Wednesday, November 08, 2017

The North Horn Formation

This is an illustration of the Alamosaurus Faunal Assemblage of the North Horn Formation of Utah, a latest Cretaceous Formation that is a bit different from the Lancian assemblages a little further north in Montana and Wyoming with the Hell Creek and Lance Formations.  As most fossil assemblages are, it's a relatively flat area, with rivers and lakes that represents a rather high energy depositional environment.  (This is because these conditions are the best to preserve fossils.  This certainly isn't to imply that dinosaurs didn't live in other environments.)  Because of the lakes, rivers, and probably wetlands that made up the plains of the Maastrichtian North Horn, there are lots of fossils of fish, amphibians, crocodiles, and champsosaurs.  There are also fossils from a large variety lizards (and snakes), turtles and mammals.  Both bird and dinosaur egg fragments have been found, and pterosaur footprints in the mud.

Of course, in dinosaur-bearing formations, what most people are most interested in are the dinosaurs.  Naturally.

However, there isn't a ton to go on, really.  Alamosaurus has been found there, as well as Torosaurus and Tyrannosaurus rex (represented by juveniles in the picture above.)  Some indeterminate hadrosaur fossils have been found.  Based on fossils found both to the north and to the South of North Horn, I'd expect ornithomimosaurs, troodontids, dromeaosaurs (maybe even quite large ones, like Dakotaraptor), oviraptors, ankylosaurs, another big ceratopsid (Triceratops or Ojoceratops), smaller leptoceratopsids, hypsilophodonts of some sort, maybe a pachycephalosaur or two.

Of course, we don't know what kind of animals we have there exactly, just that it's likely that representatives of those groups are probably mixed in there somehow, since they appear both to the north of the formation and to the south of it.

This makes something like the North Horn Formation my #1 destination if there were ever a Terra Nova project in real life to go colonize the Cretaceous.  It's got big sauropods (in fact, some Alamosaurus specimens suggest it's a contender for "the biggest"), it's got big therapods—T. rex even!—and all kinds of other stuff.  It's as if the Morrison had less diversity in its sauropods, but upgraded Allosaurus to T. rex and swapped out Stegosaurus for Triceratops (or at least a close relative.)  There's also probably less small ornithopods, because ornithomimosaurs and oviraptors replaced them.  And the flora is more modern—angiosperms (even grasses) are around.  Mammals are more diverse.  Pterosaurs are considerably less diverse, but toothed (and sometimes claw-winged) birds are plentiful.

All in all, it's a strange hybrid of all kinds of classical dinosaur action—the biggest, most iconic therapod, a really big sauropod, big ceratopsians, big hadrosaurs, all kinds of small dinosaurs, potentially big raptors, big pterosaurs (Quetzalcoatlus is present in the Ojo Alamo formation to the south.) The rice family is estimated to have appeared a good 40-50 million years earlier; there might even be native crops that are edible.  And smaller ornithopods and herbivorous (or at least omnivorous) therapods would probably be good eating for the likes of you and me. The weather probably isn't so miserably hot as it is to the south, but it's still tropical, or at least subtropical.  And although it's a floodplain with rivers and lakes and probably wetlands obviously present, it's not just pure marsh either—probably more fun for the likes of you and me to explore without getting wet, muddy, killed by crocodiles or mosquitoes, etc.  The highlands making up the mountains at Laramidia's western edge aren't too far away, although we know nothing whatsoever about the fauna that lives there.  All in all, this would be a great place to visit.  Maybe even to settle.

Speaking of the highlands and drylands; I wonder if they resemble contemporary (or nearly so, anyway) Mongolia-Chinese fossil assemblages a bit?  By which I mean: therizinsaurs were present in North America earlier, although none are known from these formations, but they continue and in fact are quite diverse in Asia.  There are also really weird animals like super-sized ovirpaptors (Gigantoraptor) and the bizarre Deinocheirus—but then there are very close relatives to T. rex and Edmontosaurus present as well.  Much of the smaller dinosaur fauna is also referable as closely related to North American faunas. 

By the way, the Nemegt would be a fun one to visit as well.  Maybe it'd be interesting to see the latest Maastrichtian of the Nemegt area to see what (if anything) changed in the NALMA.

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