For the longest time, Utahraptor, Gastonia, and sympatric Yellow Cat saurians were thought to have lived during the upper Barremian to early Aptian (127 to 122 mya), similar in age to the Weald/Wessex beasts and their cousins from Iberia, and the cold-weather beasts of Liaoning (namely the Yixian Formation), and yes, I always thought it would have been pretty cool to have a Prehistoric Planet-style documentary chronicling these three (or four) ecosystems but then, in 2019, advanced methods of radiometric and palynological dating reinterpreted the age of the Yellow Cat biome as being Valanginian to early Hauterivian (about 138 to 132 mya).
But in recent years, this anachronism has been greatly exacerbated by reevaluations of Yellow Cat’s age. Now, Bakker was already playing fast and loose with the timeline, by mixing taxa from the Yellow Cat Member and Ruby Ranch Member/greater Cloverly ecosystem, and setting it 120 million years ago, smack dab in-between the reigns of Utahraptor and its smaller cousin Deinonychus.
However, like with many other fossil formations, it’s segregated into several units with varying geological ages, but unlike say, the Dinosaur Park Formation of Alberta, where not all of its genera lived at the same time but still existed within a relatively narrow timespan during the late Campanian (76 to 74 mya), thus making overlap between them reasonable speculation, the different units of Cedar Mountain vary quite a bit in age, from the end of the Berriasian to the late Cenomanian, 140 to 94 mya, and all of its dinosaurs are neatly sprinkled throughout them, ranging from the youngest ones (Mussentuchit Member) like the neovenatorid Siats and stem-hadrosaur Eolambia to the oldest cast of characters, that being the Yellow Cat Member taxa, which include Utahraptor, Gastonia and their contemporaries. All known Utahraptor fossils come from the famous Cedar Mountain Formation in (you guessed it) Utah, which has since produced a boatload of other dinosaurs (though not many non-dinosaurs).
Now, one of the bigger complications when it comes to updating this cast is the recent reevaluation of Utahraptor’s age, and by proxy, all the other dinosaurs that were sympatric with it, like Gastonia.
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