LARVAE & TRILOBITE ORDERS: AGNOSTIDA

from Shergold, 1991.

CLASSIFICATION & LARVAE:

As larvae of representatives of three of the six families belonging to the Eodiscina have been described, we can consider that the early ontogeny of this suborder is rather well-known. That of the Agnostina, however, remains completely unknown since no protaspides confidently assigned to a member of this group have been described so far.         Quian (1982) described larvae that he assigned to Pseudagnostus benxiensis but this attribution remains controversial, as the specimens closely resemble polymerid larval stages (see Zhang, 1989 and Chatterton & Speyer, new treatise, 1997).         As emphasized by Chatterton & Speyer (new treatise, 1997), it is difficult to understand why no protaspides of Agnostina have been found so far, especially in faunas like the Orsten fauna, where the exceptional preservation enabled the early meraspid stages of Agnostus pisiformis to be described in great details (Muller & Walossek, 1987, Fossils & Strata 19). Also, it is still unkown whether or not protaspid stages occured in the ontogeny of the Agnostina.

Table 1. Classification scheme of the order Agnostida (from the new Treatise, 1997). Protaspid larvae of three (yellow & bold), possibly four, of the 16 families have been described so far.

LOCALITIES:

1. Penchi, Liaoning, China. LATE CAMBRIAN. 2. Shuigoukou Formation, Henan, China. EARLY CAMBRIAN. 3. Shuijintuo Formation, Sichuan, China. EARLY CAMBRIAN. 4. Beetle Creek Formation, Queensland, Australia. MIDDLE CAMBRIAN.

ARTICLES:

NOTE: This list only concerns articles where protaspid larvae of agnostid trilobites have been described or figured.

CHIEN, Y. 1958. Ontogeny of a new Upper Cambrian trilobite from Penchi, Liaoning. Palaeontologica Sinica, 6: 466-478. HU, C.-H. 1971. Ontogeny and sexual dimorphism of Lower Paleozoic Trilobita. Palaeontographica Americana, 7(44): 29-155. ?QIAN, Y. 1982. Ontogeny of Pseudagnostus benxiensis sp. nov. (Trilobita). Acta Palaeontologica Sinica, 21(6): 632-644. SHERGOLD, J. H. 1991. Protaspid and early meraspid growth stages of the eodiscoid trilobite Pagetia ocellata Jell, and their implications for classification. Alcheringa, 15: 65-86. ZHANG, X.-G. 1987. Moult stages and dimorphism of Early Cambrian bradoriids from Xichuan, Henan, China. Alcheringa, 11: 1-19.    NEW ZHANG, X.-G. 1989. Ontogeny of an Early Cambrian eodiscoid trilobite from Henan, China. Lethaia, 22: 13-29. ZHANG, X.-G. & E.N.K. CLARKSON. 1993. Ontogeny of the eodiscid trilobite Shizhudiscus longquanensis from the Lower Cambrian of China. Palaeontology, 36: 785-806.    pdf version

For more general information about the Order Agnostida, visit Sam Gon's Agnostida Summary page

PTYCHOPARIIDA

ASAPHIDA

LICHIDA

CORYNEXOCHIDA

PHACOPIDA

REDLICHIIDA

HARPETIDA

PROETIDA

(ASAPHIDA)

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Last modified: Jan. 10th 2008