San Diego Formation

The San Diego Formation is a coastal transitional marine and non-marine pebble and cobble conglomerate deposit and marine sandstone rock with Pliocene marine fossils, from a former bay deposited during the Middle to Late Pliocene of the Cenozoic (2 - 3 million years ago). This formation is found from the south side of Mount Soledad in San Diego County to Rosarito Beach in northern Baja California, Mexico, including Tijuana, Mexico, and the southwestern corner of San Diego County from San Ysidro to Pacific Beach. San Diego Formation deposits were formed in a large, open, crescent-shaped bay similar in size to Monterey Bay that existed on the coast in Pliocene times.[1][2]

Besides those of clams and other mollusks, quite a few bird fossils (which are generally rare) have been found in this geological formation. Among them is a possible ancestor of Cassin's Auklet (Ptychoramphus aleuticus) and the loons Gavia concinna and G. howardae. The former was quite likely a close relative or even ancestor of the large black-headed[3] loons; the latter was perhaps a small relative of the large grey-headed[4] loons.[5][6]

Fauna

Cetaceans

Mysticetes

Mysticetes reported from the San Diego Formation
Genus Species Stratigraphic position Notes Images

Balaenoptera

B. davidsonii[7]

An extinct rorqual belonging to Balaenoptera.

"Balaenoptera"

"B." portisi

Formerly assigned to Balaenoptera, represents a new, unnamed genus.

Herpetocetus

H. morrowi

A cetotheriid.

"Megaptera"

"M." miocaena

Previously considered to be a relative of humpback whale, represents a distinct genus.

Odontocetes

Odontocetes reported from the San Diego Formation
Genus Species Stratigraphic position Notes Images

Parapontoporia

P. sternbergi[8]

A close relative of the Baiji.

Semirostrum

S. ceruttii

A porpoise with a lower jaw extended few inches beyond the upper jaw (similar to a halfbeak).[9]

Pinnipeds

Pinnipeds reported from the San Diego Formation
Genus Species Stratigraphic position Notes Images

Callorhinus

C. gilmorei[10]

A relative of the northern fur seal.

Dusignathus

D. seftoni[11]

A walrus.

Valenictus

V. chulavistensis[11]

A walrus.

Sirenians

Sirenians reported from the San Diego Formation
Genus Species Stratigraphic position Notes Images

Hydrodamalis

H. cuestae

A close relative of the Steller's Sea Cow.

References

  1. ↑ California Geological Survey, Regional Geologic Map No. 3, 1:100,000 scale Compiled by: Michael P. Kennedy and Siang S. Tan, 2008.
  2. ↑ Scott Rugh, Clams of Champions: The San Diego Formation, from sdnhm.org, the San Diego Natural History Museum website accessed November 26, 2013.
  3. ↑ Common loon (G. immer) and yellow-billed loon (G. adamsii)
  4. ↑ Pacific loon (G. pacifica) and Arctic loon (G. arctica)
  5. ↑ Brodkorb, Pierce (1953). "A Review of the Pliocene Loons". Condor 55 (4): 211–214. doi:10.2307/1364769.
  6. ↑ Brodkorb, Pierce (1963). "Catalogue of fossil birds. Part 1 (Archaeopterygiformes through Ardeiformes)". Bulletin of the Florida State Museum, Biological Sciences 7 (4): 179–293 (224).
  7. ↑ T. Demere. 1986. The fossil whale, Balaenoptera davidsonii (Cope 1872), with a review of other Neogene species of Balaenoptera (Cetacea: Mysticeti). Marine Mammal Science 2(4):277-298
  8. ↑ W. K. Gregory and R. Kellogg. 1927. A fossil porpoise from California. American Museum Novitates 269:1-7
  9. ↑ Rachel A. Racicot, Thomas A. Deméré, Brian L. Beatty, Robert W. Boessenecker. Unique Feeding Morphology in a New Prognathous Extinct Porpoise from the Pliocene of California. Current Biology, 13 March 2014 DOI: 10.1016/j.cub.2014.02.031
  10. ↑ A. Berta and T. A. Demere. 1986. Callorhinus gilmorei n. sp., (Carnivora: Otariidae) from the San Diego Formation (Blancan) and its impliations for otariid phylogeny. Transactions of the San Diego Society of Natural History 21(7):111-126
  11. ↑ 11.0 11.1 T. A. Demere. 1994. Two new species of fossil walruses (Pinnipedia: Odobenidae) from the Upper Pliocene San Diego Formation, California. Proceedings of the San Diego Society of Natural History 29:77-98

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