Directions:
Read this whole page before starting.
Write an expository essay using the knowledge and ideas from writing class and the graphic organizer below.
Use the 3 attached readings as your resources.
Record the research notes on a handwritten document, in other words jotdown what you want to say during yourexpository essay. Get your ideas from the attached readings too.
–Hand written Doc must be turned in when you turn in the expository essay.
–Hand written document must have these parts
•Big events in Devonian Geologic Time to say during the essay
–3 Big events from DevonianPeriod minimum
•Evidence and facts supporting your big events in Devonian Period.
–3 Statements minimum
–Include these statements in the essay
Expository essay must address this issue:
Explain 3 big events that happened during the geologic time period called the “Devonian” time period.
Devonian Period: Climate, Animals & Plants
By Mary Bagley, Live Science Contributor | February 22, 2014 03:46am ET
The earliest known tetrapod was Tiktaalikrosae. It is considered to be the link between the lobe-finned fishes and early amphibians. Tiktaalik was probably mostly aquatic, “walking” on the bottom of shallow water estuaries.
Credit: ZinaDeretsky, National Science Foundation
The Devonian Period occurred from 416 million to 358 million years ago. It was the fourth period of the Paleozoic Era. It was preceded by the Silurian Period and followed by the Carboniferous Period. It is often known as the “Age of Fishes,” although significant events also happened in the evolution of plants, the first insects and other animals.
Climate and geography
The supercontinent Gondwana occupied most of the Southern Hemisphere, although it began significant northerly drift during the Devonian Period. Eventually, by the later Permian Period, this drift would lead to collision with the equatorial continent known as Euramerica, forming Pangaea.
The mountain building of the Caledonian Orogeny, a collision between Euramerica and the smaller northern continent of Siberia, continued in what would later be Great Britain, the northern Appalachians and the Nordic mountains. Rapid erosion of these mountains contributed large amounts of sediment to lowlands and shallow ocean basins. Sea levels were high with much of western North America under water. Climate of the continental interior regions was very warm during the Devonian Period and generally quite dry.
Marine life
The Devonian Period was a time of extensive reef building in the shallow water that surrounded each continent and separated Gondwana from Euramerica. Reef ecosystems contained numerous brachiopods, still numerous trilobites, tabulate and horn corals. Placoderms (the armored fishes) underwent wide diversification and became the dominant marine predators. Placoderms had simple jaws but not true teeth. Instead, their mouths contained bony structures used to crush or shear prey. Some Placoderms were up to 33 feet (10 meters) in length. Cartilaginous fish such as sharks and rays were common by the late Devonian. Devonian strata also contain the first fossil ammonites.
By the mid-Devonian, the fossil record shows evidence that there were two new groups of fish that had true bones, teeth, swim bladders and gills. The Ray-finned fish were the ancestors of most modern fish. Like modern fish, their paired pelvic and pectoral fins were supported by several long thin bones powered by muscles largely within the trunk. The Lobe-finned fish were more common during the Devonian than the Ray fins, but largely died out. (The coelacanth and a few species of lungfish are the only Lobe-finned fishes left today.) Lobe-finned fishes had fleshy pectoral and pelvic fins articulating to the shoulder or pelvis by a single bone (humerus or femur), which was powered by muscles within the fin itself. Some species were capable of breathing air through spiracles in the skull. Lobe-finned fishes are the accepted ancestors of all tetrapods.
Plants
Plants, which had begun colonizing the land during the Silurian Period, continued to make evolutionary progress during the Devonian. Lycophytes, horsetails and ferns grew to large sizes and formed Earth’s first forests. By the end of the Devonian, progymnosperms such as Archaeopteris were the first successful trees. Archaeopteris could grow up to 98 feet (30 meters) tall with a trunk diameter of more than 3 feet. It had a softwood trunk similar to modern conifers that grew in sequential rings. It did not have true leaves but fern-like structures connected directly to the branches (lacking the stems of true leaves). There is evidence that they were deciduous, as the most common fossils are shed branches. Reproduction was by male and female spores that are accepted as being the precursors to seed-bearing plants. By the end of the Devonian Period, the proliferation of plants increased the oxygen content of the atmosphere considerably, which was important for development of terrestrial animals. At the same time carbon dioxide (CO2), a greenhouse gas, was depleted from earlier levels. This may have contributed to the cooling climate and the extinction event at the end of the Devonian.
Animals
Arthropod fossils are concurrent with the earliest plant fossils of the Silurian. Millipedes, centipedes and arachnids continued to diversify during the Devonian Period. The earliest known insect, Rhyniellapraecusor, was a flightless hexapod with antennae and a segmented body. Fossil Rhyniella are between 412 million and 391 million years old.
Early tetrapods probably evolved from Lobe-finned fishes able to use their muscular fins to take advantage of the predator-free and food-rich environment of the new wetland ecosystems. The earliest known tetrapod is Tiktaalikrosae. Dated from the mid-Devonian, this fossil creature is considered to be the link between the lobe-finned fishes and early amphibians. Tiktaalik was probably mostly aquatic, “walking” on the bottom of shallow water estuaries. It had a fish-like pelvis, but its hind limbs were larger and stronger than those in front, suggesting it was able to propel itself outside of an aquatic environment. It had a crocodile-like head, a moveable neck, and nostrils for breathing air.
Mass extinction
The close of the Devonian Period is considered to be the second of the “big five” mass extinction events of Earth’s history. Rather than a single event, it is known to have had at least two prolonged episodes of species depletion and several shorter periods. The Kellwasser Event of the late middle Devonian was largely responsible for the demise of the great coral reefs, the jawless fishes and the trilobites. The Hangeberg Event at the Devonian/Carboniferous Boundary killed the Placoderms and most of the early ammonites. Causes of the extinction are debated but may be related to cooling climate from CO2 depletion caused by the first forests. Although up to 70 percent of invertebrate species died, terrestrial plants and animals were largely unaffected by these extinction events.
Meet Tiktaalikroseae: An Extraordinary Fossil Fish
Tiktaalikroseae is remarkably well preserved for a 375-million-year old fossil
Tiktaalikroseae, better known as the "fishapod," is a 375 million year old fossil fish which was discovered in the Canadian Arctic in 2004. Its discovery sheds light on a pivotal point in the history of life on Earth: when the very first fish ventured out onto land.
Tiktaalik has a mix of fish and amphibian traits
Tiktaalik looks like a cross between the primitive fish it lived amongst and the first four-legged animals (a group called "tetrapods" from tetra-, meaning four, and -pod, meaning foot. Actually, all animals that descended from these pioneer amphibians, including us, can be called tetrapods). Tiktaalik lived about 12 million years before the first tetrapods (which are approximately 363 million years old). So, the existence of tetrapod features in a fish like Tiktaalik is significant because it marks the earliest appearance of these novel features in the fossil record.
Why is Tiktaalik called the "fishapod"?
Tiktaalik shares anatomical features with both primitive fish and the first tetrapods. At first glance, it has features we readily associate with fish: fins, scales, and gills. But it also has a number of key features that differentiate it from its fishy contemporaries and make it very interesting to scientists.
Tiktaalik has a flat head and a neck like tetrapods but fins and scales like fish
Tiktaalik's head and body are flat with eyes on the top of its skull, more like a crocodile than most fish. Its shoulders are not connected to its skull, giving it a functional neck, a feature which fish lack. And it has ribs like some of the earliest tetrapods which were used to support the body and aid in living and breathing on land. These features in Tiktaalik show that many of the body features we associate with the earliest tetrapods actually evolved in fish first.
Could Tiktaalik walk or live on land?
It's very unlikely that Tiktaalik lived entirely on land. Based on the structure of its front fin and its shoulder, we know that it was capable of swimming and propping itself up in a push-up position. From this we can infer that Tiktaalik lived most of its life in the shallow water close to shore, using its strong front fins to push along the bottom and stabilize it in moving water. But the front fin's limited range of motion would have prevented Tiktaalik from swinging its fins forward to walk the way an amphibian does.
Tiktaalik most likely inhabited shallow streams, using its fins to push off the bottom
Living in the shallows would have been a good strategy for survival for several reasons. First, it was a convenient way to escape the huge carnivorous fish that lived in the deeper waters. It also probably helped Tiktaalik, who was a predator as well, pursue some of the smaller fish hiding in the shallows and the bug-like critters inhabiting the dense foliage banking the rivers and streams.
The Devonian perioddawned about 416 million years ago the planet was changing its appearance. The great supercontinent of Gondwana was headed steadily northward, away from the South Pole, and a second supercontinent began to form that straddled the Equator. Known as Euramerica, or Laurussia, it was created by the coming together of parts of North America, northern Europe, Russia, and Greenland.
Red-colored sediments, generated when North America collided with Europe, give the Devonian its name, as these distinguishing rocks were first studied in Devon, England.
The Devonian, part of the Paleozoic era, is otherwise known as the Age of Fishes, as it spawned a remarkable variety of fish. The most formidable of them were the armored placoderms, a group that first appeared during the Silurian with powerful jaws lined with bladelike plates that acted as teeth. Early placoderms fed on mollusks and other invertebrates, but later species developed into ferocious, fish-slicing monsters measuring up to 33 feet (10 meters) long. Other types of bone-plated fish that lacked jaws developed a range of bizarre forms. Fossil specimens include species with horseshoe-shaped heads and others that looked like rounded shields.
Shark Ancestors
Despite their heavy protection, these primitive fishes weren't built to last. The Devonian ancestors of fishes living today belonged to two main nonarmored groups. The cartilaginous fish, so-called because cartilage formed their skeletons, later gave rise to sharks and rays. They had small, rough scales, fixed fins, and sharp, replaceable teeth. The second group, the bony fish, were covered in scales and had maneuverable fins and gas-filled swim bladders for controlling their buoyancy. Most modern fishes are bony fish.
The bony fish included lobefins. Named after the thick, fleshy base to their fins, lobefins are credited with the giant evolutionary stride that led to the amphibians, making lobefins the ancestors of all four-limbed land vertebrates, including dinosaurs and mammals. The fossils of these remarkable animals come from the red rocks of Devon. Some lobefins are still around today, such as the famous "living fossil" fish, the coelacanth.
A recently discovered fossil creature from the Devonian has been hailed as a vital link between fish and the first vertebrates to walk on land. Found in the Canadian Arctic in 2004, Tiktaalik had a crocodile-like head and strong, bony fins that scientists think it used like legs to move in shallow waters or even on land. The fish showed other characteristics of terrestrial animals, including ribs, a neck, and nostrils on its snout for breathing air.
The first amphibians breathed through simple lungs and their skin. They may have spent most of their lives in the water, leaving it only to escape the attentions of predatory fish.
The first ammonoids also arose during the Devonian. Related to octopuses and squid, these marine animals survived until the end of the Cretaceous period, 65 million years ago.
Plant Proliferation
Plants began spreading beyond the wetlands during the Devonian, with new types developing that could survive on dry land. Toward the end of the Devonian the first forests arose as stemmed plants evolved strong, woody structures capable of supporting raised branches and leaves. Some Devonian trees are known to have grown 100 feet (30 meters) tall. By the end of the period the first ferns, horsetails, and seed plants had also appeared.
The new life burgeoning on land apparently escaped the worst effects of the mass extinction that ended the Devonian. The main victims were marine creatures, with up to 70 percent of species wiped out. Reef-building communities almost completely disappeared. Theories put forward to explain this extinction include global cooling due to the re-glaciation of Gondwana, or reduced atmospheric levels of the greenhouse gas carbon dioxide because of the foresting of the continents. A major asteroid impact has also been suggested.