A stupid question about the "pygmy panda" discovery...?

Question

I'm not an expert on this stuff, only a person who reads National Geographic and Discover and watches zoos' panda cams. So if this sounds ignorant, please forgive me.

The discovery of the giant panda's "pygmy panda" ancestor was in the news:
http://news.yahoo.com/s/afp/20070618/sc_afp/usanimalschinapanda_070618210510

The scientists claim that the small panda skull they found proves the existence of a now-extinct pygmy panda ancestor. My question is, how do they know it was a small ancient adult panda and not a modern panda cub? What was different?

I know panda cubs grow *really* fast, so I was thinking they'd have a lot of cartilage and their skulls would look different from adults'--would that be right, or am I off base?

Just curious. I really wish pygmy pandas were still around, so I could have one as a pet! :-)

Answer 1

As juvenile mammals grow, there are a number of skull characters which shift and change. Most notably is the joining and fusing of different bones that are connected only by cartilage in the young animal. There is also the replacement of milk teeth by the adult dentition.

The skull of an adult pygmy panda would show all of the adult signs (i.e. fused sympheses, full adult dentition) even if it is half the size of the modern panda skull. If it was still a juvenile, it would possess many of the juvenile characters.

The article didn't go into much detail, but I would imagine there are also differences in the cusps of the teeth between this pygmy panda and the modern giant panda. A lot of mammalian paleontology is based on differences between teeth.

Answer 2

Adding to the previous answer, Carbon 14 dating can be used to find out exactly how old the panda skull is.

You are right about the amount of cartilage, the only thing is cartilage decays rather quickly after an animal dies.

I think it's great you have an interest in these things!

Answer 3

Normally you can estimate an animal's age by looking closely at the teeth.
So I expect that if they have a skull they'll have looked there. Also there are the fontanelles etc. that can be used to decide whether that was a juvenile or an adult.
However,even if it was an adult, a single skull does not constitute an entirely new species in this case. It may also have been a single individual which suffered from imperfect growth.