Dinocaridida: Anomalocarididae (2)

Taxa on This Page

1. Cucumericrus X
2. Parapeytoia X
3. Schinderhannes X

Descriptions

Cucumericus decoratus Hou, Bergström & Ahlberg 1995

Horizon: Qiongzhusi Formation, Maotianshan Shales, Chengjiang Lagerstätte, Yunnan, South China, (Atdabanian age - Early Cambrian)

Phylogeny: Dinocaridida : Kerygmachela + (Pambdelurion + (Opabinia + (Anomalocarididae + (Schinderhannes + (Parapeytoia + Arthropoda) + * ))))

Comments: Cucumericrus is a genus of anomalocaridid known from a few poorly-preserved specimens. Its great appendages are never preserved (Daley & Budd 2010) but it does seem to bear walking legs, which have been interpreted as somewhere between lobopod legs and segmented arthropod legs. (Bergstrom & Hou 2003) - Wikipedia

Schinderhannes bartelsi Kühl et al 2009

Horizon: Early Devonian German Hunsrück Slate.

Phylogeny: Dinocaridida : Kerygmachela + (Pambdelurion + (Opabinia + (Anomalocarididae + (Cucumericrus + (Parapeytoia + Arthropoda) + * ))))

Comments: (modified from Christopher Taylor's posting on this creature MAK120507). Schinderhannes bartelsi, and its fossil remains are described in a paper by Kühl et al (2009) (from whence comes the reconstruction at the right). It's apparently named after an 18th century bandit in the area from which it was found. At just under ten centimetres long, it is a smaller cousin of Anomalocaris and Laggania of the Cambrian Burgess Shale. However, Schinderhannes bears a few significant differences from those taxa: (1) it has that bizarre pair of 'wings' attached to the back of the head; (2) certain details of its anatomy suggest that it is more closely related to living arthropods than is Anomalocaris, showing that arthropods are descended from an 'anomalocarid' grade; and (3) it doesn't come from the Burgess Shale or Chengjiang, but the German Hunsrück Slate, which is from the Earky Devonian, shows that 'anomalocarid'-type animals were around for some 100 million years longer than we previously knew (at the risk of repeating an old cliché about it being like discovering a Tyrannosaurus alive today, although the amount of time separating Tyrannosaurus from the present is rather less than 100 million years.

Schinderhannes resembles anomalocarids in its radial mouth, and the large pair of spiny pre-oral appendages. However, certain of its features are more like true arthropods - it has a dorsum divided into distinct, sclerotised tergite plates, and it has biramous (two-branched) appendages like crustaceans. The combination of the large 'wings' and 'flukes' on either side of the tail spine suggest that it was an active swimmer.

Large raptorial pre-oral appendages (dubbed 'great appendages') have also been found in a number of Cambrian arthropods such as Leanchoilia and Yohoia. The phylogenetic position of such 'great-appendage' arthropods has been hotly debated. Budd (2002) suggested that they were a stem grade to the arthropod crown clade, but Cotton & Brady (2004) placed them within the crown clade, in the stem group for chelicerates. Researchers have also debated whether the great appendages of these arthropods are homologous to those of anomalocarids, and whether the great appendages are homologous to the chelicerae of modern chelicerates. The (admittedly pretty rudimentary) phylogenetic analysis of Schinderhannes by Kühl et al 2009, supports a position of great-appendage arthropods as stem chelicerates (despite the great appendages of these arthropods being a priori coded as homologous to those of anomalocarid-grade animals), which supports the comparison between great appendages and chelicerae. It also suggests that trilobites are closer to crustaceans than chelicerates, contrary to the idea of a trilobite + chelicerate "Arachnomorpha" clade. In some regards, this would make sense - trilobites, like crustaceans and insects, have lost the plesiomorphic state of grasping pre-oral appendages as found in chelicerates and have filamentous antennae instead. However, the position of trilobites in the tree above seems to be primarily due to the presence of antennae, so I don't know if it can be considered well-supported. - CKT090206

Parapeytoia yunnanensis Hou, Bergstrom & Ahlberg, 1995

Horizon: Qiongzhusi Formation, Maotianshan Shales, Chengjiang Lagerstätte, Yunnan, South China, (Atdabanian age - Early Cambrian)

Phylogeny: Dinocaridida : Kerygmachela + (Pambdelurion + (Opabinia + (Anomalocarididae + (Schinderhannes + (Arthropoda + * )))))

Comments: Parapeytoia resembles anomalocaridids in having a pair of large grasping appendages, eyes on stalks, and a fleshy-lobed posterior with a fan tail. The other distinguishing feature of the group, the "Peytoia" (pineapple ring) mouth part, is unconvincingly described and illustrated, and so any statement regarding its presence must be taken with caution, at least until better fossil material turns up. In differs in possessing euarthropod-like trunk legs and strongly sclerotized, segmental sternites ((Daley et al. 2009; suppl). The presence of legs may not be so strange as it seems, as Hou & Bergström (2006) argue that anomalocaridids did have legs, but they were not sclerotised (there was no arthropod-type exoskeleton) and hence did not fossilise (or didn't fossilise clearly). This makes more sense than the premise that ancestral protoarthropods had legs, then lost them, then re-acquired them again (or alternatively developed toally new legs). Because it is assumed that anomalocaridids and even dinocaridids in general lacked legs, it is thought that Parapeytoia might be more closely related to great appendage stem euarthropods like Yohoia or Haikoucaris, If Hou & Bergström are correct this need not be the case. The Anomalocaris Homepage - Parapeytoia yunnanensis & Opabinia regalis shows drawings of Parapeytoia reconstructed as a megacheiran "great-appendage" arthropod. When compared to other megacheirans,, the similarity reagrding the anterior appendages is quite obvious. Alternatively, Parapeytoia could be a transitional form, a non-missing link, and the great anterior appendages of anomalocaridids and megacheirans may be homologous. This also fits with the hypothesis of the megacheirans being stem group arthropods, prior to the division into the various crown taxa.

Parapeytoia has 13 pairs of legs altogether; the first two pairs about half the length of the remaining ones. These may indicate a benthic rather than a nektonic lifestyle (Wikipedia). It may not have even had a pineapple-ring mouth at all, as sclerites interpreted as its mouthparts have since been assigned to a new priapulid worm genus, Omnidens. (Houetal2006) MAK120507

Links Parapeytoia yunnanensis by Sam Gon III