Im­pres­sions of the past

Australian Geographic - - Wild Australia -

Aus­tralian sci­en­tists study­ing the small­est known di­nosaur foot­prints, left by a crea­ture the size of a spar­row, also dis­cov­ered the largest, left by a di­nosaur 700,000 times as heavy.

WHILE THE FOSSILISED bones of di­nosaurs tell us about the size, shape and anatomy of the an­i­mals they once be­longed to, fossilised foot­prints can tell us a whole dif­fer­ent story about these an­i­mals, re­veal­ing clues to pre­his­toric be­hav­iour.

In 2017 Dr An­thony Romilio of the Univer­sity of Queens­land was part of the team that f irst recorded di­nosaur foot­prints on the coast of the Kim­ber­ley in West­ern Aus­tralia that were a whop­ping 1.7m in length – big enough for many peo­ple to lie down in­side. These were left by long­necked, her­biv­o­rous di­nosaurs called sauropods, which walked along river deltas 130 mil­lion years ago. Known for cen­turies by Abo­rig­i­nal peo­ple, these tracks were much big­ger than the pre­vi­ous big­gest known di­nosaur foot­prints, which mea­sured 106cm across and were dis­cov­ered the year be­fore in Mon­go­lia’s Gobi Desert.

Now, to com­ple­ment the ex­cit­ing 2017 f ind, Romilio, as part of a team that in­cludes South Korean and Chi­nese sci­en­tists, has recorded the small­est di­nosaur foot­prints ever – 1cm-long tracks left by a crea­ture with a hip height of about 4.5cm.

“These new tracks are just 1cm in length, which means the di­nosaur that made them was an an­i­mal you could have eas­ily held in your hand,” Romilio says. “The diminu­tive sizes of these new tracks are ex­tra­or­di­nary; the tracks were made by tiny di­nosaurs about the size of spar­rows.”

These are ev­i­dence of the small­est di­nosaur ever dis­cov­ered (the pre­vi­ous small­est known di­nosaur was a feath­ered species called Mi­cro­rap­tor from China, which was about the size of a crow).

The tracks’ shape re­veals they were left by tiny dro­maeosaurs – the group of preda­tory di­nosaurs to which Ve­loci­rap­tor, of Juras­sic Park fame, be­longs. Dro­maeosaur tracks are very dis­tinc­tive, be­cause these an­i­mals kept two of the three toes on each foot on the ground, with the third ‘re­curved’ claw re­tracted, a bit like that of a cat. It’s not clear if the an­i­mals that left the foot­prints were ba­bies or adults.

The tracks were found in the Jinju For­ma­tion of rocks in South Ko­rea’s Gyeongsang Basin, which is about 129–125 mil­lion years old, mean­ing it’s ver y likely the tiny di­nosaurs found here were con­tem­po­raries of the truly gi­gan­tic di­nosaurs we have ev­i­dence of in the Kim­ber­ley.

Those 1.7m-long prints are among many thou­sands of di­nosaur foot­prints that have been doc­u­mented in re­cent years all the way down that north­ern part of the coast of WA, by a team in­clud­ing Romilio, as well as his Univer­sity of Queens­land col­league Dr Steve Sal­is­bury.

Dur­ing the age of the di­nosaurs, South Amer­ica and Aus­tralia were joined as part of the su­per­con­ti­nent of Gond­wana, which means some species of di­nosaurs roamed right across this land­mass.

While in WA we only have the foot­prints of the very largest sauro­pod di­nosaurs, in Ar­gentina there are fos­sil skele­tons, such as that of the re­cently de­scribed species Patagoti­tan may­o­rum. Some es­ti­mates sug­gest this ti­tanosaur sauro­pod would have reached about 37m in length and nearly 64 tonnes in weight – that’s about as heavy as a space shut­tle.

As­sum­ing the sauro­pod foot­prints in WA were left by di­nosaurs that matched that size, and the tiny di­nosaurs from South Ko­rea weigh just 100g or less, then the very big­gest di­nosaurs weighed up to 700,000 times as much as the small­est.

That mind-bog­gling f ig­ure is tes­ta­ment to the in­cred­i­ble f lex­i­bil­ity of the di­nosaur body plan, which could build crea­tures on such vastly dif­fer­ent scales, based on the same ba­sic di­nosaur ge­netic blue­print.

JOHN PICK­RELL

is a for­mer AUS­TRALIAN GEO­GRAPHIC ed­i­tor. Fol­low him on Twit­ter: @john_pick­rell

Dubbed Dro­maeosauri­formipes rarus, the di­nosaurs that left these tiny foot­prints may have looked like this.

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