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Extraordinary Fossils Reveal the Nature of Cambrian Life: A Commentary on Whittington (1975) 'The Enigmatic Animal Opabinia Regalis, Middle Cambrian, Burgess Shale, British Columbia'

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Review

Extraordinary Fossils Reveal the Nature of Cambrian Life: A Commentary on Whittington (1975) 'The Enigmatic Animal Opabinia Regalis, Middle Cambrian, Burgess Shale, British Columbia'

Derek E G Briggs. Philos Trans R Soc Lond B Biol Sci.

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.

Keywords: Burgess Shale; Cambrian explosion; Opabinia; fossil preservation.

Figures

Figure 1.
Figure 1.
Opabinia regalis Walcott, 1912; USNM 155600 preserved in lateral view. (a,b) Counterpart ‘flipped’ horizontally to match (c), Whittington's [, fig. 35] composite explanatory drawing of the part and counterpart; (a) is illuminated from a low angle and (b) from a high angle to generate reflection in the eyes, for example, showing the method Whittington used to illustrate different features of the Burgess Shale specimens. The needle-marks evident in (a) show where Whittington prepared the specimen to reveal the terminal spines on the ‘flexible frontal process’ or proboscis which is flexed backwards underneath the body. (c) Whittington's camera lucida drawing and interpretation. L and R indicate features on the left and right sides of the body; i and o, inner and outer eyes; l, lateral lobes of the trunk, numbered from the anterior; f, blades of the tail fan; ds, dark stain representing material that has ‘leaked’ beyond the body.
Figure 2.
Figure 2.
Major published reconstructions of Opabinia regalis Walcott, 1912 through time. Whittington's [, fig. 82] version shows a dorsal and lateral view with the lobe and gill of segment 7 removed to show those of segment 8 in full. The position of the three cross sections of the body, with the outline of the gut internally, are indicated by the arrows. ((d) and (e) reproduced from [34] and [35] respectively with permission from John Wiley and Sons.)
Figure 3.
Figure 3.
Whittington's (1979) diagram of the pattern of evolution in arthropods (adapted from [, fig. 2]).
Figure 4.
Figure 4.
Illustrations of (a) Opabinia and (b) Anomalocaris from Stephen J. Gould's Wonderful life [, figs 3.21 and 3.66, respectively]. © Marianne Collins, artist.
Figure 5.
Figure 5.
The first published cladogram to include Opabinia (adapted from [, fig. 4]). Opabinia, Kerygmachela, and possibly Anomalocaris are grouped as a stem clade to the other arthropods. The enclosed clades are those that have become ‘arthropodized’, i.e. evolved a stiffened cuticle.
Figure 6.
Figure 6.
Present consensus on the position of Opabinia in the arthropod stem. (Adapted from [35, fig. 8], after [–35].)

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References

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