Nectocaris - History of Study

History of Study

Charles Doolittle Walcott, the discoverer of the Burgess Shale, had photographed the one specimen he had collected in the 1910s, but never had time to investigate it further. As such, it was not until 1976 that Nectocaris was formally described, by Simon Conway Morris.

The head had two stalked eyes, one pair of tentacles, and a flexible siphon underneath its body. Fleshy fins supported by internal spines ran along the sides of the flattened, kite-shaped body. Because the genus was only known from a single partial specimen with no counterpart, Conway Morris was unable to deduce its affinity. It had some features which were reminiscent of the arthropods, but these could well have been convergently derived. Its fins were very unlike the arthropods.

Working from photographs, the Italian palaeontologist Alberto Simonetta believed he could classify Nectocaris within the chordates. He focussed mainly on the tail and fin morphology, interpreting Conway Morris's 'gut' as a notochord – a distinctive chordate feature.

The classification of Nectocaris was revisited in 2010, when Martin Smith and Jean-Bernard Caron described 91 additional specimens, many of them better preserved than the type. These allowed them to reinterpret Nectocaris as a primitive cephalopod, with two tentacles instead of the 8 or 10 of modern cephalopods. The structure previous researchers had identified as an oval carapace or shield behind the eyes was suggested to be a soft funnel, similar to the ones used for propulsion by modern cephalopods. The interpretation would push back the origin of cephalopods by at least 30 million years, much closer to the first appearance of complex animals, in the Cambrian explosion, and implied that – against the widespread expectation – cephalopods evolved from non-mineralized ancestors.

A later analysis claimed to undermine the cephalopod interpretation, stating that it did not square with the established theory of cephalopod evolution. According to these authors, Nectocaris is best treated as a member incertae sedis of the arthropod group Dinocaridida (which includes the anomalocaridids), but they stopped short of formally changing the classification. However, it is straightforward to demonstrate that an anomalocaridid affinity is not supported. Other studies have yet to put forwards a more plausible affinity.