. . Anomalocaris saron pursues a swimming trilobite.

The studies of the mid to late 1990s have presented us with intriguing revelations, and the most complete fossils of anomalocaridids. The level of current research and discovery is at its most promising since Whittington and Briggs (1982, 1985) pieced together the first reasonable reconstruction of Anomalocaris. The anomalocaridid bauplan (body plan) All anomalocaridids are bilaterally symmetrical, bear a pair of anterior segmented appendages, these often sclerotized and armed with spines, a ventral anterior mouth is comprised of tooth-bearing sclerotized wedge-shaped segments arranged in a ring around a central aperture. Jaws, jaw segments, and anterior claws are more often preserved than the rest of the animal, suggesting that these parts are the most robust. Dorsolateral prominent eyes, most often a single pair placed to either side of the mouth, but sometimes either anterior or posterior of the mouth, are typically set on flexible stalks of various length. An elongate, metameric body bears numerous (typically 10+) pairs of lateral imbricating lobes, probably of natatorial function, sometimes accompanied by repeating sets of horizontal support rods. In the majority of species for which complete specimens are known, there are (typically three) pairs of prominent dorsolateral fins immediately posterior to the lateral lobes.

However, the anomalocaridid bauplan appears to be more variable than previously assumed, and efforts should be directed towards compiling a new, complete list of diagnostic characters for the family. A revised list of diagnostic characters could ultimately affect the relationship between the Anomalocarididae and other possible families within Collins' (1996) proposed Order Radiodonta and Class Dinocarida. Both of these taxa are important in the effort to place anomalocarids and other similar problematic metazoans (e.g. Opabinia regalis, Kerygmachela kierkegaardi) into an eventually coherent phylogenetic context. Collins' proposal of the class Dinocarida is not universally accepted by others working on anomalocaridids. Chen and Zhou (1997) place anomalocaridids at the phylum level, but without providing a formal, comprehensive diagnosis, or cladistic analysis. Variation in anomalocarid characters: The 'fantail' reported in Anomalocaris canadensis (Collins 1996), A. saron, and Amplectobelua symbrachiata (Chen et al. 1994) presents a comparative problem. Phylogenetically, it is certainly not homologous with a telson, and no other arthropod (except Opabinia, itself arguably closely related to anomalocarids) has a similar posterodorsally placed structure. It is unclear whether the 'fantail' elements were rigidly fixed, or moveable, like the lateral lobes. The presence of caudal furcae in the Chengjiang material is certainly an arthropodan character, but the 'fantail' complex is a uniquely derived feature. Part of the problem in adequately classifying the anomalocarids is that they seem to have developed a significant amount of derived features after diverging from basal arthropods. Recent studies dramatically emphasize the variations found in the anterior grasping appendages among anomalocaridid genera. Described examples are the relatively stout crushing claws of Anomalocaris canadensis (Collins 1996); the fearsome impaling claws of Amplectobelua symbrachiata; and the long, slender claws of Anomalocaris saron (Chen et al. 1994; Hou et al. 1995). In contrast, the feeding appendages of Laggania cambria (Briggs' "Appendage F") with its long, delicate rake spines, seem more appropriate for a planktonic sweep-feeder than for a rapacious predator of armored arthropods (see discussion by Dzik and Lendzion 1988, and Nedin 1995). Similar appendages on other anomalocarid species (such as those of Anomalocaris briggsi from the Emu Bay Shale, Australia, known only from  appendages with extensive comb rows on all but the first podomere endites) suggest that both predator and planktivore guilds may have been occupied by anomalocaridids (see Nedin 1995).

dorsal view

anterior appendages dorsolateral eyes circular ventral mouth elongate metameric body numerous lateral lobes     dorsolateral fantail     paired furcae Anomalocaris saron Chengjiang, China

ventral view

Anomalocaris canadensis Burgess Shale, Canada	Anomalocaris saron Chengjiang, China	Laggania cambria Burgess Shale, Canada	Amplectobelua symbrachiata Chengjiang, China
Eyes anterior of mouth, narrow anterior body, heavily armed anterior appendages, strong fantail, lacking furcae,	Eyes lateral to mouth, largest mouth segments arranged diagonally, heavily armed anterior appendages, strong fantail, with furcae	Eyes far posterior of mouth, broad anterior body, weakly armed anterior appendages, ventral, transverse lobe support rods, lacking fantail and furcae	Eyes large, lateral to mouth, impaling basal spines on anterior appendages, fantail with furcae

Some anomalocaridid morphotypes also show an increase in their degrees of tagmosis (body segmentation) and sclerotization (hardened exoskeleton), while others show the opposite. For example, Collins' complete specimens of Anomalocaris canadensis confirm that there was no evidence of trunk annulation or external segmentation preserved in this species. At least one purported anomalocaridid (Parapeytoia) had pairs of segmented gnathobasic legs associated with each trunk segment. Swimming lobes are thought to be expanded exopod elements of biramous limbs. Certain groups of anomalocaridids ceased developing biramous trunk appendages in favor of retaining only the lateral lobes. Interpreted in an arthropod context, this change translates into the loss of the endopod and the retention of the exopod. Those anomalocarids that retain segmentation, sclerotization, and endopods most strongly demonstrate arthropod origins, while taxa showing loss of endopods, poor sclerotization, and ambiguous tagmata demonstrate the derived extreme.

Organization of major grades of anomalocarids:

1. Sclerotized mouthparts and grasping appendages; body is 'naked', smooth-surfaced without visible trunk annulation or external segmentation; no apparent external gill-like structures; no body ornamentation or raised features of any kind; 13 pairs of lateral lobes; no jointed trunk appendages, and posterodorsal 'fantail' finlets arranged en echelon. (after Collins 1996) Example: Anomalocaris canadensis

2. Sclerotized mouthparts and grasping appendages; diagonal striations on the lateral lobes (interpreted as veins by some authors); setae-like structures present on lateral lobes; two exsaggital ventral rows of serially-repeated, nodular structures; no confirmed trunk annulation or external segmentation; no jointed trunk appendages; tail furcae present; and posterodorsal 'fantail' finlets arranged en echelon. (After Chen et al. 1994; Hou et al. 1995). Examples: Anomalocaris saron, Amplectobelua symbrachiata (shown here)

3. Sclerotized mouthparts and grasping appendages; body is 'naked', smooth-surfaced without visible trunk annulation or external segmentation; no apparent external gill-like structures; ventral, transverse, lateral lobe support 'rods' present. 14 pairs of lateral lobes; no jointed trunk appendages, evidence equivocal concerning presence of striations on the entire ventral surface of the lateral lobes; caudal end of body tapers to blunt extremity. No fantail or furcae. (after Collins 1996) Example: Laggania cambria

4. Significantly sclerotized body including median sternites, ?dorsal lanceolate scales, gnathobasic biramous trunk appendages, grasping appendages; diagonal striations present on lateral lobes (after Hou et al. 1995). Other forms awaiting description by Ramskold (1995) could fall into this group, further expanding its diagnostic criteria. However, Chen et al 2004 suggests Parapeytoia may be more aligned with 'great-appendage' species such as Yohoia, Haikoucaris, Leanchoilia, Jiangfengia, and Fortiforceps than with anomalocaridids. See page on Parapeytoia for further discussion. Examples: Parapeytoia yunnanensis (shown here), Cucumericrus decoratus

[no image available] 5. Anterior tagmata formed of several carapace-like components bearing two sheathed claws on stalks. Below the carapaces, the jaws have an inner set of teeth, and are surrounded by pair of claws; trunk has 11 segments and a tail; gnathobasic, biramous trunk appendages (after Collins 1992, 1996). Example: Hurdia sp., Proboscicaris sp.

6. Uncertain: Cassubia infercambriensis, Anomalocaris briggsi, and Anomalocaris pennsylvanica (incl. cf. pennsylvanica) are indeterminate forms based on grasping appendages only. Amiella ornata is a nomen dubium (Hou and Bergstrom 1997). The named species assigned to Hurdia (e.g. H. dentata, H. triangulata and H. victoria) and Proboscicaris (e.g. P. agnosta, P. ingens and P. obtusa) should all be regarded as nomina dubia, pending a full description of these genera.

Anomalocaridid References (post 2000 references highlighted yellow)

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Briggs, D.E.G. and Mount, D.J.D. 1982. The occurrence of the giant arthropod Anomalocaris in the Lower Cambrian of Southern California, and the overall distribution of the genus. Journal of Paleontology, 56, 1112-1118.

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