October 8, 2016:

by starman

Last August 21, Japanese and Mongolian researchers discovered an enormous footprint in the Gobi desert of Mongolia. It is a natural cast of a sauropod’s left pes. After a behemoth made a track in muddy terrain, sand filled it and eventually lithified to form the cast. It is well preserved, with claws clearly visible. The track and its maker were undoubtedly large. Measuring 106cm (42 inches) long and 77cm in width, the pes suggests a titanosaur up to 25-30m in length and 20m tall. That’s much bigger than the later Opisthocoelicaudia (=Nemegtosaurus?). To give us an idea of the track’s size, Professor Shinobu Ishigaki appeared alongside it in a photo.

Information on the provenance and age of the specimen is vague. The report of the discovery said it was between 70 and 90 million years old. One source more accurately indicated a Campanian age.

A map included with the report indicates the discovery was made in the southernmost part of Outer Mongolia. Known as Borzongiin Gobi, the area has an important locality, Shiluut Uul. I believe that is where the giant track was found.

Shiluut Uul is not yet renowned for the quantity of dinosaur material recovered to date. Yet it is virtually unique among LK Mongolian localities in that it has datable material. Basalt provides the basis for an absolute age determination. It has yielded various K/Ar dates e.g. 75 +/- 7 Ma, 73.5 +/- 1.6 Ma etc. Radiometric dating, and some dinosaur remains, point to a Barungoyotian or Djadokhtan age.

Shiluut Uul is, however, quite different from “classic” Djadohktan exposures such as Bayn Dzak or Tugrik. The Borzongiin Gobi beds are fluvial. Trionyx and bivalves are known. Shiluut Uul probably correlates with Alag Teg, and Zos Canyon beds underlying Red Rum. The latter exposures are also fluvial, instead of eolian, even if they are overlain by eolian strata.

Interestingly, like Shiluut Uuul, both the Zos Canyon strata and Alag Teg contain sauropod remains. All three localities document a wet era predating the “classic” Djadokhtan, and the similar Nemegt. More rainfall meant more trees capable of supporting large titanosaurs. It’s not surprising the Gobi of c 72-74 Ma harbored behemoths. It appears to have been an ephemeral heyday, however. Titanosaurs persisted to the Nemegtian period and probably the K-Pg in Asia. But they may not have revived the dimensions of Alagtegian beasts.