A Triassic giant amphipod from Nevada, USA

Journal of Crustacean Biology (Impact Factor: 1.08). 11/2013; 33(5). DOI: 10.1163/1937240X-00002192


The fossil giant amphipod Rosagammarus minichiellus n. gen., n. sp. occurs in Triassic limestone (Luning Formation, west-central Nevada) in association with giant ichthyosaurs (Shonisaurus sp.) and the deep-water trace fossil Protopaleodictyon ichnosp. Fossil pereion and pereiopod morphology suggest affinities with the Acanthogammaridae, a freshwater amphipod family largely endemic to Lake Baikal. The large size (17 cm) of the Triassic amphipod shows that supergiant, deep marine amphipods comparable to modern Alicella gigantea Chevreux, 1899 were extant during the early Mesozoic. By analogy with Alicella gigantea, Rosagammarus minichiellus n. gen., n. sp. was a necrophagous, benthopelagic scavenger that fed on ichthyosaur and other sea floor carcasses. Rosagammarus minichiellus n. gen., n. sp. appears to be the oldest known fossil amphipod. This discovery extends the known geological range of Amphipoda by at least 170 million years.

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    Paläontologische Zeitschrift 01/2014; 89:399–433. · 1.48 Impact Factor
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    ABSTRACT: The Upper Carnian-Lower Norian (Upper Triassic) Luning Formation at Berlin-Ichthyosaur State Park (BISP) in central NV (USA) has been sampled using for the first time the bed-by-bed approach for ammonoids, pelagic bivalves, and conodonts, more than 60 years after its first description by Silberling (U.S. Geological Survey Professional Paper 322: 1–63, 1959). BISP is historically important for the definition of the uppermost Carnian of the North American Triassic chronostratigraphic scale and is known worldwide as one of the most important ichthyosaur Fossil-Lagerstätte because of its extraordinary record of 37 articulated, large-sized specimens of Shonisaurus popularis. Nearly 190 ammonoids were collected from two stratigraphic sections, documenting all the latest Carnian to Early Norian ammonoid faunas previously described by Silberling. Halobiids were collected from five levels, and the first report of conodonts from BISP includes faunas from 13 levels. The ~340-m thick Brick Pile section, the most complete in the study area, includes the uppermost Carnian Macrolobatus Zone, which provides conodont faunas of the lower primitia zone and Halobia septentrionalis. The 200-m thick lowermost Norian Kerri Zone, which begins 52 m above the Macrolobatus Zone, yields conodonts of the upper primitia zone in its lower part, together with H. cf. beyrichi and H. cf. selwyni. The ichthyosaur-bearing interval, whose stratigraphic position has been interpreted quite differently by previous authors, is documented in the uppermost Carnian Macrolobatus Zone and is characterized by rich Tropites-dominated ammonoid faunas and by the onset of Halobia. All models proposed by various workers to explain the unusual ichthyosaur record are discussed and an additional explanation for the main ichthyosaur-bearing bed is proposed. The new hypothesis is that a harmful algal bloom (HAB) may have been the trigger for the mass mortality recorded in this level. Although the C/N boundary in the Brick Pile section lies within a 52 m interval that presently lacks paleontologic data, this succession is included in a small group of sections that are expected to contribute to the definition of the GSSP of the Norian stage. Correlation of the Brick Pile section with the best Carnian/Norian sections in northeastern British Columbia is discussed. Compared to the British Columbia Juvavites Cove and the GSSP candidate Black Bear Ridge sections, the Brick Pile section exhibits an ammonoid and Halobia record that is slightly more similar to that of the Tethyan sections. Correlation of the Brick Pile section with the second GSSP candidate Pizzo Mondello (Sicily, Italy) well demonstrates the significant problems encountered in calibration of the Tethyan and North American scales.
    Paläontologische Zeitschrift 09/2014; 89(3). DOI:10.1007/s12542-014-0244-2 · 1.48 Impact Factor
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    ABSTRACT: Arthropods are a major component of the marine zooplankton, functioning as intermediates between primary producers and tertiary consumers in pelagic food webs. They have likely occupied the water column ecospace since the early Cambrian, co-evolving with several major plankton groups through the Phanerozoic. Analysis of the fossil record of arthropods indicates that a zooplanktonic lifestyle has arisen independently across several arthropod groups, and that the arthropod body plan has shown adaptability to fundamental environmental change. Key anatomical adaptations and reproductive strategies that are compatible with and/or facilitate a zooplanktonic lifestyle include well-developed swimming appendages, buoyancy, an active metabolism supported by efficient respiration, visual or photoreception organs for use in detecting mates, food and predators, and the nurturing of young within the exoskeleton. Many of these characters are apparent in the earliest record of arthropods. The development and diversification of arthropod zooplankton into the food chain helped enable large secondary and tertiary consumers to enter the water column and also contributed to the export of organic matter to the seabed via the faecal stream. Although the fossil record of arthropod zooplankton is extremely poor for most of the Phanerozoic, their position in marine food webs suggests they have been fundamental to rebuilding marine trophic structure following major extinction events, and to maintaining marine plankton diversity through Phanerozoic time.
    Earth-Science Reviews 02/2015; DOI:10.1016/j.earscirev.2015.02.003 · 7.89 Impact Factor

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