Day #5 on our Christmas Countdown is…

Eolambia!

Eolambia: the “Dawn Lambeosaurine”

Eolambia were large hadrosaurs from Late Cretaceous North America. The layer of rock where their fossils can be found is known as Cedar Mountain Formation, which also has even thinner layers of time that make it easier to figure out when certain animals lived. These layers are known as members, and dividing fossils by these layers of rock makes things much easier to stay organized, because the Earth can change a lot over the course of a million years or two.

Today, certain parts of Utah and neighboring western states are dry, hot, and have cliffs, hills, buttes, and other rock formations that look like multicolored layers on a cake, or those bottles filled with layers of colored sand. The different hues of brown, cream, red, or grey each represent a slice of time in Earth’s history.

A slice of time that gives us a small glimpse into what life was like long ago, and can help us see how the world changes over time.

For example. Underneath the layers of rock known as the Cedar Mountain Formation, which has streaks of grey and dull brown like the pages of a dusty book, lies the Morrison Formation.

The Late Jurassic Morrison Formation is famous for dinosaurs like Allosaurus, Stegosaurus, Brachiosaurus, and Apatosaurus, and its rock has beautiful hues of cream, red, grey, and even a little green. A combination of mudstone, sandstone, siltstone, and limestone, depending on when the area was covered in marsh, floodplains, or even sea shores or desert as the land changed.

The Cedar Mountain Formation seems a little more stable than the Morrison. The mostly grey rock comes from layers of mud and silt from rivers and lakes on a floodplain. The top layer of this formation, the Mussentuchit Member, is grey mudstone that is mixed with volcanic ash. And it is in this layer that we find Eolambia.

This “duckbill dinosaur” was big enough as an adult that the only thing it feared was a large predator called Siats. Unfortunately, there are too few fossils of this theropod to know what group it belonged to (allosaurs, tyrannosaurs, etc.), we just know it was the biggest and toughest predator at this time and place.

Younger Eolambia had far more to worry about from dinosaurs like Deinonychus and large crocodile relatives. Some herbivores that lived in the same neighborhood are armored dinosaurs like Animantarx (big shoulder spikes, no club tail), a long necked sauropod called Abydosaurus, and some bits and pieces of other critters that look like earlier relatives of iguanodon, triceratops, and oviraptor.

Quite the change from a land once dominated by giant sauropods and spike-tailed stegosaurs…

As the Cretaceous marched on, a shallow sea would wash in with predators like Deinosuchus cruising its waters…then the water recedes to reveal the floodplains once more. Different stories told in the layers of rock, deposits of sediment with new names to catalogue the march of time. These plains were roamed by famous dinosaurs like Tyrannosaurus, Torosaurus, and the giant Alamosaurus right up until that infamous asteroid brought their reign to an abrupt end.

Of course, the world keeps turning, and life finds a way…The North Horn Formation gives way to the Green River Formation, a layer of rock famous for its beautifully preserved fossils of fish and even the very first horse!

So many amazing slices of time in this one area of land. A large area, true, but still it gives us a fascinating picture to put all these familiar prehistoric animals on a timeline. To give them context instead of blind facts on a blank page.

Do you have any favorite critters among the ones I mentioned? How does their place in the grand scale of time affect how you think of them?

See you tomorrow for day 6 of the Critter Christmas Countdown!