Genetic analysis of 64-million-year-old rocks suggests that the sea
sponge may have been the first animal to develop on Earth.


By Michael Holtz, Staff writer February 26, 2016

Scientists estimate that there are about 8.7 million species of
animals on Earth – give or take 1.3 million. But in the beginning
there could be only one.

That animal was very likely the simple sea sponge, according to a
study by researchers at the Massachusetts Institute of Technology in
Cambridge.

Based on new genetic tests, the team of scientists can say with
confidence that molecules produced by sea sponges have been found in 640-million-year-old rocks. These rocks significantly predate the
Cambrian explosion, the period 540 million years ago in which most
animal groups took over the planet, suggesting that sea sponges may
have been the first animals.


The researchers write in the study, which was published Friday in the Proceedings of the National Academy of Sciences, that their testing
provides “the oldest evidence for animal life.”

“We brought together paleontological and genetic evidence to make a
pretty strong case that this really is a molecular fossil of sponges,”
explains David Gold, a post-doctoral researcher in MIT’s Department of
Earth, Atmospheric, and Planetary Sciences (EAPS), in a press release.

Paleontologists have long struggled to determine which type of animal
was the first to the evolutionary line. While they have unearthed a
large number of fossils from the start of the Cambrian explosion, the
fossils that are known from before then are peculiar in many respects.

EAPS Professor Roger Summons has spent more than two decades searching
for the animal kingdom’s extended evolutionary tree. His lab has been
looking for clues in molecular fossils, trace amounts of molecules
that have survived in ancient rocks long after the rest of an animal
has decayed.

The so-called “‘sponge biomarker hypothesis” was first hypothesized in
1994 and partially confirmed in 2009. It focuses on
24-isopropylcholestane, a lipid molecule, or sterol, that scientists
have found in unusually high amounts in Cambrian and slightly older
rocks. Genetic testing by Dr. Gold adds “a further layer of evidence supporting” the theory that sponges or their ancestors might be their
source, Dr. Summons said in the release.

The results of the study provide strong evidence that sea sponges
appeared on Earth 640 million years ago, much earlier than any other
life form.

“This brings up all these new questions: What did these organisms look
like? What was the environment like? And why is there this big gap in
the fossil record?” Gold says. “This goes to show how much we still
don’t know about early animal life, how many discoveries there are
left, and how useful, when done properly, these molecular fossils can
be to help fill in those gaps.

http://www.csmonitor.com/Science/2016/0226/Humble-sea-sponge-may-be-the-common-ancestor-of-all-animal-life

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