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Radiodonta is a clade of stem-group arthropods that was successful worldwide during the Cambrian period, and included the earliest large predators known. Some of the most famous species included in Radiodonta are the Cambrian taxa Anomalocaris canadensis, Hurdia victoria, and Peytoia nathorsti, the Ordovician Aegirocassis benmoulai and the Devonian Schinderhannes bartelsi.

Radiodonta
Temporal range: Cambrian Stage 3 - Early Devonian, 521–400 Ma
Laggania cambria 01.JPG
Peytoia nathorsti
Scientific classification e
Kingdom: Animalia
Phylum: Arthropoda
Class: Dinocaridida
Order: Radiodonta
Collins, 1996
Subgroups

See text.

Contents

EtymologyEdit

The name Radiodonta (Latin] for radius "spoke of a wheel" and Greek for odoús "tooth") refers to the radial arrangement of tooth plates surrounding the mouth.[1]

DefinitionEdit

In 2014, the clade Radiodonta was defined as the most inclusive clade including Anomalocaris canadensis but not Paralithodes camtschaticus.[2]

ClassificationEdit

PhylogenyEdit

The first in-depth phylogenetic analysis of Radiodonta was conducted by Vinther et al. in 2014, and it was expanded by Cong et al. later that year by the addition of Lyrarapax unguispinus.[5] The analysis was further modified in 2015 by Van Roy et al. with modified characters and the inclusion of Cucumericrus decoratus and Aegirocassis benmoulae.[4]

Euarthropoda

Caryosyntrips serratus

Cucumericrus decoratus

Radiodonta
Anomalocarida

Anomalocaris pennsylvanica

Paranomalocaris multisegmentalis

Anomalocaris sp. Balang

Anomalocaris cf. saron

Anomalocaris cf. canadensis Emu Bay

Anomalocarididae

Anomalocaris canadensis

Amplectobeluidae

NIGP 154565

Anomalocaris saron

Anomalocaris kunmingensis

Amplectobelua stephenensis

Amplectobelua symbrachiata

Lyrarapax unguispinus

Cetiocaridae

Anomalocaris briggsi

Tamisiocaris borealis

Hurdiidae

Fezouata hurdiid

Peytoia nathorsti

Aegirocassis benmoulae

cf. Peytoia Balang

Schinderhannes bartelsi

Hurdia cf. victoria

Hurdia victoria

Stanleycaris hirpex

Hurdia sp. Spence Shale

Hurdia sp. B Burgess

DescriptionEdit

The original diagnosis of order Radiodonta is as follows:[1]

Radiodontids are bilaterally symmetrical, elongate arthropods with a nonmineralized cuticle typically most robust in the jaws and claws. The body is subdivided into two tagmata, much like the prosoma and opisthosoma of chelicerate arthropods.

Typically, the front part shows no external segmentation, bears one pair of preoral claws, a pair of prominent eyes, and ventral jaws with radiating teeth. Some forms have additional rows of teeth and three or four postoral gnathobasic limb pairs. The trunk is metameric, typically with about 13 segments laterally developing imbricating lobes for swimming and gills for respiration, and may end in a prominent three-part tail. Some forms have gnathobasic trunk limbs.

The most anterior structures on the head are the frontal appendages. They are homologous with the antennae of Onychophora and the labrum of Arthropoda, and not homologous with the chelicerae of Chelicerata or the antennae of other arthropods.[5] The mouth is on the ventral side of the head and is surrounded by a ring of tooth plates known as the oral cone.[1]

Contrary to the original diagnosis, no known member of Radiodonta is known to have legs.[6] Rather, the appendages were modified into fin-like lateral flaps. These flaps are homologous to the endopod of the biramous limbs of many arthropods, and dorsal to them were a second set of flaps which bore gills and are homologous to the exopod.[7]

ReferencesEdit

  1. ^ a b c d Collins, Desmond (1996). "The "evolution" of Anomalocaris and its classification in the arthropod class Dinocarida (nov.) and order Radiodonta (nov.)". Journal of Paleontology. 70 (2): 280–293.
  2. ^ Vinther, Jakob; Stein, Martin; Longrich, Nicholas R.; Harper, David A. T. (2014). "A suspension-feeding anomalocarid from the Early Cambrian". Nature. 507: 496–499. doi:10.1038/nature13010. PMID 24670770.
  3. ^ Daley, Allison C.; Budd, Graham E.; Caron, Jean-Bernard; Edgecombe, Gregory D.; Collins, Desmond (2009). "The Burgess Shale anomalocaridid Hurdia and its significance for early euarthropod evolution". Science. 323 (5921): 1597–1600. doi:10.1126/science.1169514. PMID 19299617.
  4. ^ a b Van Roy, Peter; Daley, Allison C.; Briggs, Derek E. G. (2015). "Anomalocaridid trunk limb homology revealed by a giant filter-feeder with paired flaps". Nature. 522: 77–80. doi:10.1038/nature14256. PMID 25762145.
  5. ^ a b Cong, Peiyun; Ma, Xiaoya; Hou, Xianguang; Edgecombe, Gregory D.; Strausfeld, Nicholas J. (2014). "Brain structure resolves the segmental affinity of anomalocaridid appendages". Nature. 513: 538–42. doi:10.1038/nature13486. PMID 25043032.
  6. ^ Daley, Allison C.; Edgecombe, Gregory D. (2014). "Morphology of Anomalocaris canadensis from the Burgess Shale". Journal of Paleontology. 88 (1): 68–91. doi:10.1666/13-067.
  7. ^ Van Roy, Peter; Daley, Allison C.; Briggs, Derek E. G. (2013). Anomalocaridids had two sets of lateral flaps. 57th Annual Meeting of The Paleontological Association. Zurich, Switzerland.