Goffr
Posts: 15
Joined: Feb. 2007
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| Quote (Paul Nelson @ April 25 2008,08:53) | JAM wrote:
| Quote | | The answer is that since we know that the underlying molecular mechanisms are incredibly conserved, it's not a problem. |
This assumes the point at issue. To wit: We already know the mammal-like reptiles are related by descent with modification, via the natural selection of randomly-arising variation (or an array of unknown evolutionary mechanisms, if selection does not suffice). Therefore their size differences are easy to explain.
What independent evidence do you have for the molecular mechanisms (regulating body size) at work in the extinct groups -- therapsids, etc. -- featured in the reptile-to-mammal sequence?
In what natural populations of canids, JAM, do we observe size differences on the scale seen in domesticated dogs? |
Maybe canines aren't the best example to use, considering that they have been living and have been bred by humans for millennia.
I'd recommend looking at a group of animals from a continent that hasn't had so much in the way of overpopulation of humans, Australia.
If you want to see some real diversity in size differences in a particular animal, check out the kangaroo (Macropodidae) family.
Fossils indicate the largest kangaroo, Procoptodon, was about 3 metres (10 feet) in height, and wighted an estimated 232 kg (507 pounds).
The largest living kangaroos at the moment, the red kangaroo, grows to 2 meters (6 ft 7 in) tall and weighs 90 kg (200 lb).
One of smallest of the Macropodidae family weigh in at somewhere around 2.5 to 5 kg and are only about 40 to 54 cm long.
The extended family makes it down to rat size, whilst maintaining very kangaroo orientated features.
Variation in size is quite huge in the family, they are mostly non-extinct and have been left alone by humans. Natural selection is the only force at work with these animals. The differences between the various species are piecemeal and it's quite obvious where its evolutionary roots lie - see the sub-order Macropodiformes for the extended family.
Also, one particular genus (Dendrolagus) learnt to climb trees! I don't see dogs climbing trees. ;)
Anyways, what's going on with the evisceration of Explore Evolution? I keep on checking this page to see some juicy lies being torn apart but its not happening. It makes me sad. :(
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