''Omnidens amplus'', meaning "large all-tooth", is an extinct species of large

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was 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 ...

animal known only from a series of large mouth apparatus, originally mistaken as the mouthparts of

anomalocaridid Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. They may be referred to as radiodonts, radiodontans, radiodontids, anomalocarids, or anomalocaridids, although the last two origi ...

s. When first named, it was interpreted as a giant

priapulid Priapulida (priapulid worms, from Gr. πριάπος, ''priāpos'' 'Priapus' + Lat. ''-ul-'', diminutive), sometimes referred to as penis worms, is a phylum of unsegmented marine worms. The name of the phylum relates to the Greek god of fertility ...

, but is now considered a

panarthropod Panarthropoda is a proposed animal clade containing the extant phyla Arthropoda, Tardigrada (water bears) and Onychophora (velvet worms). Panarthropods also include extinct marine legged worms known as lobopodians ("Lobopodia"), a paraphyletic gr ...

. Its mouth apparatus closely resembles that of the smaller gilled lobopodian ''

Pambdelurion ''Pambdelurion'' is an extinct genus of panarthropod from the Cambrian aged Sirius Passet site in northern Greenland. Like the morphologically similar ''Kerygmachela'' from the same locality, ''Pambdelurion'' is thought to be closely related to ar ...

'', indicating it is likely to have been a close relative of that species, with which it may be synonymous. With a maximum estimated body length of , ''Omnidens'' is suggested to have been the largest known free-living Cambrian organism. ''Omnidens'' fossils are found in the

Maotianshan Shales The Maotianshan Shales are a series of Cambrian, Early Cambrian deposits in the Chiungchussu Formation, famous for their ''Lagerstätte, Konservat Lagerstätten'', deposits known for the exceptional preservation of fossilized organisms or traces. ...

Description

''Omnidens'' is only known from mouthparts. The preserved mouthparts would have formed a short muscular, potentially protrusible pharynx surrounded by circles of spiny sclerites, which were reminiscent of the scalids of

priapulids Priapulida (priapulid worms, from Gr. πριάπος, ''priāpos'' 'Priapus' + Lat. ''-ul-'', diminutive), sometimes referred to as penis worms, is a phylum of unsegmented marine worms. The name of the phylum relates to the Greek god of fertility ...

kinorhynchs Kinorhyncha ( grc, κινέω, kīnéō, I move, ' "snout") is a phylum of small marine invertebrates that are widespread in mud or sand at all depths as part of the meiobenthos. They are also called mud dragons. Modern species are or less, ...

, and

loriciferans Loricifera (from Latin, '' lorica'', corselet (armour) + ''ferre'', to bear) is a phylum of very small to microscopic marine cycloneuralian sediment-dwelling animals that had been determined to be 37 described species, in 9 genera, bu ...

. The inside of the pharynx was also lined with several rows of pharyngeal sclerites. Based on the large size of its preserved mouthparts, ''Omnidens'' is estimated to have reached a length of up to . Its overall appearance was likely similar to that of its close relative ''Pambdelurion''. Spines preserved near the mouthparts of ''Omnidens'' may belong to frontal appendages like those of other stem-group arthropods.

Classification

''Omnidens'' is classified as a

stem-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

arthropod. It is so similar to ''Pambdelurion'' that the two taxa may be synonymous, but no ''Pambdelurion'' specimens are known from the same strata as ''Omnidens''. It is possible that ''Omnidens'' mouthparts belong to the contemporary lobopodians ''

Megadictyon ''Megadictyon'' is a genus of Cambrian lobopodian with similarities to ''Jianshanopodia'' and '' Siberion''. Occasionally mis-spelt ''Magadictyon''. Megadictyon is a large lobopodian, with body length (excluding appendages) possibly up to 20 c ...

'' or ''

Jianshanopodia ''Jianshanopodia decora'' is a Cambrian lobopodian. Its frontal, grasping appendages bear wedge-shaped plates. Its limbs branch, instead of being tipped with claws as many lobopods' are. It has a sediment-filled gut surrounded by serially repea ...

''.

Distribution

''Omnidens'' is a member of the Chengjiang Biota of China, which dates to approximately 520 Ma, during

Cambrian Stage 3 Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 and precedes Cambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approxi ...

. ''Omnidens''-like mouthparts have also been found in the slightly younger Xiaoshiba Lagerstätte. ''Pambdelurion'', which has mouthparts nearly identical to those of ''Omnidens'', is from the

Sirius Passet Sirius Passet is a Cambrian Lagerstätte in Peary Land, Greenland. The Sirius Passet Lagerstätte was named after the Sirius sledge patrol that operates in North Greenland. It comprises six places in Nansen Land, on the east shore of J.P. Koch F ...

Lagerstätte of Greenland.

History

The first-described specimen of ''Omnidens'' was first described in

1994 File:1994 Events Collage.png, From left, clockwise: The 1994 Winter Olympics are held in Lillehammer, Norway; The Kaiser Permanente building after the 1994 Northridge earthquake; A model of the MS Estonia, which Sinking of the MS Estonia, sank in ...

. At the time, it was interpreted as the oral cone of an anomalocaridid, and it was used as evidence to claim that anomalocaridids could reach a maximum body length of up to . ''Omnidens'' fossils were later described as specimens of ''

Peytoia ''Peytoia'' is a genus of hurdiid radiodont that lived in the Cambrian period, containing two species, ''Peytoia nathorsti'' from the Miaolingian of Canada and ''Peytoia infercambriensis'' from Poland, dating to Cambrian Stage 3. Its two frontal ...

'' and ''

Parapeytoia ''Parapeytoia'' was a prehistoric arthropod that lived over 530 million years ago (Cambrian Stage 3) in the Maotianshan shales of prehistoric China. It was interpreted as an anomalocaridid (radiodont) with legs, but later studies reveal it was ...

'' until finally being recognized as a distinct species in

2006 File:2006 Events Collage V1.png, From top left, clockwise: The 2006 Winter Olympics open in Turin; Twitter is founded and launched by Jack Dorsey; The Nintendo Wii is released; Montenegro 2006 Montenegrin independence referendum, votes to declare ...

and named ''Omnidens amplus''. At this time, it was reinterpreted as a gigantic priapulid, at least long, far exceeding most known priapulids in size. ''Omnidens'' was later identified as a close relative of the gilled

lobopodian The lobopodians, members of the informal group Lobopodia (from the Greek language, Greek, meaning "blunt feet"), or the formally erected phylum Lobopoda Cavalier-Smith (1998), are panarthropods with stubby legs called lobopods, a term which may ...

''Pambdelurion''.

References

{{Taxonbar, from=Q7090378 Cambrian animals Prehistoric protostome genera Fossil taxa described in 2006 Maotianshan shales fossils Cambrian genus extinctions