Abstract
Ontogeny, cryptogenesis, and the origin of the Whiterock trilobite fauna
Abstracts with programs - Geological Society of America, Vol.31(7), p.138
Geological Society of America, 1999 annual meeting
1999
Abstract
The majority of post-Cambrian trilobite orders appeared during the Early Ordovician, but their relationship to Cambrian taxa is unknown and their origin is obscure, or "cryptogenetic". As a result, the high-level phylogeny of trilobites is largely unresolved, and cryptogenesis is the most significant outstanding problem in the evolutionary history of the group. The difficulties in bridging the Cambro-Ordovician phylogenetic "gap" are so profound that it has even been suggested that post-Cambrian clades represent iterative derivations from soft-bodied trilobitomorph ancestors. The problem has direct bearing on the pattern of global events during the Ordovician. The Whiterock Fauna is a major group of trilobite familial clades which diversified rapidly during the Ordovician Radiation to dominate trilobite communities and account for all post-Ordovician trilobite diversity. Almost all members of the Whiterock Fauna belong to orders with cryptogenetic origins. Hence, pending progress, the relationship between post-Ordovician and Cambrian trilobites remains essentially unknown. The early ontogeny of post-Cambrian trilobite clades is well known, and larval synapomorphies help define all of the major groups. In contrast, ontogenetic information is lacking for most Cambrian taxa. It has been suggested that new finds of Cambrian larvae offer the best hope for resolving cryptogenesis. Here we present the first evidence for the occurrence of two major post-Cambrian trilobite orders in Cambrian rocks, based on complete silicified growth series of Marjuman age from Nevada, USA. The fauna records all ontogenetic stages for at least 27 species, including the first unequivocal Cambrian members of the orders Proetida, and possibly Phacopida. The discoveries suggest that "post-Cambrian" groups may in fact be quite common in the Laurentian Upper Cambrian. Additional recent discoveries of silicified faunas in the Cambrian of the Great Basin offer hope for resolution of the cryptogenesis problem, and a better understanding of the major features of Cambro-Ordovician trilobite evolution.
Details
- Title: Subtitle
- Ontogeny, cryptogenesis, and the origin of the Whiterock trilobite fauna
- Creators
- Jonathan M Adrain - University of IowaStephen R Westrop - University of Oklahoma
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.31(7), p.138
- Conference
- Geological Society of America, 1999 annual meeting
- Publisher
- Geological Society of America (GSA)
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, 1999 annual meeting
- Language
- English
- Date published
- 1999
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240911002771
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