Houston Museum of Natural Science's Land That Time Forgot

Triceratops is the world’s No. 1 favorite veggie-saur, and it is one of the most dangerous land herbivores to have ever evolved. Paleontologists thought we knew all there was to know about Triceratops, but this particular specimen made us reevaluate everything. This specimen is an excellent skeleton with some of the best Triceratops feet ever discovered. The giant hind paw spread its four toes widely to give maximum traction on soft, gooey ground. The forepaw was five-toed and wide, too. No doubt about it – Triceratops was a “mudder,” a beast designed to tromp across swamps and bogs. The torso was ultra-compact and short front-to-back. The barrel-shaped rib cage expanded sideways in the abdomen to hold a capacious gut.

Enormous mammoths and mastodons roamed North America in the Ice Age, and humans hunted both. The “American Mastodon,” Mammut americanum, was the last species of Mammut and kept the same simple chopping molars that had evolved in the Miocene 12 million years earlier. Different dietary preferences keep mastodons and mammoths apart in most places. Mammoths preferred grass and dry leaves in open plains and woodlands, while mastodons went for softer, wider branches in wetter forests and swamps. Many mastodon bones turned up in bogs being drained by American farmers in 1700's.

Old textbooks will tell you that the Diatryma is a sheep in wolf’s clothing. But Diatryma’s reputation was all hype and misunderstanding. The “terror bird” rap comes from the beak. Both top and bottom are huge and deep. But living predatory birds like eagles and hawks don’t have beaks like Diatryma’s. They have a big hook at the end of the snout for spearing live prey and ripping it apart. Diatryma’s beak is hook-less. Eagles and hawks have thin lower jaws, because the hook does all the work. Diatryma has an incredibly thick, strong lower beak. Eagles and hawks have curved claws on their feet for skewering live victims. Diatryma has weak, blunt claws on its feet.

By the Late Jurassic, the plant-eating dinosaur clans had expanded into a dozen families. Stegosaurs are famous for their tiny brains one- thirtieth the size of an elephant’s of the same weight and 10 times smaller than the meat-eating Allosaur’s. However, what Stegosaurs lacked in brains they made up in brawn. The muscular tail carried four sharp bone spikes, covered with an outer layer of horny skin. Tall joints let the Stegosaur twist and curl its tail in almost any direction, and it could curve its torso and neck with ease. Stegosaurs also had a tighter turning radius than any other large plant-eater. On hard ground, they were skilled swordsmen, lunging and thrashing with their four-pointed lances. Although they were as heavy as elephants, Stegosaurs had tiny feet with just three tiny toes. The foot area was only a third as big as that of other big herbivores like Triceratops and Denversaurus – an adaption to suit hard, firm ground.

If you were a full-grown saber-toothed Smilodon, what animal should you think twice about before attacking? The giant short-faced bear! One of the largest bears to ever inhabit North America, Arctodus reached heights of 15 feet and weights of a ton and a half - twice the size of the average male grizzly bear. But Arctodus was far leggier than grizzlies and polar bears and probably faster.

About 17 million years ago came the strongest tusks of all. “Normal” mastodon tusks, like Gomphotherium’s, were long and straight with pointed tips. Platybelodon, the shovel-tusked mastodon, carried lower tusks that were unbelievably wide. Together the right and left tusks made a sort of shovel.

Two carnivorous dinosaurs were responsible for inspiring the novel and popular movie Jurassic Park: Deinonychus and its close cousin, Velociraptor. Both of these raptor-dinosaurs were smart, speedy kick-boxers. Their teeth were sharp, but too small to kill big prey. Instead, their main weapon was an enlarged claw mounted on the hind foot. The hind leg was by far the strongest part of the body – far stronger than the jaws. Most predatory dinosaurs had claws, with a flat bottom-surface, like an eagle’s claw. Flat-bottomed claws are good for penetrating prey bodies and holding on. Raptor claws, in contrast, had a knife-like bottom edge that could cut a long wound. Body design in raptor-dinosaurs made them three-dimensional fighters. The torso was short and compact, and the tail had special bone rods that made the entire tail flip sideways or upward when its muscles were contracted. Tail flipping provided balance when the raptor-dinosaur twisted and turned in midair.

Sphenacodontidae. Early Permian. Belle Plains Formation. Archer County, Texas, USA.

Smilosuchus was the apex predator of Late Triassic rivers and lakes. Smilosuchus was the heaviest, most dangerous carnivore in its world and was unusual because it was a predator with nearly complete armored protection. Thick rectangular armor plates covered the back and neck, while thinner plates protected the throat and stomach.

Big herbivorous dinosaurs in the Lancian Age had to solve two problems: how to digest enough plants to grow and reproduce, and how to defend against the teeth of a T. rex. Denversaurus solved both problems the same way: by becoming a Lancian double-wide. The gut of a Denversaurus is wider than it is tall. Thick plates of bone armor covered the neck, back, and sides, as well as the tail. Spikes of bones were set in the shoulders, and the skull had an extra layer of bone armor, too. Defense was not simply passive. The long tail, studded with rough-edged armor plates, could be flung sideways and upward like a medieval flail. One good whack could break a T. rex’s shin bone or leave a long line of welts.

By the Late Triassic, the land ecosystem had recovered from extinction. Herds of Dicynodonts moved through groves and tall conifers, cutting up tough needles and branches and slicing through the fronds of cycad-like plants. Our Placerias shows the classic two-tusk design: its beak resembled a high-powered combination of parrot and giant snapping turtle. Dicynodonts like Placerias were efficient leaf-eaters, even though they had no molar teeth for chewing. Instead, they used their beaks to shear through the toughest plant fibers. Placerias' body design was similar to a modern-day duck-billed platypus. In fact, Placerias was probably warm-blooded and may have had hair. All Dicynodonts were advanced early mammal ancestors.

Saber-toothed mammals evolved many times from non-saber-toothed ancestors. The core of this saber adaptation is an enormously enlarged upper fang shaped like a sword or dagger – flat on the sides and sharp-edged in the front and back. Like many saber-toothed animals, Uintatherium evolved a special chin-guard that protects the fangs when its mouth is closed. To allow the animal to stab and slice with its sabers, the jaw joint lets the mouth open exceptionally wide. And, to increase the deadliness of the bite, the neck muscles are arranged to pull the head down, driving the fang further into the target.

We call a Dimetrodon a "fin-back" for obvious reasons. The tops of the vertebrae grew up into tall rods of bone, held together in life by a sheet of tough skin. Some scientists have hypothesized that the Dimetrodon fin may have been a solar panel. In the cool morning, the fin-back could turn sideways to the sun and let the rays heat up its body. If Dimetrodon got over-heated at noon, it could turn its fin again so the breeze went over the fin surface.

Here is the largest jaw ever assembled of the stupendous C. megalodon shark – a fish twice as long as the largest great white shark. “Meg” teeth were whale-choppers. Each tooth carried a fine, saw-toothed edge and thick central zone. Whale bones from deposits full of Meg teeth show deep cuts and gouges that match C. megalodon’s dental anatomy. Elephant tribes were on the menu, too. All members of the elephant clan are expert swimmers, and mastodons and mammoths spread across the Pacific. Mastodons dog-paddling in the surf were occasional victims of Meg attacks, as proven by bite-marks on mastodon ribs and vertebrae.

Smilodon is by far the most famous saber-tooth thanks to thousands of specimens from the La Brea Tar Pits in California. It even stars in the popular Ice Age movies as the cunning cat, Diego. However, among all saber-tooths, Smilodon is the odd man out. It is chinless. It has no deep flange to protect the saber fang when the jaw is closed. What good was a chinless lower jaw? Smilodon could strike with its mouth closed by pulling down the neck muscles. But Smilodons did break their sabers. Tar Pit specimens sometimes have one or even both fangs broken, with the fractured ends worn down. How could saber-toothed cats survive with broken sabers? The best theory is that mated pairs helped each other. If one injured a fang, the other took over the prey-killing duties. Or, like lions today, groups of sisters may have hunted together.

The zebra-like Hipparion was long-legged and fast. And in most places, its comparison was the short-legged tubby hippo-rhino. From Texas to China to East Africa, hippo-rhinos, like Chilotherium, moved in great herds that left behind bone beds with tens of thousands of bones. They were true rhinos, close kin of today’s Rhinoceros, the Greater One-horned Rhino.

Kansas today is full of wheat, corn, and prairie grass. In the Late Cretaceous, warm ocean waters covered the state. Shallow seas spread across immense areas of the other continents as well, and evolution generated a new wave of ocean-going reptiles. The newest reptiles were giant sea-lizards: the Mosasaurs.

Early in the Cretaceous, hordes of parrot dinosaurs – the Psittacosaurs – lived in China and Mongolia. Not much heavier than a big turkey, Psittacosaurs used their long, strong hind claws to dig burrows where they curled up to escape unpleasant weather. Some Psittacosaurs fossilized as entire crèches – groups of youngsters who had hatched together, huddled side by side. Sudden floods buried the babies in a thick blanket of mud. Parrot dinosaurs had, for their size, the strongest bite force of any dinosaur herbivore. Tall, strong beaks and enlarged jaw muscles let the Psittacosaurs cut through hard-shelled fruit and tough leaves. At first sight, Psittacosaurs, with their long hind limbs and short front legs, seem quite different from gigantic quadrupedal dinosaurs like Triceratops. But if you look closely at the Psittacosaur's beak, you’ll see a clue to its close relationship.

There is only one skeleton in the world of the ferocious furball that lived with T. rex. – and you’re looking at it. Known technically as Didelphodon, this marsupial mammal has been misinterpreted by paleontologists for a century. Textbooks say that it was merely a big opossum, but our skeleton proves that Didelphodon had the face of Tasmanian devil combined with the body and tail of a river otter. Pound for pound, the Tazzie was the most powerful creature of Cretaceous rivers and lakes – the terror of clams, snails, and baby alligators.

Some skeletons dug from Judith River sandstones are more than just bones – they are mummies. These fine-grained sandstones actually preserved portions of skin and other soft tissues, as with this Brachylophosaurus. This is a 3D rapid prototype of the famous Judithian-Age mummy, “Leonardo.” Besides large areas of skin, the contents of the digestive track have been preserved. These contents give us clues about the duck-bill’s digestive process. Old theories held that duck-billed dinosaurs ate soft water plants. But microscopic study shows that Leonardo’s stomach contains thousands of bits of bones and conifer needles – proof that the duck-bill used its jaws to chop tough plant parts.

Observe the scales on the forearm and ankle. These would have protected the dinosaur’s legs when it moved through rough, prickly bushes. Scales over the ribcage are smaller. Along the midline of the neck and back are a row of scaly bumps. Leonardo is an outstandingly well-preserved dinosaur.

Here is an Archegosaur, a swimming amphibian from the Early Permian. This specimen is exceedingly rare. Body armor helped the Archegosaur resist the fangs of other amphibians and the jaws of big coal-swamp fish. Archegosaurs were at home on land or in the water. The sinuous body and tail were excellent for swimming while short, strong legs were effective for walking on land. Archegosaurs were grab-and-gulp predators. Jaws could open wide and snap down on small prey. Many sharp fangs in the jaws and roof of the mouth would impale the target, which was swallowed whole.

Early Oligocene. Brule Formation, White River Badlands, South Dakota, Nebraska, and Wyoming, USA.

The most common White River vegetarians were the oreodonts. They’re extinct now, but for millions of years, this family of leaf-eaters was more numerous than all others across North America. There’s no mammal family today that compares. The body was a cross between a dog and a small deer. The paws were four-toed and built something like a coyote’s, with sharp claws good for excavating burrows.

Petrified evidence proves that oreodonts sought refuge in underground bunkers. Perfect skeletons are often dug from fossil burrows, and sometimes mother oreodonts are buried side by side with their pups.

Eocene. Kemmerer, Lincoln County, Wyoming, USA.

Miocene Period. Vaucluse, Lacoste, France.

This group of Gigantopecten lived in the shallow sea that covered part of France 3 million years ago. The immense size and thickness of shells indicate that these bivalve mollusks lived during a period of optimal habitat and resources. Groupings were important to the animals’ reproductive strategy. As broadcast spawners, individual scallops release eggs and sperm into the water simultaneously. Modern scallops are hermaphroditic, having both sets of reproductive organs. Individuals will change sex many times during their lives. Like modern scallops, ancient scallops may have been vulnerable to powerful storms that swept across their shallow habitats. Surging waves would have decimated populations, spreading individuals out too thinly to reproduce or, as with this fossil assemblage, burying them alive.

Adapidae. Late Early Eocene, Lost Cabin Age. Green River Formation. Wyoming, USA.

Primates are a warmth-loving Order. Monkeys and apes are not native to North America today, but it was different in the Green River habitats. Primitive primates – lemurs and tarsioid – climbed the tropical trees, eating fruit and chasing bugs. Notharctus tenebrosus was a long-legged leaper almost identical in body plan to some of the lemurs in modern-day Madagascar.

Late Late Jurassic, Tithonian Age. Solnhofen, Lithographic Limestone. Solnhofen, Bavaria, Germany.

The fish known as coelacanths are the most famous “living fossils” in the world. Coelacanths disappeared from the fossil record around 80 million years ago in the Cretaceous Period, so scientists thought that they had gone extinct. That is, until fisherman hauled up living coelacanths from deep water near Madagascar. Not only are these fish living fossils, they are also cousins of the missing links between fish and amphibians. The thick, muscular fins of coelacanths look a little like stubby legs; the ancestors of land animals with genuine legs were close relatives of early coelacanths.

Coelacanths illustrate the rule that ancient families can die out in fresh water and most areas of salt water but still survive in the ocean depths.

Middle Devonian. Silica Shale, Lucas County, Ohio, USA.

Brachiopods ruled the sea bottom for 300 million years. Today they are ecological fugitives; unless you night dive in the tropics, you will probably never see one alive. Brachiopods are rare and secretive, and they are outnumbered by clams 1,000 to one.

Middle Oligocene. Shannon County, South Dakota, USA.

In the sun-scorched Texas scrubland, there are living relics from the White River – brightly skinned omnivores who are nearly unchanged from 35 million years ago. They are javelinas, also known as peccaries. They are not “pigs” – as evidenced by the fangs and feet.

Late Early Eocene, Lost Cabin Age. Green River Formation. Lincoln County, Wyoming, USA.

Hyracotheres are the founding fathers of the horse family. You won’t find the signature features of modern horses. Modern equids have one toe on each foot. Hyracotheres have four up front, three in the back. Modern horses have long faces, with six molar-like teeth in each jaw. Hyracotheres had short faces with only three molars. Horses today have long, rather straight legs. Hyracotheres had highly flexed joints. We know that Hyracotheres were horses because we have wonderful series of fossils that show how toes, leg joints, molars and body size changed in small steps, from 55 million years ago through to today’s fully modern horse species.

Late Early Eocene, Lost Cabin Age. Green River Formation. Southwestern Wyoming, USA.

The armor-plated garfish is a classic living fossil – a creature alive today that has changed little from the time of the tyrannosaurs, 90 million years ago. The alligator gar has diamond-shaped, armor-plated scales – each one made from a double layer of bone. The outer layer is super-dense and so hard that even big bull alligators have a hard time biting through it. The inner layer is spongier and attached to a sheet of connective tissue that works like a shock absorber. All the scales are knit together with tongue-in-groove joints, allowing the fish to twist and flex. Gars seem to be bulletproof from extinction, too. Mass die-offs struck dinosaurs 65 million years ago and then struck giant mammals several times. But each catastrophe left the gars unscathed.

Eocene. Green River Formation, Wyoming, USA.

A fish (Misoplosus) choked to death swallowing another fish (Diplomystus).

Jurassic. Middle Lias Formation. Dorset County, England.

Eocene. Green River Formation, The Thompson Quarry, Kemmerer, Lincoln County, Wyoming, USA.

Late Silurian. Fiddlers Green Formation, Phelps Member, Lang’s Quarry, Herkimer County, New York, USA.

Euripterids, or “Sea Scorpions” lived more than 100 million years before dinosaurs evolved. They are not directly related to modern scorpions - their closest living descendant is the horseshoe crab - but they had a pair of terrifying pincers much like modern scorpions do. These euripterids are quite small, but some grew up to five feet long. Sea scorpions lived underwater, as most life did during their age. Dry land was still an inhospitable place for any creature who didn’t want to be roasted by the sun’s rays. But some of euripterid’s arthropod relatives would become the first animal colonizers of terra firma, their exoskeletons providing protection from the sun, and a way to retain moisture in the dry air.

Jurassic. Holzmaden Black Shale Formation. Holzmaden, Stuttgart, Germany

Eocene. Green River Formation, Wyoming, USA.

Early Cretaceous. Yixian Formation. Liaoning, China.

So where do dinosaurs end and birds begin? It’s a tough question, because so many dinosaurs acquired avian features. We know that the ancestor of today’s birds was one of the many types of feathered dinosaurs evolving in the Late Jurassic.

Dinosaurs are not really extinct – birds are a surviving branch of the dinosaur family tree. Archaeopteryx made headlines in the 1860s as a near-perfect link between dinosaurs and birds. The fossil showed large, complex flight feathers on the arms, but Archaeopteryx also had teeth, three-fingered claws and a long, body tail like an Allosaur’s. The raptor-dinosaurs Velociraptor and Deinonychus, discovered in the mid-1900s, filled in more evolutionary gaps. They had longer arms and bigger brains than most other dinosaur species, coming close to the cranial capacity of modern birds. In the 1900s, Chinese paleontologists studied and reported many skeletons of raptor-dinosaur with feathers, such as Caudipteryx and Sinosauropteryx.

Eocene. Green River Formation, Kemmerer, Lincoln County, Wyoming, USA.

Oligocene-Miocene. Tampa Bay, Florida, USA.

Jurassic. Holzmaden Black Shale Formation. Holzmaden, Germany.

Sea lilies (crinoids) – relatives of starfish and other echinoderms – filter small food items from the water with their long, jointed arms. Nearly all sea lilies, living and extinct, lived near the sea bottom. The Holzmaden ocean was special: long-stemmed sea lilies attached themselves to floating logs and let their bodies and feeding arms hang down into the still water. Some grew stems up to 50 feet long. Apparently the log that this specimen was attached to became water-logged and sank to the ocean depths, dragging the crinoid to its death. The low oxygen environment in the ocean depths helped to preserve this beautiful piece.

Cretaceous. Bear Paw Formation. Southern Alberta, Canada.

From the Devonian Period to the end of the Cretaceous, ammonites generated tens of thousands of species that invaded nearly every salt-water habitat in the world. Ammonites species came so fast and furiously that the average species only lasted a million years or less. This quick turnover means that ammonites are near-perfect paleo-clocks.

Late Late Cretaceous.

Ammonites are the ancient relatives of the modern nautilus. Like the nautilus, ammonites had hollow chambers inside their shell that could be filled with air or water to allow the animal to float or sink respectively. So the shells were not homes, but buoyancy tanks, like what modern submarines have. The wavy lines radiating from the center of the fossil are sutures that separated different sections inside the shell, before the open spaces inside were filled in with minerals to make the piece one solid fossil.

Middle Eocene. Verona, Italy

Late Early Cretaceous. Coober Pedy Formation. Coober Pedy, South Australia.

Belemnites are the ancient relatives of modern squids, and looked much like squids do today. The difference between squids and belemnites can be seen in their internal stuctures. Belemnites have a delicate structure within them called a phragmacone, this structure was used to regulate the animal’s buoyancy. Another structure called a guard protected the phragmacone and also counterbalanced it, making swimming easier. This fossil is a belemnite guard, and, interestingly, it has been opalized.

Early Cretaceous. Hokkaido, Japan.

Early-Middle Cambrian.

The earliest trilobites wore spiked armor, because there was danger overhead: Predatory Anomalocaris swimming above the Cambrian sea bottom. Anomalocaris grew up to be up to a yard long. It was bigger and stronger than any early trilobite. Swimming legs worked like propellers that drove the predator through the water, making it one of the speediest animals in the Cambrian ocean.

Early Devonian. Timrhanrhart Formation. Jbel Gara el Zguilma, Draa Valley, Morocco.

Early Devonian. Timrhanrhart Formation. Jbel Gara el Zguilma, Draa Valley, Morocco.

Middle Devonian. Bou DOb Formation. Jbel Issoumour & Jbel Mrakib, MaOder Region, Morocco.

Middle Devnoian. El Otfal Formation, Jbel Zireg, Morocco

Middle Ordovician. Volkhov Formation. St. Petersburg region, Russia.

Early Devonian. Ihandar Formation. Jbel Issoumour, MaOder Region, Morocco.

Early Devonian. TazoulaOt Formation. Jbel OufatEne & Jbel Issoumour, MaOder Region, Morocco.

Late Ordovician. Richmond Group, Waynesville County, Ohio, USA.

Middle Devonian. El Otfal Formation. Bou DOb, MaOder Region, Morocco.

Middle Silurian. Rochester Shale, Niagra County, New York, USA.