I've collected dinosaur fossils in a lot of places where you'd expect to find them, and quite a few from places where the discovery of their bones was a surprise. In Arizona, most researchers have focused on the Triassic, and in that time period, mostly in Northern Arizona's early Mesozoic formations. But what I've discovered in recent years is that dinosaur fossils are being found all over Arizona. While so far there hasn't yet been found another Como Bluff, or Dinosaur National Monument, my intuition tells me that there will be places just like that, and their discovery is just a matter of time and a matter of how many eyes are looking at Jurassic and Cretaceous rocks in Arizona. On these dinosaur pages, I'm offering a bit of my own perspective on Arizona's dinosaurs. I've made it user friendly, not any more technical than is absolutely necessary so youngsters and the general fossil collectors can glean something from this brief treatment. Some of the illustrations are classics, a bit out of date, and some are fresh and state of the art..that is, state of the science. At any rate, I'll update these as I obtain new images. As usual, if anyone sees any errors, has updated information or photos, or would like to comment, I'm always open for suggestions.
On my website, you'll have to pardon the use of the words "Arizona" or "here" because neither term can accurately portray a place on earth that has been slowly rafting around the earth as a tectonic plate for millions of years. So "here" in the Triassic 225 million years ago was a thousand or more miles closer to the equator, and Arizona didn't exist. On the great Pangaea supercontinent, today's familiar landscape did not exist and Arizona would have been unrecognizable. If only for the sake of convenience "here" and "Arizona" will be freely used, and should not be confused with any of the earth's geography during the Mesozoic. The story of Arizona's dinosaurs starts long before anything in the fossil record can be recognized as a dinosaur, or even remotely looking like a dinosaur. If this is to be the tale of living breathing creatures, than it must start with a peek into the dim, little known realm of ancestors and antecedents. Because Arizona is considered by many to have one of the most complete and best preserved geological records of life on Earth, many of the stories in the evolutionary story are found right here
Fossils found in Arizona document life's presence in this region for at least 600 million years. For about one-half of that time plants and animals were confined to shallow Paleozoic seas. The masses of blue-green algae, plankton, and arthropods eventually witnessed the rise of the vertebrates, but for much of that great span of time, in most of the limestones and shales of Arizona, there is not even the hint of a dinosaur, not even a biological clue that any of these life forms would produce descendants that would eventually rule the land.
Early dinosaurs, perhaps some of the earliest, did live in Arizona, but these primitive forms may have been only part of an expanding worldwide population. If the first dinosaurs began their evolutionary journey here, it was naturally only a matter of time before descendants spread across the earth's single continent to populate most other parts of their world. South America, or at least the part of Pangaea that became Argentina, appears to also be one of the places in which early dinosaurs arose from earlier creatures. Dispersal of early species would have been relatively easy. All, or at least most, land at the beginning of the Mesozoic was connected into one massive supercontinent that eventually broke apart by the slow continental rafting process of plate tectonics. No great post-Paleozoic oceans blocked migration routes, and shallow inland seas came and went and may have been obstacles for only a small bit of geological time. In fact, there is much speculation about the existence of periodic late Mesozoic land bridges that may have connected one spreading continent to another, and may have become virtual highways over which dinosaur populations came and went as did mammals between North America and Asia during the late Pleistocene Ice Age.
Over time different dinosaurs evolved differently and adapted to survive in particular habitats. Obviously not every place on earth today would be suitable for elephants or lowland gorillas, as there are ecological barriers which prevent these forms from expanding their populations from one habitat to the next. But again one of the fallacies of dinosaur mythology is that even though some were meat eaters and some ate plants, all their brain functions and their plumbing were pretty much the same, being reptiles, Clearly, now that a wealth of new evidence is in, the dinosaurs may have been just as competent in their adaptive diversity as are mammals today and that geology, topography and environment posed few restrictions to the particular niches dinosaurs could fill. The argument would be strengthened if we were eventually convinced that dinosaurs were warm-blooded or that some, in a peculiar line of evolution, had scales fluffed up with barbs and barbules and, if there were glaciers during the Mesozoic, could slide down an ice flow as well as the best of today's ice-loving Arctic beastry. The earliest of dinosaurs, perhaps being much closer biologically to their reptilian ancestors that later, more advanced species, may have for a time required special conditions in which to build on their ranks. Seas, ice packs and deserts might not have been preferred habitats, and such places may have existed in a patchwork quilt of habitats on Pangaea. But if such exotic habitats to the Mesozoic existed, so too did deltas, estuaries, lowland swamps and rain forests. Vast oasis complexes and lakes amid the dunes of the deserts would have been alive, as would a temperate or subtropical periphery of very tall, glaciated volcanic peaks. Vast stretches of highland forests or verdant plains would be nourished by rainwater or even the discharge from distant melting ice. Habitats worldwide were indeed diverse, and a diversity of habitats allowed a remarkable variety of dinosaurs to evolve. Today, we have found only a relative hand full of dinosaur species that ever existed and it is within the blank pages in this history that makes the science of paleontology so exciting.
The Mesozoic Era consists of the Triassic, Jurassic and Cretaceous Period, spanning 180 million years of earth's history. Each of these time periods is defined by its distinctive wild life and by the large extinctions that both preceded and followed them. In Arizona, all three periods are represented by massive sedimentary rock exposures; All three periods in Arizona have dinosaurs. First, lets come to an agreement on exactly what is a dinosaur...and what isn't.
So, What Exactly is a Dinosaur?
Most of us think of a dinosaur as nothing more than a big lizard, sort of like an overgrown Gila monster or Iguana. But did you know that many paleontologists, the scientists who study dinosaurs, are starting to think that animals like Tyrannosaurs rex or Brachiosaurus weren't even reptiles at all? Here's why our view of the dinosaurs has changed in America since about 140 years after the first dinosaur bones were discovered.
The vertebrate part of the animal kingdom is made up
of fish, amphibians, reptiles, birds and mammals. These classifications of living things are based on observations made centuries ago. Now, with some new thinking, much of this old classification way of thinking doesn't fit what we know about evolution, making parts this classic categorical system maybe
not wrong but a bit obsolete.
An early attempt at visualizing what exactly a dinosaur was. Sort of a cross between a lizard and a kangaroo.
They eventually figured it all out.
Evolution is a complicated process. Basically the changes we see taking place in dinosaurs' bodies over millions of years is a slow, not always steady, process. The descendants of a lanky but toothsome, ostrich-size meat eating predator of the Triassic Period 225 million years ago becomes a 12-ton tyrannosaur-like beast 100 million years later is a difficult process to observe because there are so few fossils. It's sort of like watching a football game at in a stadium with no lights during a thunderstorm. All we see of the action is when brief flashes of lighting illuminate the field. At the end of the game, we know the final score, but we only know some of the plays that brought that result. So it is with dinosaur evolution, and why we have come to know much more of the dinosaurs progress with the discovery of each new species
Not long ago, researchers began looking closely at the history of the bird in order to better understand dinosaurs. What we discovered was more than just an odd coincidental similarity between the two classes, birds and the dinosauria. In every measurable way birds began to look like certain small carnivorous dinosaurs.
Struthiomimus couldn't be much closer to a modern ratite such as an ostrich if it wanted to be. Still, it was a dinosaur in every respect.
Even the very bird-like bits such as feathers, being warm-blooded, having wings instead of arms, could easily be attributed to dinosaur parts that changed to accommodate their more active or lofty life-style. Maybe, as some think, the slow development of a complex inner ear may have improved the dinosaur's internal balance-sensing mechanism that eventually reducing the need for a long dino tail, really big down-sizing of the body, and other evolutionary change that may have opened the door to allow a few dinosaur species to fly...that is, to become the birds as we know today.
It's more than a coincidence that todays ostrich, a bird, looks like old Struthiomimus. Evolution is complex, but a few modifications ...well, a lot of them, over time, and this is what you can get.
It's not all just about a few body parts changing but every piece of bird anatomy now that we look closely at them, seen to come from a skeletal part preserved in these dinosaur's fossil record. Even Tyrannosaurus rex, one of the largest of the so far discovered meat-eaters, and seemingly as far removed from a bird as can possibly be, new fossils of T Rex show many bird-like characteristics, even its metabolism as seen in newly discovered, particularly well preserved fossils.
Tyrannosaurs as I remember him
Size and life-style are not important in any definition of a dinosaur; they could be tiny or monstrous, flesh or plant eater; and, in fact occupied nearly every available niche on earth as mammals do in their dominant role today among land animals. Dinosaurs are presently categorized into two distinct orders within the Class Reptilia: Saurischia (sor-is-key-ah), with more reptile-like pelvic structures, and the Ornithischia (or-ni-this-key-ah), the bird-hipped forms. Both Orders evolved from a common ancestor that arose from true reptiles, during the Middle Triassic Period. Unlike lizards, which have sprawling limbs extending outward away from their bodies, the first dinosaurs stood with their hind legs extending vertically down from deep socketed hips. The dinosaurs' upright posture, a body plan needed to become really big, heavy animals, was first achieved by the earliest dinosaur ancestors but was greatly improved upon. These and other changes in skeletal structures and presumably in soft tissue and metabolism set dinosaurs aside from any reptile that exists then or even today. So now we can put together a picture of what dinosaurs are, and what there aren't; Despite their great variety, all the dinosaurs - if they are to be regarded as a group - have to share at least a few common characteristics by which that group can be identified. It is now accepted that to be classified as a dinosaur, an animal must have:
1. Lived during the Mesozoic era (except for birds).

2. Hind limbs that reflect a major evolutionary change through the Triassic, when the archosaurs evolved from a sprawling posture (the primitive condition), through a semi-erect posture to the fully erect stance seen in all dinosaurs: an erect (upright) posture, primitively bipedal (standing up on their hind legs), with a ball-and-socket hip joint, a straight hinge-like knee and ankle, roller-like main ankle bones (astragalus and calcaneum) that were closely fixed to the bottom of the main shin bone (the tibia).

3.most dinosaurs had more than the basic two sacral (hip) vertebrae seen on other reptiles - sometimes three or four, or even as many as six or seven.

4. Extra openings in the skull.

5. Lived and moved on land or in the case of birds, also able to fly.

6. Likely warm-blooded, or marginally homeothermic.

Because animals such as the flying pterosaurs, the swimming ichthyosaurs and the sprawling crocodiles may share some of these characteristics, but not all of them, they cannot be considered dinosaurs.
Pterodactyls? No, not even close.
Mosasaurs? Just big wet lizards. Not dinosaurs.
As much as you want them to be dinosaurs, Crocs just aren't. But they are cousins.
Here he is. Today's Noble Dinosaur. Believe it or not.
Whatever plan nature provided these creatures must have been a good one because they succeeded for 130 million years, or more if we include the birds as descendants of dinosaurs, or as actual feathered dinosaurs. To be a dinosaur, and what separates these animals from all of the other reptiles, is probably not what you think.
At the end of the Mesozoic Era, at the close of the Cretaceous Period about 65 million years ago, it was thought that all of the dinosaurs suddenly became extinct, that the world changed and made room the furry little placental, fur-bearing mammals of a more modern age. At the end, we'll look a huge environmental catastrophe that might have ended very existence of the dinosaurs, but really didn't.
Big dinosaurs, like Allosaurus shown here, may have had enough bulk not to need self-regulating body temperatures, and maybe were only marginally warm-blooded (homeotherimc). I think this very old depiction is showing one severely constipated creature. Of course we know carnosaurs looked nothing like Godzilla; they were incredibly graceful and agile predators.
So, What are dinosaurs? This is just what I believe. Mostly I believe that some young kid out there is eventually going to prove me, or any other paleontologist, wrong...or at least partly wrong. It's the way of science.
From so many new discoveries, we now know that some dinosaurs came complete with feathers and all kind of bird parts underneath. Some dinosaurs even hand find down, as shown in this early depiction.