Eoraptor
Even though giant dinosaurs are some of the most celebrated of the “terrible lizards,” the earliest dinosaurs got off to a small start. Eoraptor lunensis , discovered in the roughly 230-million-year-old rocks of Argentina, for example, was only about 3 feet (1 m) long and weighed about as much as a jackal. But, small as it was, this dinosaur represents the beginnings of big things for dinosaur evolution.
When Eoraptor was discovered by paleontologist Ricardo Martínez in 1991, the dinosaur was thought to be a carnivore and related to the ancestry of later flesh-eaters such as Allosaurus and T. rex . But more recent analysis has changed that interpretation. Eoraptor has been recategorized as a sauropodomorph—the group of long-necked, plant-eating dinosaurs that includes species like Brachiosaurus
There are subtle characteristics of the dinosaur’s skeleton that places it closer to the ancestry of four-legged herbivores than carnivores. Eoraptor represents an early part of sauropodomorph evolution, between the earliest, insect-eating dinosaurs and later species. Not only that, but the fact that a sauropodomorph like Eoraptor evolved by 230 million years ago hints that dinosaurs split off into their major lineages very soon after the first dinosaurs appeared. Some of the largest dinosaurs that ever lived can trace their relatives all the way back to the depths of the Triassic.
During the time Eoraptor lived in prehistoric Argentina, the dinosaur’s habitat was a lush floodplain covered in ferns and conifer trees. Despite the sharp teeth of Eoraptor , however, the dinosaur was not the largest or most fearsome creature in its habitat. The apex predators of the time were large crocodile relatives, such as Saurosuchus , and Eoraptor was too small to eat the armored reptiles called aetosaurs or the pig-like protomammals called dicynodonts. Eoraptor probably dined on small prey, such as lizards and insects, as well as vegetation. Despite the impressive reputation of dinosaurs, Eoraptor was probably a rare sight in its ancient habitat. Within Argentina’s Ischigualasto Formation, where Eoraptor was uncovered, dinosaur fossils represent only about 6% of the sample. There were far more crocodile relatives, protomammals, and other creatures that framed the world dinosaurs were evolving in. Despite early interpretations that Eoraptor was a rapacious carnivore that led the rise of the dinosaurs, instead it seems early dinosaurs were on the sidelines. It would take a mass extinction at the end of the Triassic to turn the tide in their favor.
STATISTICS
Named: Eoraptor lunensis
Year named: 1993
Age: Late Triassic, 230 million years ago
Where: Argentina
Length: 3.2 feet (1 m)
Weight: 22 pounds (10 kg)
Diet: Omnivore
Group: Sauropodomorpha
Megapnosaurus
Dinosaur discoveries don’t always come fresh from the ground. Sometimes paleontologists discover new dinosaurs hiding in museum drawers, waiting for experts to take a second look. That’s what happened to Megapnosaurus, a dinosaur that has sometimes been confused for other species.
In 1969, paleontologists described a new carnivorous dinosaur—“Syntarsus” rhodesiensis. The little dinosaur was very similar to Coelophysis from North America—so similar, in fact, that some paleontologists questioned whether this new dinosaur really was a species of Coelophysis. To complicate matters further, it turned out that the name “Syntarsus” had already been given to a species of beetle and could not be used for the dinosaur. This is the science of taxonomy—how species are named—and paleontologists had a taxonomic tangle to sort out.
In 2001, paleontologists suggested that this small meat-eater receive a new name, Megapnosaurus rhodesiensis. And despite previous comparisons that confused the dinosaur with Coelophysis, recent analyses suggest that Megapnosaurus is more closely related to other species like Segisaurus and Camposaurus found in North America. Megapnosaurus was part of a vast proliferation of small, sleek carnivores through ancient Pangaea. Megapnosaurus lived just before the true Age of Dinosaurs took off. The small carnivore dwelled among ancient floodplains crossed by streams and dotted with conifer trees. There were many other dinosaurs in the same habitat. Some, such as Massospondylus, were big, long-necked herbivores that walked on two legs and had huge thumb claws. There were also many smaller, beaked herbivores that ran around on two legs, like Fabrosaurus
But Megapnosaurus was not a big game hunter. Like its Triassic ancestors, this dinosaur hunted lizards, mammals, and other small morsels that lived in its habitat. The arrangement of bones in the dinosaur’s eye, in fact, hints that Megapnosaurus was primarily active at night, a perfect time to snatch a slumbering lizard or a snuffling mammal.
STATISTICS
Named: Megapnosaurus rhodesiensis
Year named: 2001
Age: Late Triassic, 210 million years ago
Where: South Africa and Zimbabwe
Length: 10 feet (3 m)
Weight: 70 pounds (31.7 kg)
Diet: Small vertebrates like lizards Group: Coelophysidae
Pisanosaurus
Trying to understand the early days of dinosaurs isn’t easy. Some of the earliest dinosaurs and dinosaur relatives are very rare, known from only a few bones or scattered skeletal pieces. That can lead to paleontologists having different interpretations of the same animal, and that is just what happened to Pisanosaurus mertii from Argentina.
The first bones of Pisanosaurus were discovered in 1962 in the same geologic formation that contains Eoraptor and Saurosuchus . That first find included parts of the skull, spine, ribs, hips, and limbs, which was enough to know that this animal was something new to science. But what kind of Triassic reptile was Pisanosaurus ?
For many years, Pisanosaurus was thought to be an early ornithischian dinosaur. Ornithischia is the group of dinosaurs that came to include horned dinosaurs, armored dinosaurs, duckbilled dinosaurs, and others. In this view, Pisanosaurus might represent what the earliest ornithischians were like. But recent analyses have questioned whether Pisanosaurus is a dinosaur at all. Pisanosaurus doesn’t seem to have any specific features that connect it to ornithischian dinosaurs. Instead, Pisanosaurus might be something more ancient.
Dinosaurs belong to a broader group of reptiles called Dinosauriformes, or dinosaurs and their closest relatives. Recent studies hint that Pisanosaurus is a dinosauriform—not a true dinosaur, but a close relative. That interpretation has major implications for dinosaur evolution. Pisanosaurus might have been a protodinosaur that lived alongside some of the earliest true dinosaurs. If this is the case, then paleontologists are faced with a mystery of when and where the earliest ornithischian dinosaurs evolved. Debate about the identity of Pisanosaurus will continue.
Whatever the reptile’s classification, Pisanosaurus lived in the same floodplain environment that hosted Eoraptor and Saurosuchus This was a warm, humid place with a strong dry and wet season. An herbivore, Pithnosaurus likely dined on horsetails and ferns that grew there while avoiding the teeth of Herrerasaurus .
STATISTICS
Named: Pisanosaurus mertii
Year named: 1967
Age: Late Triassic, 220 million years ago
Where: Argentina
Length: 3.5 feet (1.1 m)
Weight: 15 pounds (6.8 kg)
Diet: Plants
Group: Dinosauriformes
Cryolophosaurus
Dinosaurs thrived over the entire planet. That includes the poles, challenging environments where there were months of darkness even when the world was warmer. And in the Early Jurassic of ancient Antarctica, the ancient conifer forests were stalked by Cryolophosaurus ellioti
Originally nicknamed “Elvisaurus” for the pompadour-like crest on its head, Cryolophosaurus was the first major dinosaur find made in Antarctica. The fossil was hard won. Not only is Antarctica very difficult to reach, but surprise snowstorms and the hard, frozen rock make work difficult for paleontologists. Nevertheless, experts have been able to recover a skull, vertebrae, ribs, and other assorted parts that give us an outline of what this carnivore looked like.
Cryolophosaurus lived around the same time as Dilophosaurus in Arizona, and, like its relative in North America, the most striking thing about Cryolophosaurus is its crest. The dinosaur from Antarctica had a ridged, fan-shaped crest right in front of its eyes. Just like other theropods, this crest was a social signal and would have been covered in a sheet of tough keratin in life.
Even though the bones of Cryolophosaurus were found in Antarctica, life on the continent was very different during the Early Jurassic. The land that now makes up Antarctica was closer to the equator and annual temperatures didn’t drop far below freezing even in the coldest months. Nevertheless, Cryolophosaurus lived in a more temperate climate where forests of conifers stood tall. And in those forests were plenty of prey.
The habitats Cryolophosaurus called home were populated with lineages left over from the Triassic. There were some small, weasel-like protomammals as well as sauropodomorph dinosaurs of varying size. Some of them, like the recently named Glacialisaurus , got to be about as large as Cryolophosaurus itself. But there were smaller sauropodomorphs in the forests, too, about the size of a medium-sized dog. These dinosaurs, as well as the young of the larger species,
STATISTICS
Named: Cryolophosaurus ellioti
Year named: 1994
Age: Early Jurassic, 190 million years ago
Where: Antarctica
Length: 21 feet (6.4 m)
Weight: 1,000 pounds (453.5 kg)
Diet: Smaller vertebrates, including dinosaurs Group: Theropoda
Ceratosaurus
Ceratosaurus nasicornis was one of the strangest dinosaurs discovered in the 19th century. The first skeleton, which was nearly complete, was found in Garden Park, Colorado, including a skull with a horn on the nose and another horn over each eye—a Late Jurassic oddity over a century after its discovery.
Ceratosaurus was one of the many dinosaurs found within western North America’s Morrison Formation. This ancient environment was the stomping ground of famous species like Stegosaurus and Apatosaurus , a landscape of winding rivers between towering stands of conifer trees and carpets of ferns. Like western North America today, the Morrison Formation had a seasonal environment with a wet and dry season.
While not the largest of the Morrison Formation carnivores, Ceratosaurus was still an apex predator. Small, relatively defenseless dinosaurs like Dryosaurus might have been favored prey for Ceratosaurus , as well as creatures that lived along the lakes and streams like lungfish. But Ceratosaurus was not the largest predator of its habitat. Large
Allosaurus and Torvosaurus could reach nearly 40 feet (12 m) in length, about twice its size, and would have been more than a match for Ceratosaurus
Compared to the other carnivores of its time, Ceratosaurus was strange. In addition to the dinosaur’s distinctive horns, Ceratosaurus had very small arms, large shoulderblades, bony armor embedded along its back, and legs that were adapted more for walking than running. Perhaps, some researchers have speculated, Ceratosaurus focused more on small prey along bodies of water than trying to compete with larger carnivores. Ceratosaurus fossils are rarer than those of Allosaurus . Paleontologists are not sure why, but the rarity of Ceratosaurus might mean that this dinosaur preferred different prey than its larger competitors.
Much like other decorated dinosaurs, the horns of Ceratosaurus were not for attack or defense. The bones were light and fragile, a clue that these structures were social signals. A keratin covering would have made them even more prominent in life, meaning Ceratosaurus always cut a striking figure on the Jurassic landscape.
STATISTICS
Named: Ceratosaurus nasicornis
Year named: 1884
Age: Late Jurassic, 150 million years ago
Where: Colorado, Wyoming, and Utah, USA
Length: 23 feet (7 m)
Weight: 1,500 pounds (680.3 kg)
Diet: Smaller vertebrates, including other dinosaurs
Group: Ceratosauridae
Brachiosaurus
Few dinosaurs stood taller than Brachiosaurus altithorax . Named the “arm lizard” for the length of the dinosaur’s column-like forelimbs, this sauropod dinosaur reached high into the trees to nibble on conifer branches that other plant-eaters could only ever dream of reaching.
The first Brachiosaurus fossils known to paleontologists were uncovered in 1903 in western Colorado. Said to be one of the largest dinosaurs ever found when it was discovered, the original fossil only included a handful of the giant’s bones. The find included an arm bone, some of the leg bones, several vertebrae, and a few ribs. Still, even those pieces were enough to know that Brachiosaurus was different from other sauropod dinosaurs of the time.
Paleontologists have turned up additional bones since then—including parts of the skull—but Brachiosaurus is a very rare dinosaur. Experts are still awaiting the discovery of a more complete skeleton. And experts have turned to related dinosaurs to fill in some of the gaps. A dinosaur found in Tanzania, Giraffatitan , was once thought to be a species of Brachiosaurus and its bones are sometimes used as a model for what’s still missing from Brachiosaurus
A sauropod, Brachiosaurus stood out amongst its neighbors during the time of the Late Jurassic Morrison Formation. The long arms of Brachiosaurus elevated the dinosaur’s chest and neck into a much higher resting position. The dinosaur is also thought to have had broad, spoon-shaped teeth, and likely fed high up on conifer trees to help avoid competition with other, shorter herbivores like Camarasaurus and Apatosaurus .
The heart of Brachiosaurus had to pump blood high up the neck, requiring a massive heart and blood pressure twice that of a giraffe. To get around this, Brachiosaurus and similar dinosaurs moved their heads side-to-side more often than up-and-down. This allowed Brachiosaurus to stand in place and graze over a broad area before moving on to its next meal.
STATISTICS
Named: Brachiosaurus altithorax
Year named: 1903
Age: Late Jurassic, 150 million years ago
Where: Western United States
Length: 65 feet (19.8 m)
Weight: 50 tons (45.3 t)
Diet: Conifers and other plants
Group: Brachiosauridae
66 To date, no one has ever found a complete Brachiosaurus altithorax skull. Most restorations of this iconic dinosaur are based on the skull of Giraffatitan , a related dinosaur found in Tanzania. New discoveries may change what we think Brachiosaurus looked like.
STATISTICS
Named: Psittacosaurus mong oliensis
Year named: 1923
Age: Early Cretaceous, over 101 million years ago
Where: Mongolia
Length: 6.5 feet (1.9 m)
Weight: 44 pounds (19.9 kg)
Diet: Ferns and similar plants
Group: Ceratopsia
Psittacosaurus
The term “horned dinosaur” often conjures up images of enormous, scaly herbivores festooned with impressive horns—dinosaurs like Triceratops , Styracosaurus , and Torosaurus . But the horned dinosaur family was small for much of their early history. And among those little, early ceratopsids, few have had such outsized influence on what we think about horned dinosaurs as Psittacosaurus mongoliensis
There may be as many as a dozen known species of Psittacosaurus , all with their own slight differences in horn and skull shape. But the iconic Psittacosaurus —the first to be named and perhaps the best known—is Psittacosaurus mongoliensis from the Gobi Desert.
The first Psittacosaurus fossils known to paleontologists came from expeditions led by the American Museum of Natural History to Mongolia carried out in the 1920s. A driver named Wong, a driver for the expedition, found what turned out to be a partial skeleton and complete skull of an unknown dinosaur. The dinosaur had a parrot-like beak at the front of its boxy skull. This is where the dinosaur got its name from, as Psittacosaurus translates to “parrot lizard.”
The geographical and temporal range of Psittacosaurus species is impressive. Many dinosaurs are known only from a few bones from a single skeleton or a collection of bones all attributable to one species. But various Psittacosaurus lived in what’s now Mongolia and China between 126 and 101 million years ago, some leaving complete skeletons. In fact, some Psittacosaurus are so well-preserved that we know what color they were.
A particular Psittacosaurus found in China and known as SMF R 4970 has been incredibly informative for paleontologists. In addition to a complete, articular skeleton, the fossil includes a great deal of skin impressions and even bristle-like feathers.
Paleontologists started reporting more dinosaurs with preserved feathers and feather-like structures in the late 1990s. Most of these were theropods that were more or less related to the earliest birds.
Caihong
For a very long time, paleontologists envisioned dinosaurs with very drab colors. Large species, especially, were often depicted as shades of gray, brown, and green. But we now know that at least some dinosaurs were very brightly colored. The Late Jurassic dinosaur Caihong juji was practically a rainbow-colored dinosaur.
A relative of dromaeosaurs and Archaeopteryx , Caihong was a small dinosaur. An adult could stand in the palm of your hand. Back in the Jurassic, many different feathered dinosaurs lived in the same forests. Most discovered to date were small and seem adapted to life in the trees. But even in a place with many other fuzzy dinosaurs, this Late Jurassic carnivore would have been immediately recognizable. Not only did Caihong have a small crest on top of its snout, but this dinosaur was brightly colored. The feathers of Caihong were densely packed.
This Jurassic didn’t just have feathers, but was covered in thick plumage. And in those preserved feathers were pigment-carrying bodies called melanosomes. By studying these tiny structures, experts discerned that Caihong had shiny, iridescent feathers around its head and neck like those of some hummingbirds. Rather than being the dark sheen of Microraptor , some of the Caihong feathers were rainbow-colored.
Precisely why Caihong was such a colorful dinosaur is a puzzle. Carrying striking colors could be a risk for a small dinosaur, making it more visible to larger carnivores. But bright coloration can be very important for social signaling, such as finding a mate or facing off against rivals. And if Caihong could be so brightly colored, then there are likely other dinosaurs with brilliant hues that have yet to be uncovered.
STATISTICS
Named: Caihong juji
Year named: 2018
Age: Late Jurassic, 161 million years old
Where: China
Length: 16 inches (0.4 m)
Weight: 1 pound (0.4 kg)
Diet: Insects and small prey
Group: Anchiornithidae
Velociraptor
Before 1993, Velociraptor mongoliensis was not a celebrity dinosaur. Initially known from a skull and a claw found during a 1923 expedition to Mongolia, the dinosaur was rather obscure. Thanks to the bigscreen adaptation of Jurassic Park , however, this turkey-sized dinosaur was immediately placed in the celebrity spotlight—even though the real animal was very different from its Hollywood counterparts.
Multiple Velociraptor skeletons have been found since the initial discovery, making this dromaeosaur one of the best-known species of all. Paleontologists have even discovered a Velociraptor locked in combat with a Protoceratops when the two were buried and fossilized—famously known as “the Fighting Dinosaurs.” Though much smaller and more slender than other dromaeosaurs like Deinonychus , Velociraptor was still an accomplished hunter.
In life, Velociraptor roamed the dune-covered landscapes of Cretaceous Mongolia about 73 million years ago. These were the same habitats inhabited by Protoceratops , Oviraptor , and other familiar species, and collapsing sand dunes are at least partially responsible for why we know Velociraptor so much better than some of its relatives.
Velociraptor is one of the few known dromaeosaurs with direct evidence of feathery body coverings. Often, which dinosaurs were feathered is inferred through the relationships between feathered species and where paleontologists expect feathers evolved on the dinosaur family tree. But even though paleontologists have only found Velociraptor bones so far, one of the lower arm bones in some specimens show a row of dots—quill knobs that were anchor points for long arm feathers. This discovery left little doubt that Velociraptor was a very feathery dinosaur and that its relatives were also covered in elaborate plumage.
STATISTICS
Named: Velociraptor mongoliensis
Year named: 1924
Age: Late Cretaceous, 73 million years ago
Where: Mongolia
Length: 7 feet (2.1 m)
Weight: 40 pounds (18.1 kg)
Diet: Smaller dinosaurs and vertebrates
Group: Dromaeosauridae
