Amplectobeluidae

Amplectobeluidae
Amplectobelua (left) and Lyrarapax (right)
Kingdom:	Animalia
Stem group:	Arthropoda
Class:	†Dinocaridida
Order:	†Radiodonta
Family:	†AmplectobeluidaePates et al., 2019
†Amplectobelua
†Guanshancaris
†Houcaris?
†Lyrarapax
†Ramskoeldia
†Shucaris?

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Amplectobeluidae is a clade of Cambrian radiodonts. It currently includes five definitive genera, Amplectobelua, Lyrarapax, Ramskoeldia, Guanshancaris and a currently unnamed genus from the lower Cambrian aged Sirius Passet site in Greenland. There is also a potential fifth genus, Houcaris, but that genus has become problematic in terms of its taxonomic placement.

In 2014, Amplectobeluidae was defined as the most inclusive clade including Amplectobelua symbrachiata but not Anomalocaris canadensis, Tamisiocaris borealis, or Hurdia victoria.

Amplectobeluids could be recognized by frontal appendages with well-developed first distal endite, which forming a pincer-like structure that presumably better suited for a grasping function. Complete body fossils of amplectobeluids are only known by Amplectobelua and Lyrarapax, both showing combination of characters resembling Anomalocaris (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).

Early in 2014, "Anomalocaris" kunmingensis was tentatively assigned to Amplectobelua by Vinther et al. Later that year, however, the discoverers of Lyrarapax unguispinus ignored that assessment and created a genus within Amplectobelua sensu Vinther et al. An indeterminate frontal appendage assignable to this group is known from the Parker Slate of Vermont.

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

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