Located in the core of the Big Apple,   the American Museum of Natural History is home  to some of the world’s 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 doesn’t mean that there’s 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 don’t 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 what’s   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 don’t 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,” it’s 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 weren’t 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 what’s 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.

But…is 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 what’s 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 we’d 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,   they’re still rare compared to Laramidia.

But they are finally bigger – more like the  size we’d expect dinosaurs to be by this time.

And yet, they don’t 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 aren’t 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 undisturbed…like  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 there’s 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   can’t 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 doesn’t  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 just…gone.

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 we’re used to from out West.

Even though they weren’t 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, didn’t 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.