A eucrustacean from the Cambrian ‘Orsten’ of Sweden with epipods and a maxillary excretory opening
Authors:
Waloszek et al
Abstract:
The Cambrian species Paulinecaris siveterae n. gen. n. sp., known from two trunk fragments, represents the first record of epipods (serving as gills and osmoregulatory structures) in a crustacean from the Swedish ‘Orsten’. Moreover, it is the first report of the maxillary excretory opening of a crustacean based on Cambrian material of ‘Orsten’-type preservation. One specimen comprises the maxillary segment with an appendage and several thoracic segments with parts of their limbs; a second specimen is a fragment possibly of a more posterior part of the trunk. As in other known small eucrustaceans, the tergites of the new species lack prominent tergopleurae, so that the limbs insert directly ventral to the tergal margins. Limb preservation includes the maxilla and several thoracopods, all possessing a prominent, fleshy basipod with six setose endites along their median rim distally to the proximal endite. The presence of long and prominent limbs of P. siveterae suggests that it had good swimming ability, while the slight C-like curvature of their basal limb part, basipod, indicates involvement of the limbs also in so-called ‘sucking chambers’ for suspension feeding coupled with locomotion. The estimated total length of P. siveterae, 2–3 mm, is comparable to that of extant cephalocarids, but its appendages are twice as long and wide. The limbs of P. siveterae also differ in size and armature from extant eucrustaceans as well as early representatives of this group known from the ‘Orsten’ assemblages. The general morphology of the limbs, for example in having a fleshy and C-shaped basipod with several setae-bearing endites medially, identifies P. siveterae as an entomostracan eucrustacean, but a lack of further details precludes its affinity with any of the in-group taxa. Three epipods on the outer edge of the basipod, as in P. siveterae, are also known from the Cambrian eucrustacean Yicaris dianensis from China and early ontogenetic stages of extant fairy shrimps (Anostraca); their adult stages have two epipods. This hints at an original number of three epipods in the ground pattern of Entomostraca, but some uncertainty remains with regard to the eucrustacean ground pattern because Malacostraca possess a maximum number of two.
A Marrella-like arthropod from Cambrian of Australia: A new link between "Orsten"-type and Burgess Shale assemblages
Authors:
Haug et al
Abstract:
An isolated exopod in uncompressed three−dimensional “Orsten”−type preservation from the Cambrian of Australia represents a new species of Marrellomorpha, Austromarrella klausmuelleri gen. et sp. nov. The exopod is composed of at least 17 annuli. Each of the proximal annuli carries a pair of lamellae: one lamella on the lateral side and one on the median side. The distal annuli bear stout spines in the corresponding position instead of lamellae, most likely representing early ontogenetic equivalents of the lamellae. The new find extends the geographical range of the taxon Marrellomorpha. Additionally, it offers a partial view into marrellomorph ontogeny. The occurrence of a marrellomorph fragment in “Orsten”−type preservation provides new palaeo−ecological insights into the possible connections between the “Orsten” biotas and other fossil Lagerstätten. Finding such connections is necessary for understanding the complex ecosystems of early Palaeozoic times.
The search for Orsten-type fossils in southern China
Authors:
Shen et al
Abstract:
Orsten-type fossils, mainly arthropod juveniles and even tiny embryos exquisitely preserved in apatite, have been well documented from several localities in southern China. This particular type of Lagerstätte is known from just a few places around the world but has led to significant breakthroughs in the understanding of the early diversity of animals and evolution of metazoans. The original ‘orsten’ from southern Sweden are limestone concretions within black shales, whereas in China this kind of preservation occurs in lime mudstone thin beds and nodules interbedded with shale. Thus there is a taphonomic bias in that this kind of preservation is localized to a deeper water carbonate facies which can be regarded as concretionary due to early cementation under shallow burial. Nonetheless, we observe that even within a laterally extensive bed of the seemingly appropriate lithofacies, preservation may be highly localized. Thus, in addition to the extreme rarity of Orsten-type preservation globally, serendipity in discovering fossiliferous localities plays a significant role. Because of their predominant occurrence in the Cambrian they are also a temporally restricted window. To extract Orsten-type material from the limestone matrix, mild acetic acid digestion has been widely applied, but certain procedures can be employed to aid recovery by limiting damage to these delicate but fragile specimens. Here, we describe our method for etching out specimens and review some of the discoveries recently made in southern China.
