New research has genotyped the ancient mtDNA of a wild aurochs from Italy. Importantly, the research challenges current understanding of Bos taurus phylogeny, suggesting that clades T1, T3 and T4 are paraphiletic, or more precisely: that they cannot be resolved phylogenetically to full satisfaction because:
Bayesian phylogenetic analysis of the European cattle and aurochs mtDNA coding genomes revealed that a model allowing for polytomies is strongly supported over a strict bifurcating model (Bayes Factor >100). Therefore, the pattern of previously classified bovid clades and sub-clades is not supported, suggesting that recurrent mutations and short internal branches may limit meaningful evolutionary information.
M. Lari et al., The Complete Mitochondrial Genome of an 11,450-year-old Aurochsen (Bos primigenius) from Central Italy. BMC Evolutionary Biology, 2011. Open access.
The aurochs sequence falls within T3 but the authors warn against this classification because of the issues mentioned before.