Aussie fish fossil gives birth to history

[Cirith Ungol]

And here is the link

New fuel for the oldest debate topic in history

 

[DrAce]

I REALLY want to see what was happening inside that fish.

That's freaking cool!

 

[Cirith Ungol]

I might just be able to show you a little more...

Click on the three images that are in a row. There you can see more details.

 

[Stylopidae]

I REALLY want to see what was happening inside that fish.

That's freaking cool!

Perhaps something similar to what happens in sharks?

 

[DrAce]

Perhaps something similar to what happens in sharks?

Perhaps... but there are two types of internal incubation in sharks... ovivoparity and vivoparity. The first is where the eggs are basically internal - but they are still eggs. The second is where there is a placental feeding type arrangement between mum and the embryo/fetus (not always, I seem to recall that some sharks basically bathe the embryos in milky secretions...).

Of course, Sharks are a fairly well evolved group which are actually quite different from many other fish. Maybe this fossil has a completely different way of doing things.

 

[Thoth]

It seems similiar to the way some shark species give birth, though it still seems unclear to me where it is a true live birth or an internally held egg, which also occurs with some fish species. Interesting nonetheless. (edit: Drat my slow typing. My point is now moot.)

Though I don't think it'll make much difference in the raging debate (unless the umbilical cord is found to be a strand of pasta.

 

[Travis K]

Yeah, I fail to see how this is evidence for or against evolution.

 

[Cirith Ungol]

Yeah, I fail to see how this is evidence for or against evolution.

Interesting. You are the first to say anything of the sort.

 

[Stylopidae]

Interesting. You are the first to say anything of the sort.

Especially seeing as how nobody actually mentioned that topic at all...either in the sources you posted or anybody else who's posted so far. The reference was completely imagined by Travis and nobody else.

From what I read (well, skimmed really), all we can really see is a handful of fetal bones, the yolk sac and the umbilical cord. Nothing else.

What makes this unique is that this proves that (some) Placoderms were much more complex than originally thought. It's not every day you see details such as this in a 300 million year old fossil.

http://scienceblogs.com/pharyngula/2008/05/materpiscis_attenboroughi.php

PZ Myers has a pretty good writeup on it as well. Short, but good.

 

[DrAce]

Yeah, I fail to see how this is evidence for or against evolution.

Right, Travis. Just to show you exactly how much we know about evolution, and some of the very specific research which more closely shows what's going on, focusing on the placenta.

The placenta is one of the more remarkable organs we have. Not only does it form as a result of some of the more spectacular epigenetic markings, but it is one of the few structures in the human body which forms a multinucleate cellular structure (i.e. the initial portions of the placenta, called the syncytiotrophoblast, is one very big cell, with a lot of nuclei floating in it).

Mammals are not the only animals with a placenta. As mentioned, some species of fish have a 'placenta'... although it's different to ours (but does the same job... JUST like the eye is different in some species, but does the same job).

The job of the placenta is to act as an interface between the foetus and the mother. There is not only a insulation against things happening in the mother, but a semi-permiable layer which transports things accross the barrier into the foetus. It's also endocrine/secretory. It produces hormones and chemicals which act on mother and baby, and which suppress the maternal immune system. Much of this is still being studies (the lab next to mine works on it).

In animals, there are three main ways to raise a baby. You can lay an egg - and the foetus will feed of a supply in that egg. You can keep the baby internally and feed it from your personal stores (like via a placenta, or a nutrient broth). You can keep the egg internally, and let it develop there.

In the case of eggs, the total weight of the egg/fetus drops over time as you develop. This is because some of the energy and mass of the egg is emitted as carbon dioxide or similar as the foetus grows. If maternal nutrients are being supplied, the baby is always bigger than the egg, because there is no limit to the supply being given.

A paper which Cheshire forwarded me explains this excellently. You can find it here. The Poeciliopsis genus of fish have INDEPENDANTLY evolved placentas THREE times.

Here's how we know.

DNA gets errors slowly over time. Say, one code per gene, per 10 years. Most of these are completely harmless, and obviously the fish just keep on living. But if they occur in a different species, then you get a difference in the genes which doesn't then get weeded back into the original population. So you can compare sequences of genes and see how 'different' they are, and use it to get a family tree. This has been done with people, and other animals with a known pedigree and it's a very good solid technique.

So, this group used two genes (called cytochrome-b, and nicotinamide adenine dinucleotide, reduced form, subunit 2) to get a family tree of the Poeciliopsis genus:

The colours are important. In RED are those species with placentas. In BLUE are those without. In GREEN are those which show something inbetween (meaning, a TRANSITION SPECIES... Ohhh, one of those horrible things).

There are three close sets of species which are clumped in red. They have blue clumps between them. This MEANS (not implies, MEANS) that they have independantly evolved placentation... and there are a range of species between without, or with 'most' of a placenta.

This is just as significant as finding a whole pile of species with a rainbow of 'with eye', 'without eye' and everything inbetween.

Seriously, Travis, the placenta is a very good model of evolution.