MAMMALIAN EVOLUTION AND THE INTERPHOTORECEPTOR RETINOID-BINDING PROTEIN (IRBP) GENE - CONVINCING EVIDENCE FOR SEVERAL SUPERORDINAL CLADES

Phylogenetic relationships of 25 mammalian species representing 17 of the 18 eutherian orders were examined using DNA sequences from a 1.2-k b region of the 5' end of exon 1 of the single-copy nuclear gene known as interphotoreceptor retinoid binding protein (IRBP). A wide variety of methods of analysis of the DNA sequence, and of the translated pro ducts, all supported a five-order clade consisting of elephant shrew ( Macroscelidea)/aardvark (Tubulidentata)/and the paenungulates (hyracoi ds, sirenians, and elephants), with bootstrap support in all cases of 100%. The Paenungulata was also strongly supported by these IRBP data. In the majority of analyses this monophyletic five-order grouping was the first branch off the tree after the Edentata. These results are h ighly congruent with two other recent sources of molecular data. Anoth er superordinal grouping, with similar 100% bootstrap support in all o f the same wide-ranging types of analyses, was Artiodactyla/ Cetacea. Other superordinal affinities, suggested by the analyses, but with les s convincing support, included a Perissodactyla/Artiodactyla/Cetacea c lade, an Insectivora/Chiroptera clade, and Glires (an association of r odents and lagomorphs).