text: According to Michael Lee of the University of Sydney and Michael Caldwell of Chicago 's Field Museum , the 100-million-year-old fossil , christened Pachyrachis problematicus ( problematic thick-ribbed animal ) in the late 1970s , is a proto-snake with two legs .
  
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  The 100-million-year-old fossil has been identified as a proto-snake with two legs by two experts in the field .