''Amplectobelua'' (meaning "embracing beast") is an extinct genus of late Early Cambrian amplectobeluid

radiodont 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 original ...

, a group of stem arthropods that mostly lived as free-swimming predators during the first half of the

Paleozoic Era The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ''z ...

Anatomy

The body structures other than frontal appendages are only known from the type species ''Amplectobelua symbrachiata''. Like other

s, ''Amplectobelua'' had a pair of jointed frontal appendages, a head covered by dorsal and lateral sclerites (the latter had been misinterpreted as huge eyes), a limbless body with dorsal gills (setal blades), and a series of flaps on both sides that extended along the length of its body. ''Amplectobelua'' had a specialized frontal appendage, in which it has a distinct 3-segmented shaft region and 12-segmented distal articulated region, and the spine on the fourth segment (first segment of distal articulated region) hooked forward to oppose the tip of the appendage, allowing it to grasp prey like a pincer. ''Amplectobelua'' had 11 pairs of body flaps in total, they are relatively elongated and straight in outline. The size of the flaps decrease posteriory, and each of their frontal margin have rows of vein-like structures (strengthening rays). The neck region have at least 3 pairs of slender, reduced anterior flaps. The trunk terminated with a pair of long furcae (streamers). File:20191221 Radiodonta frontal appendage Amplectobelua.png, Frontal appendages of ''A. symbrachiata'' and ''A. stephenensis''. Note the shaft region of ''A. stephenensis'' is unknown. File:20200103 Radiodonta gnathobase‐like structures.png, Ventral view of a generalized GLS-bearing radiodont, showing 3 pairs of gnathobase‐like structures (GLSs) and corresponded anterior flaps. ''Amplectobelua'' shares a unique feature among radiodonts with ''

Ramskoeldia ''Ramskoeldia'' is a genus of amplectobeluid radiodont described in 2018. It was the second genus of radiodont found to possess gnathobase-like structures (abbreviated as GLS) and an atypical oral cone after '' Amplectobelua''. It was discovered ...

'', in having gnathobase-like structures (GLSs) underneath its neck region, at least 6, up to eight. They functioned like the gnathobases of arthropods, being able to rotate and move to shred prey. They were connected to reduced anterior flaps. Additionally, the mouth (oral cone) of ''Amplectobelua'' were interpreted as different from typical radiodont, lacking the typical ''

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 front ...

''-style oral cone and possessing numerous flat tooth-plates with unclear, but possibly non-radial arrangement.

Species

Two species are known, ''Amplectobelua symbrachiata'' from the Chengjiang biota and ''Amplectobelua stephenensis'' from the later

Burgess Shale 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 old (middle Cambrian), it is one of the earliest fo ...

. ''A. symbrachiata'' is known from complete specimens, while ''A. stephenensis'' is known only from isolated frontal appendages. ''A. stephenensis'' is more advanced, with the frontal appendages being more specialized for grasping: the fourth spine is larger and the spines on outer segments are reduced.

References

Fossil Museum

External links

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Cambrian arthropods Maotianshan shales fossils Anomalocaridids Burgess Shale fossils Cambrian genus extinctions {{paleo-arthropod-stub