Worth a Thousand Words

Very, very long time ago, around 500 million years ago, in Cambrian, an unfortunate (for the animals involved, fortunate for science) event occurred in what is today Canada and a large number of animals met an untimely death. Buried in the sediment for all those years, the animals – both the hard and soft parts of their bodies – were wonderfully preserved in rock. A century ago, this treasure of fossils was discovered by palaeontologist Charles Walcott and named Burgess Shale Formation.

This is one of the most famous fossil fields in the world where many species of the earliest animals were beautifully preserved. These fossils tell us about the very beginnings of the evolution of animal body plans. With so many ecological niches wide open to be invaded, animals experimented wildly, adopting a large variety of new anatomies, physiologies and behaviors. This is the time when first (relatively) large predators evolved. This period, known as Cambrian Explosion, was a time of much evolutionary experimentation. Some species were luckier than others, some were perhaps better fitted to the environment than others or were more successful at breeding in large numbers. They are the ancestors of all the body plans and all the animal phyla we have had on Earth since then. The others? The others went extinct and their fossils are sometimes so strange, they look more like space aliens than anything we are familiar with today.

The fossils of Burgess Shale became more widely known in 2000 when Stephen Jay Gould published a book about them – The Wonderful Life. This best-seller introduced words like Opabinia, Hallucinogenia and Anomalocaris into the day-to-day language (OK, OK, I know, not everyone is as geeky as I am). But since the book was written science did not stop. The Shale is still been diligently explored, fossils are reinterpreted and new fossil species are discovered all the time, each such finding helping us refine our understanding of early animal evolution, the principles of speciation, the early ecology and behavior of animals, and the phylogenetic relationships between the phyla.

A number of the strangest fossils from the Shale are so difficult to classify using current animal classification, they were given designation Problematica until more information is uncovered. One such new fossil that helps move some members of Problematica into a more specific group, was recently discovered. This fossil, Herpetogaster collinsi , was described last week in PLoS ONE by Jean-Bernard Caron of the Royal Ontario Museum, Simon Conway Morris from University of Cambridge and Degan Shu from the Northwest University in China in the article Tentaculate Fossils from the Cambrian of Canada (British Columbia) and China (Yunnan) Interpreted as Primitive Deuterostomes:

Molecular and morphological evidence unite the hemichordates and echinoderms as the Ambulacraria, but their earliest history remains almost entirely conjectural. This is on account of the morphological disparity of the ambulacrarians and a paucity of obvious stem-groups. We describe here a new taxon Herpetogaster collinsi gen. et sp. nov. from the Burgess Shale (Middle Cambrian) Lagerstätte. This soft-bodied vermiform animal has a pair of elongate dendritic oral tentacles, a flexible stolon with an attachment disc, and a re-curved trunk with at least 13 segments that is directed dextrally. A differentiated but un-looped gut is enclosed in a sac suspended by mesenteries. It consists of a short pharynx, a conspicuous lenticular stomach, followed by a narrow intestine sub-equal in length. This new taxon, together with the Lower Cambrian Phlogites and more intriguingly the hitherto enigmatic discoidal eldoniids (Cambrian-Devonian), form a distinctive clade (herein the cambroernids). Although one hypothesis of their relationships would look to the lophotrochozoans (specifically the entoprocts), we suggest that the evidence is more consistent with their being primitive deuterostomes, with specific comparisons being made to the pterobranch hemichordates and pre-radial echinoderms. On this basis some of the earliest ambulacrarians are interpreted as soft-bodied animals with a muscular stalk, and possessing prominent tentacles.

Even if the new classification is not 100% certain yet, one cannot help but gasp at the amazing quality of preservation of the fossil over 500 million years, and the strange beauty of this ancient, long-extinct animal:

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