Eons

Located in the core of the Big Apple, the American Museum of Natural History is home to some of the worlds most iconic dinosaurs.

And while it would be easy to assume that the dinosaurs on display there were found nearby giving us the image of T. rex stalking through prehistoric Times Square the vast majority of them actually traveled a long way to get there.

Most were shipped in from the American west.

This doesnt mean that theres no fossil evidence for dinosaurs along the East Coast, though.

In fact, the first dinosaurs ever found in North America were from New Jersey like Hadrosaurus foulki, described in 1858.

And other rocks from the East may contain the geologically oldest evidence for dinosaurs in North America, period!

But these discoveries have been overshadowed by those from the West.

So, where are all the east coast dinosaurs?

Why dont we find famous species like Triceratops in Central Park?

Turns out, evolution and geology came together to make the east coast into an ancient lost world of weird dinosaurs.

When dinosaurs first got their start during the middle Triassic Period, maybe as early as 245 million years ago, North America was connected to the other continents as part of Pangaea.

And while some of the earliest undisputed evidence for dinosaurs comes from whats now South America, the fact that the continents were linked meant that they could just walk from there to basically any other continent.

Back then, North America sat just above the equator, with the east coast still dominated by the Appalachian Mountains.

And while we dont find many body fossils of early dinosaurs in this region around this time, the rocks of what they call the Newark Supergroup of the Late Triassic and Early Jurassic do preserve fossil footprints.

These footprints show that the East Coast already had some dinosaur diversity during these early periods of the Mesozoic Era.

The majority of these trace fossils are from 3-toed, small-bodied carnivorous dinosaurs that were up to 3 meters long.

These dinosaurs probably looked like a common early dinosaur from the American West, Coelophysis.

New Mexico, represent.

Other footprints indicate that a bigger carnivore, maybe 3 to 4 meters long, was also present.

These are thought to have been made by an animal like Dilophosaurus.

A combination of footprints, along with some fossil evidence, also shows early relatives of the giant sauropods, like the still-small-bodied 6-meter-long Anchisaurus.

And other tracks show small-bodied ornithischian dinosaurs were living there, too ancestors of the great herbivores like Triceratops and Ankylosaurus, my personal favorite.

Now, while these footprints tell us that dinosaurs were here, its pretty hard to know exactly what they looked like and who they were related to.

And as the Triassic gave way to the Jurassic around 200 million years ago, North America began to separate from Africa and Europe, forming the Atlantic Ocean and isolating the dinosaurs.

During this period, fossil evidence on the East Coast remains pretty much the same: footprints.

These Early Jurassic footprints still only show us that dinosaurs were present along the East Coast and tell us they werent very big yet.

But then something changed.

Suddenly, the fossil record disappears.

From the Middle Jurassic until the Early Cretaceous, we have no dinosaur fossils for about the next 50 to 70 million years.

But meanwhile, in western North America, the Morrison Formation is full of iconic dinosaurs, like Brachiosaurus, Allosaurus, and Stegosaurus.

And whats weird is, reconstructions of the paleogeography of the time suggest there were no real barriers like oceans or mountains separating the eastern and western halves of the continent.

So, the lack of body fossils is kind of confusing.

It almost looks like dinosaurs were thriving out West, but went completely extinct in the East.

Butis that what really happened?

Well, the dinosaur fossil record picks back up on the East Coast by the Cretaceous Period, around 115 million years ago.

And this time, they look more familiar.

In the area around whats now Washington, D.C., for example, there is a giant sauropod, carnivorous dromaeosaurs, armored ankylosaurs, and even a ceratopsian.

And the biggest find is a giant predatory dinosaur that was originally known from the West, but also shows up in Maryland: Acrocanthosaurus.

This east-west crossover is more of what wed expect, given those paleogeographic reconstructions dinosaurs moving freely across the continent.

But then, things start to get interesting.

By the Late Cretaceous, around 90 million years ago, the Western Interior Seaway formed, flooding a stretch of land from the Arctic Ocean to the Gulf of Mexico and splitting North America into two.

To the west was Laramidia, the landmass where the vast majority of dinosaur fossils come from.

This region was still connected to Asia via a land bridge from time to time.

The East Coast, on the other hand, became fully isolated, a landmass we call Appalachia.

And while more dinosaur fossils begin to pop up around this time in Appalachia, theyre still rare compared to Laramidia.

But they are finally bigger more like the size wed expect dinosaurs to be by this time.

And yet, they dont look like their contemporaries in Laramidia.

For example, take the two relatives of T. rex that were found in Alabama and New Jersey, Appalachiosaurus and Dryptosaurus.

Both of them sit at the base of the tyrannosaur family tree, and they have a mixture of traits common to much older tyrannosaurs.

Yet they were living at the same time as the more famous tyrannosaurs of the Late Cretaceous.

And scientists had long thought that dinosaurs with these traits had gone extinct, replaced by their bigger, more charismatic relatives.

But tyrannosaurs arent the only weird finds in Appalachia.

Duckbill dinosaurs like Hadrosaurus, Eotrachodon, and Lophorhothon were also living on the east-coast-island.

They, too, sit at the base of the hadrosaur evolutionary tree, but were still around when their younger relatives evolved.

For example, when researchers described the 85-million-year-old Eotrachodon from Alabama, they suggested that it might have been part of an evolving lineage that ultimately gave rise to the duckbill dinosaurs of Late Cretaceous Laramidia.

But, like with the tyrannosaurs, members of the basal lineage survived in Appalachia and took their own evolutionary paths while retaining their more primitive features.

And we see the same situation with the horned dinosaurs, the ceratopsians.

It was as if the island of Appalachia was a sort of refuge, preserving ancient ancestors who hung out undisturbedlike a lost world of east coast dinosaurs.

But where did they come from?

Did all these dinosaurs just suddenly appear in Appalachia right at the end of the Cretaceous, out of nowhere?

Well, I mean, probably not Remember how I said theres a major time jump in the east coast fossil record from the Middle Jurassic to the Early Cretaceous, spanning at least 50 million years?

Well, it turns out this gap is because we cant find any Mesozoic-aged rocks with dinosaur fossils.

The gap represents what paleontologists call a type of megabias or an unconformity, which is a large-scale pattern in preservation where entire chunks of time are just missing.

In this case, the scale is the entire region of Appalachia spanning several million years.

So dinosaurs probably lived on Appalachia throughout the Jurassic and Cretaceous, but the geology of the region doesnt preserve their fossils, creating a megabias.

If there are no rocks, there can be no fossils.

Now, the question of what happened to those rocks is still being debated by paleontologists, though they do have some ideas.

Either the rocks were eroded away or there was no space for eroded sediments to accumulate to form rocks in the first place.

Instead, the Appalachian Mountains slowly eroded away, with rivers carrying the sediments away from the land out toward the Atlantic instead of piling up in basins and burying dead dinosaurs.

In the West, on the other hand, as the ancestral Rocky Mountains were uplifted by tectonic forces, they provided a major source of sediment that was eroded by rivers and deposited in basins and along coastal margins.

Which is kind of a bummer for the East Coast, when you think about it.

All those millions of years of dinosaur evolution justgone.

But what we do know is, once the fossil record comes back online, the dinosaurs of the East Coast were pretty unique.

When we look at the dinosaurs from Laramidia and Appalachia that coexisted during the Late Cretaceous, the East Coast dinosaurs seem to represent relict older lineages of dinosaurs that had already gone extinct in Laramidia, but survived in Appalachia and charted their own evolutionary path.

Relict lineages are where the last remnants of older groups that used to be abundant, but have since gone extinct elsewhere, still hang on like the last mammoths that ended up on Wrangel Island, to call back to an old episode.

A region that supports isolated and relict populations of once widespread species is called a refugium and conditions in Appalachia were ripe to make it a refugium Because it was isolated from Europe and Africa during the rifting process that broke apart Pangaea in the Jurassic.

And then it was cut off from Laramidia during the Cretaceous, when the Western Interior Seaway formed.

So, while ancient dinosaur lineages in Laramidia were being replaced by icons like the famous heavy hitters T. rex, Edmontosaurus, Ankylosaurus, and Triceratops, there was no such replacement in Appalachia.

And these lineages stuck around and, in many cases, followed their own evolutionary trajectories that paralleled their Laramidian counterparts.

They seem to be species that time and evolution forgot.

So, despite the missing chunks of time of the megabias, dinosaurs in Appalachia seem to have been just as diverse as those were used to from out West.

Even though they werent the same groups at least, not at the same time.

And the seaway running through the middle of the continent meant that those later species from Laramidia, like T. rex, didnt make it to the east coast to stomp through places like Times Square.

But the eastern residents likely represented a unique group of animals that found refuge on the island continent.

There, they avoided extinction, and continued to evolve throughout the later parts of the Mesozoic.

Sometimes, the places that seem forgotten are precisely where species persist.