Trilobite extinctions, facies changes and the ROECE carbon isotope excursion at the Cambrian Series 2–3 boundary, Great Basin, western USA (original) (raw)
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Sundberg, F.A. and L.B. McCollum 2003 Early & Mid Cambrian trilobites Palaeo.pdf
A latest Early Cambrian and earliest Mid Cambrian polymeroid trilobite fauna, consisting of 16 genera and 25 species, is reported from the peritidal deposits of the Mule Spring Limestone and outer-shelf deposits of the Emigrant and Monola formations of Nevada and California. The Mid Cambrian fauna includes a new genus, Tonopahella, and four new species, T. gold®eldensis, Oryctocephalus americanus, Onchocephalites claytonensis, and Syspacephalus variosus. The peri-Gondwana species Oryctocephalus orientalis, Oryctocephalites runcinatus, and Paraantagmus latus are recorded in Laurentia for the ®rst time.
Geological Magazine, 2010
Two completely dissimilar faunal changes occur between the Sunwaptan and Skullrockian Stages (Ptychaspid and Symphysurid ‘Biomeres’) in the uppermost Cambrian on the east Laurentian craton. An undolomitized section in the Little Falls Formation in Washington County, New York, shows a typical ‘biomere’ extinction, with highest Sunwaptan trilobites followed by the abrupt appearance of Cordylodus proavus Zone conodonts and the lowest post-extinction trilobites (Parakoldinioidia Endo) 5.0 m higher. This stage boundary interval is very condensed by comparison with coeval Great Basin and Texas sections. Approximately 70 km southwest, typical pre-extinction taxa (the catillicephalid Acheilops Ulrich and several dikelocephalid species) are shown for the first time to persist well beyond the extinction as they occur with middle C. proavus Zone conodonts (Clavohamulus elongatus or, more likely, Hirsutodontus simplex Subzone). The Ritchie Limestone member of the uppermost Little Falls Formatio...
Quantitative approach of diversity and decline in late Palaeozoic trilobites.
Quantitative data reveal a complex evolution of late trilobite diversity. In the Mid- to early Late Devonian, a series of extinction events led to a drastic taxonomic impoverishment. In the Famennian, while only two orders remained, originations started to compensate still high extinction rates marking the onset of a remarkable diversification. Though interrupted by the major Hangenberg turnover, the general diversification trend accelerated in the Tournaisian whilst extinctions became modest. Originations notably diminished during the Viséan and the Serphukovian, making the diversity to step down at the level of the Frasnian. It has never been much higher thereafter, despite a profound restructuring of trilobite communities in the early Pennsylvanian permitting the progressive domination of ditomopygines. After another drop in the Kasimovian a period of stasis occurred with very low diversity levels and almost no renewal. The last diversification burst took place in the Wordian, but it ceased rapidly in the Capitanian when the degradation of environmental conditions started to inhibit originations. Thus, the extinction of the Trilobita at the end of the Permian resulted from the disappearance of merely a handful of genera.
Trilobite diversity patterns in the Middle Cambrian of southwestern Europe: a comparative study
Palaeogeography Palaeoclimatology Palaeoecology, 1999
This paper describes the pattern of trilobite diversity throughout the Middle Cambrian in two fossiliferous basins of the western Gondwana margin: the Iberian Chains (northeastern Spain) and the Montagne Noire (southern France). The documented fluctuations of species diversity allow us to recognize: (1) a substantial extinction event recorded in latest Early Cambrian times (named Valdemiedes event), which separates the culmination of a widespread decline of trilobites and the stepwise immigration of cosmopolitan invaders; (2) a major trilobite radiation occurring in the earliest Leonian and culminating across the Caesaraugustian/Languedocian transition, in which a peak in diversity of trilobites and carpoids was close to a major flooding surface; (3) a major reduction of trilobite taxa across the early/middle Languedocian transition related to a well-documented regressional trend; and (4) a second immigration of trilobite fauna in the late Languedocian which coincided with trangressional pulses and the establishment of suitable shaly substrates. In addition, we summarize the known trilobite occurrences from the Middle Cambrian of southwestern Europe. Maps of the distribution of some relevant taxa (genera and species) over the western Gondwana margin are documented.
New Mexico Museum of Natural History and Science Bulletin, 2021
Analysis of a sample of more than 2600 fossil specimens from fine-grained siliciclastic deposits of the Bolbolenellus euryparia-Nephrolenellus multinodus trilobite zones of the latest Dyeran (Stage 4), across a craton-to-outer shelf transect of the Cambrian passive margin wedge of southwestern Laurentia, demonstrates several patterns from shallow, proximal settings to those of deeper, offshore environments. These patterns include: 1) a decrease in overall fossil abundance from cratonic/nearshore to offshore settings; 2) higher taxonomic diversity on the inner and middle shelves compared to craton/ nearshore, and lowest diversity on the outer shelf; 3) low degree of articulation of trilobites across all environments (~1% of identifiable trilobite specimens), with fragmentation of sclerites increasing offshore and highest degrees of fragmentation and disarticulation on the outer shelf; and 4) trilobite cephalon size and compass orientation show no discernible pattern across the shelf; trilobite cephala up-down orientation varies by site and shows no clear paleogeographic pattern. These results suggest that sclerite burial rates and possibly population densities were higher in middle shelf to cratonic/ nearshore settings, that possibly fluctuating abiotic conditions in nearshore settings limited taxonomic diversity relative to the open shelf, and that long bottom-exposure times and possibly scavenging near or below storm wave base were more responsible for the disarticulation and breakage of trilobite remains than mechanical transport (current action) in more distal settings.