The Fezouata Formation or Fezouata Shale is a geological formation in Morocco which dates to the Early Ordovician. It was deposited in a marine environment, and is known for its exceptionally preserved fossils, filling an important preservational window beyond the earlier and more common Cambrian Burgess shale-type deposits. The fauna of this geological unit is often described as the Fezouata biota, and the particular strata within the formation which exhibit exceptional preservation are generally termed the Fezouata Lagerstätte.
Biota Over 1,500 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. Major burrowing is not present, but there are small (1–3 mm wide) burrows in the sediment, which may indicate that there is not enough 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, radiodonts (e.g. Aegirocassis), possible halkieriids, marrellomorphs, paleoscolecid worms, nektaspidids, skaniids as well as the expected problematica. Other Ordovician oddballs are also present, including mitrates, machaeridians, cheloniellids and xiphosurans in abundance.
Depositional setting
The fossiliferous strata were deposited just above storm wave base (offshore to lower shoreface transition), at between water depth. Organisms were likely buried in situ. Because of its placement above storm wave base, storms would have mobilized sediment that could be quickly deposited, trapping animals and leading to their preservation. Consequently, the assemblage is dominated by benthic organisms.
Preservation 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. While the formation as a whole is over thick, only two intervals, and thick, provide exceptional preservation. Both of these intervals are located near the top of the lower formation, corresponding to the Araneograptus murrayi and Hunnegraptus copiosus graptolite zones respectively.
Location and stratigraphy The fossils occur within an area of , in southeast Morocco's Draa Valley, north of Zagora. Stratigraphically productive layers are found through a -thick column of rock that spans the Tremadocian and Floian epochs. Two stratigraphic intervals of the formation are fossiliferous: the lower is Late Tremadocian and sits above the base of the formation; the upper, at , is mid-Floian in age.
History The Lagerstätten were first identified in the late 1990s when a local fossil collector, Ben Moula, showed some of the finds to a PhD student who was then working in the area.
IUGS geological heritage site In respect of the "exceptional fossil preservation bridging the Cambrian Explosion and the Great Ordovician Biodiversification", the International Union of Geological Sciences (IUGS) included the "Ordovician Fezouata Shale Fossil Site at Jbel Tizagzaouine" in its assemblage of 100 "geological heritage sites" around the world, in a listing published in October 2022. The organisation defines an IUGS Geological Heritage Site as "a key place with geological elements and/or processes of international scientific relevance, used as a reference, and/or with a substantial contribution to the development of geological sciences through history."
Paleobiota After and subsequent literature:
Radiodonts Apart from the four named species of Fezouata radiodonts, three other unnamed species occur in the formation: a third species of Pseudoangustidontus, an aegirocassisine, and a sediment-sifting hurdiid. A potential fourth species of radiodont has been found in the Floian section and is known from probable head sclerites. Radiodonts of the Fezouata FormationGenusSpeciesStratigraphyNotesImagesAegirocassis A. benmoulaeAraneograptus murrayi zone, Baltograptus minutus zone?A giant filter-feeding aegirocassisine hurdiid radiodont. The largest known radiodont and one of the largest known panarthropods, at in length.FalciscarisF. mumakianaSagenograptus (Araneograptus) murrayi zoneA benthivorous hurdiid radiodont around a meter long. Unlike aegirocassisines, it likely sifted through sediment to capture prey, as shown by its less fine enditesPseudoangustidontusP. duplospineusSagenograptus (Araneograptus) murrayi zone and Upper FezouataA filter-feeding aegirocassisine hurdiid radiodont. Originally considered enigmatic until 2023, where it was redescribed as a radiodont. Like the contemporary Aegirocassis, this genus was most likely a filter feeder, but it could have preyed upon larger food.P. izdiguaSagenograptus (Araneograptus) murrayi zoneP. sp.Sagenograptus (Araneograptus) murrayi zone
Trilobites The largest trilobite individuals in the Fezouata Formation tend to inhabit deep oxygenated waters, with minimal influence from storms or larger predators. Trilobites of the Fezouata FormationGenusSpeciesStratigraphyNotesImagesAgerinaA. quadrata?Cymatograptus protobalticus zone, ?Baltograptus jacksoni zoneA leiostegiid which is common at intermediate depths in the transitional zone between shoreface and offshore sediments.AmpyxA. priscusAraneograptus murrayi zone up to the ?Baltograptus jacksoni zone.A long-spined eyeless raphiophorid which often occurs in distinctive linear clusters. These clusters are interpreted as collective behavior akin to modern Palinurus lobsters, either as biological aggregations (for spawning or moulting), or migrating groups due to environmental pressures such as storms. Other trilobites occasionally become entangled with the Ampyx clusters. This species is widely distributed in time and is most common in relatively deep (upper offshore) sediments.AnacheirurusA. adseraiAraneograptus murrayi zoneA small pilekiine cheirurid, up to long, which is common in relatively deep (upper offshore) sediments. Fossils of this species are known to preserve appendages similar in form to those of Cambrian trilobites. Known from multiple life stages, including late meraspids. Some specimens may have previously been misidentified as Lehua or Parapilekia.ApatokephalusA. cf. incisusAraneograptus murrayi zone, ?Cymatograptus protobalticus zoneAn uncommon remopleuridid found in relatively shallow (lower nearshore) sediments.A. sp.Lower Fezouata, Upper FezouataA remopleuridid.AsaphellusA. fezouataensis?Baltograptus jacksoni zoneAn endemic asaphid. Associated body fossils and trace fossils help to identify this species as the tracemaker for a distinctive resting trace, Rusophycus carleyi. Found at intermediate depths in the transitional zone between shoreface and offshore sediments.A. aff. jujuanusAraneograptus murrayi zone, ?Cymatograptus protobalticus zone,
?Baltograptus jacksoni zoneA small and common asaphid up to long, without clear preferences for specific depths.A. sp.Araneograptus murrayi zoneAn asaphid. Known from multiple life stages, including late meraspids.A. stubbsiAraneograptus murrayi zoneA large endemic asaphid up to long. Found in relatively shallow (lower nearshore) sediments.A. tataensisAraneograptus murrayi zone, Upper FezouataAn uncommon medium-sized endemic asaphid. Some specimens have been fossilized with unusual flattened antennae, the only reliable attributions of these structures in asaphids. The antennae may have had a particular sensory function to assist in hunting or scavenging. Found in relatively shallow (lower nearshore) sediments.AsaphopsisA. sp.Lower FezouataA Dikelokephalina-like trilobite.BasilicusB. destombesiBaltograptus jacksoni zoneA large asaphine asaphid up to long.B. sp.A very large asaphine asaphid up to long.B. vidaliA large asaphine asaphid up to long.BathycheilusB. gallicusUpper FezouataA bathycheilid.BavarillaB. sp.Araneograptus murrayi zoneA small bavarillid up to long.B. zemmourensisAraneograptus murrayi zone, Upper FezouataAn endemic bavarillid common in relatively shallow (lower nearshore) sediments.Ceraurinella?C.? sp.Upper FezouataA cheirurid.ColpocorypheC. pradesensis?Baltograptus jacksoni zone, Baltograptus minutus zoneA rare calymenid.C. thorali?Cymatograptus protobalticus zone, Baltograptus minutus zoneA rare calymenid.C. sp.Araneograptus murrayi zone, ?Cymatograptus protobalticus zoneA rare calymenid found in relatively deep (upper offshore) sediments.DactylocephalusD. sp.A large asaphid up to long.DikelokephalinaD. brenchleyiAraneograptus murrayi zoneA large endemic dikelokephalinid up to long. Often found in mass death assemblages, possibly for spawning akin to modern horseshoe crabs.D. sp.Lower FezouataA large dikelokephalinid up to long.Ectillaenus?E.? sp.Baltograptus minutus zoneAn illaenid.EoharpesE. sp.A harpetid.EulomaE. sp.Araneograptus murrayi zone, ?Cymatograptus protobalticus zone,
?Baltograptus jacksoni zoneA small eulomid up to long. Found at intermediate depths in the transitional zone between shoreface and offshore sediments.FouloniaF. peregrinaAraneograptus murrayi zone, ?Baltograptus jacksoni zoneA cheirurid.GeragnostusG. sp.Araneograptus murrayi zone, ?Baltograptus jacksoni zoneA very rare artiopodan arthropod in the order Agnostida, which is often considered a group of trilobites. Very small, at up to long.HarpidesH. sp.A harpidid of questionable occurrence.IndiligensI. sp.Araneograptus murrayi zoneA ptychopariid known from multiple life stages, including mid-stage meraspids.LeptoplastidesL. salteriAnisograptus matanensis zone, Rhabdinopora flabelliformis anglica zoneAn olenid, the only diagnostic member of the family to be found in Africa. Previously misidentified as Beltella.LichakephalusL. stubbsiA large lichakephalid.Megistaspis (Ekeraspis)M. (E.) hammondiAraneograptus murrayi zoneA large isoteline asaphid up to long, not counting a pronounced spine on the pygidium. Some specimens preserving gut traces and appendages showing new anatomical traits not seen in other trilobites. The cephalic appendages hosted long spines capable of combing through sediment for food. This species' feeding behavior may be responsible for Cruziana rugosa, a trace fossil common throughout Ordovician Gondwana. Known from multiple life stages, including mid to late meraspids.NeseuretusN. cf. attenuatus?Cymatograptus protobalticus zone, Baltograptus minutus zoneA calymenid found in particularly shallow sediments.NileusN. deynouxiAraneograptus murrayi zoneA nileid known from multiple life stages, including late meraspids.Nobiliasaphus?N.? sp.A large asaphine asaphid up to long.OgyginusO. forteyi hammondiA very large ogygiocaridinine asaphid, up to long.O. sp.Araneograptus murrayi zoneA very large ogygiocaridinine asaphid, up to long.OrometopusO. sp.Araneograptus murrayi zoneKnown from multiple life stages, including early to late meraspids.ParabathycheilusP. gallicusAraneograptus murrayi zone, ?Cymatograptus protobalticus zone,