The mystery of North America's missing eastern dinosaurs

Hidden within North America is a long-forgotten continent once ruled by a bizarre cast of dinosaurs – but only a handful of fossils have ever been found.

It was a typically warm, humid day in the Late Cretaceous. A strange, pallid mass was floating in the cobalt-blue waters of a shallow sea, above what is now New Jersey. It was a dead dinosaur, the bloated carcass of a monstrous, 6.4m (21ft)-long distant relative of Tyrannosaurus rex.

With an athletic frame and jaws full of flesh-ripping teeth, Dryptosaurus aquilunguis looked remarkably like its cousin, but with a bloodcurdling twist: on the ends of its stubby little arms were great, grasping "hands", complete with an array of unwieldy eight-inch (20cm) talons. Its fingers were meat hooks, its teeth like piercing bananas. This ancient beast could wrap its hands around you while it bit your head off.

The peculiar dinosaur had staggered its final steps some weeks earlier, though this was just the beginning of its adventures. First its body slipped into the local river – possibly after a flood – where it bobbed around, miraculously avoiding the attention of marauding crocodiles. Eventually, it was flushed out into an ancient inland sea. As the fallen giant decomposed, it sank to the bottom. There its body parts would remain, safely interred in their silty crypt for the coming 67 million years.

That was, until this peaceful sleep was interrupted by workers at the West Jersey Marl Company one summer's day in 1866. They had been digging up a seam of green, muddy rock to sell as fertiliser when they uncovered a jumble of suspiciously large bones.

The fossils caught the attention of a young zoologist, Edward Drinker Cope – a "dandyish character" with a luxurious moustache who would go on to discover many of the most iconic dinosaurs in North America. He promptly identified the New Jersey remains, writing that they belonged to a "totally new gigantic carnivorous Dinosaurian!" Other than this, it wasn't immediately clear just how special the find really was. 

Today the remains of the Dryptosaurus are tucked away in a small drawer at the Academy of Natural Sciences, Pennsylvania – a neat arrangement of crumbling vertebrae, jaw fragments, occasional limb bones and teeth. But it turns out these sparse artifacts aren't just all that's left of this single individual, nor are they simply the last physical evidence of its species. In fact, they're among the few surviving remnants of an entire continent – a forgotten land of strange dinosaurs most people have never heard of. How has this happened? And what was it like?

A mystery history

Hidden beneath North America is a secret past. For 27 million years in the Late Cretaceous, it was cleaved into two pieces. In the west was the ancient continent of Laramidia. In the east, the long-vanished continent of Appalachia. Between them was a shallow, predator-infested sea, the Western Interior Seaway. At times, it was decidedly tropical – almost like a warm bath, but swimming with crocodiles, sharks, and the gaping mouths of 18m- (59ft)-long mosasaurs.  

As far as dinosaurs were concerned, the two halves might as well have existed on different planets – they were totally isolated from each other. Though they were contemporaries, Dryptosaurus would never have sparred with a T. rex, ripped the flesh from a triceratops, or fled from the flattening feet of a brontosaurus.

To this day, the last relics of Laramidia can be found in rock layers that stretch from the otherworldly, cacti-filled landscapes of the Mexican desert to the frigid oilfields of western Alaska. In the east, the last hints of Appalachia lie under a region extending from the cypress swamps of Mississippi to the arctic tundra around Hudson Bay in Manitoba, Canada.

And yet, the prehistoric inhabitants of only one of these landmasses have dominated in the popular imagination.

Over the last century and a half, Laramidia has yielded the vast majority of the dinosaurs we are familiar with – at least 32 near-complete skeletons of T. rexes, herds of Triceratops, bones from around 80 stegosaurs, and an Alamosaurus that weighed as much as a small commercial aircraft. In fact, America's natural history museums are almost exclusively populated with dinosaurs from this western continent.

Like Laramidia, Appalachia was also thronging with feathery, scaly and armoured giants. But they're virtually absent from public displays – and you won't find them represented in documentaries, Hollywood films, or children's toyboxes.

In contrast to its western counterpart, Appalachia left few traces behind. In the 169 years or so that people have been looking, it has provided little more than a few crumbling partial dinosaur specimens and a handful of bones and teeth. In fact, the continent's prehistoric wildlife has almost entirely vanished from the fossil record.

Until recently, these enigmatic eastern beasts – and the land they inhabited – were so obscure, they were rarely even discussed by palaeontologists.

Now, thanks to a few new discoveries and fresh interest in the sparse remains uncovered in the past, a picture of a lost world is emerging – a subtly garbled rendering of the usual vision of prehistoric North America. This was a place where compact, pony-sized relatives of triceratops roamed the landscape alongside giant, cow-like hadrosaurs, scythe-handed tyrannosaurs, towering dino-ostriches and heavyset, reptilian "armadillos".

In short, the familiar cast of dinosaurs that we all grow up with is only half the story.

A strong start

In the small town of Haddonfield, New Jersey, at the end of a quiet suburban street, is the grave of a long-dead resident. Houses give way to a patch of muddy forest, where there is a stone-mounted memorial plaque. A few hundred feet below, in a deep, vine-covered ravine, is a small depression in the clay. This is where the body was found.

In 1830, a farmer had been digging for mineral-rich marl in this small pit, when he uncovered an assortment of giant bones resembling vertebrae. It was the find of a lifetime – but he wouldn't know it until he was an old man.

In fact, though collectors such as Mary Anning had already begun to discover the bones of ancient marine reptiles, such as plesiosaurs, dinosaurs didn't even have a name yet, and would only acquire one over a decade later. At the time, their remains were often associated with mythological beasts or explained away as particularly large specimens of ordinary animals. Sioux Native Americans believed them to belong to monsters destroyed by thunder spirits, while European scientists had historically mistaken them for the bones of elephants or large reptiles. To confound matters even further, no one had ever found a dinosaur in the United States before.

Naturally, the farmer didn't think much of the fossils, except as minor curiosities. He took them home, and stashed them away. There they remained for 28 years, occasionally brought out to impress guests. Some were even casually given away.

That was, until a fateful evening in 1858 when an amateur geologist stopped by for dinner. The first US dinosaur had been found in Missouri four years earlier, so he knew exactly what he was looking at. Eventually he led a team to excavate the original site and retrieve the rest of the animal. It was a duck-billed dinosaur, a hadrosaur, and it just so happened to have been an inhabitant of the lost continent of Appalachia.

A neglected land

Though Appalachian dinosaurs are obscure today, it hasn't always been this way.

In the mid-19th Century, the Haddonfield hadrosaur was the most complete the world had seen yet – with some 55 out of an estimated 80 bones. And right from the beginning, it was famous. It was the first ever dinosaur to be put on public display, and quickly became a household name – immortalised in paintings and discussed rapturously in newspapers. Over a century and a half later, it has prominent status as New Jersey's official state dinosaur and remains the most intact ever found from Appalachia.

The hadrosaur was so good, it triggered a rush to explore the region for others, and two palaeontologists in particular began frantically unearthing as many as they could – mostly so they could claim the credit. In fact, the treasure was the direct trigger for the infamous Bone Wars – a bitter and often tragically petty feud between Cope and one of his friends that nearly bankrupted them both. (Read more about how the rivalry laid the foundations for our knowledge of American dinosaurs.)

In the decades that followed the discovery, a surprisingly large number of dinosaur fossils were found in the region – Cope unearthed the big-handed Dryptosaur in New Jersey less than a decade later. Initially he called it Laelaps, but after an unfortunate blunder involving an eponymous mite, it was later renamed.  

This golden age of eastern dinosaurs did not last long. By the late 1870s, interest was mounting in a promising new cluster of fossils emerging from Wyoming and Colorado. This was the beginning of America's love affair with the Morrison formation – a seam of sedimentary rock from the Late Jurassic that stretches from Montana to New Mexico. And it is this hallowed ground that has yielded the vast majority of the US' fossil riches, including mega-stars such as Brachiosaurus, Stegosaurus, Triceratops, Diplodocus and T. rex.

A crumbling legacy

The sandy, clay-rich "greensands" of New Jersey, so-named because of their characteristic olive tinge, include rocks that formed during the Late Cretaceous, when a sizeable strip down the middle of North America had been swallowed up by the Western Interior Seaway.

As a result, most of the fossils within are from marine animals that drifted down into sediment on the seafloor when they died. But muddled up with the remains of ancient sharks, exotic sea snails, and unusual plesiosaurs with formidable 1.75m (5.7ft) heads, are a large number of conifer trees and even occasional dinosaurs – the best-preserved remains from Appalachia.

Like the New Jersey Dryptosaurusand Hadrosaurus, these fossils are thought to belong to animals that died inland, near the coast, and were somehow transported out to sea by rivers or the tides. Many Appalachian dinosaurs carry tantalising echoes of this final journey in their bones, in the form of bite marks from sharks and crocodiles, and boreholes by foraging molluscs. 

In contrast, most fossils found in western north America formed in terrestrial rivers and coastal plains – places where dinosaurs were actively living before they were transformed into fossils. This is the first problem with fossil-hunting in Appalachia.

Even in optimal conditions, dinosaur fossils occur at a fairly low density. Their remains have run the gauntlet of scavengers, the forces of decomposition, and becoming entombed in the right sort of sediment before they formed fossils. For the Appalachian fauna, being washed out to sea is just another rare event to add to that list. There just aren't as many dead dinosaurs in the ocean as there are on land, and the fossils are correspondingly hard to find.

This is compounded by the landscape in the east, which is a major challenge for palaeontologists.

"So generally speaking, I just don't dig until I hit something," says Nick Longrich, a palaeontologist and evolutionary biologist at the University of Bath. "Let's be generous and say there's a dinosaur fossil every 100m (328ft), how much rock are you going to have to move to find that one skeleton?"

Instead, it's standard practice to start with an "outcrop" – a place where rock layers are visible already, such as cliffs, hills and riverbanks – and simply take a stroll. "You're walking, walking, walking and you find a few scraps of bone coming out, so you dig back into the hill," says Longrich. 

In the eastern United States, where the land is flatter, there just aren't as many outcrops – and consequently, opportunities for stumbling upon fossils – as there are among the strange carved hills found in the western Badlands.  

Then there's the issue of vegetation. The overgrown grave of the Haddonfield hadrosaur is typical of the drawbacks of Appalachian digs – with a warm, humid summer climate and around triple the rainfall of the western bone beds, the region is extremely popular with foliage.

"Plants are kind of the enemy of palaeontologists," says Longrich, who laments that they grow all over their precious fossils. Not only do their roots break up the rocks beneath them, often destroying any dinosaurs lurking near the surface in the process, but they smother outcrops where digging might otherwise be fruitful.

"And so historically, that's one of the main reasons we know a lot less about it [the eastern continent], it's just very vegetated," says Longrich. To dig among the remains of Appalachia requires battling through a throng of muddy roots. He explains that it's one of the same reasons you hardly ever hear of dinosaurs being discovered in tropical locations like the Amazon basin, where the first ever fossils were found as recently as 2004 – they are there, but they're almost impossible to access. 

And it gets worse. Even once Appalachian fossils have made it out of the ground, they're often riddled with disease – not one that affected the living animal, but a malady of stone. "Pyrite disease" occurs when the glistening metallic mineral pyrite, otherwise known as "fool's gold", reacts with humid air to create a cocktail of rust, sulphur dioxide and sulphuric acid.

It can turn fossils that have lain safely underground for millions of years to dust in a matter of decades and is particularly problematic in eastern North America, where it's wet.

In contrast, palaeontologists working on the sun-baked Badlands of Montana or Wyoming spend their time chiselling away satisfying flakes of dry rock. Often, they don't even have to do that.

"You just walk around and you find them," says Longrich, who points out that common or imperfect specimens are frequently just left lying around, half-submerged in stone. "In Alberta they have so many dinosaur skeletons they literally can't collect them… it's like 'oh it's a duckbill [a hadrosaur], let's leave it here'," he says.

An enigmatic crowd

As a result, the fauna of Appalachia remains deeply mysterious.

By 1997, there were fewer than 10 known species of eastern dinosaurs, including bones from several hadrosaur individuals, Cope's Dryptosaurus, and a few assorted individual bones and teeth – the pantheon of known inhabitants had barely changed since the 1860s.

However, over the last few decades, scraps of information have slowly been emerging.

Take the group that encompasses all the flesh-eating dinosaurs, the theropods. "Right now there are only three specimens that represent individuals for which we have multiple bones," says Chase Doran Brownstein, an undergraduate student at a research associate at the Stamford Museum and Nature Center. These include Cope's Dryptosaurus, as well as two other tyrannosaurs – one found identified in 2005, and the other described by Brownstein himself in 2021.

"So you can see it's like two discoveries in the last two decades, after over a hundred years of silence – nothing happening," says Brownstein.

The vast majority of recent discoveries haven't come from new digs – they were found by rummaging around in museum drawers, where some bones have been mislabelled or overlooked. "Some of these fossils have been collected decades or a century ago," says Longrich.

For now, the fossil record still conjures a scene dominated by giant 35ft-long (10.6m) hadrosaurs, and ferocious relatives of T. rex. But it turns out Dryptosaurus didn't have a full monopoly on terror, and had to share its home with Appalachiosaurus, a similar bipedal predator of unknown size.

"It's kind of a lost world that's off doing its own thing, evolving its own fauna," says Longrich.

These would have shared their tropical, rainforest home with ornithomimosaurs – feathered dinosaurs resembling ostriches that may have been mostly vegetarian. In 2022, Lindsay Zanno, a palaeontologist at the North Carolina Museum of Natural Sciences, and colleagues discovered that the ones in Appalachia were exceptionally big-boned – one 13-14 year old individual (represented by a single bone) was over three times heavier than a modern ostrich.

There was also a healthy population of unusually large tank-like dinosaurs – nodosaurs – though these were rare in Laramidia.

On the other hand, no one has ever found evidence of any giant sauropods – the group of long-necked vegetarian dinosaurs that includes Diplodocus and Brontosaurus – and scientists have only found a single tooth from a possible horned dinosaur like Triceratops.

Many of the dinosaur residents weren't totally original, but quirky takes on long-established groups.

In 2016, Longrich was rummaging in a drawer at Yale University's Peabody Museum when he came across something intriguing: a little piece of jawbone. It was labelled as belonging to a hadrosaur, but he immediately thought this must be a mistake – he had seen a bone like that before. It turned out to belong to a leptoceratopsian, a compact distant relative of Triceratops.

Now there's growing interest in Appalachia as an evolutionary experiment. After the Western Interior Seaway cleaved North America in two, the eastern half was utterly isolated for 27 million years. But its western counterpart had a neighbour – it was connected to Asia via an ancient land bridge.

"And what that does is creates a corridor where – I don't know if it's intermittent, or permanent – but dinosaurs can go back and forth between Asia and North America. And there's a kind of ping pong where dinosaurs evolve in Asia, move to north America, move back and vice versa," says Longrich.

But while Laramidia was engaged in a lengthy exchange programme with Asia, Appalachia was on its own, so it's thought that it may not have developed such a diverse array of dinosaurs. "We could be wrong, maybe we're just not finding these things," says Longrich.

As interest builds in the eastern continent, Longrich is optimistic that we will soon uncover more hidden fossils from this long-forgotten land. But for now, one thing is clear: America's lost continent isn't giving up its secrets just yet. 

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