Soft tissue in fossils?

[Helios]

I'm certain you've all heard about the soft tissue of a Tyrannosaurus which was discovered a while back. So now my question is, now that we know soft tissues can be preserved, what efforts are being done to find more (if any at all)?

 

You'd think we could learn a great deal from any other discoveries, so what's the justification for not looking?

[Sisyphus]

My guess is you look for soft tissue (which is incredibly rare) the same way you look for other fossils. So they're not "not looking," it's just hard to find.

[lucaspa]

I'm certain you've all heard about the soft tissue of a Tyrannosaurus which was discovered a while back. So now my question is, now that we know soft tissues can be preserved, what efforts are being done to find more (if any at all)?

 

You'd think we could learn a great deal from any other discoveries, so what's the justification for not looking?

 

Who says people are "not looking"? How many fossils of dinos from that time period have been found? How many had surviving marrow stroma?

 

I suspect that every paleontologist is looking inside every new bone that they find, all looking to see if there is marrow stroma there.

[lucaspa]

The April 13 Science has 2 articles looking further at "soft tissues" in fossils. They are actually using mass spectrophotometry to get the amino acid sequences of the type I collagen in bones! They did 2 fossils: a 100,000 to 600,000 year old mammoth and the 65 Mya T. rex fossil.

 

The paper describes quite elaborate techniques to get the amino acid sequences. First they demineralize the bone with EDTA, then extract the protein. 90% of protein in bone is type I collagen. They then do a trypsin digest of the collagen and purify the resulting peptides. Trypsin cleaves proteins where there is an arginine or lysine. Thus, each species will give slightly different peptides depending where the lysine or arginine comes in the sequence in their collagen. But type I collagen is highly conserved, so the mass spec of trypsin fragments from the mammoth and T rex collagen can be compared to the known amino acid sequences of the mass spec from existing species where this has been done. This gives the amino acid sequences for those fragments from the mammoth and T. rex.

 

It turns out that only about 38% of the amino acid sequence for the mammoth could be determined this way, but that is 38% more than we knew before. Only 7 fragments could be identified from the T. rex, but that represents sequences of over 50 amino acids we didn't know before.

 

It was enough to show that the modern animal with the closest sequence of type I collagen to T. rex is the chicken. Not much of a surprise, but independent support that birds are the closest living relatives to dinos.