Crunching Numbers | 220 Million

The oldest known animal species has been around for 220 million years

["Numbers rule the universe," Greek philosopher and mathematician Pythagoras said. For the month of May, 13.7 Billion Years will reprise the theme from September 2010, presenting a new number to think about each weekday with the series Crunching Numbers.]

The tadpole shrimp (Triops cancriformis), also known as the shield shrimp is so perfect, so adaptable, so stable, that unlike the vast majority of the Earth's species, it has barely evolved, remaining the same species for some 220 million years, around the time the earliest dinosaurs appeared. Based on fossil evidence, the tadpole shrimp's external morphology has remained unchanged. Triops cancriformis can be found in Europe, the Middle East and Japan, and is an endangered species in the United Kingdom.

"And they are tough," writes Roger Di Silvestro of the National Wildlife Federation. "They lay their eggs in water, and the eggs can survive freezing and, even more amazing, they can tolerate temperatures up to 176 degrees F, only 46 degrees short of boiling water. And they can withstand horrendous amounts of drying. If the water dries up, the eggs may remain fertile for 25 years (sometimes the eggs are sold in packets and can be revived and grown in an aquarium). They'll lie in the dirt waiting for the next rainstorm to revitalize them, or they may be blown around by the wind. Even so, if they eventually get to water, they will hatch."

READ MORE: http://www.nwf.org/News-and-Magazines/National-Wildlife/Animals/Archives/2010/Worlds-oldest-animal-species.aspx

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image: tadpole shrimp (Triops cancriformis), the oldest known species (credit: Federico Faci Miguel (Sekano), Wikimedia Commons)