Sequence-based molecular phylogenies have provided new models of early eu- karyotic evolution. This includes the widely accepted hypothesis that animals are related most closely to fungi, and that the two should be grouped together as the Opisthokonta. Although most published phylogenies have supported an opisthokont relationship, a number of genes contain a tree-building signal that clusters animal and green plant sequences, to the exclusion of fungi. The alter- native tree-building signal is especially intriguing in light of emerging data from genomic and proteomic studies that indicate striking and potentially synapomor- phic similarities between plants and animals. This paper reviews these new lines of evidence, which have yet to be incorporated into models of broad scale eukaryotic evolution.
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