Notes on Crassatella lomitensis (Oldroyd, 1924)
From the Plio-Pleistocene of Southern California
Jack D. Mount
Department of Earth Sciences
University of California, Riverside, California 92502
The Lower Pleistocene Lomita Marl of southwestern Los Angeles County, California, abounds in its variety and number of taxa of fossil marine Mollusca. My recent discovery of the holotype of one of the characteristic species in this fauna, Crassatella lomitensis (Oldroyd, 1924), which had been missing for many years, has prompted the preparation of this report.
Ida S. Oldroyd, then Curator of Conchology at Stanford University, named and described Crassatellites lomitensis in 1924 in the Bulletin of the Southern California Academy of Sciences. The types were included in a lot of vertebrate and invertebrate fossils loaned to Stanford University by Mr. Samuel Maus Purple. The vertebrates were studied by David Starr Jordan and Harold Hannibal, and Oldroyd examined the mollusks. The specimens were obtained from the Lomita lime quarry in the community of Lomita, Los Angeles County, California, which was developed in the Lomita Marl of Early Pleistocene age. Purple, an inveterate collector of all sorts of natural history curiosities, was then general manager of the quarry operations. A preliminary list of the Mollusca from the quarry, prepared by Oldroyd, was included in Jordan and Hannibal's (1923) monograph describing the sharks and rays. Following their study the fossils were returned to Purple apparently with the instructions that they be placed in the collections of either the Southern California Academy of Sciences, the Los Angeles County Museum, or Stanford University; however, unfortunately being possessive of his personally collected specimens, Purple retained the types for his private collection. Purple retired to Monterey, California, and after his death the material remained there neglected for many years until 1968, when the Purple collection was donated to the Municipal Museum of Riverside, California, by his widow.
Recently I was invited to examine the collection and identify the Mollusca. In addition to the holotype of C. lomitensis, I discovered 24 primary and secondary types of fossil vertebrates, mostly shark teeth, which were described by Jordan and Hannibal. These I segregated and labeled since they were not clearly marked and I published a note (Mount, 1974) making known the location of their repository. The holotype of C. lomitensis was placed in the Type Collection of the Department of Earth Sciences, University of California, Riverside (UCR).
The purpose of this paper is to redescribe Crassatella lomitensis and to define the morphologic characteristics upon which this species may be differentiated from the Recent Crassatella fluctuata (Carpenter, 1864: 611, 642). Most authors have regarded C. lomitensis to be a valid species, although Woodring (in Woodring, Bramlette and Kew, 1946) believed the holotype of C. lomitensis to be a large specimen of C. fluctuata. Woodring noted, however, that at the time of writing he had no large Recent shells of C. fluctuata for reference and that the holotype was a small immature right valve. I am of the opinion that the two species are distinct, based on a comparison of the recently located holotype of C. lomitensis with a large lot of adult topotypes of C. fluctuata (pl. 1, figs. 7-10) at my disposal.
Genus Crassatella Lamarck, 1799
Crassatella lomitensis (Oldroyd, 1924)
Pl. 1, figs. 1 to 6
Crassatellites sp. indescr. I. S. Oldroyd in Jordan and Hannibal, 1923, p.65.
Crassatellites lomitensis Oldroyd. Oldroyd, 1924, p.10, pl.C, 2 figs. Grant and Gale, 1931, p.271.
Crassatella lomitensis (Oldroyd). S. S. Berry in Schenck, 1945, p.513.
Eucrassatella fluctuata (Carpenter). Woodring in Woodring, Bramlette and Kew, 1946, p.81, pl.31, figs. 1-8.
?Eucrassatella aff. E. fluctuata (Carpenter). Winterer and Durham, 1962, p.302.
Type Material: Holotype, UCR 6621/1 (figs.1,2). Paratype, missing.
Type Locality: Lomita lime quarry, in the southern part of Lomita, Los Angeles County, California. Lomita Marl, Lower Pleistocene.
Original Description: Shell of medium size, thick, solid, subtrigonal, about two-thirds as long as wide. Umbones small not prominent, strongly plicated. Anterior end broadly rounded, posterior bluntly truncated; the anterior portion of the lower edge rounded, posterior straight; umbonal ridge prominent, broad and rounded. Surface marked with small lines of growth. Inner margin crenulated. Both valves are complete and well preserved. (Oldroyd, 1924, p.10)
Additional Description: Shell of moderate size, height about four-fifths of length, moderately inflated, rounded-triangular in outline, shell substance thick and solid; umbones not very prominent, centrally located, wide, blunt, prosogyrate; lunule depressed, narrow, short, about one-half the length of the anterior dorsal border; anterior dorsal border nearly straight; anterior portion of ventral border rounded; posterior end slightly rounded to nearly straight; posterior dorsal border straight to slightly rounded; escutcheon short, narrow; sculpture of coarse, undulating, rather irregular, concentric ridges covering entire outer surface.
Dentition of right valve: one strong trigonal posterior cardinal tooth just anterior of center bounded anteriorly by a narrow, deep, oblique socket and posteriorly by a shallow, small, subcircular socket; anterior cardinal tooth reduced to nearly obsolete; ligament pit a triangular depression in the dorsal half of the hinge plate immediately behind the posterior cardinal tooth; anterior dorsal border bearing a shallow lateral socket situated below the forward part of the lunule; posterior lateral tooth long, narrow, straight. Dentition of the left valve: anterior cardinal tooth moderately narrow and oblique; posterior cardinal tooth somewhat shorter, bounded above by the chondrophore; anterior lateral tooth short and narrow, situated below the anterior third of the lunule; posterior lateral socket long, narrow, extending nearly the full length of the escutcheon and slightly beyond the posterior end.
The measurements are listed in Table 1.
Upper Pliocene: Fernando Formation, Upper Newport Bay, Orange County (UCR locality 4915)
?Lower Pliocene: Towsley Formation, near Honby, Los Angeles County (Winterer and Durham, 1962)
Measurements (in mm) of the type specimens of
Crassatella lomitensis (Oldroyd) and C. fluctuata
Discussion: As originally noted by Oldroyd, Crassatella lomitensis appears to be closely related to the Recent C. fluctuata and is most likely its precursor. Crassatella fluctuata differs from the fossil species principally in its higher, more pronounced beak which is closer to the anterior end; the undulating sculpture is generally absent and when present it is located only on the umbones. The general shell profile and the configuration of the hinge plate also serve to distinguish the two species. Many specimens of C. fluctuata are larger than any of the specimens of C. lomitensis that I have examined.
The differences in the ecologic requirements of the two species of Crassatella also suggest that the two taxa are distinct. Although the two species appear to have enjoyed the same depth range, C. lomitensis may have lived in colder water. Crassatella fluctuata ranges from Santa Barbara Island to Santa Catalina Island, California (McLean, 1969), and is found at a depth of 54 to 83 meters. Paleoecologic studies on the Lower Pleistocene Lomita Marl, Timms Point Silt and San Pedro Sand in the San Pedro area by Clark (1931), DeLong (1941), Schenck (1945), Woodring, Bramlette and Kew (1946) and Valentine and Meade (1961) have shown that these formations were deposited at moderate depths, approximately 45 to 90 meters, and that the water at this time may have been somewhat colder than at the present time at the latitude of San Pedro. An equivalent fauna would perhaps be found today off the coast of Monterey to San Francisco. My paleotemperature analysis (Mount, 1971) of a large molluscan fauna, which includes C. lomitensis (pl.1, figs.5,6), from the Upper Pliocene portion of the Fernando Formation on the east bluff of upper Newport Bay, Orange County, California, suggests that the sea temperature at the depth of 27 to 360 meters was considerably colder than at the present time. Today many of the extant members of this fauna do not range south of Puget Sound.
Carpenter, P. P., 1864. Supplementary report on the present state of our knowledge with regard to the Mollusca of the west coast of North America. Rept. British Assoc. Adv. Sci. 1863: 517-686.
Clark, A., 1931. The cool-water Timms Point Pleistocene horizon at San Pedro, California. San Diego Soc. Nat. Hist., Trans. 7:27-41.
DeLong, J. H., 1941. The paleontology and stratigraphy of the Pleistocene at Signal Hill, Long Beach, California. San Diego Soc. Nat. Hist., Trans. 9:231-250.
Grant, U. S., IV, and H. R. Gale, 1931. Catalogue of the marine Pliocene and Pleistocene Mollusca of California and adjacent regions. San Diego Soc. Nat. Hist., Mem. 1:1-1036, 32 pls.
Jordan, D. S., and H. Hannibal, 1923. Fossil sharks and rays of the Pacific slope of North America. So. California Acad. Sci., Bull. 22:27-68, 10 pls.
McLean, J. H., 1969. Marine shells of southern California. Los Angeles Co. Mus. Nat. Hist., Sci. Ser. 24:1-104, 54 figs.
Mount, J. D., 1971. Paleoecology of a Late Pliocene marine invertebrate fauna from southern California. Geol. Soc. America Abstracts with Programs 3:167-168.
_____, (1974, in press). Type vertebrates from Lomita, California, in the Municipal Museum, Riverside, California. Journ. Paleontology 48.
Oldroyd, I. S., 1924. Description of a new fossil species of a clam of the genus (Crassatellites). So. California Acad. Sci., Bull. 23:10, 1 pl.
Schenck, H. G., 1945. Geologic application of biometrical analysis of molluscan assemblages. Journ. Paleontology 19:504-521, pls.66-67.
Valentine, J. W., and R. F. Meade, 1961. Californian Pleistocene paleotemperatures. Univ. California Publications Geol. Sci. 40:1-46.
Winterer, E. L., and D. L. Durham, 1962. Geology of southeastern Ventura Basin, Los Angeles County, California. U. S. Geol. Survey Prof. Paper. 334-H: 275-366.
Woodring, W. P., M. N. Bramlette, and W. S. W. Kew, 1946. Geology and paleontology of Palos Verdes Hills, California. U. S. Geol. Survey Prof. Paper. 207:1-145, 37 pls.
Explanation of Plate 1
All figures xl.5
|Figs. 1-6.||Crassatella lomitensis (Oldroyd). 1,2, left valve, Holotype, UCR 6621/1; UCR loc. 6621, Lomita quarry, Los Angeles County, California; Lomita Marl, Lower Pleistocene. 3,4, right valve, Hypotype, UCR 1040/20; UCR loc. 1040, Hilltop Quarry, San Pedro, Los Angeles County, California; Lomita Marl, Lower Pleistocene. 5,6, left valve, Hypotype, UCR 4915/273; UCR loc. 4915, east bluff of upper Newport Bay, Orange County, California; Fernando Formation, Upper Pliocene.|
|Figs. 7-10.||Crassatella fluctuata (Carpenter). 7,8, left valve, Topotype, UCR 7279/1; UCR loc. 7279, in 54.9 to 82.3 meters off Santa Catalina Island, Los Angeles County, California; Recent. 9,10, right valve, Topotype, UCR 7279/2; UCR loc. 7279.|
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