The Fezouata Formation or Fezouata Shale is a geological formation in Morocco which dates to the Early Ordovician.[2][3][4][5] 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.[6] 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.
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.[6] The make-up of the community varies significantly through the stratigraphic sequence, with both abundances and faunal composition changing as time progresses.[6] 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.[6] Particularly notable is the presence of bryozoa and graptolites,[6] 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.[6] The non-mineralized cohort contains a range of forms familiar from the Burgess Shale: Demosponges,[7]lobopods, barnacles, annelids, radiodonts (e.g. Aegirocassis),[8] possible halkieriids, marrellomorphs, paleoscolecid worms, nektaspids, skaniids as well as the expected problematica. Other Ordovician oddballs are also present, including mitrates,[9]machaeridians,[10]cheloniellids and xiphosurans in abundance.[6]
Depositional setting
South Polar paleogeography of the Middle Ordovician, 460 Ma
The fossiliferous strata were deposited just above storm wave base (offshore to lower shoreface transition), at between 50 and 150 metres (160 and 490ft) water depth. Organisms were likely buried in situ.[11] 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.[6][12] Consequently, the assemblage is dominated by benthic organisms.[6]
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.[6] Non-mineralized appendages are often preserved.[6] While the formation as a whole is over 1,000 metres (3,300ft) thick, only two intervals, 25 metres (82ft) and 15 metres (49ft) thick, provide exceptional preservation.[13][14] Both of these intervals are located near the top of the lower formation, corresponding to the Araneograptus murrayi and Hunnegraptus copiosusgraptolite zones respectively.[11]
Location and stratigraphy
The fossils occur within an area of 500 square kilometres (190sqmi), in southeast Morocco's Draa Valley, north of Zagora. Stratigraphically productive layers are found through a 1.1 kilometres (0.68mi)-thick column of rock that spans the Tremadocian and Floian epochs.[6] Two stratigraphic intervals of the formation are fossiliferous: the lower is Late Tremadocian and sits 260 to 330 metres (850 to 1,080ft) above the base of the formation; the upper, at 570 to 620 metres (1,870 to 2,030ft), is mid-Floian in age.[1]
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.[15][16]
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 Jbeltizagzaouine' 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.'[17]
Apart from the three 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.[19]
Sagenograptus (Araneograptus) murrayi zone and Upper Fezouata
A 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.[22][19]
The largest trilobite individuals in the Fezouata Formation tend to inhabit deep oxygenated waters with minimal influence from storms or larger predators.[23]
Araneograptus murrayi zone up to the?Baltograptus jacksoni zone.[24][25]
A long-spined eyeless raphiophorid which often occurs in distinctive linear clusters.[25] 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.[25] This species is widely distributed in time and is most common in relatively deep (upper offshore) sediments.[24]
A small pilekiinecheirurid, up to 4.8 centimetres (1.9in) long,[23] which is common in relatively deep (upper offshore) sediments.[24] Fossils of this species are known to preserve appendages similar in form to those of Cambrian trilobites.[26] Known from multiple life stages, including late meraspids.[27] Some specimens may have previously been misidentified as Lehua[24] or Parapilekia.[26]
An endemicasaphid. Associated body fossils and trace fossils help to identify this species as the tracemaker for a distinctive resting trace, Rusophycus carleyi.[29] Found at intermediate depths in the transitional zone between shoreface and offshore sediments.[24]
A. aff. jujuanus
Araneograptus murrayi zone,
?Cymatograptus protobalticus zone,
?Baltograptus jacksoni zone
A small and common asaphid up to 6.2 centimetres (2.4in) long,[23] without clear preferences for specific depths.[24]
An 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.[31] Found in relatively shallow (lower nearshore) sediments.[24]
A large endemic dikelokephalinid up to 33.7 centimetres (13.3in) long.[23] Often found in mass death assemblages, possibly for spawning akin to modern horseshoe crabs.[33]
A small eulomid up to 3.8 centimetres (1.5in) long.[23] Found at intermediate depths in the transitional zone between shoreface and offshore sediments.[24]
A very rare[24]artiopodan arthropod in the order Agnostida, which is often considered a group of trilobites. Very small, at up to 0.9 centimetres (0.35in) long.[23]
A large isoteline asaphid up to 28.5 centimetres (11.2in) long, not counting a pronounced spine on the pygidium.[32] 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.[36] Known from multiple life stages, including mid to late meraspids.[27]
A large endemic nileid, up to 23 centimetres (9.1in) long.[23] Sometimes split into multiple species (P. magrebiensis, P. hammondi, P. carmenae, P. cuervoae),[38] but more typically considered a single species.[28][23][27] Known from multiple life stages, including early to late meraspids.[27] Found in relatively shallow (lower nearshore) sediments.[24]
A common nileid with gregarious habits, often associated with graptolite debris at multiple water depths.[39] Some specimens have been fossilized in the process of a mass moulting event, including some of the few known fossils of post-moult trilobites.[40] Known from multiple life stages, including mid to late meraspids.[27]
S. sicardi
?
A small nileid up to 4.5 centimetres (1.8in) long[39]
A marrellid marrellomorph which has not been formally named or described in detail. It had three pairs of cephalic appendages, 13 pairs of trunk appendages, and a cephalic shield with six large setae-bearing spines. Both adult and juvenile specimens are known of this species,[44] including individuals caught in the act of moulting.[45] The name "Furca mauretanica" is an informal nomen nudum for this species, first introduced in a PhD thesis. Multiple marrellid species may be present in the formation.
A liwiidnektaspid with a large cephalon and pygidium and sharply angled thoraxtergites. One of the few liwiid fossils with soft tissue of the digestive system preserved.[46]
Specific echinoderm species may form dense fossil beds in some layers of the formation, a phenomenon which is particularly common in the mid-late Tremadocian (Araneograptus murrayi graptolite zone).[48] Most echinoderm beds are dominated by only a few species, often representatives of stylophorans or the eocrinoid Rhopalocystis, with few other animal fossils. Through nearly the entire the formation, small Rhopalocystis species dominate "meadow"-like ecosystems in shallow waters impacted by storms. In the youngest layers of the formations, diploporites usurp this niche. Conversely, stylophorans are opportunistic colonizers of deeper low-oxygen seabeds in some intervals of the Araneograptus murrayi zone. Echinoderms are uncommon at intermediate depths, which have a higher proportion of brachiopod and trilobite fossils.[48]
Nevertheless, there are quite a few exceptions which contradict these broad rules. Many sites record diverse deep-water ecosystems protected from both storms and insufficient oxygen. Numerous species of echinoderms and other invertebrates coexist at these localities, even if one echinoderm species outnumbers other fossils at any given time. Large Rhopalocystis species, Macrocystella, Plasiacystis, and Balantiocystis are common components of these assemblages.[48]
Fezouata reconstructs the uneven nature of the Cambrian-Ordovician transition of echinoderm faunas. Cosmopolitan Late Cambrian hallmarks (such as cornute stylophorans) maintian their abundance in oxygen-poor areas, while newer groups (crinoids, diploporites, asterozoans) make inroads into more oxygenated waters. The rarity of carbonate platforms and hard substrates in the Gondwanan area delayed the diversification of crinoids and edrioasteroids in the region. This also provided more space for the establishment of a distinctive South Polar ecosystem dominated by eocrinoids, mitrates, solutans, and eventually diploporites.[48]
A common eocrinoid. The dominant echinoderm at sites Z-F26 and Z-F23, which preserve diverse fossil assemblages buried in calm-water fine-grained siltstone of the?Cymatograptus protobalticus zone. Also abundant in higher-energy deposits of the?Baltograptus jacksoni zone.[48]
A locally abundant cornute with a large sample size, allowing for a reconstruction of decay pathways in stylophoran soft tissue and skeletal material.[50]
A common glyptocystitidrhombiferan. Crushed but complete skeletons of this species are abundant at Oued Beni Zoli locality Z-F5, a site preserving a diverse assemblage of storm-influenced siltstone in the Araneograptus murrayi zone.[48]
Araneograptus murrayi zone[48] up to the Baltograptus minutus zone[21]
A common minervaecystid solutan. Paddles of this species are abundant at sites Z-F13c and Z-F24, a pair of diverse faunal assemblages emplaced in sandy storm deposits of the Hunnegraptus copuosus zone.[48][51]
A common and endemic eocrinoid which can be abundant in certain layers. It is a small but robust species often found in densely jumbled fossiliferous lenses. These lenses are interpreted as debris from shallow-water "meadows", uprooted and washed down into deeper areas by storms.[48][52]
R. fraga
Araneograptus murrayi zone
A rare and endemic eocrinoid, similar to R. destombesi in form and preservation style.[48][52]
R. grandis
Araneograptus murrayi zone
A rare and endemic eocrinoid, similar to R. havliceki in form and preservation style.[48][52]
R. havliceki
Araneograptus murrayi zone
A common and endemic eocrinoid. It is a large but fragile species which is often found disarticulated in siltstone beds. Unlike R. destombesi, it was likely a deep-water specialist buried in place.[48][52]
R. zagoraensis
Araneograptus murrayi zone,
Hunnegraptus copiosus zone
A common and endemic eocrinoid, similar to R. destombesi in form and preservation style.[48][52]
A chinianasteridsomasteroid, a sea star-like echinoderm with a broad pentagonal body. Originally described in a new genus, Cantabrigiaster,[54] but subsequently referred to Villebrunaster.[53]
A common bivalve, tentatively identified as one of the oldest lucinids (hatchet shells). It was likely an infaunal filter-feeder capable of rapid vertical movement within sediment. Like modern lucinids, it may have been a specialist in oxygen-poor environments thanks to endosymbioticsulfide-oxidizing bacteria.[55]
A mollusc in the group Sachitida (the proposed clade containing living aculiferans and their extinct stem group relatives such as halkieriids). It had a flattened body with an extensive radula, a mantle covered in bristle-like sclerites, and a single flat calcareous shell on the head.[57]
A common bivalve, tentatively identified as one of the oldest lucinids (hatchet shells). It was likely an infaunal filter-feeder capable of rapid vertical movement within sediment. Like modern lucinids, it may have been a specialist in oxygen-poor environments thanks to endosymbiotic sulfide-oxidizing bacteria.[55]
A common onychochilidparagastropod, an extinct group of gastropod-like molluscs with asymmetrically coiled shells. It was gregarious and primarily found in shallow oxygenated waters represented at the Oued Beni Zoli locality.[59][58]
A very common actinodontid bivalve in the family Redoniidae. It was likely a shallowly infaunal filter-feeder capable of rapid reburial, with the majority of the shell embedded in sediment.[55]
Conodonts from the Fezouata Formation are mostly coniform elements of Early Ordovician species.[60] Overall diversity is rather low, and species which were common in temperate and tropical seas are apparently absent. The Fezouata Formation appears to be an exemplar of the 'subpolar domain', an assemblage of cold-water coastal conodonts native to the South Polar region of the Early Ordovician. Similar conodont faunas are known from Early Ordovician deposits in Central Europe, which was also located near the South Pole. The 'subpolar domain' survived into the Middle Ordovician and expanded into areas now found in the Middle East.[60]
Fezouata conodonts are difficult to correlate to biostratigraphic systems in nearby temperate regions such as Baltica. Most species appear to correspond to the time interval stretching from the Oelandodus elongatus-Acodus deltatus subzone of the Paroistodus proteus zone (uppermost Tremadocian) up through the Prioniodus oepiki zone (lower Floian).[60]
Graptolites in the Fezouata Formation are important for biostratigraphic correlation to other regions. Most species found in the formation are assigned to planktic (graptoloid) groups, though some mesh-shaped taxa (like Araneograptus and Rhabdinopora) may have been transitional between sessile (dendroid) graptolites and free-floating graptoloids.[61] Sessile forms, such as Didymograptus, Dictyonema, Webbyites, and rhabdopleurids, are also present but much more rare.[62]
The graptolites of the Fezouata Formation are distributed over 10 biozones. In order, these zones are: the Anisograptus matanensis zone (1), Rhabdinopora flabelliformis anglica zone (2), “Adelograptus” tenellus zone (3), Aorograptus victoriae zone (4), Araneograptus murrayi zone (5), Hunnegraptus copiosus zone (6),?Cymatograptus protobalticus zone (7),?Baltograptus jacksoni zone (8), Baltograptus minutus zone (9), and the “Azygograptus interval” (10). Not all of the index taxa which these zones are named for are known from the Fezouata Formation. The Tremadocian-Floian boundary is approximately at the level between the Hunnegraptus copiosus and ?Cymatograptus probalticus zones.[61]
The most well-preserved fossils in the Fezouata Formation generally come from strata of the late Tremadocian (late Araneograptus murrayi zone and early Hunnegraptus copiosus zone) and the mid-late Floian (late Baltograptus minutus zone and early "Azygograptus interval").[61]
A basal graptoloid with a mesh-like conical colony form transitional between dendroids (such as Dictyonema) and early graptoloids such as anisograptids.
Tubes of Rhabdopleura-like pterobranchs have been found growing around the edge of a cephalopod shell, one of the few examples of hard substrate to be found in the formation. This association is similar to the ecology reported for Yuknessia from the Burgess Shale.[62]
Many sponges from the Fezouata biota remain unnamed, including protomonaxoniddemosponges (leptomitids, "choiids", hamptoniids, piraniids), a hazeliid, reticulosanhexactinellids (asthenospongiids,[7] etc.), and other indeterminate forms.[64] Many of the sponges have affinities with Cambrian taxa common in Burgess Shale-type faunas.[7] Though at least 27 sponge species have been recorded in the biota, nearly all occurrences are monospecific death assemblages, with the exception of Pirania auraeum, which has a broader and less dense distribution in the formation. Periodic unstable seafloor conditions (potentially related to seasonal disruptions) would have favored species-poor colonization events over short time periods, rather than a stable and diverse equilibrium.[64]
This is unusual relative to other Ordovician sponge ecosystems, such as the Builth Inlier of Wales. Another difference is how Fezouata's sponge fauna consists mostly of protomonaxonids, with a few reticulosans occupying course-grained shallow seabeds. Conversely, in Wales there is a clear succession of diverse and sturdy lithistids and thick-walled hexactinellids in shallow reefs and other energetic areas, with protomonaxonids at intermediate depths, and reticulosans in the deepest and calmest environments.[64]
A palaeoscolecid worm. Though most palaeoscolecids are inferred to be burrowing carnivores, remains from the Fezouata Formation are more consistent with an opportunistic epibenthic lifestyle, patrolling for organic matter on the surface of the seabed.[66][67]
A machaeridian (armored annelid worm). This species is the only machaeridian known to preserve soft tissue and jaw material, helping to demonstrate their affinities with aphroditiformpolychaetes (scaleworms and kin).[10][69]
The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At 508 million years old, it is one of the earliest fossil beds containing soft-part imprints.
The Cambrian is the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran period 538.8 million years ago (mya) to the beginning of the Ordovician period 485.4 mya. Its subdivisions, and its base, are somewhat in flux.
The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period 485.4 Ma to the start of the Silurian Period 443.8 Ma.
The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out.
A lagerstätte is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These formations may have resulted from carcass burial in an anoxic environment with minimal bacteria, thus delaying the decomposition of both gross and fine biological features until long after a durable impression was created in the surrounding matrix. Lagerstätten span geological time from the Neoproterozoic era to the present.
The Tremadocian is the lowest stage of Ordovician. Together with the later Floian Stage it forms the Lower Ordovician Epoch. The Tremadocian lasted from 485.4 to 477.7 million years ago. The base of the Tremadocian is defined as the first appearance of the conodont species Iapetognathus fluctivagus at the Global Boundary Stratotype Section and Point (GSSP) section on Newfoundland.
The Cambrian–Ordovician extinction event, also known as the Cambrian-Ordovician boundary event, was an extinction event that occurred approximately 485 million years ago (mya) in the Paleozoic era of the early Phanerozoic eon. It was preceded by the less-documented End-Botomian mass extinction around 517 million years ago, and the Dresbachian extinction event about 502 million years ago.
The stylophorans are an extinct, possibly polyphyletic group allied to the Paleozoic Era echinoderms, comprising the prehistoric cornutes and mitrates. It is synonymous with the subphylum Calcichordata. Their unusual appearances have led to a variety of very different reconstructions of their anatomy, how they lived, and their relationships to other organisms.
The Burgess Shale of British Columbia is famous for its exceptional preservation of mid-Cambrian organisms. Around 69 other sites have been discovered of a similar age, with soft tissues preserved in a similar, though not identical, fashion. Additional sites with a similar form of preservation are known from the Ediacaran and Ordovician periods.
The Great Ordovician Biodiversification Event (GOBE), was an evolutionary radiation of animal life throughout the Ordovician period, 40 million years after the Cambrian explosion, whereby the distinctive Cambrian fauna fizzled out to be replaced with a Paleozoic fauna rich in suspension feeder and pelagic animals.
The Wheeler Shale is a Cambrian (c. 507 Ma) fossil locality world-famous for prolific agnostid and Elrathia kingii trilobite remains and represents a Konzentrat-Lagerstätte. Varied soft bodied organisms are locally preserved, a fauna and preservation style normally associated with the more famous Burgess Shale. As such, the Wheeler Shale also represents a Konservat-Lagerstätten.
The Pioche Shale is an Early to Middle Cambrian Burgess shale-type Lagerstätte in Nevada. It spans the Early–Middle Cambrian boundary; fossils from the Early Cambrian are preserved in botryoidal hematite, whereas those from the Middle Cambrian are preserved in the more familiar carbon films, and very reminiscent of the Chengjiang County preservation.
Hamptonia is an extinct genus of sea sponge known from the Middle Cambrian Burgess Shale and the Lower Ordovician Fezouata formation. It was first described in 1920 by Charles Doolittle Walcott. 48 specimens of Hamptonia are known from the Greater Phyllopod bed, where they comprise < 0.1% of the community.
Eldoniids or eldonioids are an extinct clade of enigmatic disc-shaped animals which lived in the early to middle Paleozoic. They are characterized by their "medusoid" (jellyfish-shaped) bodies, with the form of a shallow dome opening below to an offset mouth supplemented by filamentous tentacles. Internally, they have a distinctive C-shaped cavity encompassing the gut, as well as hollow radial (radiating) structures arranged around a central ring canal. Most eldoniids are soft-bodied and can only be preserved in lagerstätten, but a few species may have hosted mineralized deposits. Historically, the affinities of eldoniids was enigmatic; recently, they been assessed as cambroernid deuterostomes. Their lifestyle is still an unresolved question; some authors reconstruct eldoniids as free-floating planktonic predators similar to jellyfish, while others argue that they were passive detritivores, embedded within the seabed for much of their life.
The cambroernids are an informally-named clade of unusual Paleozoic animals with coiled bodies and filamentous tentacles. They include a number of early to middle Paleozoic genera noted as 'bizarre" or "orphan" taxa, meaning that their affinities with other animals, living or extinct, has long been uncertain. One leading hypothesis is that cambroernids were unusual ambulacrarian deuterostomes, related to echinoderms and hemichordates. Previously some cambroernids were compared to members of the broad invertebrate clade Lophotrochozoa; in particularly they were allied with lophophorates, a subset of lophotrochozoans bearing ciliated tentacles known as lophophores. However, this interpretation has more recently been considered unlikely relative to the deuterostome hypothesis for cambroernid origins.
Aegirocassis is an extinct genus of giant radiodont arthropod belonging to the family Hurdiidae that lived 480 million years ago during the early Ordovician in the Fezouata Formation of Morocco. It is known by a single species, Aegirocassis benmoulai. Van Roy initiated scientific study of the fossil, the earliest known of a "giant" filter-feeder discovered to date. Aegirocassis is considered to have evolved from early predatory radiodonts. This animal is characterized by its long, forward facing head sclerite, and the endites on its frontal appendages that bore copious amounts of baleen-like auxiliary spines. This animal evolving filter-feeding traits was most likely a result of the Great Ordovician Biodiversification Event, when environmental changes caused a diversification of plankton, which in turn allowed for the evolution of new suspension feeding lifeforms. Alongside the closely related Pseudoangustidontus, an unnamed hurdiid from Wales, the middle Ordovician dinocaridid Mieridduryn, and the Devonian hurdiid Schinderhannes this radiodont is one of the few dinocaridids known from post-Cambrian rocks.
The Waukesha Biota is an important fossil site located in Waukesha County and Franklin, Milwaukee County within the state of Wisconsin. This biota is preserved in certain strata within the Brandon Bridge Formation, which dates to the early Silurian period. It is known for the exceptional preservation of soft-bodied organisms, including many species found nowhere else in rocks of similar age. The site's discovery was announced in 1985, leading to a plethora of discoveries. This biota is one of the few well studied Lagerstätten from the Silurian, making it important in our understanding of the period's biodiversity. Some of the species are not easily classified into known animal groups, showing that much research remains to be done on this site. Other taxa that are normally common in Silurian deposits are rare here, but trilobites are quite common.
The Letná Formation is a Late Ordovician geologic formation of the Prague Basin, Bohemian Massif in the Czech Republic. The formation crops out in the Czech capital, more specifically at Letná Hill, after which the formation is named. The type locality is located at Malá Strana, Holešovice district.
Pseudoangustidontus is a genus of hurdiid radiodont from the Lower Ordovician of Morocco. This genus is known from two described species, P. duplospineus and P. izidigua, with some specimens that are hard to determine which species to belong to. This animal is only known from the Fezouata Formation, a fossil site in Morocco that is of Lagerstätte status, meaning that the fossils from this site are exceptionally preserved. Because of its partial remains, its classification was debated, but with more complete fossils it is identified as radiodont frontal appendage.
Aegirocassisinae is a subfamily of radiodonts from the lower Paleozoic era. It belongs to the larger hurdiidae family, which were the most diverse and long lasting radiodonts. The members of this subfamily are restricted to the lower-Ordovician-aged Fezouata Formation of Morocco. Currently only two genera are included: Aegirocassis and Pseudoangustidontus. These two genera possess large Baleen-like auxiliary spines on their frontal appendages, which suggests a suspension feeding lifestyle for the group. These radiodonts are some of the few known from sediments beyond the Cambrian period. This subfamily shows that following the Great Ordovician Biodiversification Event, which saw a rise in the plankton population in the worlds oceans, suspension feeding became more common in radiodonts then other feeding styles. It also seems that due to the evolution of new predators, like large nautiloid cephalopods, and other arthropod groups like the eurypterids, the radiodonts evolved suspension feeding lifestyles in order to minimize competition for food.
↑ 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. Bibcode:2007AnPal..93..183L. doi:10.1016/j.annpal.2007.06.003.
↑ Saleh, Farid; Candela, Yves; Harper, David A. T.; Polechová, Marika; Lefebvre, Bertrand; Pittet, Bernard. "Storm-Induced Community Dynamics in the Fezouata Biota (Lower Ordovician, Morocco)". (limited access to full article) geoscienceworld.org. Society for Sedimentary Geology PALAIOS, print edition: 21 December 2018, pp. 535-541 (Vol. 33, No. 12). Retrieved 1 March 2019.
↑ Fortey, Richard A. (2009). "A New Giant Asaphid Trilobite from the Lower Ordovician of Morocco". Memoirs of the Association of Australasian Palaeontologists. 37: 9–16.
1 2 Fortey, Richard A. (2012). "The first known complete Lichakephalid trilobite, lower Ordovician of Morocco". Memoirs of the Association of Australasian Palaeontologists. 42: 1–7.
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