Among the items for sale at Heritage Auction Galleries’ 2009 May Signature Natural History Auction (www.ha.com), to be held on May 17 and 18 in Dallas, is the skull of a Smilodon californicus, or saber-toothed tiger. The skull was unearthed during the late 1960s at the La Brea Tar Pits Formation in Los Angeles. “A fossil of this kind comes up for sale only around every eight years,” says David Herskowitz, the auction house’s director of natural history. The skull, which is fully intact and is said to be 10,000 to 40,000 years old, carries a presale estimate of $200,000 to $250,000. The auction will also include the skull of a duck-billed dinosaur and the claw of a Tyrannosaurus rex.