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:Archaefructus, from the BarremianAptian Yixian Formation (see node 10), has been assigned to total group Nymphaeales (Friis et al., 2003; Doyle, 2008), but other phylogenetic analyses suggest that it is a stem Angiosperm (Sun et al., 2002).
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