The platypus genome

Posted 10 May 2008 by PZ Myers

Finals week is upon me, and I should be working on piles of paper work right now, but I need a break … and I have to vent some frustration with the popular press coverage of an important scientific event this week, the publication of a draft of the platypus genome. Over and over again, the newspaper lead is that the platypus is "weird" or "odd" or worse, they imply that the animal is a chimera — "the egg-laying critter is a genetic potpourri — part bird, part reptile and part lactating mammal". No, no, no, a thousand times no; this is the wrong message. The platypus is not part bird, as birds are an independent and (directly) unrelated lineage; you can say it is part reptile, but that is because it is a member of a great reptilian clade that includes prototherians, marsupials, birds, lizards and snakes, dinosaurs, and us eutherian mammals. We can say with equal justification that we are part reptile, too. What's interesting about the platypus is that it belongs to a lineage that separated from ours approximately 166 million years ago, deep in the Mesozoic, and it has independently lost different elements of our last common ancestor, and by comparing bits, we can get a clearer picture of what the Jurassic mammals were like, and what we contemporary mammals have gained and lost genetically over the course of evolution.

We can see that the journalistic convention of emphasizing the platypus as an odd duck of a composite creature is missing the whole point if we just look at the title of the paper: "Genome analysis of the platypus reveals unique signatures of evolution." This is work that is describing the evidence for evolution in a comparative analysis of the genomes of multiple organisms, with emphasis on the newly revealed data from the platypus.

Continue reading "The platypus genome" (on Pharyngula)

10 Comments

Pete Dunkelberg · 10 May 2008

...you can say it is part reptile, but that is because it is a member of a great reptilian clade that includes prototherians, marsupials, birds, lizards and snakes, dinosaurs, and us eutherian mammals.

Not quite. There is an amniote clade which includes all that and more. Reptilia as a clade is just the right hand branch of this cladogram.

Rob · 10 May 2008

I think this is a definitional thing. In the sense you mean, it obviously is not a chimera. Literally? there is NO such thing as a chimera, although given modern means, we can create one. In the sense in which the newspapers use the term, I think they could be (not must be) justified. And in terms of mammal versus reptile, chimera is not a horribly bad description.

cath · 10 May 2008

I don't object to the use of the word chimera. It's a perfectly sound classical metaphor; only in modern technical usage is it incorrect. And the classical meaning pre-dates the technical meaning by a couple of thousand years.

The original Chimera was a mythical animal that was part lion, part dragon, and part goat. It's a mix up of other animals, a common mythical theme as seen in sphinxes, griffins, pegasus, centaurs and many more.

Torbjörn Larsson, OM · 11 May 2008

As I understand that cladogram homeothermy and four-chambered hearts evolved at least twice, in mammals and in archosaurs (or at least modern dinosaurs as opposed to crocodilians).

Is that why IIRC birds lack mammals brown fat for thermal regulation and have the mirror solution for hearth circulation?

R Ward · 11 May 2008

Does the platypus produce uric acid or urea?

I haven't seen this information on egg-laying mammals. If it's urea, like placental mammals, how do they deal with build-up of urea in the developing eggs?

Henry J · 11 May 2008

Wouldn't reptiles have had that same issue, if that stuff is produced during the embryo stage?

Or is urea/uric an issue for warm blooded creatures that wasn't a problem for cold blooded creatures?

Henry

Stanton · 11 May 2008

Henry J said: Wouldn't reptiles have had that same issue, if that stuff is produced during the embryo stage? Or is urea/uric an issue for warm blooded creatures that wasn't a problem for cold blooded creatures? Henry

Birds and most living reptiles secrete uric acid in order to conserve metabolic water, so I don't think it's a concern over ectothermy vs endothermy. Freshwater turtles, such as the red-eared slider, secrete uric acid when they are still in the egg, but then switch to secreting the metabolically less-expensive urea soon after hatching. The platypus, like other living mammals, secretes urea. Apparently, no one has attempted to find out whether or not monotremes secrete uric acid as embryos, and then switch to secreting urea after hatching, like freshwater turtles. I'm thinking it's because monotremes rarely, if ever, lay eggs in captivity, and that, what with monotremes being painfully endangered species, it may be that scientists consider the eggs too valuable to sacrifice, also. http://www.madsci.org/posts/archives/2006-04/1145099204.Zo.r.html

Dolly Sheriff · 15 May 2008

Odd that it it hasn't evolved much in about a 100 million years! Seems like this little beastie ressists any pigeon-hole-ing from the Darwin lobby.

Science Avenger · 15 May 2008

The only people concerned with "pigeon-hole-ing" are the baraminologists. Just what "kind" is a platypus anyway?

Stanton · 15 May 2008

Dolly Sheriff said: Odd that it it hasn't evolved much in about a 100 million years! Seems like this little beastie ressists any pigeon-hole-ing from the Darwin lobby.

100 million years ago, the ancestors of monotremes diverged from the ancestors of marsupials and placental mammals. You would have realized that if you actually read this article rather than arrogantly flaunt your idiotic ignorance. Furthermore, the platypus strongly resembles its ancestors, Obdurodon and Steropodon because it has not changed its ecological niche. You would have known this if you did not willingly put your eyes out. Lastly, Creationists and Intelligent Design proponents, such as yourself, have proven time and time and time again that they do not care crap about doing any science whatsoever. All they care about is making a Bronze Age book of philosophy and poetry into the science textbook of the land, and they don't care that doing this will plunge the country back into the Stone Age.