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Contributions in Science, Number 520 Squires: Pico Formation Paleontology & 87

Figure 107 Chronostratigraphic distribution of the study area species with the most constrained geologic ranges indicating a late Pliocene age.

SUBSTRATE most localities in the Newhall area preferred to live in close
proximity to a river delta because the river would deliver nutrients
At least three substrate types are recognized for the study area on which it feeds. During the winter, individuals could migrate,
deposits: fine-grained offshore sediments, fine- to medium-grained from silty substrate to shallower water and sandy and gravelly
sandy deltaic sediments, and hard surfaces. The first type was substrates, in order to lay their eggs.
located immediately seaward of the delta and essentially fringed The fine- to medium-grained sandy delta substrate is indicated
the delta; the second occurred on the delta complex itself; and the by paired-valved epifaunal bivalves (e.g., Argopecten, Lyropec-
third occurred in association with coarse debris on the delta. The ten, Patinopecten), epifaunal gastropods (e.g., Glossaulax,
presence of fine-grained offshore substrate is indicated by the very Conus), and paired-valved infaunal bivalves (e.g., Trachycar-
abundant gastropod Turritella cooperi. Valentine and Mallory dium, Saxidomus, Tresus, Panopea). Hard-surface biotopes were
(1965) assigned this species to their Group III Pleistocene offshore very localized. The Haliotis specimen and the Terebratalia
fossil community, along with the bivalve Lucinoma annulatum occidentalis brachiopods most likely attached to shell debris or
(Reeve, 1850), another megafaunal element, but a rare one, of the larger rock clasts. The latter, in a few cases, provided hard
Newhall Pico Formation assemblages. Although details are lacking substrate for encrusting bryozoan and spirorbid tubes. Some
about how T. cooperi lives, it is probably like most species of individuals of the plicate oyster Myrakeena veatchii lived
extant Turritella. Bandel (1976) reported that Turritella variegata attached to each other, based on a cluster of specimens found
(Linnaeus, 1758) from the Caribbean coast of Colombia lives as a attached to each other at LACMIP loc. 9659, where a growth
suspension feeder shallowly buried in soft substrates. Large series of this oyster was also found. The occurrence of the paired-
populations migrate only at the time of spawning once a year, valved single specimen of the pholadid ?Chaecia ovoidea (Gould,
and they crawl to more sandy bottoms or bottom covered with 1851) is anomalous because this species normally bores into clay
gravel where they can attach their spawn more firmly in coarse or shale (Coan et al., 2000). Kennedy (1974:39) reported that C.
debris than is possible in muddy environments. Allmon et al. ovoidea has been known to bore into waterlogged wood, and this
(1992) reported that Turritella gonostoma Valenciennes, 1832, could explain its presence in the study area megafauna.
from the northern Gulf of California lives in depths less than 5 m The above-mentioned three types of substrate are compatible
and, in the winter, migrates into shallow water to reach nutrient- with the findings derived from Table 2 showing that the majority
rich waters and to lay its eggs. It seems very likely that the of the 41 extant species of the Pico Formation megafauna live in/
specimens of T. cooperi that dominate the fossil assemblages at on sand or mud; only a few live on hard surfaces (Table 2).

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LACMIP loc. 7752, height 23.8 mm, 30.9. 96. Cancellaria hamlini Carson, 1926, hypotype LACMIP 14413, LACMIP loc. 17919, height 21.5 mm,
30.9. 97. Turbonilla sp., hypotype LACMIP 14414, LACMIP loc. 17918, upper spire missing, height 6 mm, 33.1. 98. Rictaxis painei grandior Grant
and Gale, 1931, hypotype LACMIP 14415, LACMIP loc. 7752, height 13.3 mm, 31.7. 99. Acteocina culcitella? (Gould, 1853), hypotype LACMIP
14416, LACMIP loc. 7760, height 3 mm, 37.5. 100–101. Scaphopod Dentalium neohexagonum Sharp and Pilsbry, in Pilsbry and Sharp, 1897, LACMIP
loc. 7752. 100. Hypotype LACMIP 14417, height 9.8 mm, 32.4. 101. Hypotype LACMIP 14418, diameter 2.3 mm, 33.7. 102. Barnacle Balanus? sp.,
hypotype LACMIP 14419, LACMIP loc. 17917, side view, height 5.5 mm, 32. 103. Crab leg (partial), hypotype LACMIP 14420, LACMIP loc. 17918,
height 10.2 mm, 32.2. 104. Echinoid spine Eucidaris sp., hypotype LACMIP 144421, LACMIP loc. 17917, height 4.2, 35.4. 105. Ray tooth Myliobatis
sp., hypotype LACMIP 14422, LACMIP loc. 7752, maximum dimension 25 mm, 30.9. 106. Pine cone, hypotype LACMIP 14423, LACMIP loc. 7752,
cross-section, height 50 mm, 30.6.