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Hooking some stem‐group “worms”: fossil lophotrochozoans in the Burgess Shale
Author(s) -
Butterfield Nicholas J.
Publication year - 2006
Publication title -
bioessays
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.175
H-Index - 184
eISSN - 1521-1878
pISSN - 0265-9247
DOI - 10.1002/bies.20507
Subject(s) - annelid , phylum , polychaete , biology , extant taxon , dorsum , zoology , group (periodic table) , evolutionary biology , paleontology , anatomy , ecology , chemistry , organic chemistry , bacteria
The fossil record plays a key role in reconstructing deep evolutionary relationships through its documentation of the early diverging stem groups leading to extant phyla. In the middle Cambrian Burgess Shale, two famously problematic worms, Odontogriphus and Wiwaxia , have recently been reinterpreted as stem‐group molluscs based on their shared expression of a putative radula and putative ctenidia in Odontogriphus .1 More detailed analysis of these fossil structures, however, reveals pronounced anatomical and histological discrepancies with molluscan analogues, such that they are more reliably interpreted as primitive features of the superphylum Lophotrochozoa. In the absence of any obviously derived characters, Odontogriphus could be placed in the stem group of the Lophotrochozoa or on the stem of any of its constituent phyla, whereas the dorsal covering of chaetae in Wiwaxia identifies it as a stem‐group polychaete. Despite their close relationship, these two jawed, segmented worms could conceivably represent the early stages of two separate phyla. BioEssays 28: 1161–1166, 2006. © 2006 Wiley Periodicals, Inc.