Lemdadella
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Lemdadella
Sdzuy, 1978
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Lemdadella is an extinct genus of redlichiid trilobites that lived during the late Atdabanian stage,[1] which lasted from 530 to 524 million years ago during the early part of the Cambrian Period.
Distribution
- Lemdadella sp. occurs in the Lower Cambrian of Morocco (Botomian, Ounein A bioherm, Lemdad 1 section, High Atlas )[2]
- Lemdadella linaresae was collected in the Lower Cambrian of Spain (Atdabanian, Pedroche Formation, Member 1, Puente de Hierro Section)[3]
- Lemdadella sp. was found in the Lower Cambrian of Antarctica (Toyonian, Shackleton Limestone; BC-BD collections)[4]
- Lemdadella antarcticae occurs in the Lower Cambrian of Antarctica (Atdabanian, Shackleton Limestone; BC-BD collections)[5]
Description
Glabella gently tapered forward. At the midline, a ridge between the glabella and the border of the cephalon (a so-called plectrum) may be present. Crescent-shaped eye-ridges. Thorax not divided in prothorax and opisthothorax, no macropleural segment.[6]
Biostratigraphy
Lemdadella is currently the oldest trilobite genus known, dating back to about ~521 million years ago. The International Commission on Stratigraphy has proposed that the first appearance datum of trilobites should be used as the lower boundary of Cambrian Series 2 and Cambrian Stage 3.[7] If this proposal will be defined as a GSSP, it will most likely use the first appearance of Lemdadella, a species of Lemdadella, or a trilobite zone that includes Lemdadella. The age and global distribution of Lemdadella are therefore of key importance for the Stratigraphy of the Cambrian.[8]
The following trilobite zones contain Lemdadella (Brackets contain geographic distribution):[8]
- Fallotaspis zone (Spain, Laurentia)
- Eoredlichia-Yunnanocephalus zone (Antarctica)
References
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