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Cephalopods from the Late Eocene Hoko River Formation, Northwestern Washington Richard L

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Cephalopods from the Late Eocene Hoko River Formation, Northwestern Washington Richard L Oi<~e2> K A.. Natural History Museum ifiCl^i Of Los Angeles County IVooCL Invertebrate Paleontology J. Vakom.. 62(1). 1988. pp. 76-82 Copyright 1488. The- Paleontologual Society 0022-3360,88/0062-0076S03.00 CEPHALOPODS FROM THE LATE EOCENE HOKO RIVER FORMATION, NORTHWESTERN WASHINGTON RICHARD L. SQUIRES Department of Geological Sciences, California State University, Northridge 91330 ABSTRACT—Rare specimens of the nautiloids Nautilus and Aturia and extremely rare specimens of a sepiamorph sepiid are described from the late Eocene Hoko River Formation, northern Olympic Peninsula, Washington. The well-preserved partial phragmocones are from channel-fill clastics deposited on the inner and middle slopes of a submarine-fan system. The Nautilus specimen is allied to N. cookanum Whitfield from middle Eocene strata, New Jersey, and is probably conspecific with Nautilus sp. (Miller) from late Eocene strata, northwestern Oregon, both of which were previously assigned to Eutrephoceras. This is the first record of Nautilus in the northeastern Pacific. The Aturia specimen is tentatively identified as A. cf. A. alabamensis (Morton), a species previously only known from late Eocene strata in the Atlantic-Gulf Coastal area and northeastern Mexico. Aturia alabamensis may be the same as numerous Eocene North American aturiid species. The two sepiamorph sepiid specimens resemble Belosepia Voltz but are probably generically distinct. They are only the second record of sepiids in the Eocene of the northeastern Pacific. INTRODUCTION rizian Stage (late Eocene). He also inferred, based on the benthic ATE EOCENE cephalopods are rare in the northeastern Pacific. foraminifers, that the formation was deposited in relatively cool, L moderately shallow ocean waters between lower neritic and up- The occurrence of three genera at a locality in northwestern permost bathyal depths. Snavely et al. (1978), who formalized Washington, therefore, is especially noteworthy. Single speci- the name "Hoko River Formation," mentioned that crabs pres- mens of Nautilus aff. N. cookanum Whitfield and Aturia cf. A. ent in the formation at Kydikabbit Point are late Eocene in age, alabamensis (Morton) and two specimens of a sepiamorph se- and Rathbun (1926) also reported crabs from strata in the vi- piid have been found in the late Eocene Hoko River Formation, cinity of Kydikabbit Point. northwestern Olympic Peninsula, Washington (Figure 1). The The cephalopod specimens from locality LACMIP 6938 are specimens are part of a collection accumulated over many years well-preserved portions of phragmocones, and they occur in by James L. Goedert, Marion Berglund, and William Buchanan. concretions. The crabs are well preserved, numerous, and also The sepiid specimens are extremely rare and represent only the occur in concretions. Many specimens are complete with che- second time Eocene sepiids have ever been found in the north- lipeds and legs, and they appear to have been rapidly buried in eastern Pacific. The first discovery was reported by Squires (1983, situ. Most are Branchioplax washingtoniana Rathbun (1916, p. 1984). 345, text-fig. 1), which, according to Rathbun (1926), ranges The Hoko River Formation conformably overlies the early from late Eocene through early? Oligocene. Carapaces of raninid late Eocene Lyre Formation and underlies the late Eocene through crabs are common also. A few gastropods were also found at late Oligocene Makah Formation. For a generalized geologic this locality. They include a single specimen of Ectinochilus map of the area see Snavely et al. (1980). The upper contact of (Cowlitzia) washingtonensis (Clark and Palmer, 1923, p. 283- the Hoko River Formation appears to be gradational with the 284, PI. 51, figs. 11-14), which has been reported from the late overlying Makah Formation. About 15-20 km east of the study Eocene Cowlitz Formation of southwestern Washington (Clark area, however, there is a local unconformity between the two and Palmer, 1923; Weaver. 1943), a single specimen of a poorly formations (Snavely et al., 1978). preserved Conns sp. indet., and an internal mold of a naticid. The Hoko River Formation consists of 1,500-2,300 m of An internal mold of a pitarid bivalve was also found. All mol- sedimentary rocks deposited on the inner and middle slopes of luscs were in concretions. a submarine-fan system. In the vicinity of Neah Bay (Figure 1), the formation consists mostly of inner-fan, channel-fill con- The cephalopod specimens are deposited in the Los Angeles glomerate interbedded with hemipelagic siltstone (DeChant, County Museum of Natural History, Invertebrate Paleontology 1986). Macrofossils are uncommon in the formation and most collections. The technique of Elias (1938) was used in drawing occur about 300 m above the base of the formation in the the septal sutures (Figure 2). Whorl-height and whorl-width vicinity of Kydikabbit Point (Figure I) (DeChant, personal com- terminology is the same as that used by Sweet (1964, fig. 8). mun.). The Nautilus and sepiid specimens were found in a siltstone, SYSTEMATIC PALEONTOLOGY and the Aturia specimen was found in a granule to large pebble, Family NAUTILIDAE Blainville, 1825 phyllite and basalt conglomerate at Los Angeles County Mu- Genus NAUTILUS Linne, 1758 seum of Natural History, Invertebrate Paleontology locality NAUTILUS afT. N. COOKANUM Whitfield, 1892 LACMIP 6938 in the lower part of the Hoko River Formation. Figures 2.1, 3.1-3.4 The locality is at a garbage dump at 78 m (260 ft) elevation on a ridge top approximately 675 m south of Kydikabbit Point, Description. — Internal mold of a juvenile phragmocone with NFJ/4, SW'/4, sec. 4, T33N, R15W, Cape Flattery quadrangle 9.5 chambers; nautiliconic, involute with small umbilicus, whorls (15-minute series, 1957), Washington. somewhat flattened laterally; septal suture with a very broad Rau (1964) studied the benthic foraminiferal fauna of the rounded ventral saddle, a broad shallow lateral lobe, a small Hoko River Formation (then known as the lower member of shallow lateral saddle near umbilical shoulder, a shallow lobe the Twin River Formation) and assigned the formation to the on the umbilical wall, and near the inner umbilical seam a broad northeastern Pacific provincial benthic foraminiferal upper Na- saddle that extends to a well-developed, broad, "V'-shaped 76 SQUIRES-EOCENE CEPHALOPODS FROM WASHINGTON 2 FIGURE 7 —Index map of study area in Hoko River Formation, north- western Olympic Peninsula, Washington. dorsal lobe (annular lobe) (Figure 2.1); siphuncle near center in FIGURE 2—Septal sutures of the Hoko River Formation cephalopods. early whorls, becoming subcentral and nearer dorsum with 1, Nautilus aff. N. cookanum Whitfield, LACMIP 7197, at whorl growth; where whorl width is about 13.5 mm, the center of the height of 20 mm, x 2. 2, Aturia cf. A. alabamensis (Morton), LACMIP 1 mm thick siphuncle is about 8 mm from venter; maximum 7198, at whorl height of 70 mm, x 0.7.3, sepiamorph sepiid, LACMIP whorl height 24 mm; test diameter 42 mm. 7580, at chamber height of 13 mm, x3.7. Discussion.—Nautilus aff. N. cookanum is similar to Nautilus cookanum Whitfield (1892, p. 285-286, PI. 48, fig. 1, PI. 49, figs. 4, 5) from the top of the Eocene Shark River Marl, Mon- anum has the first two of these features. Nautilus aff. N. cook- mouth County, northeastern New Jersey. Other workers who anum has all three. The type species of Eutrephoceras has only have described and/or illustrated this species are Stenzel (1940, slightly sinuous external sutures and does not have an annular p. 741, fig. 115(4); 1942, cards 3a-b) and Miller (1947, p. 30- lobe. Based on the suture-line drawing (Kummel, 1964, fig. 330, 31, PI. 10, figs. 1, 2, PI. 11, figs. 1-3, PI. 12, fig. 1, PI. 13, figs. 2c) of Eutrephoceras aff. E. dekayi, apparently E. dekayi also 1, 2). The Hoko River specimen especially resembles Miller's does not have a shallow lobe on the umbilical wall, but instead (1947, PI. 11, fig. 3, PI. 12, fig. 1) illustrations oftopotypes of has a saddle there. N. cookanum. Cooke and Stephenson (1928) reported the age Miller (1947), Miller and Downs (1950), and Palmer (1961, of the Shark River Marl as middle Eocene. 1965) discussed and illustrated the known northeastern Pacific The Hoko River specimen differs from N. cookanum in hav- Paleogene nautiloids as Eutrephoceras (i.e., they did not rec- ing a shallow lobe on the umbilical wall and a siphuncle halfway ognize Nautilus except as a Recent genus). In comparison with between center and dorsum rather than midway between dor- these particular taxa, Nautilus aff. N. cookanum has more sin- sum and the venter. This siphuncle position difference may uous external sutures, except for Eutrephoceras sp. Miller, 1947, result from the small size of the Hoko River specimen. The and possibly E. oregonense Miller, 1947. Eutrephoceras sp. Mil- most complete description of N. cookanum is given by Miller ler (1947, p. 37-38, PI. 22, figs. 3, 4) is from latest Eocene (or (1947) and is based on mature specimens between 105 and 208 possibly earliest Oligocene) strata, northwestern Oregon. It is mm in diameter, 2.5-5 times larger than the Hoko River spec- known only from a single small specimen that is too fragmentary imen. to allow its specific affinities to be positively determined, but Most workers have assigned Whitfield's species to Eutrephoc- the partial suture pattern that is preserved is very close to that eras, but the suture is closer to the description (Miller, 1947, p. of the Hoko River specimen. The two specimens, which are 25, fig. 3; Kummel, 1964, p. 448, figs. 330, la-c) of Nautilus very likely conspecific, also have the same position of the si- pompilius, the type species of Nautilus, than it is to the descrip- phuncle in the same sized chamber.
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