Extraordinary fossils reveal the nature of Cambrian life: a commentary on Whittington (1975) ‘The enigmatic animalOpabinia regalis, Middle Cambrian, Burgess Shale, British Columbia’

Abstract

Harry Whittington's 1975 monograph on Opabinia was the first to highlight how some of the Burgess Shale animals differ markedly from those that populate today's oceans. Categorized by Stephen J. Gould as a ‘weird wonder’ (Wonderful life, 1989) Opabinia, together with other unusual Burgess Shale fossils, stimulated ongoing debates about the early evolution of the major animal groups and the nature of the Cambrian explosion. The subsequent discovery of a number of other exceptionally preserved fossil faunas of Cambrian and early Ordovician age has significantly augmented the information available on this critical interval in the history of life. Although Opabinia initially defied assignment to any group of modern animals, it is now interpreted as lying below anomalocaridids on the stem leading to the living arthropods. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.

The trilobite upper limb branch is a well-developed gill

“…Comparable to the filaments in the euarthropods such as trilobites, the setal blades in the lower stem euarthropods, e.g., gilled lobopodians and radiodonts, have also attracted much attention and been widely suggested to have had respiratory function ( 19 , 20 , 35 , 36 ). These blades are thin and flexible, show rounded termination, and are displayed as fine lamellae ( 19 , 20 ).…”

“…The latter would have limited the effectiveness of a distributed system of cuticular diffusion, which is restricted to small-sized animals ( 53 ). At larger sizes, increased metabolic demand for oxygen exceeds that provided by cuticular diffusion alone ( 54 ) and requires specialized respiratory organs, as are apparent in the setal blades of Radiodonta ( 19 , 20 , 36 , 37 ). Here, we reveal details of gill structure among early arthropods that were acquiring an increasingly reinforced exoskeleton.…”

An embryological perspective on the early arthropod fossil record

“…The fossil Opabinia regalis from the Burgess Shale is the “poster-child” of the weird and wonderful view of the Cambrian world [ 37 ]. Despite its many seemingly bizarre characteristics, its germband stage embryos can be reconstructed as fairly simple (Fig.…”

“…There is an ongoing debate as to whether O. regalis had lobopods as well as dorso-lateral flaps [ 38 , 39 ], or whether the putative lobopods are actually gut diverticula [ 37 , 40 ]. In this reconstruction I have accepted the latter approach.…”

On the edge of exceptional preservation: insights into the role of redox state in Burgess Shale-type taphonomic windows from the Mural Formation, Alberta, Canada

“…[10] for definitions). Critically, these Lagerstätten preserve the soft parts of animals, and while the communities do not preserve a completely unbiased snapshot of early Cambrian life (for instance, size; [11]), they do provide our best glimpse of early metazoan ecosystems [12][13][14][15]. Most important, by preserving most or all characters of an organism, fossils from BST biotas have been critical in understanding the polarity and order of morphological character evolution within each individual phylum [16].…”