Climates And Habitats
The Middle and Late Jurassic Epochs were evenly warm and temperate across much of the globe. This is not to say that the world had only one uniform climate during the Jurassic. Just like today, there were Jurassic deserts, Jurassic mountains, Jurassic islands, and other regions, each of them with their own unique climatic regimes. Although the poles were warmer than they are at present, they were still cooler than equatorial regions. The submergence of large portions of continental landmasses...
Theropod Giants and Feathered Dinosaurs
The story of predatory dinosaurs began during the early stages of dinosaur evolution with the appearance of the first theropods in the Late Triassic Epoch. By the Middle and Late Jurassic Epochs, the evolutionary lineages of meat-eating dinosaurs had diversified dramatically, leading in one direction to such large carnivores as Allosaurus Late Jurassic, western North America and in another direction to such small, chicken-sized insectivores as Compsogna-thus Late Jurassic, Germany . The Late...
Horned and BoneHeaded Dinosaurs
One of the most familiar images in the folklore of dinosaurs is a battle to the death between Tyrannosaurus and the horned dinosaur Triceratops Late Cretaceous, western North America . Triceratops was a large horned dinosaur, one of the last of its kind, and probably would have made a formidable foe for T. rex had the theropod been careless enough to engage it in a tussle. Weighing as much as 6 tons 5.4 tonnes , a defensive-minded Triceratops had many advantages to draw upon in battle. Its...
Sexual Dimorphism
Sexual dimorphism occurs when male and female individuals of a single species exhibit different anatomical traits. Such traits can be determined reliably in dinosaurs only when an abundance of specimens from the same species can be compared. Such traits helped dinosaurs distinguish male individuals of their species from females, and may have also been related to particular behaviors. For example, male African elephants have tusks, while females do not. These tusks are used during combat or...
Cretaceous Sauropods
The sauropod group Neosauropoda is subdivided into two major clades the Diplodocoidea comprising the Rebbachisauridae, Di-craeosauridae, and Diplodocidae and the Macronaria composed mainly of the Camarasauridae, Brachiosauridae, and Titanosauria . Of these, only the Macronaria had taxa that survived into the Early and Late Cretaceous Epochs as members of the brachiosaurs and titanosaurs. The Macronaria were distinguished from other sauro-pods by skull features that included a nasal opening that...
Hesperornithes
The Hesperornithes were a highly specialized subgroup of aquatic ornithuromorphs. Also loonlike but probably all flightless, these large birds measured up to 3.3 feet 1 m long and were divers. There are about nine valid taxa of Hesperornithes and they are definitely known only from fossil localities in the Northern Hemisphere. The best-known hesperornithean is Hesperornis Late Cretaceous, western North America , for which several skulls and partial skeletons have been found. When it was first...
The Early and Late Cretaceous Epochs
The Cretaceous Period, which spanned 80 million years, was the last great time span of the Mesozoic Era. Coming to a crashing climax 65.5 million years ago, it marked the last reign of the dinosaurs and their reptilian cousins in the oceans and in the air. The name Cretaceous is Latin for chalk and refers to the abundant layers of chalk deposits that are found in sedimentary rocks of Europe that date from this period. The Cretaceous Period is further subdivided into two epochs the Early...
Carnosauria
The Carnosauria is a group of mostly large theropods measuring 16 feet 5 m long or more and characterized by massive heads burly, powerful necks relatively short arms with three fingers per hand powerful hind limbs and long, deep tails. Except for the spinosaurs and tyrannosaurs, the largest theropods come from the ranks of the carnosaurs. Carnosauria includes three subgroups the Sinraptori-dae, the Allosauridae, and the Carcharodontosauridae. The Sinraptoridae were large predators that...
Basal Titanosaurs
The last surviving group of sauropods were titanosaurs, and their distribution was nearly worldwide. Titanosaurs had roots in the Late Jurassic of Tanzania, Thailand, and western North America. Although specimens have been found all over the world, most titanosaur remains are fragmentary and lack skull elements. The most complete specimens have been found in Argentina and Madagascar, where the recent discoveries of two exquisite skulls have enabled paleontologists to better understand the...
Spinosauroidea
The Spinosauroidea were a group of related theropods considered to be basal within the Tetanurae. The group is further broken down into two smaller groups. The Megalosauridae were medium- to large-sized theropods that mostly lived during the Middle and Late Jurassic Epochs. The Spinosauridae included several large-bodied forms that reigned as the largest carnivores in their ecosystems up until the early part of the Late Cretaceous, at which time they were replaced by more derived tetanurans....
The Form and Function of Hadrosaur Crests
The crested lambeosaurine hadrosaurs displayed an enormous variety of helmets, hatchets, and hood ornaments on their skulls. As a functional piece of anatomy, the crest was part of the nose. Fossil hadrosaurs, for which a cross-section of the skull can be observed, show that the nostrils were connected to the throat by a hollow set of cavities and tubes through which the dinosaur breathed. Most other kinds of dinosaurs did not have such crests, however, so we may assume that hollow crests had a...
The Braincase
The braincase of a pterosaur skull holds clues to the many connections between the brain and other parts of the body. Evidence of these nerve connections can be seen in the form of holes in the braincase through which nerves were once threaded to attach the brain to other organs. One of the first scientists to study the structure of brains in extinct creatures was Tilly Edinger. In 1927, she published an important study of the brains of pterosaurs based on casts of their brain cavities. She...
Extinct Marine Crocodiles
Today's crocodiles are what remain of a long line of reptiles that first appeared during the Middle Triassic Epoch. Only a few kinds survive today, including crocodiles, alligators, and gavials. Forms of crocodiles that lived in the ocean were highly successful during the Jurassic and Cretaceous Periods. They returned to the sea, as did other forms of reptiles, to take advantage of abundant food supplies in the form of fishes, cephalopods, and other marine reptiles. Nearly all marine crocodiles...
Chapter The Sauropods Diversify
Bakker, Robert T. The Dinosaur Heresies. New York William Morrow, 1986. -. Ecology of the Brontosaurs. Nature 229 January 15, 1971 Benton, Michael J. Vertebrate Paleontology, 3rd ed. Oxford Blackwell Publishing, 2005. Bonnan, Matthew F. The Evolution of Manus Shape in Sauropod Dinosaurs Implications for Functional Morphology, Forelimb Orientation, and Phylogeny. Journal of Vertebrate Paleontology 23, no. 3 September 2003 595-613. -. Morphometric Analysis of Humerus and Femur Shape in Morrison...
Eggs Nests and Parental Care in Ornithopods
Dinosaurs hatched from eggs, like their bird descendants and most living reptiles. Hundreds of dinosaur egg sites have been discovered three-quarters of these are in North America and Asia. Most of the sites that have been found date from the Late Cretaceous Epoch, and many are associated with hadrosaurs. Knowledge of the lifestyle and behavior of ornithopod dinosaurs has been greatly enriched by the discovery of their fossilized eggs, nests, and young. This is largely due to the pioneering...
Basal Ceratopsians
The most primitive members of the Ceratopsia are represented by Yinlong, a group called the Chaoyangsauridae, the Psittacosauridae, and a number of basal members of the Neoceratopsia, most notably the protoceratopsids. Most basal Ceratopsia have been found in Asia, whereas the larger, more derived horned dinosaurs all hail from western North America. Yinlong hidden dragon is a basal ceratopsian from the Late Jurassic Epoch of China. It was small and primarily bipedal, measuring only 4 feet 1.2...
Chapter The Early and Late Cretaceous Epochs
Berner, Robert A. Atmospheric Oxygen Over Phanerozoic Time. Proceedings of the National Academy of Sciences of the United States of America 96, no. 20 September 28, 1999 10955-10957. Chumakov, N.M. Trends in Global Climate Changes Inferred from Geological Data. Stratigraphy and Geological Correlation 12, no. 2 2004 7-32. Clemens, W.A., and L.G. Nelms. Paleoecological Implications of Alaskan Terrestrial Vertebrate Fauna in Latest Cretaceous Time at High Paleolatitudes. Geology 21 1993 503-506....
Marine Turtle Anatomy
Marine turtles evolved several features to improve their ability to live in the ocean. The most obvious changes were to develop a more lightweight, streamlined body that could propel itself in the water. The shell of a turtle has two parts. The top part, protecting its back, is called the carapace. The bottom part, protecting its belly, is the plastron. The shells of land-dwelling turtles are designed to enclose the body in a tightly knit mosaic of bony plates. This was an effective form of...
Internet Sites
American Museum of Natural History. Vertebrate Evolution An interactive diagram of vertebrate evolution with links to example fossil specimens in the world-famous collection of this museum. vertebrate An extensive visual guide to Australian fossils. Bernard Price Institute For Palaeontological Research, University of the Witwatersrand, Johannesburg. Fossil Picture Gallery Information for a wide variety of South African vertebrate fossils. Carnegie Museum of Natural History. Dinosaurs in Their...
Fossil Skin Impressions
An abundance of fossilized skin impressions have been associated with specimens of hadrosaurs. These trace fossils left the pattern of the animal's skin in the mud where a given dinosaur died. All of the evidence uncovered so far regarding the skin of unfeathered dinosaurs shows that they had nonoverlapping scales similar to those of the modern monitor lizard. These scales varied in size across different parts of the body. The scales were generally smaller, for flexibility, around the head and...
Marine Crocodile Anatomy
Although the head was generally more lightly built with a long, narrow snout, extinct marine crocodiles resembled today's crocodiles in many ways. Here are some of the anatomical features that marine crocodiles share Long, narrow skull. The skulls of marine crocodiles were lightweight and had a long, narrow snout. When viewed from above, they had an extremely elongated triangular shape. Eyes on the sides. The eyes of marine crocodiles were on the sides of the skull rather than the top as in...
Evolution and Geography The Geographic Distribution of the Sauropods
The discovery of fossils gives us the only hard facts about the distribution of dinosaurs across the Mesozoic Earth. As such, an understanding of dinosaur distribution is strongly dependent on the availability of fossils, which is subject, in turn, to the availability of fossil deposits of Mesozoic age. The time of the dinosaurs spanned an enormous gulf in time 164 million years composing the better part of three long geologic periods the Triassic, the Jurassic, and the Cretaceous. There is a...
Pterosaurs Flying Reptiles of the Mesozoic Era
The first vertebrates to achieve powered flight were the Pterosauria, the winged lizards. Their rise and success paralleled that of the dinosaurs and lasted as long. Pterosaurs mastered the air in many forms and ranged in size from that of a small bird to the largest vertebrate ever to soar through the skies, Quetzalcoatlus Late Cretaceous, Texas , a creature with a wingspan of 40 feet 12 m . Pterosauria, the flying reptiles, were not dinosaurs. They were also not related to birds. All...
Ceratopsian Horns and Frills
The evolution of highly specialized, increasingly robust and varied horns and frills in ceratopsians begs the question of their utility and function. No one doubts that horns and frills were used for protection. The ceratopsian frill provided protection for the neck, normally one of the most vulnerable parts of the body to be targeted by predators. Horns on the nose and brow were undoubtedly dangerous weapons when thrust into action by an angry ceratopsian. Why, however, was there such a great...
The Iguanodontia
The significance of the iguanodonts to the history of dinosaur science is a matter of record. In the year 1822 19 years before the term dinosaur became a part of scientific literature a physician and amateur geologist named Gideon Mantell 1790-1852 was visiting a patient near Lewes, in the English countryside. Accompanying him was his wife, Mary Ann. As the story goes, while the doctor tended to his patient, Mary Ann took a stroll along a country road, where she noticed a jumbled pile of...
Mosasaur Anatomy
The sharp, conical teeth of mosasaurs were able to cut through or crush most any kind of fleshy or bony creature they could fit inside their mouth. Mosasaurs probably hunted by lying in wait and ambushing their prey. Some mosasaurs had a bony rod at the end of the snout, and it has been suggested that they used it to ram their prey, stunning them. All mosasaurs shared the following anatomical traits Many sizes. The largest mosasaurs, including Mosasaurus and Tylosaurus knob snout lizard , could...
Sauropods Of The Cretaceous Period
All sauropods had a generally similar body plan featuring a small head, a long neck, a huge body, quadrupedal posture, and a long tail. The presence of pneumatic concavities in the spinal bones of sauropods provided lightness without sacrificing strength. The presence of pneumatic concavities in the spinal bones of sauropods provided lightness without sacrificing strength. Traits that united the sauropods included sturdy, upright limbs to support their massive weight four or more fused or...
The Hadrosauridae
The advanced iguanodontian ornithopods known as the Hadrosau-ridae bulky lizards include some of the best-understood dinosaur taxa because of the abundance of their specimens and often because of excellent preservation. Hadrosaurs evolved some of the most effective methods for eating plants ever seen. These dinosaurs had more teeth than any other known land animals. There are more than 35 scientifically accepted taxa of hadrosaurs. Hadrosaurs have also played an important role in the...
SUMMARY Gdi
This chapter explored the evolution and lifestyles of the Margino-cephalia. 1. The Marginocephalia were ornithischian dinosaurs that included the Ceratopsia horned faces and Pachycephalosauria thick-headed lizards' . They were a subgroup of the Cerapoda, the same group that included the ornithopods. 2. The name Marginocephalia refers to a bony shelf at the back of the skull that is characteristic of all members of the clade. 3. Marginocephalia are found only in the Northern Hemisphere and...
Confuciusornithidae
The Confuciusornithidae is another small clade of primitive birds, but it is represented by hundreds of complete specimens of its best-known taxon, Confuciusornis Early Cretaceous, China . All three known taxa of confuciusornithids were discovered in the exquisite fossil deposits of Liaoning and neighboring provinces in northeastern China. These basal birds were closer to modern birds than was Archaeopteryx and had already shed most of the traits of non-avian dinosaurs teeth and a long tail...
Pliosaur Anatomy
With their large heads and streamlined bodies, pliosaurs were probably capable of quick movement and sustained chases at high speed. They were pursuit predators, but not as fast as ichthyosaurs. They would chase large prey until they could grab them in their powerful jaws. Pliosaur teeth were sturdy, cone-shaped, and sharp, capable of cutting through thick flesh and even bones. Their mouths were huge, making any sea creature of the time a possible meal, including the long-necked plesiosaurs,...
The Mosasaurs
Mosasaurs retain many of the attributes of their terrestrial ancestors. Unlike ichthyosaurs and plesiosaurs, which are presumed to have had smooth skin, mosasaurs still had reptilian scales. Their ancestry can be traced to ancient snakes, although for many years some paleontologists have thought that mosasaurs were more closely related to extinct monitor lizards. Mosasaur species ranged in size from the length of a minibus to that of the longest tractor-trailer, from about 10 to 57 feet 3 to...
Plesiosaur Anatomy
The Plesiosauria were more fully adapted to the ocean than the Nothosauria. It is difficult to imagine that they willfully crawled out of the water except when they were still young and small. Imagine how clumsy they would have been on land, dragging themselves along on their paddles. It would have made them extremely vulner--able to dinosaurs and other terrestrial predators. Even the sturdy belly ribs of a 30- to 50-foot 9 to 15 m plesiosaur or pliosaur might not have been strong enough to...
Marine Reptile Evolution
Reptiles had already found success on land when some taxa began to explore the oceans again. Life in the ocean required good swimming skills so that marine reptiles could catch prey and escape predators. Marine reptiles adapted to ocean life by optimizing anatomical traits that reduced drag and provided them with speed and maneuverability in the water. Features such as webbed or flipperlike limbs and a vertical flattening of the tail aided in locomotion and could have also helped them to dive...
Nothosaurs Plesiosaurs And Pliosaurs
The group of marine reptiles known as the Plesiosauria dominated the oceans of the Mesozoic for about 140 million years, up until the last days of the dinosaurs. Nested within the Plesiosauria were the subgroups Plesiosauroidea, the long-necked plesiosaurs, and the Pliosauroidea, the short-necked plesiosaurs. The Nothosauria, also discussed here, were a sister group of long-necked marine reptiles that evolved before the plesiosaurs. It is interesting to note, however, that at just about the...
Placodont Anatomy
Because placodonts were adapted for living in shallow near-shore ocean environments, their anatomy was optimized to help them plod along the seafloor looking for stationary prey such as hard-shelled mollusks and crustaceans. Placodonts fall into two body types the unarmored placodonts, informally known as the Placodontoidea, and the armored placodonts, known as the Cyamodontoidea. Body characteristics of the placodonts included Skull. The placodont skull was strong and heavily built. It was...
Ichthyosaur Anatomy
Ichthyosaurs were the most fishlike in appearance of all marine reptiles, but this resemblance is superficial because the two kinds of animals are not related. The flippers of ichthyosaurs and other marine reptiles are a highly modified form of foot once used to walk on land. The bones are thick and still show the evidence of having once consisted of a wrist or ankle and fingers or toes. Anatomical traits of ichthyosaurs included Streamlined body. Except for the earliest forms, ichthyosaurs had...
Overview Of Last Of The Dinosaurs
Last of the Dinosaurs begins by looking at the geological and ecological conditions that created opportunities for the expansion of dinosaurs of the Early and Late Cretaceous Epochs. Section One encompasses worldwide geologic and climatic changes of the Cretaceous Period. Chapter 1 describes widespread changes to ocean and land environments, including changes to climates worldwide, that served as catalysts for the radiation of dinosaurs and other vertebrates. Temperate global climates allowed...
Marine Reptiles of the Mesozoic Era
Marine reptiles were air-breathing creatures that lived in the water. Their ancestors were land-dwelling reptiles from the Permian and Triassic Periods. Except for the marine crocodiles, they were not closely related to dinosaurs. Some marine reptiles trace their ancestry to the roots of the reptilian evolutionary tree, while others were close relatives of lizards and snakes. Like today's turtles and crocodiles, they would hold their breath while under water. Reptiles first dominated life on...
Nothosaur Anatomy
Nothosaurs represent an early attempt of land-dwelling reptiles to find a home in the sea. Except for their webbed feet and long, streamlined necks, the earliest nothosaurs resemble lizards that simply took to the water to find food. Although the last of the nothosaurs had evolved paddles that made them better swimmers, they still moved about in the water by undulating their bodies from side to side. Their tail was the main source of their propulsion. Their shoulder and hip bones never changed...
Pterosaur Anatomy And Adaptations
Pterosaurs ranged in size from small, crow-sized creatures with a wingspan of 1 foot 0.3 m to giants of the sky with wingspans up to 40 feet 12 m the size of a small airplane. During their time, pterosaurs were the dominant flying inhabitants of the coastal areas of the world, skimming the oceans for a bounty of fish and invertebrates. They may have lived in great nesting colonies, forming a unique place for themselves in a world otherwise ruled by dinosaurs. Anatomical features that were...
Pterosaur Thermoregulation
The question of thermoregulation in dinosaurs has been the source of lively debate, but there is more agreement among paleontologists when it comes to the flying reptiles. From the earliest days of pterosaur study, scientists have concluded that these creatures were endothermic warm-blooded , not ectothermic cold-blooded . Warm-blooded creatures have an internal source of body heat regulated by their heart and circulatory systems. They are not dependent on the environment as their source of...
Shaping The World Of The Dinosaurs
Whereas the Jurassic Period was relatively quiet geologically, the geography of the Cretaceous Period witnessed a dramatic resurgence of tectonic plate movements. Continental drift during the Cretaceous Period caused the continued breakup of the northern and southern supercontinents of Laurasia and Gondwana, separating them into landmasses approximating their present-day configuration. The northern Laurasia included areas that became North America, Europe, and Asia. The southern landmass of...
The Pachycephalosauria Boneheaded Dinosaurs
The Pachycephalosauria thick-headed lizards consisted of small to medium-sized bipedal, ornithischian herbivores that measured in length up to about 15 feet 4.5 m . They are the only dinosaur group distinguished by a thick, bony skull cap. Of the 14-plus recognized genera of pachycephalosaurs, nine are known only from skulls and skull fragments. Only a single new taxon of pachycephalosaur has been named in the past 25 years Sphaerotholus, in 2002 , indicating the relative scarcity of this clade...