Introduction
The history of life goes back over a billion years. There are many developments that have taken place. Let’s go back in time. We are going on a voyage to the Mesozoic Era. Before we depart, we must prepare ourselves for the trip. It is very important to understand that in this period or time, there are no contributions made by man. It is about 200 million years before man appeared on the scene. So we are only there to observe the period of which the dinosaurs ruled the earth. There is no way that we can alter prehistoric life. It is our objective to understand it and how we might benefit from learning about it. In this unit, the major concern will be on the form and function of the dinosaurs. The dinosaurs were the most successful group of land animals ever to inhabit this planet. For over 150 million years these creatures ruled the world and suddenly became extinct.
The content of this unit can be taught in the middle school, grades 5-8. The science, social studies, art and music teachers can use a team teaching approach. The suggested teaching time for this unit is two to three weeks. It will include a pre-post test, vocabulary, lesson plans, teacher and student reading lists, a list of field trips, speakers and a bibliography.
Teachers will be especially interested in teaching a unit on dinosaurs because they have always been fascinating prehistoric animals. Dinosaurs were the largest land vertebrates.
Some of the best of the dinosaurs from various quarries have been mounted at Peabody Museum at Yale University here in New Haven. At Peabody there are several mounted skeletons of different kinds of dinosaurs. There is a wall mural depicting the age of the dinosaurs by R. Zallinger, noted artist who graduated from the Yale School of Art. Students will be very impressed to see the display of dinosaurs at Peabody and will get the opportunity to study the form and function of the dinosaur. They will be able to compare the difference in the structure of several of the large dinosaurs such as Brachiosaurus, Trachodon, Tyrannosaurus Rex and Stegosaurus.
During the Upper Triassic of the Connecticut Valley, dinosaurs roamed our land in large numbers. The track of land between Hartford and Cromwell contains thousands of dinosaur footprints. Dinosaur Park in Rocky Hill, Connecticut has one of the world’s largest tracking systems. Students can do castings or dinosaur footprints.
In our study of the dinosaur, it is necessary to look at the era and period or which it existed. This will give us a better understanding of life in the days of the dinosaurs.
Well, sit back and listen carefully as we explore a part of geologic times. It is important to know that all the dinosaurs did not live at the same time. The dinosaurs reigned over this earth for some 150 million years during the
Mesozoic Era
, the Age of Reptiles. This era is subdivided into three periods. The
Triassic Period
(230 to 180 million years ago), the
Jurassic Period
(180 to 135 million years ago) and the
Cretaceous Period
(135 to 63 million years ago). Dinosaurs are first known from the middle Triassic Period, some forms attaining gigantic sizes. Following the conclusion of the Cretaceous Period, roughly 70 million years before present, dinosaurs became extinct. See figure accompanying lesson plan II.
As we explore the dinosaurs, a major concern is whether or not its body was equipped enough to deal with its environment. The unit will focus on the controversial issues of the dinosaurs as reptiles or warmblooded—such as mammals and why the dinosaurs became extinct.
It is hoped that this paper will be informative and enjoyable to teach. It is designed to help students better understand why it is important for us to have diversity among
species
and that we must co-exist in the world together as living
organisms.
Each must find its niche and adapt to the changing
ecosystem,
if it is to survive.
Background
The history of the dinosaurs has been reconstructed through the study of fossils. Fossils may be the remains, impressions, or molds of ancient plants and animals.
Fossils
have given a lot of information concerning past animal and plant life. The study of fossils is called
Paleontology,
which is the science of living things.
Bones
may be preserved with relatively little change except that the organic material that once filled cavities and microscopic spaces in the bone decays and disappears, leaving only the hard, mineral substance of the bone. Usually the empty spaces become filled with other mineral. Bone is a
hydroxyapatite.
Our knowledge of the dinosaurs is based on their bones. It is possible to tell their size, and to know something of their appearance and habits. The study of bones can show relationships of various kinds of dinosaurs. Fossils in older rocks help us to understand where dinosaurs come from, who their ancestors were and how different kinds developed.
Another type of fossils are footprints. Fossil footprints and trails are present in certain deposits. If an animal walked or crawled over soft mud or sand and this was covered over by another layer of
sediment
before the trail was wiped out, the track may still be preserved after the whole deposit has hardened into rock.
The skeleton of a dinosaur was built for strength and support. The skeleton will tell us all about this vertebrate. The proper support is critical in the structure of an organism. The backbone of the vertebrates is their main body support.
Some
dinosaurs
were reptiles, and all reptiles are
vertebrates
or backboned animals. Reptiles are cold-blooded animals. Reptiles developed skin with scales, plates, and later with bony armor. This helped protect them against sun, dryness, disease and enemies.
Traditionally, dinosaurs have been regarded as reptiles. Today,
Paleontologists
are re-evaluating the dinosaurs. There is considerable evidence that indicate that dinosaurs may have been endothermic creatures, with some physiological characteristics seen in birds and mammals, rather than the cold-blooded reptile. The outcome of the dinosaur as a cold-blooded reptile as opposed to a warm-blooded mammal will not be known for many years.
Today reptiles eggs have a hard or horny porous covering. Inside the egg is a yolk with a stored supply of food and a membrane to protect the young reptile and enable it to breath while still within the shell. These eggs can be laid on land, this allowed reptiles to wander far and wide. The food in a reptile egg enable the young to grow more before they hatch. Most young reptiles can take care of themselves right after they leave the egg.
The typical reptile today is cold-blooded such as, the alligators, crocodiles, and lizards and has a protective covering of scales or plates, five clawed toes on each foot, and lungs instead of gills. Most species are
carnivores
and most lay eggs. But no one trait separates the reptiles from all other animals, as feathers do for birds.
The
Cotylosaurs,
a primitive reptile, might be considered grandfathers of all the reptiles. The descendents, the Thecodonts that lived about 200 million years ago, were the dinosaurs’ direct ancestors.
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The crani show they had a more advanced kind of skull than Cotylosaurs. This allowed them to be more intelligent than their ancestors. Several of them were in effect bipedal. If you compare the picture of a hipbone of man with that of a four-legged animal, you can see that both have the same bones, but they are formed differently, see figure 1. The hipbones of reptiles are different from ours, but these bones show that some Thecodonts walked on their hind legs. The size or the front and hind leg bones will still show this. The front legs in two-legged animals are shorter than those of animals who walk on four legs.
By the time the Thecodonts had developed, other groups of dinosaurs had branched off, see figure. One of these groups have rise to the mammals. Another developed into present day turtles.
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The
Thecodonts
were also ancestors of the Crocodiles, birds, and Pterosaurs, the flying reptile. Through a long process of
evolution,
meaning that one group of animals moving to another over a long period of time, we finally reach the dinosaurs.
From the order Thecodontia evolved the two great orders of dinosaurs, Saurischia and Ornithischia.
Saurischia
is the order of lizard-hipped dinosaurs. In the Saurischia pelvis, the pubis extends down from the ilium behind the pubis, see figure 3.
Ornithischia
, the order of bird-hipped dinosaurs, is typified by a pelvis in which the ilium is considerably elongated while the pubis is usually parallel with the ilium, see figure 3.
The teeth in the Saurischia skull appear along the front and side margins of the jaw, or only in the front. Teeth are usually absent from the front of the Ornithischia mouth. Some genera of this order display premaxillary teeth. In many Ornithischian forms there is a horny, birdlike beak, and all have a predentary bone at the front of the lower jaw. The Saurischia skull is equipped with openings in front of the orbits. Usually such
fenestrae
are absent in the Ornithischian skull. Behind the orbits of the Saurischian skull are two large openings that provide attachment areas for the jaw muscles of the animal. In the Ornithischian’s large muscular skull, the teeth have usually been considerably reduced or eliminated. All the carnivorous forms are Saurischians, and virtually all the armored forms are Ornithischians.
We have landed in the Triassic Period, which is the lower part of the Mesozoic Era. The location is North America. The dominant form of life in the Mesozoic Era are vertebrates, animals with backbones. Let’s look at some of the dinosaurs of this era. The Brachiosaurus is the most massive, though not the longest, known terrestrial animal of all time.
Brachiosaurus
, largest specimen unearthed, weighed 66 metric tons, has skeleton 23.5 meters long with a height of 11.75 meters. Unlike most Sauropods, Brachiosaurus has front limbs longer than the hind limbs, so that the body slopes down to the back, terminating in a relatively short tail. The nostrils are located atop a raised mound above the eyes. Brachiosaurus, one of the largest dinosaurs, is known from North America, Europe and Africa.
As we continue on our voyage through the Mesozoic Era, let’s take a look at more of the various dinosaurs.
Stegosaurus
was discovered in Jefferson County, Colorado in 1877. Two series of alternating, erect, leaf-shaped bony plates surmount the neck, back and tail. Once thought to serve as armor, these plates are known to contain blood vessels and were probably used in heat regulation. The animal’s real protection came from the four spikes at the end of the tail. This dinosaur is best known for its supposed “three brains,” two of which were actual enlargements of the spinal cord in the shoulder and pelvic regions.
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These nerve centers much larger than the actual brain, controlled the movements of the head and tail. This arrangement was not uncommon among dinosaurs and is even found in mammals. Stegosaurus grew to a length of about 25 feet (7.4 meters) and weighed approximately four tons (3.5 metric tons). Some paleontologists have proposed that the animal might have been able to rear up on its hind legs or that the plates lay flat against the body. Stegosaurus is known from Wyoming, Oklahoma, Montana, Utah and Gloucestershire, England.
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Iguanodon
remains has been found in 1825 in Europe, Asia, Africa and North America. Iguanodon was originally named for some fossil teeth, roughly resembling those of the modern-day iguana lizard, found in Kent, England. Early restorations showed the dinosaur as a giant, horned and quadrupedal iguana somewhat resembling a rhinoceros.
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With the discovery of the complete skeletons, Iguanodon is now known to be a biped and the horn is identified as a spiked thumb. Iguanodon was strong, and bulky, probably weighing about 6.2 metric tons and reaching a length of about 8.9 meters and a height of 4.7 meters.
Tyrannosaurus Rex
is one of the most highly evolved of all known dinosaurs, This “tyrant lizard” was one of the most powerful
carnivores
ever to walk this planet.
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It was one of the largest Theropods, this dinosaur stands 5.3.meters tall and is approximately 11.75 meters long. The head is gigantic, with daggerlike teeth measuring 7.8 to 15.5 centimeters in length. The forelimbs are small, almost useless appendages, each equipped with two claws. These tiny forelimbs were utilized in helping the animal rise off the ground to stand up after its repose and that such animals walked with their bodies horizontal to the ground, their head and tail couterbalancing one another. Tyrannosaurus was discovered in the Hell Creek beds of Dawson County, Montana, and is also known from Wyoming, Texas, possibly North and South Dakota and Saskatchewan, Canada. It has been reported from poor indeterminate material, from Shandong, China.
Triceratops
is the largest of the Ceratopsians. The largest known individual may have measured 9 meters in length and weighed approximately 10.5 metric tons. The skull alone measures over 2 meters long, with a short, solid frill and three horns. One short horn surmounts the snout while two long horns appear above the orbits. The top of the frill was probably armed with a series of bony nodes. Triceratops is a fierce looking animal, well fortified in defending itself. Skulls often show puncture wounds. Triceratops was one of the last dinosaurs to become extinct. The dinosaur was discovered in Converse County, Wyoming. It is also known in the Dakotas, Montana, Saskatchewan and Alberta, Canada. This animal is one of the most commonly known of dinosaurs.
There are several speculations as to why the dinosaurs became extinct. Among the factors that contributed to their downfall may have been a drop in temperature at the end of the Cretaceous Period, and/or the appearance on the earth of egg-eating mammals.
Another reason for the disappearance of the dinosaurs may have been that they were so long and overdeveloped that it was hard for them to get enough food, because of specialized animal predators.
The May 6, 1985 issue of “Time Magazine” offered alternatives or is shedding more light on why the dinosaurs became extinct. This new theory is talking about mass extinction. This theory suggests that every 28 million years the shifting orbit of the earth intersects a disk of comets that lies in the outer reaches of the Solar System. As a Planet designated X passes through the disk, it dislodges comets, sending them toward Earth. Somehow this disrupts the Solar System. This dust or particles cause damage to various plant and animal life, sometimes causing mass extinction to several species of both plants and animals.
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As scientists continue to do research, the final results are not in, but through the information that has been found from using clues from bones, teeth, footprints and rocks they have somewhat untangled the dinosaurs’ history.
Perhaps understanding the evolution process of organisms such as the reptiles and mammals will help us to better understand the ecosystem in which we live. Also it will help us probe into the question to find answers to our own mere existence.
