Exceptionally Preserved Jellyfishes from the Middle Cambrian

Cnidarians represent an early diverging animal group and thus insight into their origin and diversification is key to understanding metazoan evolution. Further, cnidarian jellyfish comprise an important component of modern marine planktonic ecosystems. Here we report on exceptionally preserved cnidarian jellyfish fossils from the Middle Cambrian (∼505 million years old) Marjum Formation of Utah. These are the first described Cambrian jellyfish fossils to display exquisite preservation of soft part anatomy including detailed features of structures interpreted as trailing tentacles and subumbrellar and exumbrellar surfaces. If the interpretation of these preserved characters is correct, their presence is diagnostic of modern jellyfish taxa. These new discoveries may provide insight into the scope of cnidarian diversity shortly after the Cambrian radiation, and would reinforce the notion that important taxonomic components of the modern planktonic realm were in place by the Cambrian period

Rare primitive deuterostomes from the Cambrian (Series 3) of Utah

The fossil record of early deuterostome history largely depends on soft-bodied material that is generally rare and often of controversial status. Banffiids and vetulicystids exemplify these problems. From the Cambrian (Series 3) of Utah, we describe specimens of Banffia episoma n. sp. (from the Spence Shale) and Thylacocercus ignota n. gen. n. sp. (from the Wheeler Formation). The new species of Banffia Walcott, 1911 shows significant differences to the type species (B. constricta Walcott, 1911) from the Cambrian (Series 3, Stage 5) Burgess Shale, notably in possessing a prominent posterior unit but diminished anterior section. Not only does this point to a greater diversity of form among the banffiids, but also B. episoma indicates that the diagnostic median constriction and crossover of either side of the body are unlikely to be the result of taphonomic twisting but are original features. Comparisons extend also to the Cambrian (Series 2) Heteromorphus Luo and Hu in Luo et al., 1999 and, collectively, these observations support an assignment of the banffiids to the vetulicolians. The new taxon T. ignota represents the first discovery of a vetulicystid from beyond China and also significantly extends its stratigraphic range from Series 2 Cambrian into Series 3 Cambrian. Despite overall similarities in bodyplan, T. ignota differs from other vetulicystids in a number of respects, notably the possession of an anterior zone with broad tentacle-like structures. This new discovery is consistent with the vetulicystids representing stem-group ambulacrarians

Photograph and interpretive drawing of Middle Cambrian cnidarian jellyfish in oblique lateral view possibly referable to the order Coronatae, class Scyphozoa.

<p>Specimen UU07021.05, scale bar equals 5 mm. Structure marked <i>Cg</i> in drawing interpreted as a coronal groove; structures marked <i>L</i> interpreted as lappets; structures marked <i>T</i> interpreted as tentacles.</p

Stratigraphic column for Utah emphasizing Cambrian strata in the region where the new jellyfishes were collected.

<p>The new fossils come from an interval approximately 41–48 meters above the base of the Marjum Formation <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001121#pone.0001121-Briggs1" target="_blank">[26]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001121#pone.0001121-2" target="_blank">[27]</a>; approximate ages of some stratigraphic horizons are shown.</p

Photograph of Middle Cambrian cnidarian jellyfish in oblique subumbrellar view possibly referable to the family Narcomedusae, class Hydrozoa.

<p>Specimen UU07021.04, scale bar equals 5 mm.</p

Paleogeographic reconstruction for the Middle Cambrian emphasizing the position of North America.

<p>Approximate positions of locality in Utah yielding fossil jellyfishes and the site of the famous Burgess Shale are marked as indicated. Map derived using <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001121#pone.0001121-Ross1" target="_blank">[41]</a>.</p

Photograph and interpretive drawing of Middle Cambrian cnidarian jellyfish in lateral view possibly referable to the family Narcomedusae, class Hydrozoa.

<p>Specimen UU07021.03, scale bar equals 5 mm.</p

Close-up photograph showing structures interpreted as radially arranged coronal muscles.

<p>Specimen UU07021. 09.</p

Photograph and interpretive drawing of Middle Cambrian cnidarian jellyfish in lateral view possibly referable to the class Cubozoa.

<p>Specimen UU07021.02, scale bar equals 5 mm. Structures marked <i>Nb</i> in drawing are interpreted as nematocyst batteries.</p