Boletín de la Sociedad Geológica Mexicana

Volumen 65, núm. 2, 2013, p. 235-248

An exceptionally preserved upogebiid (Decapoda: Reptantia) from the Eocene of California

Carolin Haug1,*, Torrey Nyborg2, Francisco J. Vega3

1 Department of Cytology and Evolutionary Biology, Zoological Institute and Museum, University of Greifswald, Soldmannstrasse 23, 17487 Greifswald, Germany.
2 Department of Earth and Biological Sciences, Loma Linda University, Loma Linda California, 92350, United States of America.
3 Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, 04510 México, D.F., México.

* This email address is being protected from spambots. You need JavaScript enabled to view it.


 Construction excavation within member “B” of the middle Eocene-aged Santiago Formation at Bressi Ranch in the southern part of the City of Carlsbad, California, USA, have produced exceptionally preserved upogebiid fossils. While most fossil upogebiids are only known fragmentarily, the specimens described here are preserved as relatively complete articulated specimens. Preserved structures include: the cephalothoracic shield with a short rostrum, a well-developed cervical groove and anterior coarse tuberculation; the pleon, with a characteristic trapezoidal first tergite and the second tergite representing the largest of the series; the appendages including (fragmentary) maxillipeds two and three, and the five walking limbs; the tail fan with uropods with both sub-triangular rami possessing bulging anterior edges and one (endopod) or two (exopod) keels running in parallel to the anterior bulging edge, the exopod lacking a diaresis, and the telson being sub-rectangular with a median suture. Exceptional minute details preserved are the bases of setae on the uropods and muscles in pleomere six. These muscles show fiber bundles about 80 µm in diameter, and individual fibers about 10 µm in diameter. The specimens were documented with up-to-date imaging techniques, including stereo photography or depth-map-based surface reconstructions. Due to the exceptional preservation, the fossils can be recognized as an upogebiid of the species Upogebia aronaesp. nov. As numerous specimens have been found at that locality, this discovery indicates similarly dense populations as seen in modern fauna.

Keywords: Upogebiidae, fossilized muscles, paleo-population, calcium phosphate, 3D-imaging.