The Upper and Lower Fezouata formations of Morocco are Burgess shale-type deposits dating to the Lower Ordovician, filling an important preservational window between the common Cambrian lagerstätten and the Late Ordovician Soom shale. In the fossilized fauna were numerous organisms previously thought to have died out after the mid-Cambrian.
Over 1500 non-mineralized specimens, representing 50 distinct taxa that have a composition similar to earlier Burgess Shale type biotas, have been recovered from the formations in addition to a less abundant shelly fauna. The make-up of the community varies significantly through the stratigraphic sequence, with both abundances and faunal composition changing as time progresses. Small (1–3 mm wide) burrows are present in the sediment, but major burrowing is absent; this may suggest a paucity of oxygen in the water or sediment. Particularly notable is the presence of bryozoa and graptolites, forms that are absent in the Cambrian period. Diverse echinoderms indicate a normal range of salinity, and the overall shelly assemblage is not significantly different from the normal shelly fauna expected in open Ordovician waters. The non-mineralized cohort contains a range of forms familiar from the Burgess Shale: Demosponges, lobopods, barnacles, annelids, anomalocaridids, possible halkieriids, marrellomorphs, paleoscolecid worms, naraoiids, skaniids as well as the expected problematica. Other Ordovician oddballs are also present, including mitrates, machaeridia, cheloniellids and horseshoe crabs in abundance.
The fossiliferous strata were deposited in quiet, deep waters, below the influence of wave action in all but the fiercest of storms. Such storms, or similar high-energy events, would have mobilized sediment that could be quickly deposited, trapping animals and leading to their preservation. Consequently, the assemblage is dominated by benthic organisms.
Fossils of the Fezouata formation, which are usually squashed flat (although some do retain some degree of their original three-dimensionality) are often coated with a dusting of pyrite, and tin??; this aspect of the fossil preservation is very similar to that at Chengjiang. Non-mineralized appendages are often preserved.
The fossils occur within an area of 500 km2, in southeast Morocco's Draa Valley, north of Zagora. Stratigraphically productive layers are found through a 1.1 km-thick column of rock that spans the Tremadocian and Floian epochs.
- Van Roy, P.; Orr, P. J.; Botting, J. P.; Muir, L. A.; Vinther, J.; Lefebvre, B.; Hariri, K. E.; Briggs, D. E. G. (2010). "Ordovician faunas of Burgess Shale type". Nature 465 (7295): 215–8. Bibcode:2010Natur.465..215V. doi:10.1038/nature09038. PMID 20463737.
- (BBC News) Victoria Gill, "Fossil find resolves ancient extinction mystery": accessed 13 May 2010
- Botting, J. (2007). "‘Cambrian’ demosponges in the Ordovician of Morocco: Insights into the early evolutionary history of sponges". Geobios 40 (6): 737–748. doi:10.1016/j.geobios.2007.02.006.
- Van Roy, P.; Briggs, D. E. G. (2011). "A giant Ordovician anomalocaridid". Nature 473 (7348): 510–513. doi:10.1038/nature09920.
- Lefebvre, B.; Botting, J. (2007). "First report of the mitrate Peltocystis cornuta Thoral (Echinodermata, Stylophora) in the Lower Ordovician of central Anti-Atlas (Morocco)". Annales de Paléontologie 93 (3): 183. doi:10.1016/j.annpal.2007.06.003.
- Vinther, J.; Van Roy, P.; Briggs, D. (2008). "Machaeridians are Palaeozoic armoured annelids". Nature 451 (7175): 185–188. Bibcode:2008Natur.451..185V. doi:10.1038/nature06474. PMID 18185586.
- Van Roy, P; Lefebvre, B; El Hariri, K; Hafid, A (2008). Exceptionally Preserved Faunas from the Lower Ordovician of the Anti-Atlas, Morocco (PDF). First international Conference and Exhibition, Marrakech, Morroco.
- Jones, N. (2010). "Weird wonders lived past the Cambrian". Nature. doi:10.1038/news.2010.234.
|Preceded by Proterozoic Eon||Phanerozoic Eon|
|Paleozoic Era||Mesozoic Era||Cenozoic Era|