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New palaeoscolecidan worms from the Lower Cambrian: Sirius Passet, Latham Shale and Kinzers Shale

100%

Morris S. C., Peel J. S.

Acta Palaeontologica Polonica

2010

tom 55

nr 1

Palaeoscolecidan worms are an important component of many Lower Palaeozoic marine assemblages, with notable occurrences in a number of Burgess Shale−type Fossil−Lagerstätten. In addition to material from the lower Cambrian Kinzers Formation and Latham Shale, we also describe two new palaeoscolecidan taxa from the lower Cambrian Sirius Passet Fossil−Lagerstätte of North Greenland: Chalazoscolex pharkus gen. et sp. nov and Xystoscolex boreogyrus gen. et sp. nov. These palaeoscolecidans appear to be the oldest known (Cambrian Series 2, Stage 3) soft−bodied examples, being somewhat older than the diverse assemblages from the Chengjiang Fossil−Lagerstätte of China. In the Sirius Passet taxa the body is composed of a spinose introvert (or proboscis), trunk with ornamentation that includes regions bearing cuticular ridges and sclerites, and a caudal zone with prominent circles of sclerites. The taxa are evidently quite closely related; generic differentiation is based on degree of trunk ornamentation, details of introvert structure and nature of the caudal region. The worms were probably infaunal or semi−epifaunal; gut contents suggest that at least X. boreogyrus may have preyed on the arthropod Isoxys. Comparison with other palaeoscolecidans is relatively straightforward in terms of comparable examples in other Burgess Shale−type occurrences, but is much more tenuous with respect to the important record of isolated sclerites. These finds from Greenland provide further evidence that palaeoscolecidans possessed a complex anterior introvert directly comparable to a number of priapulid−like taxa from other Burgess Shale−type assemblages. Although these palaeoscolecidans have been allied with the nematomorphs, molecular data in conjunction with our observations suggest that this hypothesis is untenable. Palaeoscolecidans and similar priapulid−like taxa are probably primitive cycloneuralians and as such may indicate the original bodyplan of this important group of ecdysozoans. In addition, we describe another sclerite−bearing fossil from the Sirius Passet Fossil−Lagerstätte that may be related to the cambroclaves.

Trunk ornament on the palaeoscolecid worms Cricocosmia and Tabelliscolex from the Early Cambrian Chengjiang deposits of China

100%

Han J., Liu J., Zhang Z., Zhang X., Shu D.

Acta Palaeontologica Polonica

2007

tom 52

nr 2

Cricocosmia jinningensis, one of the most abundant palaeoscolecid worms from the Lower Cambrian Chengjiang deposits of south China, was originally described as bearing double longitudinal rows of lateral conical sclerites on the trunk. New observation reveals that the ventral trunk bears an additional set of ventral sclerites while the lateral sclerites display a tubercle−bearing (inner surface) and net−like (outer surface) microstructure similar to that of Tabelliscolex hexagonus. These findings mean that: (1) Cricocosmia shows a dorso−ventral and antero−posterior differentiation in trunk ornament; (2) as seen from the microstructure, Cricocosmia is close to Tabelliscolex hexagonus, supporting the idea that lobopodians and arthropods, both of which show an upper capping layer in the outer sclerites, are more closely related than the palaeoscolecidans; and (3) the similarities among the scalids, pharyngeal teeth and the trunk spines of palaeoscolecidans are superficial. Tabelliscolex maanshanensis sp. nov., characterized by an inner concentric circlet of laminae in each tubercle of the lateral trunk plate, is proposed herein. Element mapping reveal that four known pathways of preservation can be found co−occurring in a single specimen of Cricocosmia or Tabelliscolex, which sheds new light on the preservation of the Chengjiang fossils.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

1 Han J.

1 Liu J.

1 Morris S. C.

1 Peel J. S.

1 Shu D.

1 Zhang X.

1 Zhang Z.

1 2010

1 2007

Wyniki wyszukiwania

New palaeoscolecidan worms from the Lower Cambrian: Sirius Passet, Latham Shale and Kinzers Shale

Trunk ornament on the palaeoscolecid worms Cricocosmia and Tabelliscolex from the Early Cambrian Chengjiang deposits of China