Di­nosaur sur­vivor de­bate lives on

The Washington Post Sunday - - POLITICS & THE NATION - BY BRIAN VASTAG vastagb@wash­post.com

And now, an­other episode of “Di­nosaur Sur­vivor.”

In this show, the ques­tion isn’t which di­nosaur to throw off the is­land. In­stead, sci­en­tists ask whether any of the an­cient rep­tiles sur­vived the cat­a­clysmic strike of a space rock in the Gulf of Mex­ico some 65 mil­lion years ago.

Rep­re­sent­ing the no team: Pretty much ev­ery di­nosaur hunter in the world.

Rep­re­sent­ing the yes team: A re­tired fed­eral ge­ol­o­gist from NewMex­ico, James Fas­sett.

For 25 years, Fas­sett has been tout­ing a fos­silized fe­mur he found as proof that a pocket of long-necked her­bi­vores called sauropods sur­vived for hun­dreds of thou­sands of years af­ter all the other di­nosaurs.

“I’m not to­tally a Lone Ranger,” Fas­sett said of his the­ory. “But I guess I am still in the mi­nor­ity.”

In the lat­est in­stall­ment of this long-run­ning se­ries, Fas­sett and two col­leagues re­port in the jour­nal Ge­ol­ogy that a new tech­nique dates the fe­mur to 700,000 years af­ter the ex­tinc­tion event.

But few ex­perts are buy­ing it. One of Fas­sett’s crit­ics of­fered a sar­cas­tic re­sponse. “Any­thing is pos­si­ble,” said Spencer Lu­cas, a pa­le­on­tol­o­gist at the NewMex­ico Mu­seum of Nat­u­ral His­tory and Sci­ence in Al­bu­querque. “ There could also be a Big­foot inmy back yard.”

With the new dat­ing tech­nique, Larry Hea­man and An­to­nio Si­mon­etti from the Uni­ver­sity of Al­berta in Ed­mon­ton va­por­ized tiny bits of Fas­sett’s fos­sil with a laser. They then mea­sured the amount of ura­nium and lead in the re­sult­ing dust. Be­cause ura­nium ra­dioac­tively de­cays into lead over mil­lions of years, the process acts as an atomic clock.

If proved, the laser tech­nique could rev­o­lu­tion­ize fos­sil dat­ing, said Paul Renne, di­rec­tor of the non­profit Berkeley Geochronol­ogy Cen­ter in Cal­i­for­nia. Cur­rently, pa­le­on­tol­o­gists date fos­sils in­di­rectly, by de­ter­min­ing the age of the rocks in which they’re found or by hunt­ing for specks of fos­silized pollen nearby, which also of­fer strong age clues. In con­trast, the laser blast­ing method at­tempts to date fos­sils di­rectly.

How­ever, Renne and sev­eral other fos­sil-dat­ing ex­perts said the tech­nique is too new to be re­li­able. “Ura­nium-lead dat­ing is tricky busi­ness,” said Alan Koenig, a rock-dat­ing ex­pert with theU.S. Ge­o­log­i­cal Sur­vey in Den­ver.

A pri­mary con­cern: It is im­pos­si­ble to know when, ex­actly, ura­nium leached into the bone. Af­ter the sauro­pod died in what is now north­ern New Mex­ico, the cal­cium in its bones was even­tu­ally re­placed by harder, longer-last­ing min­er­als, in­clud­ing ura­nium. That’s the fos­siliza­tion process. But pa­le­on­tol­o­gists say there is no way to know how long this might take. “It could be 10 years; it could be a mil­lion,” Renne said.

The laser method, then, pro­vides some in­di­ca­tion of when ura­nium en­tered the fos­sil. It does not pin­point when the an­i­mal died. To fur­ther com­pli­cate mat­ters, ura­nium may have leached into the fos­sil mul­ti­ple times as, say, floods sep­a­rated by mil­lions of years washed over it.

Hea­man said he tried to ac­count for this by laser blast­ing only “pris­tine” ar­eas of the fos­sil. For in­stance, he avoided sec­tions near cracks, which might have al­lowed newer ura­nium to leach in.

The tech­nique yielded an es­ti­mated age of 64.8 mil­lion years, give or take 900,000 years. That range strad­dles the so-called K/T bound­ary, the ge­o­log­i­cal flash point that marks the end of the age of di­nosaurs. Fas­sett said that other data he has col­lected and pub­lished prove that the fos­sil is younger than the K/T bound­ary. In par­tic­u­lar, he said that fos­silized pollen from the Ojo Alamo sand­stone for­ma­tion near the fos­sil could only have come from an era af­ter the K/T bound­ary.

To prove it, about 10 years ago, Fas­sett took Lu­cas and an­other skep­ti­cal pa­le­on­tol­o­gist, Robert Sul­li­van of the State Mu­seum of Penn­syl­va­nia in Harrisburg, to the fos­sil site and pointed to where he sam­pled the pollen. The two pa­le­on­tol­o­gists col­lected their own sam­ple and tested it. But they ob­tained dif­fer­ent re­sults, con­clud­ing that the pollen was not, in fact, as young as Fas­sett had claimed. In 2009, Lu­cas and Sul­li­van pub­lished this and other ev­i­dence re­but­ting Fas­sett’s the­ory.

Fas­sett’s new paper fails to ad­dress the re­but­tal. Lu­cas went so far as to call it “ bad sci­ence.” Inthe past 20 years, other prospects of sur­vivor di­nosaurs in Mon­tana, South Amer­ica and China have failed to hold up un­der scru­tiny.

As for how the erst­while sur­vivors might have marched on, Fas­sett said, “All I can do is guess.” One idea: Sauropods buried their eggs im­me­di­ately be­fore the as­ter­oid im­pact; months later, the young­sters hatched into a dev­as­tated world to start a new herd. Or, per­haps some sauropods sur­vived far from the blast — in Alaska, where sauro­pod fos­sils have been found — and later mi­grated south.

What­ever the case, ex­pect more episodes of “Di­nosaur Sur­vivor.”

Even Lu­cas called the search for sur­vivors worth­while. “ The world is a big place, so why couldn’t there be a refugium where a few di­nosaurs limped on?” he said. “But you’re go­ing to need re­ally strong ev­i­dence.”

COUR­TESY OF JAMES FAS­SETT

Does this fos­sil prove that di­nosaurs lived af­ter the great ex­tinc­tion?

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