Last Updated 2/27/2003 2/26/2003
Dino Count Current total number of "Official" Dinosaurs.
What does modern science have to say about the dinosaurs? Are they truly obsolete, long-extinct relics of a more primitive and experimental stage in the history of life, or is there more to the Dinosauria than meets the eye?
Dinosaurs are animals that evolved into many sizes and
shapes. Dinosaurs were and are quite diverse, and often one person will think of an animal
like a long-necked sauropod, while another person will think of a large, fierce meat-eater
like Tyrannosaurus rex. It should be clear then that the term
"dinosaurs", or the scientific version "Dinosauria", is describing a
diverse group of animals with widely different modes of living. The term was invented by Sir Richard Owen in 1842 to
describe these "fearfully great reptiles", specifically Megalosaurus, Iguanodon,
and Hylaeosaurus, the only three dinosaurs known at the time. The creatures that we
normally think of as dinosaurs lived from late in the Triassic period (about 225 million
years ago) until the end of the Mesozoic era (about 65 million years ago); but actually
they live on today as the birds.
The term "dinosaur" has had a long history of misrepresentation. A few simple points must be kept in mind when discussing these animals:
Not everything big and dead is a dinosaur.
All too often books written for a popular audience include animals such as mammoths, mastodons, plesiosaurs, ichthyosaurs, and the sail-backed Dimetrodon. Dinosaurs are a specific subgroup of the archosaurs, a group that includes crocodiles and birds, whereas mammoths and mastodons are mammals. Other archosaurs included the pterosaurs, relatives of dinosaurs but not true dinosaurs. More distantly related to true dinosaurs were the marine plesiosaurs and ichthyosaurs. These were marine reptiles, not dinosaurs or even close relatives of them. Dimetrodon is neither a reptile nor a mammal, but a basal synapsid -- that is, an early relative of the ancestors of mammals.
Not all dinosaurs lived at the same time.
Different dinosaurs lived at different times. Despite the portrayals in movies like Fantasia and Jurassic Park, no Stegosaurus ever saw a Tyrannosaurus, because Tyrannosaurus wasn't alive for another 80 or so million years. Ditto for Apatosaurus (a.k.a. "Brontosaurus").
Dinosaurs are not extinct.
Technically. Based on features of the skeleton, most people studying dinosaurs consider birds to be dinosaurs. This shocking realization would make even the smallest hummingbird a legitimate dinosaur. Rather than refer to "dinosaurs" and birds as discrete, separate groups, it is best to refer to the traditional, extinct animals as "non-avian dinosaurs" and birds as, well, birds are birds, or avian dinosaurs. Whatever works for you. It is incorrect to say that dinosaurs are extinct, because they have left living descendants in the form of cockatoos, cassowaries, and their pals -- just like modern vertebrates are still vertebrates even though their Cambrian ancestors are long extinct. Yes, even birds have ancestors, funny looking as birds may be.
Dinosaurs represent failure and
Rather, dinosaurs are the best examples of success and adaptation. They ruled the Earth longer than any other land animals (over 150 million years), and gave rise to BIRDS.
Dinosaurs and "humans"
The death of the last dinosaur and the appearance of the first "human" (genus HOMO) was separated by about 62 million years.
Dinosaurs were either all hot-blooded or
Mesozoic dinosaurs were not "warm-blooded" like modern mammals, nor were they "cold-blooded" like modern lizards. Most specialists believe that dinosaurs were "dinosaur-blooded", a condition that combines certain aspects of "warm-bloodedness" with a changing metabolism over the animal's lifetime.
The word dinosaur means
Actually it was originally defined to mean "fearfully-great lizard", by Richard Owen in 1842. The greek word "deinos", when used as a superlative, means "fearfully-great" (as used by Homer in THE ILIAD). It became simplified over time, as a simple adjective, to mean "terrible". Dinosaurs are neither terrible nor are they lizards!
Whatever you read in the latest "dinosaur book" or see on T.V. or in the movies must be true.
Popular books, movies, and TV specials need not be 100% accurate. They often contain errors and outdated information, and may reflect the personal bias of the writer. (Most dinosaur books and TV scripts are not reviewed by professional dinosaur paleontologists).
Dinosaurs all lived and died at the same time.
The distance in time between Tyrannosaurus and Apatosaurus (formerly called "Brontosaurus") is more than the time between Tyrannosaurus and your parents, about 65 million years. Of the (approximately) 900 named species of Mesozoic dinosaurs, only two or three dozen species faced the final extinction in North America.
Mammals arose after the dinosaurs, and helped drive the dinosaurs into extinction by eating dinosaur eggs.
Mammals and dinosaurs both appeared in the Late Triassic Period. There is no evidence that dinosaurs went extinct because of predation on their eggs.
An asteroid (or comet) killed the dinosaurs.
The controversy over the cause of the dinosaur extinction continues among paleontologists. However, evidence from a deep sea core drilled off the coast of Florida proves that an asteroid hit the Earth at the end of the Cretaceous which caused the dinosaur extinction. Most dinosaur specialists are willing to accept that an asteroid hit the Earth, but do not think that it was the sole cause of the Mesozoic extinctions. Instead, the fossil record reveals that dinosaurian diversity was already in decline by the end of the Cretaceous. The asteroid impact may have been "the straw that broke the camel's back."
All big reptiles from the prehistoric past ["Monsters"] are dinosaurs.
Dinosaurs represented less than 10% of the 40 groups of reptiles from the Mesozoic Era (Pterodactyls, sea-serpents, giant lizards, pelycosaurs, and other BIG prehistoric beasts are NOT dinosaurs). "Monsters" and Dragons are the products of fiction and mythology. Dinosaurs are better because they are real!!
Archaeologists dig up dinosaurs.
Archaeology and paleoanthropology (subdivisions of Anthropology) only deals with man and covers the last 3-4 million years. Paleontology (a combination of Geology and Biology), deals with all fossils and covers the last 3.5 billion years!
1824 - Buckland published the first description of a dinosaur called Megalosaurus.
1809 - A lower
shin- bone of a large unknown animal was collected at Cuckfield by William
Smith ("Father of English Geology"). This fossil was deposited at the British Museum in London and years later was identified as that of Iguanodon.
Dinosaur fossils had been known for centuries as "dragon bones" or the remains of giants, but it wasn't until Dean William Buckland of Oxford, England described the carnivorous "lizard" Megalosaurus (in 1824) that they were formally studied as an extinct group of giant reptiles. The English country doctor Gideon Mantell described Iguanodon in 1825, and today there are more than 800 known types of non-avian dinosaurs (plus some 10,000-plus birds).
The term "Dinosauria" was invented by Sir Richard Owen in 1842 to describe these "fearfully
great reptiles", specifically Megalosaurus, Iguanodon, and Hylaeosaurus,
the only three dinosaurs known at the time. The irony of Owen's invention of Dinosauria is
that he devised the taxonomic group as an argument against progressive evolution, but
actually had presented evidence supporting evolution.
The First Discoveries
The clade Dinosauria was originally defined by Sir Richard Owen in 1842, in a two hour speech that reportedly held the audience captivated. The original dinosaurs of this new group were Megalosaurus, Iguanodon and Hylaeosaurus. However, each of these animals was known only from fragmentary specimens. It wasn't until the discoveries of dinosaurs in North America in the mid-19th century that people began to get a clearer picture of what dinosaurs looked like.
It is generally accepted that the first discovery of dinosaur remains in North America was made in 1854 by Ferdinand Vandiveer Hayden during his exploration of the upper Missouri River.
Near the confluence of the Judith and Missouri Rivers (shown
above) Hayden's party recovered a small collection of isolated teeth which were later
described by the Philadelphia paleontologist Joseph Leidy in 1856, in the Proceedings
of the Academy of Natural Sciences of Philadelphia.
An important, more complete
A short two years later, Leidy had the honor of describing
the first reasonably complete dinosaur skeleton the world would know, Hadrosaurus foulkii. Named after its
discoverer William Parker Foulke, this specimen was
recovered during quarrying of a sand pit in Haddonfield, New Jersey.
The real significance of this specimen was in its limb
proportions. For the first time scientists studying these animals could see that some
dinosaurs were bipedal, walking on two legs instead of on all fours. Bipedalism was a
revolutionary thought for a reptilian posture.
This specimen, now on display at the Academy of Natural Sciences of Philadelphia, was
originally mounted in a free-standing bipedal pose by Benjamin Waterhouse Hawkins in 1868.
The records for attendance at the Academy show that visitation increased three-fold with this new exhibit, testimony to the public's long-standing and intense fascination with dinosaurs.
For many years, Hadrosaurus foulkii was the only dinosaur on public display. Duplicate casts of the skeleton were made for other institutions both in the United States and in Europe.
Events surrounding the discovery of the Bushmans River dinosaur.
Remains of Dinosaurs
If the diverse and numerous dinosaurs (except birds) are extinct, then how can we better understand they lived? Despite the fact that the great dinosaurs of the Mesozoic are gone, they have left us many clues about what they looked like and how they lived. This is because dinosaur fossils are not limited to bones, but include skin, eggs, nests, footprints, and other special kinds of fossils that give us clues about their lifestyles.
The news has recently carried several stories of wonderful finds of nesting dinosaurs, and it is true that an explosion of data on dinosaurian nesting and social behavior has been uncovered in the past 20 years. Some of the most well known and compelling evidence comes from Dr. Jack Horner's (Museum of the Rockies) ongoing work at the "Egg Mountain" site in Montana, where he has documented evidence of a large nesting area used by hadrosaurian (duckbill) dinosaurs. These dinosaurs were named Maiasaura, "good mother reptile," referring to the closely packed nests that contain fossilized eggs, embryos, and juveniles (such as the one pictured at right). This is one case where we can be fairly confident that parental care was involved in these dinosaurs' lifestyle. Actually, this is not a surprising assertion, because both crocodilians (their closest living relatives) and birds (their living descendants), both show some degree of parental care and extensive nest building.
Other dramatic finds of dinosaur nests include theropod dinosaurs (Oviraptor and Troodon) that apparently died while brooding their nests, and abundant nests of the early ceratopsian dinosaur Protoceratops. An interesting story about Oviraptor: the so-called "egg stealer" was so named because it was found atop a clutch of eggs that were assumed to belong to Protoceratops. This idea held for some 70 years until a find in the 1990s showed an Oviraptor embryo inside one of those eggs... Egg stealer exonerated!
We know of literally thousands of non-avian dinosaur footprints scattered around the globe, from Late Triassic to Late Cretaceous age. You might not think that a footprint, or a sequence of footprints (called a trackway), could tell us much, but actually it can tell us some general things about the biology of dinosaurs.
From trackway data, we can tell that (1) some non-avian dinosaurs travelled in large groups; (2) non-avian dinosaurs moved with their feet held underneath their body (as birds and mammals do); and (3) some non-avian dinosaurs moved rather quickly, but some plodded along at a more leisurely pace -- see our section on dinosaur speeds for more info. See Dinosaurs Tracks
Dinosaurs, living and extinct, have varied diets. We have some strong evidence of exactly what the diets of some of the extinct dinosaurs was, and we can observe birds directly to learn about their diets. Dentition (tooth structure) is one of the most abundant lines of evidence useful for determining dinosaur diets. Most ornithischian and sauropodomorph dinosaurs had rather simple, short stubby crenellated teeth, which are similar to those of living herbivores, and clearly not too good for eating much meat.
Theropod teeth, on the other hand, retain the primitive archosaurian characteristic of being recurved, serrated, laterally -compressed, and knife-like. There is some variation in tooth structure among extinct theropods, but most are fairly similar and obviously related to a carnivorous diet.
Stomach contents are another line of evidence, somewhat more direct but also a bit more tricky to interpret accurately. Well-preserved dinosaur skeletons sometimes have traces of apparent food items preserved in their abdominal cavity, where it's safe to assume that they had a stomach. This includes pine cones and/or needles in some herbivores' guts, and traces of some vertebrates in some theropods' guts. So this independent line of inquiry substantiates the data from tooth morphology. Also, some sauropodomorph stomachs contain well- rounded stones, caled gastroliths, that were probably used to grind food in a muscular crop or gizzard, like some birds (and crocodilians) do.
The general hypothesis that most ornithischians and sauropodomorphs were largely, if not completely herbivorous, and that theropods (at least before the origin of birds) were mostly carnivorous, thus holds. More specific hypotheses have been proposed and supported by data, while others have fallen by the wayside. It is likely that new discoveries will illuminate more about dinosaur diets as the global "dinosaur renaissance" continues.
You can learn more about the diets of sauropods from our page on that
With the discovery of many new species since the 1840s, the Dinosauria now contains two major groups of dinosaurs: the Ornithischia, or "bird-hipped" dinosaurs, and the Saurischia, or "lizard-hipped" dinosaurs. The division between the two groups was made by H.G. Seeley in 1888. The etymology behind the two names ("bird-hipped" vs. "lizard-hipped") is not very accurate, since some saurischians had bird-like hips, and ornithischians' hips were somewhat birdlike due to convergent evolution, not due to direct ancestry. In fact, birds are saurischians! Goto Dinosaur Groups to see examples.
Saurischia contains two main groups:
Ornithischia contains several groups of herbivorous dinosaurs, including several basal groups, but primarily three large ones:
Geologic Time Scale
Dinosaurs and other Mesozoic Animals
DinoData Dinosaur Index
Go to Blast From the Past To see the Asteroid Theory of Extinction
Sixty-five million years ago the curtain came down on the Age of Dinosaurs when a cataclysmic event led to mass extinctions of life. This interval of abrupt change in Earth's history, called the "K/T Boundary", closed the Cretaceous (K) Period and opened the Tertiary (T) Period.
A recently recovered deep-sea core provides convincing
support to the hypothesis that an asteroid collision devastated terrestrial and marine
environments world-wide. It shows a record of flourishing marine life before the event,
followed by mass extinction and then evolution of new species and slow recovery of
surviving life forms after the event.
There have been LOTS of extinctions that affected animals
besides dinosaurs. There were even some that the dinosaurs lived through and survived.
On-Line Dinosaur Omnipedia
Dinosaurium Hooper Virtual Natural History Museum. The Department of Earth Sciences, Carleton University, Ottawa, Ontario, Canada
Dinosaur List This page lists all known Dinosaur genera.
Dinosaur News Here you will find all the latest bits of dinosaur news. New discoveries, theories, statements, research, etc. Be the first to find out.
Dinosauria Translation and Pronunciation Guide A Pronunciation, meaning, and information of all dinosaur species.
Dinosaurs End, The Gravitational Process
Earth's Geologic Time Line
Journal of Dinosaur Paleontology
Oceans of Kansas Paleontology: Fossils From the Western Interior Sea
Official State Dinosaur Page