The Monotremes

Monotremes are a small but remarkable group of mammals that consists of a single species of duckbill platypus (Ornithorhynchus anatinus) found in Australia and three (perhaps four) species of spiny anteaters (echidnas) found in Australia and New Guinea.

These animals retain several traits of their therapsid ancestors including Despite these reptilian features, the monotremes meet all the criteria of true mammals:

In the May 8 issue of Nature, a consortium of gene sequencers reported the results of sequencing the complete genome of the platypus.

They identified 18,527 protein-coding genes distributed on 52 chromosomes.

The mix of mammalian and reptilian phenotypic features turns out to be reflected in the genome as well. Examples: Other features of their genome reflect their unique biology:
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20 May 2008