Twilight of the Mammoths: Ice Age Extinctions - Research Paper Example

Twilight of the Mammoths: Ice Age Extinctions The term mammoth refers to several extinct species belonging to the elephant family. Prominent features include high, domelike skull, small ears and woolly under fur. They have long, curved tasks which can grow up to 5 meters (10.5 ft) long and a defining hump on their back. The earliest remains of mammoths have been found in Africa lying in geological layers that dates back 5 million years ago during the Pliocene Epoch. From there, mammoths are believed to have travelled to Asia and into Alaska through the Bering Strait when sea levels were low about 2 million years ago. At the beginning of the Pleistocene Epoch, around 1.6 million years ago, mammoths can be found in every continent except for Australia and South America (Martin, 2005). There are currently four well documented mammoth species and they are presented in the following (Vartanyan, 2005): Mammuthus trogontheri – commonly known as the steppe mammoth. Discovered remains indicate that adults can grow up to 5 meters (about 16 ft) high and weigh about 18 metric tons. These mammoths roamed Eurasian wooded and meadowlike habitats Mammuthus primigenius – otherwise known as woolly mammoths because of their thick hairy coat that helped it to live in northern tundra regions. Adults can grow about 3 m (10ft) tall about the size of a modern Asian elephant. Mammuthus lamarmorae – the smallest of mammoths, this specie is less than 1.5 m (5 ft) tall. Remains were found in the Mediterranean Island of Sardinia. Mammuthus imperator – refers to the mammoths found in North America. The first complete specimen of a frozen mammoth was found in the Lena River of Siberia in 1806 by Russian botanist Mikhail Adams. Since then, frozen complete mammoth remains have been found in North America and Northern Europe. A study of their intestinal tracts indicated that the beast’s diet was plants and foliage (Vartanyan, 2005). Mammoths were believed to have died out during the Pleistocene Epoch around 11,000 years. However, dwarf mammoth remains were discovered in an island in the Arctic Ocean and dating techniques place their extinction around 3,700 years ago. The cause of extinction is still to be decided but there is considerable evidence that humans hunted them down in large numbers for food. Megatherium Megatherium is the name given to extinct massive ground sloths found in the woodlands and grasslands of Central and South America. They are believed to have walked the earth 5.3 million years ago during the Pliocene epoch. Adults can weigh as much as 5 metric tons and as large as an African bull elephant. When it stood in its two hind legs, adult megatheriums were 20 feet tall (Bargo, 1997) Unlike tree sloths, megatheriums travel the land. They were first believed to be quadripedal but footprints indicate that the mammal is capable of standing on its two feet even with its weight. This is largely possible due to a robust skeletal system and a broad muscular tail that forms a tripod along with its two hind legs. Megatheriums also have massive cursed claws which prevented its paws from being made flat to the ground. Hence, it walked on the sides of its feet much like the modern-day anteater (Fariña & Blanco, 1996). Figure 2 shows a megatherium with a person standing on the background providing a scale of how large the mammal was. Figure 2: Reconstructed skeletal remains of Megatherium (Encarta, 2006) Megatheriums are believed to have fed on trees and plants such as yuccas, agaves and grasses. Scientists also believe that aside from its claws which it uses to pull down branches, they also have long tongues used to pull leaves into its mouth like the modern-day tree sloths. However, there is some disagreement whether megatheriums only consumed leaves and hard, fibrous food. An analysis of its teeth indicated that they were more appropriate for cutting rather than grinding. The olecranon, a part of the elbow where the triceps were connected, was also very short making it possible for claws to act like daggers. Due to its weight, megatheriums were believed to be capable only of taking over the kill of carnivores like Smilodon. Glyptodons, another bulky animal living in the area, were also believed to have been killed by megatheriums because they are only animals in existence during that time capable of slaying and overturning glyptodons (Bargo, 1997). Megatherium populations is said to have flourished due to the absence of competitors and abundance of plant food. Specimens found in Chile and other parts of South America indicate that the specie were present until 10,000 years ago. As with mammoths, megatherium is believed to have been made extinct by wide-scale hunting activities of megatherium meat-eating humans. Sabre-Toothed Cat Sabre-toothed cats, also known as sabre-tooth tigers, are extinct cats with a powerful body structure the size of a lion. They are called as such because of their pronounced maxillary canines which resembled sabres or curved daggers. These canines can grow as much as 18 cm (7 in) long with the biggest on record being 28 cm (11 in) long. Fossils indicate that the felines can be found both in Eastern and Western hemispheres and that they started roaming the planet around 40 million years ago. Sabre-toothed cats are the most massive feline in record as they can weigh as much as 400 kg (Turner, 1997) Scientists have previously identified 3 kinds of sabre-toothed cat coexisting in North America: the Smilodon, Homotherium and Xenosmilus. Smilodons have long finely serrated canine teeth (about 18 cm) and legs built for power but not speed. A Smilodon is shown on Figure 3. This sabre-toothed cat is believed to primarily rely on ambushing and killing slow moving prey such as mastodons. Homotheriums have smaller canine teeths (about 10 cm) but had swift legs similar to that of the modern-day cheetah. They use these swift legs to chase down prey. Xenosmilus had the short canine teeth of the Hometherium but powerful legs of the Smilodon. All three used their canines to deliver a killing blow to their prey. In spite of the large canines, sabre-toothed cats are believed to have a biting strength a third of modern-day lions. This is due to the small zygomatic arches found in fossils which meant that the bite-strengthening temporalis muscles were smaller and less thick. Nonetheless, sabre-toothed cats were more efficient in dealing a killer blow as it can flex its jaws 120 degrees compared to 65 degrees for modern day lions (Christiansen, 2007) Figure 3: Reconstructed skeletal remains of Smilodon (Encarta, 2006) Diet for sabre-toothed cats is well documented especially with Smilodons whose bodies were partially preserved in tar pits particularly in California. Their prey consisted of bison, American camels, horses, deer, ground sloths and even small mastodons and mammoths. In fact, hundreds of Smilodons were believed to have been trapped in the La Brea tar pits because of trying to eat trapped mammoths. Like the mammoths and megatheriums, sabre-toothed cats became extinct around 11,000 years ago. Human hunting activities could have provided fierce competition for these cats but scientists believe it to be due to the mass wipe-out of megafauna that happened around 11,000 years ago. Triceratops Triceratops are four-legged, horned dinosaurs that began roaming the Earth around 67 million years ago during the Cretacious period. There were three horns on its skull, one horn above each eye and another on its nose. They are one of the biggest horned dinosaurs as they can grow 8 meters (26 ft) long and weigh as much as 12 metric tons. The horned skull was massive by itself as it was 2.5 meter (8 ft) long. Two other defining features are its birdlike beak and a neck shield or frill. An artist’s rendering of triceratops is shown in Figure 4. Figure 4: Triceratops (Encarta. 2006) Triceratops are herbivores as evidenced by its rows of large shearing teeth inside its birdlike beak. They feed by opening its jaws sideways and chop up the food with its teeth. This feeding process involve head and neck joint rotation. They are believed to have been particularly fond of cattails and palmettos as this is prominent in the surrounding area where the fossils were located. Through a study of its fossils, scientists were able to determine that the neck frill contained a network of blood vessels used to radiate heat much in the same way as elephants radiate heat from their ears. The first fossil evidence of triceratops was found in the sediments that floods deposited 65 million years ago in low-coastal plains near a seaway shared by the United States and Canada. Fossil remains have since been found in other parts of North America and Asia. Some scientists believe that triceratops could gallop like modern day rhinoceros but there is not much evidence on how this dinosaur could have managed to do so with its weight. What scientists were sure of was that the triceratops engaged in horn fights much in the same way as male deer fight with their antlers. The evidence for this was the partially healed puncture wounds in the skulls. Triceratops are believed to have died out along with most dinosaurs as a result of the global fallout when the earth was impacted by an asteroid impacting what is now known as the Yucatan peninsula and leaving a 200 km crater. While the impact must have caused fires and volcanic activity, dinosaurs were believed to have been killed by ejected dust and the ensuing acid rain. Timeline An Earth timeline is provided in Table 1 where the periods where the mammoth, megatherium, sabre-toothed cat and triceratops lived have been identified. Eon Era Period Epoch Beginning (yrs ago) Life forms originating Phanerozoic Cenozoic Neogene Holocene 11,500   Pleistocene 1.8 million Human Beings Paleogene Pliocene 5.3 million Mammoths and Megatheriums Milocene 23 million Grazing and Oligocene 34 million Sabre tooth Cat Eocene 56 million   Paleocene 65 million   Mesozoic Cretacious   145 million Triceratops, Primates, Flowering Plants Jurassic   200 million Birds Triassic   251 million Dinosaurs, Mammals Paleozoic Permian   299 million   Carboniferous Pennsylvanian 318 million Reptiles Mississipian 359 million Fern Forests Devonian   416 million Amphibians, Insects Silurian   444 million Vascular Land Plants Ordovician   488 million Fish, Chordates Cambrian   542 million Shelffish, Trilobites Proterozoic 2.5 billion Eukaryotic Cells Archean 3.8 billion Prokaryotic Cells Table 1: Earth Timeline (modified from Encarta 2006 - provided timeline) Reference: Bargo, M.S. 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Radiocarbon (Department of Geosciences, The University of Arizona) 37 (1): pp 1–6. Read More