Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…metazon divergence
Molecular clock analyses have challenged the conventional wisdom about the emergence of several metazoan phyla in late Vendian and early Cambrian periods [<600 million years ago (mya)] (e.g., Runnager 1982; Doolittle et al. 1996; Wray et al. 1996; Nikoh et al. 1997).
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