Metazoica

The second article I found was this one that says animal life is much older than first expected. Seems every time I turn around, I hear that animal life is actually getting older. Not that it's a bad thing, but sometimes I wonder how old animal life really is. Will the scientists ever really find out? The more I look, the more I realize sooner or later it's going to be proven that the chart on my site is wrong.


http://dsc.discovery.com/news/2009/02/04/fossils-life.html


Fossils Push Animal Life Back Millions of Years
AFP

Feb. 4, 2009 -- Animal life first appeared on Earth tens of millions of years earlier than thought, according to a new study released Wednesday.

A novel technique used to date fossils buried in rock sediment in Oman shows that sponges, among the most primitive of animal organisms, flourished there more than 635 million years ago.

The new dating answers a puzzle that beset Charles Darwin.

In the mid-19th century, the first evidence for the kingdom of Animalia, also called Metazoa, came from the so-called Cambrian explosion of biodiversity, around 540 million years ago.

Darwin reasoned that this eruption of life forms could not have occurred without previous evolution, but no fossils emerged during his lifetime to confirm his hunch.

In recent years, various pieces have come forward that have indeed pushed back the rise of Animalia by some millions of years.

But the new find dates their emergence even earlier, into the final stages of a massive ice age at the end of the Neoproterozoic Era.

The Oman sponges are part of the Demospongiae class, which accounts for more than 90 percent of all sponges in existence today, notes the study, published in the London-based science journal Nature.

To find them, a team of scientists led by Gordon Love of the University of California had to come up with a new trick, for sponges lack the calcium-rich shells or bones that palaeontologists seek to provide a data signature.

So they developed an elaborate method -- based on gas chromatography and mass spectrometry, laboratory techniques for isolating molecules -- that detects unique biomarkers derived from the lipid membranes of once-living organisms.

The key biomarker is a 30-carbon steroid called 24-isopropylcholestrane, or 24-ipc for short.
To date, the only known source of 24-ipc are species of the Demospongiae, one of the three main classes of sponges.

Metazoa are by definition mobile at some stage of their life cycle and ingest other organisms for sustenance.

Most are also multicellular, meaning that they have evolved different cell types that serve divergent biological functions.

Sponges are the simplest of all multi-celled animals.

As a rule, their open-ended, sack-like bodies are fixed to rocks in shallow seas and pull in water to filter out nutrients.

Sponges were long considered the earliest common ancestor of all animals, but a genetics study last year suggested that Ctenophora, or comb jellyfish, reach even further back on the evolutionary ladder.