Exceptionally preserved ostracodes from a Middle Miocene palaeolake, California, USA

Abstract

Exceptionally well-preserved specimens of a new cypridid ostracod (Crustacea), Raepula ira sp. nov., are described from palaeolake sediments of the Middle Miocene Barstow Formation of the Mud Hills, southern California. This is only the second occurrence of exceptionally preserved ostracods from the Miocene. Based on ages obtained from associated volcanic tuffs the palaeolake sediments were deposited between 16.3 and 15.8 Ma. The ostracods form one element of a diverse lake community dominated by fairy shrimps, copepods, diatoms, larvae of diving beetles, flies and mosquitoes, and body fossils and ephippia of branchiopods and anomopods. The ostracods are preserved three-dimensionally with their soft anatomy replicated in microcrystalline silica. Sub-micron scale details such as sensory setae are preserved, surpassing the resolution of most other ostracodbearing lagerstätten and allowing their biology to be compared with extant taxa.

Copepod Mandible Palynomorphs From the Nolichucky Shale (Cambrian, Tennessee): Implications for the Taphonomy and Recovery of Small Carbonaceous Fossils

“…The three-dimensionally preserved copepod fossils were found in Rainbow Canyon in the Mud Hills, 17 km north of Barstow (southern California; 35.024° N, 117.041° W) along with cypridid ostracod fossils with soft anatomy described by Wilkinson et al (2010).…”

“…The fossil-bearing calcareous concretions were collected in the middle member of the Barstow Formation about halfway between the Rak Tuff (16.3±0.3 mya) and the Oreodont Tuff (15.8±0.3 mya) (Wilkinson et al 2010), the cyclopid fossils therefore likely date back to the latest Burdigalian (or earliest Langhian). The few centimeters large concretions, found over a horizontal distance of about 500 m, are early diagenetic carbonate formed within the lake sediments, i.e.…”

“…1000 m thick lacustrine and fluvial deposits (Park and Downing 2001). Mineralogy of the sediments, the composition of the arthropod fauna (e.g., fairy shrimps, biting midge Dasyhelea) and the presence of halophile diatoms indicated that Barstow lake was a shallow, poorly mixed, saline-alkaline lake in a warm temperate environment moister than today (Park 1995;Park and Downing 2001;Wilkinson et al 2010). Concerning the zoogeographic affinities, Palmer (1957: 244) found that Barstow arthropods did not show "clear-cut resemblance" with the faunas of Central and South America, instead some forms seemed more related to groups now living in Europe, North Africa, Asia Minor and Central Asia (Turkestan), or to taxa distributed in SE Asia and tropical Americas.…”

Subcellular preservation in giant ostracod sperm from an early Miocene cave deposit in Australia

“…The rare occasions that 'soft-parts', i.e. appendages and internal body, are fossilized can reveal exquisite detail and provide unparalleled data on the evolution of the group [7][8][9][10][11][12][13][14][15]. For example, preserved Zenker organs, which are muscular-chitinous pumps used to transfer giant sperm to females [16] (figure 1c), in Cretaceous ostracods have been used as indirect evidence that giant sperm are a long-lived trait in the group [9].…”

A Silurian myodocope with preserved soft-parts: cautioning the interpretation of the shell-based ostracod record

“…Myodocopes typically have weakly calcified valves and, consequently, a scant fossil record [8][9][10][11], which begins in the Late Ordovician [12]. The soft-parts of ostracods are rarely fossilized [13,14]. From the Palaeozoic a single ostracod-type limb is known from the Late Cambrian [15]; a podocopid specimen with some soft-parts [16] and an undescribed, partially open carapace with poorly preserved limbs [17] from the Devonian; and three myodocope species, each based on an essentially completely preserved specimen, from the Herefordshire (Silurian) Konservat-Lagerstätte, UK [18][19][20].…”