''Amplectobeluidae'' is a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

radiodonts Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. Radiodonts are distinguished by their distinctive frontal appendages, which are morphologically diverse and were used for a variety ...

. It currently includes five definitive genera, ''

Amplectobelua ''Amplectobelua'' (meaning "embracing beast") is an extinct genus of late Early Cambrian amplectobeluid radiodont, a group of stem arthropods that mostly lived as free-swimming predators during the first half of the Paleozoic Era. Anatomy '' ...

'', '' Lyrarapax'', '' Ramskoeldia'', '' Guanshancaris'' and a currently unnamed genus from the lower Cambrian aged

Sirius Passet Sirius Passet is a Cambrian Lagerstätte in Peary Land, Greenland. The Sirius Passet Lagerstätte was named after the Slædepatruljen Sirius, Sirius sledge patrol that operates in North Greenland. It comprises six places in Nansen Land, on the eas ...

site in

Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...

. There is also a potential fifth genus, ''

Houcaris ''Houcaris'' is a possibly paraphyletic radiodont genus, tentatively assigned to either Amplectobeluidae, Anomalocarididae or Tamisiocarididae, known from Cambrian Series 2 of China and the United States. The type species is ''Houcaris saron'' ...

'', but that genus has become problematic in terms of its taxonomic placement.

Definition

In 2014, ''Amplectobeluidae'' was defined as the most inclusive clade including '' Amplectobelua symbrachiata'' but not ''

Anomalocaris canadensis ''Anomalocaris'' (from Ancient Greek , meaning "unlike", and , meaning "shrimp", with the intended meaning "unlike other shrimp") is an extinct genus of radiodont, an order of early-diverging stem-group marine arthropods. It is best known from ...

'', '' Tamisiocaris borealis'', or '' Hurdia victoria''.

Description

Amplectobeluids could be recognized by frontal appendages with well-developed first distal endite, which forming a

pincer Pincer may refer to: *Pincers (tool) *Pincer (biology), part of an animal *Pincer ligand, a terdentate, often planar molecule that tightly binds a variety of metal ions *Pincer (Go), a move in the game of Go *"Pincers!", an episode of the TV series ...

-like structure that presumably better suited for a grasping function. Complete body fossils of amplectobeluids are only known by ''

'' and '' Lyrarapax'', both showing combination of characters resembling ''

Anomalocaris ''Anomalocaris'' (from Ancient Greek , meaning "unlike", and , meaning "shrimp", with the intended meaning "unlike other shrimp") is an extinct genus of radiodont, an order of early-diverging stem-group marine arthropods. It is best known fro ...

'' (i.e. streamlined body; small head with ovoid sclerites; well-developed swimming flaps; a pair of caudal furcae). Another distinctive features only known in amplectobeluid genera were pairs of gnathobase-like structures (known by ''Amplectobelua'' and '' Ramskoeldia''), or an oral cone with combination of tetraradial arrangement and scale-like nodes (known by ''Lyrarapax'' and ''Guanshancaris'').

Classification

Early in 2014, ''"Anomalocaris" kunmingensis'' was tentatively assigned to ''

'' by Vinther ''et al''. Later that year, however, the discoverers of '' Lyrarapax unguispinus'' ignored that assessment and created a genus within ''

'' ''sensu'' Vinther ''et al''. An indeterminate frontal appendage assignable to this group is known from the Parker Slate of Vermont.

Phylogeny

An ''a posteriori''-weighted phylogenetic analysis in 2014 found the following relationships within the Amplectobeluidae:

References

{{Taxonbar, from=Q17409560 Radiodonta Prehistoric arthropod families