Lemdadella

Lemdadella Temporal range: Late Atdabanian PreЄ Є O S D C P T J K Pg N [1]
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Trilobita
Order:	Redlichiida
Suborder:	Redlichiina
Family:	Redlichiidae
Genus:	Lemdadella Sdzuy, 1978
Species
L. spectabilis Sdzuy, 1978 (Type) L. antarcticae Palmer in Palmer and Rowell, 1995 L. linaresae Liñán Guijarro, 1978 L. perejoni Liñán c.s., 2005

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

1. Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (Trilobita entry)". Bulletins of American Paleontology 364: 560. Retrieved 2008-01-12.
2. Geyer, G.; Landing, E.; Heldmaier, W. (1995). "Faunas and depositional environments of the Cambrian of the Moroccan Atlas regions". Beringeria. Special Issue 2: 47–119.
3. Liñán, E.; Dies, M.E.; Vintaned, J.A.G.; Gozalo, R.; Mayoral, E.; Muñiz, F (2005). "Lower Ovetian (Lower Cambrian) trilobites and biostratigraphy of the Pedroche Formation (Sierra de Córdoba, southern Spain)". Géobios 38: 365–381. doi:10.1016/j.geobios.2003.11.007.
4. Palmer, A.R.; Rowell, A.J. (1995). "Early Cambrian trilobites from the Shackleton Limestone of the Central Mountains". Journal of Paleontology Memoir 69 (6): 1–28.
5. Palmer, A.R.; Rowell, A.J. (1995). "Early Cambrian trilobites from the Shackleton Limestone of the Central Mountains". Journal of Paleontology Memoir 69 (6): 1–28.
6. Paterson, R.J.; Jago, J.B. (2006). "New trilobites from the Lower Cambrian Emu Bay Shale Lagerstätte at Big Gully, Kangaroo Island, South Australia.". Memoirs of the Association of Australasian Palaeontologists 32: 43–57. ISSN 0810-8889.
7. "GSSP Table - Paleozoic Era". Retrieved 18 November 2012.
8. Yuan, J.L.; Zhu, X.J.; Lin, J.P.; Zhu, M.Y. (22 September 2011). "Tentative correlation of Cambrian Series 2 between South China and other continents" (PDF). Bulletin of Geosciences: 397–404. doi:10.3140/bull.geosci.1274. Retrieved 23 November 2012.