TWO VERY RARE FOSSILS FROM SOUTHERN CALIFORNIA

FOSSIL 1:

Many years ago, Greg Slack, one of my colleagues, graciously gave me a rare specimen of an Upper Cretaceous, Turonian Stage, crinoid fossil “stem” that he found. This fossil is from siltstone in the Holz-Baker gradational transition zone of the Ladd Formation in the Santa Ana Mountains of Orange County, southern California. These sediments were deposited in shallow to moderately deep depths, during warm-water times.

As far as I know, this is the first crinoid fossil from this locale. Even though the specimen is missing its calyx (“head”), I was able to identify its “stem” as belonging to genus Neocrinus, a “relict” genus belonging either to family Balanocrinidae or Isocrinidae [depending on the researcher]. Both families have a geologic time range of about 23 million years ago [= earliest Miocene] to Recent.

Genus Neocrinus lives today in moderately shallow to relatively deep water [as deep as 1219 m] (from Florida, Grenada, Bahamas, and Cuba). A modern specimen of a Neocrinus blakei stem is shown below for comparison.

Classification

Kingdom Animalia

Phylum Echinodermata

Class Crinoidea

Family Balanocrinidae [or Isocrindae] 

Genus Neocrinus

Figure 1. A Late Cretaceous (Turonian Stage) Neocrinus sp. stem (7.8 cm length, 4 cm diameter) from the Ladd Formation in the Santa Ana Mountains of Orange County, southern California. This fossil is shown [alongside] a Recent specimen of Neocrinus blakei [= bright white color, calyx missing, length 8 cm, diameter 3 mm]. This Recent specimen is from 402-411 m depth, in the Old Bahama Channel of Punta Alegre, Cuba. Collector: unknown]. 

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FOSSIL 2:

After years of extensive collecting (see Squires, 1984), only a single specimen of a myliobatid shark-tooth plate has been found in the middle Eocene Llajas Formation of southern California (Squires, 1984). It was collected by, David Advocate, one of my Master’s Degree student, who graciously donated the specimen, which is figured for the first time herein.

Family Myliobatidae

   Aetobatus? sp.---this genus is characterized by having  narrow teeth

Figured below is a tooth plate called “pavement teeth,” which are used to crush crustaceans and clams living in shallow sandy ocean waters. This genus is characterized by having a toothplate comprised of narrow teeth.

Figure 2. Aetobatus? sp. (each division of the "ruler" is 1 cm); therefore the toothplate is 50 mm in length.

References

De Anda, M.V. 2011. Taxonomia y biogeografia de los crinoideos (Echinodermata: Crinoidea) de Mexico. [Tesis] Thesis, 181 pp. [Available online, for free].

Ebersole, J.A., D. Cicimurri, and G. L. Stringer. 2019. Taxonomy and biostratigraphy of the elasmobranch and bony fishes (Chondrichthyes and Osteichtyes) of the lower-to-middle Eocene (Ypresian to Bartonian) Group in Alabama, USA, including Claiborne and analysis of otoliths. European Journal of Taxonomy 585, pp. 1-274.

Squires, R.L. 1984. Megapaleontology of the Eocene Llajas Formation, Simi Valley, California. Contributions in Science No. 350, 76 pp.