+ Cowabunga dudes: Western Pond Turtles and Rancho LaBrea Riperian Zones+
[published in the April 2010 edition of the Cat's Meow, docent newsletter of the Page Museum, where i am a monthly columnist]
Last November, excavator Michelle Tabencki found 7 silver-dollar-sized and 13 nickel-sized plates of a turtle shell in the asphalt west of the main Project 23 bone deposit, an area thought to be devoid of fossils.
Eureka! Apart from the excitement of finding something where you thought there was nothing, recovering a 2/3 complete turtle shell fossil is unusual! This gleaming specimen of reptile-hood is in fact the most complete partly articulated turtle shell ever found at Rancho La Brea.
Trevor Valle assembled Donatello--the fossil Western pond turtle, not the cartoon techie become ninja--using masking tape to sub for the sutures that would have held the underside of it's shell together during its life. The center and top portions of its oval-shaped shell are missing. Resting beside the u-shaped shell on a tray in the Page Museum collections are the turtle's 2 stocky femur bones, 3 rib fragments, 4 toes, 4 vertebra, and a few other bones found close by.
So, Clemmys marmorata, with an olive marble-patterned shell and skin, must have inhabited Rancho LaBrea 10-000 to 40,000 years ago (we’re still waiting on C14 to date this specimen more exactly.) So what? They aren't even extinct! In fact they are still roaming the west coast of the Unites States.
Only 1 of 29 species of wet-loving reptiles and amphibians uncovered in decades of excavations at Rancho LaBrea is extinct (a species of large toad died resigned to evolutionary pressures.) Reptiles and amphibians are resilient, evolutionarily speaking.
As opposed to mammals, reptiles adapt a lot easier, in assistant lab supervisor Valle's opinion. They can enter a hibernation state and sleep out a tough time or borough down in the sand/dirt to cool off. Donatello would have spend much time regulating his body temperature--plunging into the relatively cool water during the hot summers in the LA basin or camping out on a river rock to catch some sunshine to escape frigid winter water. Modern Western Pond turtles burrow under silt at the bottom of the riverbeds to hibernate for long periods of time.
But in Donatello's case, a sticky death awaited at the edge of the water in which he lived.
Wait a second--what do you mean water? In the LA Basin? Absolutely.
The presence of H20-dependent animals and plants helps us realize that the terra on which the Page Museum, LACMA, and the rest of Los Angeles was built could have been much different than today. The turtle, lizard, garter snake, and rattlesnake fossils found at Rancho LaBrea excavations help paleontologists paint a picture of a riperian ecosystem circa 10,000-40,000 years ago. At the time Donatello was kicking around Rancho LaBrea, streams meandered through the area (Pit 91 is centered on a bend in one such former stream.) The running water may have been seasonal--drying up in summer when the asphalt had a chance to seep through, and gushing forth in winter, covering asphalt-trapped animals with sand and gravel. Shallow ponds may have dotted the streams course. Fish fossils found at Rancho LaBrea suggest a permanent flowing stream, but the lack of aquatic mammals suggests otherwise.
However steadfast the water source, the climate of late Pleistocene La Brea would have been significantly more humid than today. And, as long as insects were there, Clemmys marmorata would have been happy. That is, until he discovered the black muck at the edge of his watery home, got stuck, and met the same end as all of our other fossils in the Page Museum collections.