Figure 2. Reconstruction of the rodent phylogenetic relationships based on a gross beaver genome assembly and retroposon presence/absence screening (highlighted in blue).

3,780 potential phylogenetically informative retroposons were extracted from the beaver reference assembly and projected onto sequence information of other rodent genomes and onto PCR-amplified orthologs from Anomaluromorpha. These newly revealed markers are shown as enlarged red balls. Previously identified phylogenetically diagnostic retroposon markers are indicated by black and two conflicting yellow balls⁵. The two screening strategies and the resulting diagnostic presence/absence patterns are indicated for Castorimorpha and also the mouse-related clade. The myomorphous, sciurimorphous, and hystricomorphous zygomasseteric systems¹⁸,¹⁹ are illustrated to the right (blue and red lines show anterior parts of medial and lateral masseter, respectively; for details of zygomasseteric systems in rodents see Potapova²⁷). The mandible types²⁰ are noted: sciurognathous and hystricognathous. For the squirrel-related clade, only the zygomasseteric system of Sciuridae is presented. The rodent paintings were provided by Jón Baldur Hlíðberg.