Recent molecular studies have established strong evidence for four primary, superordinal mammalian clades: Afrotheria, Xenarthra, Euarchontoglires and Laurasiatheria [27, 28] . The CEA gene family is well known in primates (humans) and rodents (mice and rats). However, both orders belong to the same principal lineage of placental mammals, the Euarchontoglires. Since carnivores belong to the Laurasiatheria clade, we expected to gain new insights into the evolution of the rapidly diverging CEA family by analysis of the CEA family of the dog. First of all, identification of CEACAM1, CEACAM16, CEACAM18, CEACAM19 and CEACAM20 orthologs in the dog genome at corresponding chromosomal locations, strongly indicates that the CEA gene family of the common ancestor of Euarchontoglires and Laurasiatheria consisted of at least five genes. It remains to be seen whether species which represent older mammalian lineages like Afrotheria, marsupials and monotremes contain the same set of primordial genes. Furthermore, the findings of this work supports our previous hypothesis that CEACAM3-CEACAM8, CEACAM21 and CEACAM9-CEACAM15, CEACAM17, none of which is present in the dog genome ( Figure 2A and data not shown), represent primate and rodent-specific genes, respectively [3] . The ancestral members of the CEA gene family are located in three different loci (Figure 1 ). While CEACAM16, CEACAM19 and CEACAM20 are close together (CEACAM16 and CEACAM19 are next to each other), CEACAM1 is separated from this locus by more than 1 Mbp and CEACAM18 is displaced into the SIGLEC gene cluster in humans, mice and dogs.