Paleontology
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Updated: 11 Jan 2004 |
AbstractThis page presents a collection of notes from diverse sources, discussing Collins' (1996) class Dinocarida, and likely member taxa. Keywords: Dinocarida, Opabiniida, Opabiniidae, Radiodonta, anomalocaridids, Anomalocarididae, Anomalocaris Introduction"Anomalocarid arthropods have been reported from Cambrian fossil lagerstätten localities around the world. While exceptional fossil preservation, skilful preparators, and comprehensive studies have revealed much about the palaeobiology of some of these formerly enigmatic metazoans, much work still needs to be done in order properly to address the more detailed aspects of anomalocarid anatomy and the interrelationships among the genera and species placed within the family. ... "The studies of the mid to late 1990s have presented us with intriguing revelations, and the most complete fossils of these animals. The level of current research and discovery is at its most promising since Whittington and Briggs (1982) pieced together the first reasonable reconstruction of Anomalocaris. Collins (1996) has provided a complete account of the history of Anomalocaris reconstructions. "While the studies of the previous decade tended to be dominated by the publications of Whittington, Briggs, and Conway-Morris, attention in the mid to late 1990s has shifted towards three investigative ‘blocs’ represented by Hou, and Bergström; Chen, Zhou, and Ramsköld; and Collins. The studies of these competing researchers are characterized by descriptions of complete anomalocarids, identifications of new anomalocarid genera, and/or more aggressive attempts to define the family systematically (e.g. Chen et al. 1994; Collins 1996; Hou et al. 1995; Ramsköld 1995). Despite the thoroughness of the above studies, questions still remain unanswered. "Briggs (1994) and Ramsköld (1995) are correct in demanding a phylogenetic analysis of the Anomalocaridae. Since the anomalocarid bauplan appears to be more variable than previously assumed, 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 Anomalocaridae 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" (Minicucci 1999). |
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MorphologyMouthparts"Using deductive logic, Rudkin (1979) postulated the existence of a large Cambrian predator responsible for inflicting wounds on individuals of the trilobite Ogygopsis klotzi. The association of this trilobite with A. canadensis grasping appendages from the Middle Cambrian Stephen Formation (Bathyuriscus-Elrathia Zone, O. klotzi faunule) prompted him to consider the enigmatic A. canadensis as the culprit. Other authors have since envisioned Anomalocaris a trilobite terror (e.g., Briggs and Mount 1982; Babcock and Robison 1989; Babcock 1993). "In direct opposition to such studies, Hou, Bergström and Ahlberg (1995) suggest that anomalocarid mouthparts could not ‘bite off pieces of trilobites and other arthropods with a hard exoskeleton’ (p.181) and further allege that the mouthparts of previously reported anomalocarids were ‘not directed ventrally as in previous reconstructions’ (p.163). Alleged backward-facing mouthparts present in their Parapeytoia yunnanensis specimen are introduced as evidence. A major flaw in their argument is that the evidence derives from an unrepresentative sample. There are assorted complete specimens of other genera confirming the presence of mouthparts in the familiar, ventral position (see Chen et al. 1994; Collins 1996). Further, both the illustration (Hou et al. 1995, p.173, Fig. 10) and description suggest that the mouthparts of P. yunnanensis are, perhaps, different from the typical ‘Peytoia’ jaws of other anomalocarids. "Both in appearance, and in proposed function, typical anomalocarid mouthparts must have been deadly weapons possessed of substantial cutting and crushing power. Certainly, the fact that mouthparts are more readily preserved attests to their durability. The recommendation of ... Chen and Zhou (1997) that anomalocarids should be sorted among different Dinocarid orders because of alleged differences in mouthpart morphology is probably not warranted. "The anomalocarid referred to as Hurdia by Collins (1992) is described as having mouthparts with an extra set of teeth that would have lined the interior of the buccal cavity (Whittington and Briggs 1985). This configuration, suggestive of a ‘pharyngeal mill’, could have been even more effective at processing hard-bodied prey" (Minicucci 1999). |
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| "The aperture itself [of Anomalocaris] was rectangular, not circular. It could not be closed; the teeth did not meet in the middle. The jaw could be opened, however, to admit prey, and the plates could then be pulled together to draw the prey into the mouth. This would have had the effect of cracking or breaking the exoskeleton of an arthropod. Indeed, trilobites are known with healed bites in the edge of the exoskeleton that may have been made by the jaw of Anomalocaris. Some specimens of the jaw preserve additional teeth inside ..., which lined the wall of the mouth and further processed the food" (Briggs et al. 1994, pp. 201-202). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Lateral Lobes"Linear striations present on the surface of the lateral lobes of anomalocarids have been reported in several genera. Chen et al. (1994) have interpreted these features as a vein network. Hou et al. (1995) simply note them as ‘lines’. Collins (1996) suggests that A. canadensis and L. cambria possess gills on the lateral lobes, but no identifiable gill-like structures appear on the lateral lobes of his photographed specimens. Collins’ complete specimens of A. canadensis indicate a virtually ‘naked’ animal, without any surface ornamentation or raised features of any kind on the integument (pers. obs.). Examinations of L. cambria material by Whittington and Briggs (1985) suggest the equivocal presence of linear markings on the lateral lobes. Both A. saron and A. symbrachiata in Chen et al. (1994) seem to preserve traces of setae / gill-like structures (in addition to the vein network) on several of the lateral lobes. In these specimens, the alleged setae appear to lie on the ventral surface of each lateral lobe. Setae performing an alleged respiratory / gill function are usually attached to the distal edge of either a thin or paddle-shaped exopod in Cambrian arthropods and trilobites, but seeing the setae originate from the exopod surface is more complicated to explain (a similar situation exists in Opabinia regalis). In order to address the inconsistencies, we must formulate a diagnosis for correctly identifying what constitutes an anomalocarid gill. Hou and Bergström (1997) have wisely and justifiably identified problems with the fundamentally colloquial use of the term ‘gill’ in relation to descriptions of other Burgess Shale-type arthropods. If neither A. canadensis nor L. cambria possessed external gills, other locations for organs of gas exchange must be found. Further preparation of existing specimens or discoveries of new material should help to settle the issue" (Minicucci 1999). |
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| "Chen et al. (1994) reported the existence of ‘two exsaggital rows of segmentally repeated ventral or internal structures of unknown function, preserved as black or light-reflective patches’ (p. 1308) in the specimens Hou et al. (1995) would later identify as A. saron and A. symbrachiata. They further allege that these nodular structures are ‘composed of bunches of fine, curved threads’ (Chen et al. 1994, p. 1305) and describe them as ‘equalling the nodular mineralized areas’ described in Anomalocaris nathorsti (p.1306). Collins (1996) mentions the same structures in his discussion of the transverse mineralized strips (lateral lobe supports) on the ventral surface of L. cambria. I believe that any attempts to draw a connection between the nodular structures identified by Chen et al. with the club-shaped structures found on the ventral surface of L. cambria are premature. Such structures appear on the lateral lobes as the terminal ends of the lateral lobe support rods. The nodular structures discussed by Chen et al. (1994) are present only on the trunk region, and are isolated from each other, not being transversely connected by mineralized strips. The possibility could exist that the nodular structures represent caeca. In Ramsköld et al. (1997), the Lower Cambrian petalopleuran xandarellid Cindarella eucalla shows evidence of caeca preserved as serially-repeated, dark stains with an ‘internal system of approximately transverse or slightly splayed tubules’ (p.29). It is tempting to compare the thread-like structures observed by Chen et al. (1994) with these" (Minicucci 1999). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Cuticle"Collins’ complete specimens of A. canadensis confirm that there was no evidence of trunk annulation or external segmentation in this genus. The trunk region of A. saron in Chen et al. (1994) is described as having transverse lines, but the ‘irregularity and wrinkling of the lines’ (p.1305) suggests that these are most probably preservational folds caused during diagenensis and compaction of the carcass. Ramsköld (1997) has successfully demonstrated the existence of such misleading folds in naraoiid and tegopeltid arthropods. He has, however, hinted at the existence of certain undescribed genera with higher degrees of tagmosis possessing intersegmental trunk bars (Ramsköld 1995). A fact not discussed by researchers is the significant disparity between the virtually ‘naked’ soft-cuticle condition of A. canadensis and the high degree of tagmosis and sclerotization of P. yunanensis. According to the fossil evidence, while the most complete specimen of P. yunanensis (NIGPAS 115334) represents a substantial body moult (Hou et al. 1995), ecdysis in A. canadensis would seem to have been limited to moulting of the grasping appendages and mouthparts (Collins 1996). Persistent collecting seems to show that Royal Ontario Museum specimens of A. canadensis remains tend to consist of either a complete carcass or isolated mouthparts and grasping appendages (as seen in Collins 1996). Anything in between consists of a smeared blob (pers. obs.). As a consequence, it can be inferred that P. yunnanensis had a more significantly sclerotized cuticle. An increase in the degree of cuticle sclerotization may be correlated with an increased complexity of tagmosis in each genus" (Minicucci 1999). |
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| "The high degree of anatomical detail preserved in specimens of Chengjiang anomalocarids attests to the quality of Chengjiang fossils. If the criticisms of Hou and Bergström (1997) are accepted at face value, it is arguable that the apparently smooth, featureless surface of the soft-cuticle of Collins’ Burgess Shale A. canadensis is an artefact resulting from comparably inferior preservation associated with fossils from the Burgess Shale biota. The small size of reported Chengjiang anomalocarids correlates with the assumption that their remains represent juveniles, while Collins’ described A. canadensis specimens represent adult organisms. Whether the preservational environments or different ontogenetic stages account for the differences in visible anatomical details is unclear" (Minicucci 1999). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Tail"The ‘fantail’ reported in A. canadensis (Collins 1996), A. saron, and A. symbrachiata (Chen et al. 1994) presents a comparative problem. Phylogenetically, it is certainly not homologous with a telson, and no other arthropod has a similar posterodorsally placed structure. 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 developed a significant amount of derived features masking their ancestry after diverging from basal arthropods. Unclear is whether the ‘fantail’ elements were rigidly fixed in position, or moveable, like the pliable lateral lobes. If the animals could adjust their orientation with respect to the flow of water, they may have stabilized the anomalocarid body in a manner comparable to the way in which rudders stabilize ... aircraft in the air" (Minicucci 1999). |
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Grasping Appendages"Recent studies dramatically emphasize the variations found in frontal grasping appendages among anomalocarid genera. Described examples are the relatively stout crushing claws of A. canadensis (Collins 1996); the wicked impaling claws of A. symbrachiata; and the long, slender claws of A. saron (Chen et al. 1994; Hou et al. 1995). The morphology of the grasping appendages of L. cambria, Cassubia infercambriensis and the unknown ‘appendage F’ anomalocarid (Briggs 1979) may militate against the view that all anomalocarids were active hunters (Whittington and Briggs 1985) because such appendages could be interpreted as the instruments of sweep-feeders (see discussion by Dzik and Lendzion 1988, and Nedin 1995). The Emu Bay Shale anomalocarid Anomalocaris briggsi, known only from grasping appendages with extensive comb rows on all but the first podomere endites, also seems to be a confirmed sweep-feeder (Nedin 1995). Nedin alleges that the serrated endites on the first podomere were capable of impaling prey caught within the flexed appendage. In sharp contrast to the morphology of the fourth podomere endite on the grasping appendage of the confirmed impaler Amplectobelua symbrachiata (Chen et al. 1994), these particular endites show no appreciable increase in length relative to the lengths of the other podomere endites, casting some doubt on their effectiveness as impaling organs. The morphological differences between the grasping appendages of A. briggsi and those of other species of Anomalocaris are probably both sufficient and necessary to warrant assigning this species to a new genus. The grasping appendages of P. yunnanensis are worth mentioning because these differ significantly from those of other described anomalocarids. According to Hou et al. (1995), a complete appendage consists of five segments the lowest number yet reported in any genus. Rather than being composed of several podomeres, the proximal half of the grasping appendage consists of a long, stout podomere, and the arrangement of endites on each subsequent podomere gives the distal half of the appendage an almost chelate appearance. An approximately chelate grasping appendage has not been reported in any other anomalocarid" (Minicucci 1999). |
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| "Superficially comparable are the frontal grasping appendages of the megacheiran fortiforcipid Fortiforceps foliosa (Hou and Bergström 1997; p.36, Fig. C). The functional morphology and development of the above type of appendage in anomalocarids merits further investigation. The endites are long, but the fact that there are only four probably indicates that they did not form a comb filter-feeding mechanism. Flexing the four distal podomeres would bring them into contact, making the appendages seem better suited for picking and manipulating, as opposed to squeezing and crushing using a deadly ‘bear-hug’ embrace, as suggested by the morphology of ‘typical’ predatory anomalocarid appendages. No less intriguing will be the complete description and analysis of whatever kind of grasping appendages are present in the Hurdia-type anomalocarids reported by Collins (1992)" (Minicucci 1999). |
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Phylogeny and EvolutionAffinities |
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| "The majority of conclusions on anomalocarid functional morphology and anatomy in Hou et al. (1995) tend to be based on evidence from an unrepresentative sample. The described material of P. yunnanensis is hardly complete. Contrary to what Hou et al. (1995) clearly state in their paper, their best-preserved specimen of a single genus cannot reasonably serve as a template for redefining or dismissing the reconstructions of other anomalocarids. The ventral reconstruction (p. 180, Fig. 19) is problematical because there is no direct, conclusive evidence confirming the form of the anterior tagmata, and backward-facing position of the mouthparts and grasping appendages. It is ironic that Hou et al. choose ‘the radial arrangement of circum-oral sclerites’ (p. 163) as an homologous feature uniting aschelminthes and anomalocarids, while dismissing a virtual mountain of arthropod characters as irrelevant convergent features. Also problematical is their assertion that anomalocarids were dorsally covered in lanceolate scales. Such structures are allegedly identified in their specimens of P. yunnanensis, [they are not visible in the the photographs published in Hou et al. 1999 (figs. 77-78) - CC] Anomalocaris saron, and Cucumericrus decoratus. The scales are almost impossible to identify from the published photographs, casting doubt on the accuracy of the camera lucida drawings. The fact that Chen et al. (1994) did not observe the same markings in more complete specimens of the same genera casts even further doubt on the observations of Hou et al. (1995). The interpretation by the latter authors of ‘Peytoia nathorsti’ (= Laggania cambria of Collins 1996) assumes that USNM 274142 represents a dorsal view of the animal showing ‘transverse sets of lanceolate scales’ (Hou et al. 1995, p.179, Fig. 17A). Collins (1996) has successfully proven that this particular fossil represents a ventral view, and that the so-called ‘scales’ are better interpreted as ‘flexible rod supports of the lateral lobes’ (p. 290). Thus one key piece of evidence for the existence of dorsal lanceolate scales evaporates. Rather than being scales, the markings observed (if they truly exist) in the other above genera could be artefacts of preservation / effects of Neogene weathering, wrinkling caused by decay of the carcass, or a surface wrinkling of the integument actually present in life" (Minicucci 1999). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Fossil RecordOriginsEvolutionsee Collins 1996 Extinction... |
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Systematics
Phylum Arthropoda von Siebold & Stannius 1845
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Supersubphylum cf. Protarthropoda Lankester 1904
Discussion: Arthropod systematics has long been in a state of flux; no more so than now. The taxonomic hierarchy is quite incomplete, and here is one example. Whereas taxa having the rank of supersubphyla have been defined for the Onychophora and the euarthropods, no equivalents (that I am aware of) exist for the Dinocarida or Tardigrada. |
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Class Dinocarida Collins 1996
Type: (Order) Radiodonta Collins 1996 Description: As defined by Collins, Dinocarids are bilaterally symmetrical arthropods with a body divided into two principal tagmata, recalling the prosoma and opisthosoma of chelicerates, and a non-mineralised cuticle. The front part shows no external segmentation, bears one or more pre-oral claws, one or more pairs of prominent eyes, and a ventral mouth; differing from other arthropod classes in possessing no antennae and only one appendage or pair of pre-oral appendages on the prosoma, and in bearing gilled lateral lobes on the metameric trunk. The jaws vary from none to forms with both radiating teeth and teeth in rows. |
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| Discussion: "Of course it remains to be seen whether Collins’ conclusions can be supported by a comprehensive cladistic analysis. Chen and Zhou (1997) do not even believe that anomalocarids comprise a family level taxon. Curiously, they place anomalocarids at the phylum level, but without providing a formal, comprehensive diagnosis, or cladistic analysis. Of prime importance is the need to identify and trace morphological trends relating to the acquisition and loss of characters. For example, at some point in their evolution, certain groups of anomalocarids ceased developing biramous trunk appendages in favour 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. The assumption that the anomalocarid lateral lobe may be a true exopod is partly based on the presence of reported ventral, limb-like appendages being consistent with the gross morphology of the arthropod endopod. Some morphotypes also show an increase in their degrees of tagmosis and sclerotization, while others show the opposite" (Minicucci 1999). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Order Opabiniida Størmer 1944
Type: ? Discussion: ? 1959 Treatise, O32 |
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Family Opabiniidae Walcott 1912
Type: ? Discussion: ? 1959 Treatise, O32 |
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Genus Opabinia Walcott 1912
Type Species: Opabinia regalis Walcott 1912 Discussion: Opabinia has five eyes at the front of the head and a long, flexible proboscis ending in an array of grasping spines. The trunk comprises 15 segments, each bearing a pair of downward-directed lateral lobes, thought to have been used for propulsion, each overlain by a lamallate gill. Three pairs of upward-directed flaps form a tail fan (cf. Parapeytoia???), possibly served a stabilising or steering function during swimming. The systematic position of Opabinia is very unclear: early interpretations as a branchiopod or as a member of the trilobite clade are almost certainly incorrect. Whittington thought it might belong to the stem group leading to a annelid+arthropod clade. Placement within the Dinocarida, as here, is based on 'homologies' which may prove to be merely convergent characters rather than true synapomorphies. (After Briggs et al. 1994, p. 210.) |
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Opabinia regalis Walcott 1912
Discussion: The animal is thought to have lived primarily in the soft sediment of the seabed, but to have been a predator capable of active swimming. The proboscis was presumably used to capture and handle prey, and may possibly have served to extract burrowing organisms from their burrows. (After Briggs et al. 1994, p. 210.) |
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cf. Order Radiodonta Collins 1996Discussion: Collins (1996, p. 291) restricted the Radiodonta to exclude the Opabiniidae and, although these genera were not described at the time, certainly he would have excluded Kerygmachela and Pambdelurion also. These two taxa are highly problematic, being known from a single locality, the Sirius Passet location in northeastern Greenland, and occupying an uncertain position intermediate between the onychophorans, anomalocaridids, and euarthropods. Graham Budd, who described both taxa, interprets them to imply that at least the biramous arthropods actually arose from within the anomalocaridids, the biramous limb having evolved before full cuticular sclerotisation. |
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Genus Kerygmachela Budd 1998
Type Species: Kerygmachela kierkegaardi Budd 1998 Description (of type species): The cephalic region is characterised by a pair of stout unsegmented appendages each bearing long spinose processes, and an anterior mouth. The trunk shows alternating rows of tubercles and transverse annulations along the axis, to which are attached 11 pairs of gill-bearing lateral lobes and lobopodous limbs. The caudal region is small, and bears two long tail spines. There is some evidence for circular musculature arranged around the trunk and a dorsal, longitudinal sinus, and several details of the muscular pharynx have been preserved. |
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Genus Pambdelurion Budd 1997
Type Species: Pambdelurion whittingtoni Budd 1997 Description (of type species): ... |
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Order Radiodonta Collins 1996
Type: ? Anomalocaris ? Discussion: ? from Collins |
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Family Anomalocarididae Raymond 1935
Type: Anomalocaris Whiteaves 1892 Discussion: "In accordance with the criteria established by Collins (1996), all anomalocarids may be diagnosed as being bilaterally symmetrical, with two distinct tagmata, but other features, such as lateral lobes, grasping appendages, biramous appendages, form of the trunk, and anterior tagmata vary between types of genera. "Based only on the current descriptions of anomalocarids, and a casual observation of the available evidence, I have listed several groups possibly comprising distinct grades of anomalocarid body organization. The inadequately described Chen and Zhou arthropod (1997), if it is truly an anomalocarid, could very well represent an ancestral grade of anomalocarid body organization unknown in other described forms. Groups 1, 2 and 3 comprise a grade of genera possessing a soft cuticle, simple body organization, and uniramous trunk appendages. Group 4 contains the grade of genera with complex degrees of tagmosis and sclerotization, and biramous trunk appendages, while group 5 represents the grade of genera that have made a radical departure from the body designs of the other grades. A thorough cladistic analysis incorporating all described and undescribed taxa will ultimately determine the viability of this concept" (Minicucci 1999). |
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Genus Anomalocaris Whiteaves 1892
Type: Anomalocaris canadensis Whiteaves 1892 Discussion: Anomalocaris is the largest of the Burgess Shale animals, approaching 0.5 m., and made famous by books such as Wonderful Life and The Crucible of Creation. Whiteaves described isolated Anomalocaris canadensis appendages from the Ogygopsis Shale on Mount Stephen; Walcott found similar limbs in the Burgess Shale, together with those of A. nathorsti. Walcott also discovered the circlets of plates, that he named Peytoia and interpreted as a medusoid, which are now known to be anomalocaridid mouthparts. "Recent discoveries have shown Anomalocaris to be one of the most widely distributed of the Burgess Shale animals. It is now known not only from North America, but also from China, Australia, and Greenland" (Briggs et al. 1994, pp. 201-202). "Anomalocaris briggsi, Anomalocaris pennsylvanica (incl. cf. pennsylvanica), Anomalocaris sp. and the ‘appendage F’ anomalocarid are indeterminate forms based on grasping appendages only" (Minicucci 1999). |
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Anomalocaris canadensis Whiteaves 1892
Discussion: ... |
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Anomalocaris nathorsti (Walcott 1911a)Discussion: A junior synonym of Laggania cambria. |
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Anomalocaris saron Hou, Bergström & Ahlberg 1995
Discussion: ... |
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Anomalocaris symbrachiata author
Discussion: ... |
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Anomalocaris sp. 1 Chen and Zhou 1997
Discussion: "Aside from containing some very misleading syntactical and spelling errors, the spectacular, sumptuously illustrated monograph on fossils of the Chengjiang fauna by Chen and Zhou (1997) presents an extremely brief description and two colour photographs of an alleged anomalocarid from the Chengjiang locality. |
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| "Although the argument that this fossil represents an ancestral grade of anomalocarid body organization is presented (Chen and Zhou 1997), I cannot help but notice more than a passing similarity between this animal and Fortiforceps foliosa (Hou and Bergström 1997). The single, preserved grasping appendage, endopods, stalked eyes, telson, and number of tergites of the Chen and Zhou arthropod seem to bear striking similarities to the corresponding structures in F. foliosa. The absence of sclerotized, circular mouthparts is also a problem. I have not seen the actual, un-named specimen, and cannot make a final decision, but the preliminary comparisons cast some serious reasonable doubt on the proposed anomalocarid affinities of the Chen and Zhou (1997) arthropod. Are we, in fact, dealing with a second fortiforcipid?" (Minicucci 1999) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Genus Amiella Walcott 1911d (verify)
Discussion: ... |
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Amiella ornata Walcott 1911d
Discussion: "Amiella ornata is a nomen dubium (Hou and Bergström 1997)" (Minicucci 1999). |
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Genus Amplectobelua Hou, Bergström & Ahlberg 1995
Discussion: ... |
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Amplectobelua symbrachiata Hou, Bergström & Ahlberg 1995
Discussion: ... |
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Genus Cassubia
Discussion: ... "Cassubia infercambriensis is an indeterminate form based on grasping appendages only" (Minicucci 1999). |
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Genus Cucumericrus Hou, Bergström & Ahlberg 1995
Discussion: ... |
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Cucumericus decoratus Hou, Bergström & Ahlberg 1995
Discussion: ... |
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Genus Hurdia
Discussion: ... "The named species assigned to Hurdia (e.g. H. dentata, H. triangulata and H. victoria) should all be regarded as nomina dubia, pending a full description of the genus" (Minicucci 1999). |
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Hurdia dentata Simonetta & Delle Cave 1975
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Hurdia triangulata Walcott 1912a
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Hurdia victoria Walcott 1912a
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Genus Laggania
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Laggania cambria Walcott 1911
Discussion: .... See Collins 1996, pp. 285-287, for complete synonymy. |
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Genus Parapeytoia Hou, Bergström & Ahlberg 1995
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Parapeytoia yunnanensis Hou, Bergström & Ahlberg 1995
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Genus Peytoia
Discussion: A junior synonym of Anomalocaris. |
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Genus Proboscicaris Rolfe 1962 (verify)
Discussion: "The named species assigned to Proboscicaris (e.g. P. agnosta, P. ingens and P. obtusa) should all be regarded as nomina dubia, pending a full description of the genus" (Minicucci 1999). |
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Proboscicaris agnosta Rolfe 1962
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Proboscicaris ingens Rolfe 1962
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Proboscicaris obtusa Simonetta & Delle Cave 1975
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Conclusions"The reported morphological variations present in assorted anomalocarid genera emphatically illustrate the former diversity of these animals. Indeed, preliminary descriptions of very unusual genera with several frontal carapace-like components forming the anterior tagmata (Collins 1992, 1996), and reports of more genera with gnathobasic, biramous appendages (Ramsköld 1995) indicate that anomalocarids evolved an assortment of specialized forms, and varying degrees of tagmosis and sclerotization, perhaps enabling them to occupy different feeding guilds. At this juncture, virtually no substantive information has been published on such forms. It appears that all described and even undescribed genera may be sorted according to several distinct grades of anomalocarid body organization. Superficially identifiable are the genera with a soft-cuticle or minimal sclerotization, possessing uniramous trunk appendages (lateral lobes only); the genera with complex degrees of tagmosis and sclerotization, possessing biramous trunk appendages; and the Hurdia-type genera, which radically depart from the two former body designs (see Collins 1992). Assigning the different grades taxonomic rankings, either by assigning each to sub-familial status within the Anomalocaridae, or by erecting family level taxa for each within an Order, depends on how each grade could be proven to be distinct cladistically. More grades of body organization must surely have existed, and are as yet unrepresented or unrecognized in fossil collections. It is, of course, possible that the same type of body organization expressed among similar genera could merely reflect homoplasy in anomalocarids not closely related" (Minicucci 1999). |
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ReferencesBabcock, L.E. 1993. Trilobite malformations and the fossil record of behavioral asymmetry. Journal of Paleontology, 67, 217-229. Babcock, L.E. and Robison, R.A. 1989. Preferences of Palaeozoic predators. Nature, 337, 695-696. Briggs, D.E.G. 1979. Anomalocaris, the largest known Cambrian Arthropod. Palaeontology, 20, 631-664. Briggs, D.E.G. 1994. Giant predators from the Cambrian of China. Science, 264, 1283-1284. Briggs, Erwin & Collier 1994: The Fossils of the Burgess Shale. Smithsonian, 238 pp. Briggs, D.E.G.; 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. Chen, Junyuan, Ramsköld, L. and Zhou Guiquing, 1994. Evidence for monophyly and arthropod affinity of Cambrian giant predators. Science, 264, 1304-1308. Chen Junyuan and Zhou Guiquing, 1997. Biology of the Chengjiang Fauna. Bulletin of the National Museum of Natural Science, 10, 11-105 Collins, D. 1992. Whither Anomalocaris? The search in the Burgess Shale Continues. Abstracts, Fifth North American Paleontological Convention, Chicago, Paleontological Society Special Publication, 6, 66. Collins, D. 1996. The "evolution" of Anomalocaris and its classification in the arthropod class Dinocarida (nov.) and order Radiodonta (nov.). Journal of Paleontology, 70, 280-293. Collins, D., Bergström, J. and Seilacher, A. 1991. Chengjiang Fauna. National Geographic Research and Exploration 7(2), 238-239. Dzik, J. and Lendzion, K. 1988. The oldest arthropods of the East European Platform. Lethaia, 21, 29-38. Hou, Xianguang; Bergström, J. 1997: Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. Fossils and Strata, 45, 1-116. Hou, Xianguang; Bergström, J.; Ahlberg, P. 1995: Anomalocaris and other large animals in the Lower Cambrian Chengjiang fauna of southwest China. GFF, 117, 163-183. Hou, Xianguang; Bergström, Jan; Wang, Haifeng; Feng, Xianghong; Chen, Ailin 1999: The Chengjiang Fauna. Exceptionally Well-Preserved Animals from 530 Million Years Ago. Yunnan Science and Technology Press. 170 pp. [In Chinese with English summary.] Minicucci, Jeffrey M. 1999: Forward to the Cambrian - Anomalocarid Studies at the End of the Millennium. Palaeontological Association Newsletter 41: 23-32. Nedin, C. 1995. The Emu Bay Shale, a Lower Cambrian fossil Lagerstätten, Kangaroo Island, South Australia. Memoirs of the Association of Australasian Palaeontologists 18, 31-40. Ramsköld, L. 1995. From characters to clades: interpreting Lobopodians and Anomalocaridids. 22. In Chen Junyuan, Edgecombe, G. and Ramsköld, L. (eds). International Cambrian Explosion symposium (April, 1995, Nanjing) (Programme and Abstracts). Nanjing Institute of Geology and Palaeontology, Academia Sinica, 48 pp. Ramsköld, L. 1997. Preservational folds simulating tergite junctions in tegopeltid and naraoiid Arthropods. Lethaia, 29,15-20. Ramsköld, L., Chen Junyuan., Edgecombe, D. and Zhou Guiquing, 1997. Cindarella and the arachnate clade Xandarellida (Arthropoda, Early Cambrian) from China. Transactions of the Royal Society of Edinburgh: Earth Sciences, 88, 19-38. Rudkin, D.M. 1979. Healed injuries in Ogygopsis klotzi (Trilobita) from the Middle Cambrian of British Columbia. Royal Ontario Museum, Life Sciences Occasional Paper, 32, 1-18. Whittington, H.B., and Briggs, D.E.G. 1982. A new conundrum from the Middle Cambrian Burgess Shale. 573- 575. In Mamet, B., and Copeland, M. J. (eds). Proceedings of the Third North American Paleontological Convention, Montreal, 2. Department of Geology, University of Montreal, and Geological Survey of Canada, Ottawa. Whittington, H.B., and Briggs, D.E.G. 1985. The largest Cambrian animal, Anomalocaris, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society of London, Series B, 309, 569-609. |
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