and supported by our study, the Coregoninae can be defined by three derived osteological features: 23 [ 11 palatine toothless or with vestigial teeth, 28 [ 11 teeth on premaxilla absent or vestigial in adults, and 44[1] ceratohyal perforate (see Fig. 9). Thymallinae differ from other salmonids in lacking an orbitosphenoid (15 [O]) and in having “17 or more dorsal fin rays” (also see Stearley & Smith, 1993; Nelson, 1994). Stearley & Smith (1993) recognized a sister-group relationship between the Thymallinae and Salmoninae based on nine features. Our examination suggests that some states used by Stearley and Smith might be pleisiomorphic to Thymallinae and Salmoninae. These include 4[1] absence of ethmoid, 18[0] toothed vomer, OSTEOLOGY AND PHYLOGENY OF tEOSAUIO 305

23[0] well-toothed palatines, and 25[0] toothed maxillae, which are also seen in some or all of the out-group taxa. However, our study confirms the following derived features as uniquely present in Thymallinae and Salmoninae: 29[ 13 Premaxilla with broad ascending process. The process deflects posteriorly and is typically arched in breeding males of Salmo and Oncorhynchus (29[2]) (also see Stearley & Smith, 1993: chs. 57-58). 3 1 [ 11 Supramaxilla thin and lanceolate. This element may be long and inflected in Hucho and Salvelinus (3 1 [2]) (also see Stearley & Smith, 1993: ch. 63). 34[1] Posterior process of angulo-articular extending at an angle to the horizontal (Fig. 6B, also see Stearley & Smith, 1993: ch. 71). In addition, our study suggests a fourth derived osteological feature shared only by Thymallinae and Salmoninae: 36[1] A short supraorbital bordering only the anterior half to third of the dorsal margin of the orbit. In the out-group taxa that have this bone the supraorbital is long, bordering most of the dorsal margin of the orbit. These four derived character states strongly support the sister-group relationship between Thymallinae and Salmoninae.

Phylugery of the subjiiamib Salmoninae

The suggested sister-group relationship between TEosalmo and all living salmonines (Wilson, 1977; Wilson & Williams, 1992; Stearley, 1992; Stearley & Smith, 1993) is supported by eight derived character states. 5[1] Scales small. Scales in Coregoninae and Thymallinae are large, with each vertebral centrum opposite fewer than two lateral line scales, while in Salmoninae, scales are much smaller and more numerous, with each vertebral centrum opposite more than two lateral line scales (pers. observ.; also see Scott & Crossman, 1973). 7 [ 11 Posterior part of frontal widely expanded above autosphenotic (also see Stearley & Smith, 1993: ch. 13). 12[1] Hyomandibular fossa on pterotic long (also see Stearley & Smith, 1993: ch. 19). The fossa extends the entire length of the pterotic in all salmonines, while in all the out-group taxa, it extends only about half the length of the pterotic. 22[1] Posterior part of endopterygoid (= mesopterygoid in Stearley & Smith, 1993: ch. 45) extending posteriorly and broadly overlapped by both metapterygoid and quadrate. This state is absent in all other salmonids though a similar condition may be seen in some primitive euteleosts such as Novumbra. 27[1] As already mentioned, the premaxillary process of the maxilla in TEosalmo extends dorsally at an angle larger than 10". This state may be secondarily lost in several species of Oncorhynchus (cf. Stearley & Smith, 1993: ch. 53), but is present in all other extant salmonines (Fig. 9). 38 [ 11 Presence of suprapreopercle. Stearley & Smith (1993: ch. 80) designated this as one of the most important features in support of the monophyly of the Salmoninae. Its presence in TEusalmo and all the extant salmonines strongly supports the salmonine relationship of TEosalmo. 40[1] Anterior end of preopercular canal on horizontal arm of preopercle turns anteroventrally. In other taxa the canal is usually parallel with the ventral edge of the bone. All salmonines including TEusalmo share this derived state (Table 1; also see Stearley & Smith, 1993: fig. 8). 306 M. V. H. WILSON AND G.-Q LI

48[1] First uroneural amplified into large fan-shaped stegural. We agree with Stearley & Smith (1993) that this is a synapomorphy of Salmoninae because it is definitely present in tEosalmo (Figs 7B and 8). A less elaborate expansion of the stegural may also be seen in Coregonus as a convergence @ers. observ.; also see Nybelin, 1973: fig. lc; Fujita, 1990: fig. 70). Distribution of derived states within the subfamily Salmoninae points to three main evolutionary stages after that indicated by the Eocene tEosalmo (Fig. 9). The first marks the evolution of the clade containing all the extant genera of the subfamily (Fig. 9), defined by five unambiguous synapomorphies: 6[1] frontals included as part of the floor of the posttemporal fossae (= Stearley & Smith, 1993: ch. 12); 9[1] parietals flanking the posterolateral edge of the frontals that are extended posteriorly along the midline (= Stearley & Smith, 1993: ch. 14); 24[1] premaxillary process of the palatine with long blade-like crest ( = Stearley & Smith, 1993: ch. 47); 42 [ 11 extrascapulars tubular (= Stearley & Smith, 1993: ch. 84); and 43[1] basihyal tooth plate with strong teeth around perimeter (= Stearley & Smith, 1993: ch. 86). These five features support a sister-group relationship between Brachymystax and all other living salmonines. The second stage resulted in the separation of Brachymystax from the main clade of extant salmonines (Fig. 9) and supported by three synapomorphies: 17 [l] vomer long with teeth along shaft (= Stearley & Smith, 1993: ch. 35), 30[1] presence of mesial pocket for rostra1 cartilage on premaxilla (= Stearley & Smith, 1993: ch. 61), and 5 1 [l] two epurals (= Stearley & Smith, 1993: ch. 98). As mentioned by Stearley & Smith (1993), the position ofAcantholingua is not well resolved. It may be the sister-group of the clade consisting of Salmothymus and Pla&salmo or the sister group of the clade consisting of Salmothymus and Pla&salmo plus the clade containing Hucho, Salvelinus, Salmo, and Oncorhynchus. In this study, we found one synapomorphy for Salmothymus, Pla@almo, Hucho, Salvelinus, Salmo, and Oncorhynchus. In all these genera, the horizontal arm of the preopercle is half or less than half as long as the vertical arm (39[1]) (modified from Stearley & Smith, 1993: ch. 81) (Fig. 9). The third stage marks the separation of the clade consisting of Salmothymus and Pla&salmo from the clade consisting of Hucho, Salvelinus, Salmo, and Oncorhynchus (Fig. 9). The sister-group relationship between Salmothymus and Pla&salmo is supported by the presence of a depression at the posterior midline of frontal (lO[l]) (= Stearley & Smith, 1993: ch. 15[1]), a feature unique to these two genera. Hucho, Salvelinus, Salmo, and Oncorh_nchus from a clade defined by the following derived features: 14[1] foramen for anterior branch of trigemino-facial nerve on the anterolateral margin of the prootic (modified from Stearley & Smith, 1993: ch. 24); 16 [ 11 orbitosphenoid without anterior emargination (Stearley & Smith, 1993: ch. 26); 20[1] metapterygoid dorsal to quadrate and symplectic with minimal or no contact with symplectic (modified from Stearley & Smith, 1993: ch. 42; and 26[1] long maxilla with posterior end extending posterior to orbit (= Stearley & Smith, 1993: ch. 50). Finally, our analysis supports the phylogenetic relationships among Hucho, Salvelinus, Salmo, and Oncorhynchus proposed by Stearley & Smith (1993), though the number of relevant characters used by us is small. The sister group relationship between Hucho and Salvelinus is supported by 1 1 [ 11 sphenotic with stout and anteriorly directed anterior ramus (= Stearley & Smith, 1993: ch. 18), and 31 [l] long and inflected supramaxilla (= Stearley & Smith, 1993: ch. 63). Salmo is sister to Oncorhynchus OSTEOLOGY AND PHYLOGENY OF tEOSALMO 307 according to 19[1] presence of anterior extension of vomer in breeding males (= Stearley & Smith, 1993: ch. 39) and 29[2] ascending process of premaxilla posteriorly deflected and typically arched in breeding males (modified from Stearley & Smith, 1993: chs. 57 and 58).

CONCLUSIONS

Study of new material of TEosalmo driiioodensis supports previous ideas that it is the most primitive salmonine yet known, with a mixture of primitive and derived salmonid features in its skull, while its postcranial skeleton is uniformly of full (extant) salmonine construction. Numbers of vertebrae and fin rays are consistent with expectations for primitive extant salmonines. A long anterodorsal process of the subopercle meeting the dorsal edge of the bone at an angle of about 60" and the apparent lack of teeth on the flat dermal basihyd plate represent two unique derived character states defining TEosalmo, the first derived features to be identified for the genus. The Salmoninae, as documented by fossil and extant genera, have passed through four major stages, each marked by numbers of convincing synapomorphies in the phylogram (Fig. 9). The first stage is documented by the synapomorphies uniting TEosalmo with the extant genera. The second is marked by synapomorphies uniting the extant genera. The third is indicated by synapomorphies uniting all the extant genera except Brachymystax. The fourth marks the separation of the clade consisting of Salmothymus and Platysalmo from the clade consisting of Hucho, Salvelinus, Salmo, and Oncorhynchus.

ACKNOWLEDGEMENTS

We thank H.-P. Schultze and G.R. Smith for suggestions and discussion, and L. Grande and G.D. Johnson for helpful reviews of the manuscript. L.A. Lindoe collected and prepared some of the fossil specimens. L. Grande generously provided facilities for study of specimens by M.V.H. Wilson at the FMNH. Financial support for this research is from Natural Sciences and Engineering Research Council of Canada (NSERC) operating grant A9 180 to M.V.H. Wilson.

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APPENDIX

Characters used in the cladistic analysis 1. Dermethmoid (Ndm) single = [O]; paired = [I]. 2. Length to width of dermethmoid (Stearley & Smith, 1993) (L/Wdm) less than 2 = [O]; greater than 2 = [I]. 3. Dennethmoid posteriorly overlapping frontal (Stearley & Smith, 1993) (Dm-Fr) = [O]; not overlapping = [I]. 4. Ethmoid (Stearley & Smith, 1993) (Em) present = [O]; absent = [I]. 5. Scales (Sc) large, fewer than two lateral line scales per vertebral centrum = [O]; small, more than two lateral line scales per vertebral centrum = [I]. 6. Frontal (Fr) posteriorly not included in floor of temporal fossa = [O]; included in floor of fossa (except Salvelinus malma and S. alpinus) = [I]. 7. Posterolateral part of frontal above the autosphenotic (Plfr) not widely expanded = [O]; widely expanded laterally, covering all or most of the autosphenotic = [I]. 8. Post-temporal fossa (Johnson & Patterson, 1996) (Ptf) roofed = [O], open = [I]. 9. Parietal (Pa) directly posterior to the frontal = [O]; flanking posterolateral edge of frontal = [I]. 10. Depression at posterior midline of frontal (Dpfr) absent = [O]; present = [I]. 1 1. Anterior ramus of sphenotic (= autosphenotic) (Arsp) thin and directed laterally = [O]; stout and directed anteriorly = [I]. 12. Hyomandibular fossa on pterotic (Hfp) short, extending half length of pterotic = [O]; long, extending entire length of pterotic = [I]. 13. Epiotic (Epo) with flat posterior surface = [O]; surface with sulcus = [I]. 14. Foramen for anterior branch of trigemino-facial nerve on prootic (Fabt): on anteromesial margin of prootic = [O]; on anterolateral margin of prootic = [l]. (tEosalmo = [I], see UALVP 1238213). 15. Orbitosphenoid (Osp) absent = [O]; present = [I] (tEosalmo = [I] (see UALVP 12382b and 27 138). 16. Anterior emargination of orbitosphenoid (Aeosp) present = [O]; absent = [I] (present in two species of Oncorhynchus, see Stearley & Smith, 1993). 17. Vomer (Vo) short = [O]; long with teeth along shaft = [I]. 18. Teeth on vomer (Tvo) present = [O]; absent or vestigial in adults = [I]. 19. Anterior extension of vomer in breeding males (Aev) not present = [O]; present = [I]. OSTEOLOGY AND PHYLOGENY OF tEOSALM0 31 I

20. Metapterygoid (Pmep) between quadrate and symplectic and in broad contact with symplectic = [O]; dorsal to quadrate and symplectic with minimal (or no) contact with symplectic = [I]. 21. Teeth on endopterygoid (= mesopterygoid) (Tenp) present = [O]; absent = [I]. 22. Posterior part of endopterygoid (Stearley & Smith, 1993) (E-mep) in marginal contact with metapterygoid and quadrate = [O]; extended posteriorly and broadly overlapped by both metapterygoid and quadrate = [I]. 23. Palatine (Pal) well-toothed = [O]; toothless or with vestigial teeth = [I]. 24. Premaxillary process of palatine (Pmpl) with small or no posterior crest = [O]; with long blade- like crest = [I]. 25. Teeth on maxilla (Tmx) present = [O]; absent in adult = [I]. 26. Maxilla (Lmx) short, not extending posterior to orbit = [O]; long, extending posterior to orbit = [I]. 27. Premaxillary process of maxilla (Ppmx) meeting main axis of maxilla at angle of less than 10" = [O]; at angle of 10" or more = [I] (see Smith & Stearley, 1989; Stearley & Smith, 1993). 28. Teeth on premaxilla (Tpmx) present = [O]; absent or vestigial in adults = [I] (see Norden, 1961). 29. Ascending process of premaxilla (Apmx) narrow or rudimentary = [O]; broad = [I]; deflected posteriorly and typically arched in breeding males = [2] (see Stearley & Smith, 1993: ch. 57-58). 30. Mesial pocket for rostra1 cartilage on the premaxilla (Mpmx) absent = [O]; present = [I] (Stearley & Smith, 1993). 31. Supramaxilla (when present) (Smx) broad and ovate = [O]; thin and lanceolate = [I]; long and inflected = [2]. 32. Oral margin of dentary before coronoid process (modified from Stearley & Smith, 1993) (Omden) rising steeply at angle greater than 45" = [O]; at angle less than 25" = [I]. 33. Kype (hook-like cartilaginous expansion) of dentary in breeding males (see Stearley & Smith, 1993) (Kden) absent = [O]; present = [I]. 34. Posterior process of angulo-articular (Ppanga) extending horizontally = [O] ; extending at an angle to the horizontal = [I]. 35. Retroarticular (Rart) sutured with angulo-articular at low angle = [O]; at angle greater than 45" = [I]. 36. Supraorbital (So) long and bordering most of dorsal margin of orbit = [O]; short and bordering anterior half to third of dorsal margin of orbit = [I]. 37. Infraorbitals 3 to 5 (103-5) wide and covering most of hyomandibular = [O]; narrow and covering less than half the hyomandibular = [I] (also see Smith & Stearley, 1989; Stearley & Smith, 1993). 38. Suprapreopercle (Spop) absent = [O]; present = [I]. 39. Horizontal arm of preopercle (Hpop) at least 2/3 as long as the vertical arm = [O]; half or less as long as vertical arm = [I] (modified from ch. 81 in Stearley & Smith, 1993). 40. Anterior end of preopercular canal on horizontal arm of preopercle (Pop.) anteriorly directed = [O]; anteroventrally directed = [I]. 41. Subopercle (Sop) deep, up to 2/3 as deep as wide = [O]; shallow, half or less than half as deep as wide = [I] (modified from Stearley & Smith, 1993: ch. 83). 42. Extrascapular (Esca) flat = [O]; tubular = [I]. 43. Basihyal tooth plate (= glossohyal) (Btp) toothless or having small teeth on perimeter = [O]; with large teeth around perimeter = [I]. 44. Ceratohyal (Chy) imperforate = [O]; perforate = [I]. 45. Branchiostegals (Br) fewer than 10 = [O]; 10 or more = [I]. 46. Peg-and-socket connections on 1st hypural, parhypural, and haemal and neural spines of pu2 to pu4 (Psc) lacking = [O]; developed = [I]. 47. Ossifications (tendon bone) in urostyle (see Stearley & Smith, 1993: ch. 95) (Tbu) present = [O]; absent = [I]. 48. First uroneural (see Stearley & Smith, 1993: ch. 96) (Unl) normal (not amplified into a large fan- shaped stegural) = [O]; amplified into fan shaped stegural = [I]. 49. Un2 slender and posterodorsal to unl (Johnson & Patterson, 1996) (Unp) = [O], broad and anterodorsal to un 1 = [I]. 50. Preural centrum 2 (Pu2) with complete neural arch and spine = [O]; with neural spine detached from neural arch = [I]. 51. Number of epurals (Nep) three = [O]; two = [I]. 52. Scales (Scr) with radii (Johnson & Patterson, 1996) = [O], without = [I]. 53. Lateral line scales (see Stearley & Smith, 1993: ch. 103) (Lls) roughly circular = [O]; elliptical, or reduced to little more than the nerve tube = [I]. 54. Karyotype (Johnson & Patterson, 1996) (Kar) diploid = [O]; tetraploid = [I].