{footprint, or simply a coincidental shape anomaly?] BELIEVE IT OR NOT "Giant footprint [4-feet long] 'could shed light on titanosaurus behaviour'"- BBC News

how do they prove it is a footprint other than "it looks like one"? 
"
Found in the Gobi desert and measuring 106cm (42in) long and 77cm wide, it is believed to be of a titanosaurus.
It was discovered in August in a geological layer formed ..."
http://www.bbc.com/news/world-asia-37559499

-vk-