"So we thought Platypus is just a mammal..."

Platypus is probably one of the most bizarre living creatures, whom body feature could not wholly represent neither of the animal phyla. Recent evidences have suggested platypus genome might have conserved much of the reptile genomes long before their convergence with mammals.

Undoubtedly platypus (Order Monotremata) and other mammals are one distinct divergent of amniotes from reptiles and birds, who commonly share the feature of fluidic membrane enclosing a developing fetus.

Although previous studies have segregated platypus from birds and reptiles’ classification, as there are vast similarity with mammals’ gene sequencing and protein development; it is found that platypus reproductive system has retained two ZPAX genes that are found in bird, fish and amphibian merely. Ovary size and protein secretion in sperm production are also comparable with relative reptiles. Male platypus also undergoes venom development alike to reptiles, where genome congregation process gives rise to a mixture of 19 chemicals forming the unique toxin. Moreover, density of chromosomal microsatellite shares a common distribution with most of the reptile; nevertheless with the number of microsatellite similar to the avian group. Platypus has also found to have multiple sex chromosomes that may have suggested a bird-like ancestral trait genetically. These have proven platypus is not just a mammal derivative, but a missing link of where prehistoric organisms may originate from the same ancestor.

With a developing veterinary genomes technology, these findings provide a valuable insight of mammalian evolution, with the integration of other species genetics. Further researches would certainly be done upon this; however this discovery is as fascinating to imagine how millions of species could be derived from a single genome.

Shuk Wai Belinda LI

Primary reference:
Warren, W.C. et al, 2008, Genome analysis of the platypus reveals unique signatures of evolution, Nature, 453 (8 May 2008), 175- 83
Cited 24th May
[Available: http://www.nature.com/nature/journal/v453/n7192/full/nature06936.html]

Secondary references:
Derbyshire, D., 2008, ‘It's a bird, it's a beaver.... actually the duck-billed platypus is neither as scientists decode its DNA for the first time’, Daily Mail, 8th May
Cited 24th May [Available: http://www.dailymail.co.uk/news/article-564748/Its-bird-beaver---actually-duck-billed-platypus-scientists-decode-DNA-time.html]

Warren, W.C. et al, 2008, Genome analysis of the platypus reveals unique signatures of evolution, Nature, 453 (8 May 2008), 175- 83 - Table 1
[Available : http://www.nature.com/nature/journal/v453/n7192/fig_tab/nature06936_T1.html]

Warren, W.C. et al, 2008, Genome analysis of the platypus reveals unique signatures of evolution, Nature, 453 (8 May 2008), 175- 83 - Notes S22
[Available : http://www.nature.com/nature/journal/v453/n7192/extref/nature06936-s1.pdf ]