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Environment Throught Time: The Extinction Files
Transcript of Environment Throught Time: The Extinction Files
Megafauna Why??? What species
extinct??? The Aftermath Why??? What species
extinct??? The Aftermath Why??? What species
extinct??? The Aftermath Why??? What species
extinct??? The Aftermath Why??? What species
extinct??? The Aftermath Why??? What species
extinct??? The Aftermath References The Cretaceous-Tertiary Boundary: +The Cretaceous-Tertiary boundary contains evidence for the cause of the mass extinction.
+The boundary is found in a layer of sediment that happened to be deposited concurrently with the event.
+The layer contains an unusually high concentration of Iridium, which is found in the Earth’s mantle, as well as meteors and comets. Some palaeontologists believe that this Iridium occurrence could have only been caused by a meteorite impact. +The abundance of small droplets of basalt, called spherules, in the boundary layer can be used as evidence.
+Basalt from the Earth's crust was melted and flung into the air upon impact. +The presence of shocked quartz found in the boundary layer also provides evidence for the theory that there was a meteorite impact.
+Recent research suggests that the Yucatan Peninsula of Mexico is a possible impact point. Theory #1! Theory #2! Theory #2! Some scientists believe that the Iridium layer may be the result of a massive volcanic eruption! +Evidence is provided with the Deccan Traps - extensive volcanic deposits laid down at the Cretaceous-Tertiary boundary - of India and Pakistan. +These lava flows were created when India moved over a "hot spot" in the Indian Ocean. This produced flows that exceeded one hundred thousand square kilometres in area and one hundred and fifty metres in thickness. +The flows that probably occurred would have produced enormous amounts of ash which would have altered global climatic conditions and changed the ocean’s chemistry. +The presence of spherules and shocked quartz worldwide in the boundary layer also provide evidence of such a volcanic explosion. Although both theories are probable, a meteorite impact is the more popular. For example:
The Pterosaurs At the end of the Cretaceous period many species became extinct. The most famous extinction, was that of the dinosaurs. Other species to become no more were the plesiosaurs, mosasaurs, ammonoids, belemnoids and rudists. Planktonic foraminiferids and plant species such as caytonaleans and bennettitaleans also became extinct. Belemnoids Ammonoids and Pelagic carbonate productivity was significantly reduced for several hundred thousand years. This resulted in the accumulation of carbon and alkalinity in the oceans. This led to the atmospheric partial pressure of CO2 to fall dramatically. This would have caused the deep ocean to become fully saturated with calcite. The effects of this mass extinction are present in today’s biogeography. There is evidence of a permanent increase in origination rates of living marine bivalves. A post-extinction recovery rate occurred. This left a permanent mark on the taxonomic and biogeographic structures of modern life forms. http://www.google.com.au/imgres?um=1&hl=en&safe=active&sa=N&biw=1280&bih=528&tbm=isch&tbnid=jDFNy_f-D544mM:&imgrefurl=http://blogs.sundaymercury.net/weirdscience/2010/11/pterosaurs-flew-like-paper-pla.html&docid=e1U_889pn4UVSM&imgurl=http://blogs.sundaymercury.net/weirdscience/pterosaurs1.jpg&w=600&h=440&ei=xcM_UeeAGYfQmAWUx4Ew&zoom=1&ved=1t:3588,r:7,s:0,i:100&iact=rc&dur=285&page=1&tbnh=174&tbnw=238&start=0&ndsp=10&tx=76&ty=96 http://www.google.com.au/imgres?um=1&hl=en&safe=active&sa=N&biw=1280&bih=528&tbm=isch&tbnid=nR9-NPt0h5aeyM:&imgrefurl=http://www.britannica.com/EBchecked/media/91400/Reconstruction-of-squidlike-belemnoid-cephalopods-from-the-Cretaceous-Period&docid=oqX0LYH9jH9aCM&imgurl=http://media-1.web.britannica.com/eb-media/11/28611-004-5C02CD2B.jpg&w=550&h=382&ei=vcM_UaedKI-KmQWKz4CgCQ&zoom=1&ved=1t:3588,r:6,s:0,i:97&iact=rc&dur=77&page=1&tbnh=150&tbnw=182&start=0&ndsp=11&tx=117&ty=39 http://www.google.com.au/imgres?um=1&hl=en&safe=active&sa=N&biw=1280&bih=528&tbm=isch&tbnid=6pUS93qH5Txm2M:&imgrefurl=http://www.kgs.ku.edu/Extension/fossils/ammonoid.html&docid=NCtOt1lqpzOFxM&imgurl=http://www.kgs.ku.edu/Extension/fossils/gifs/Ammonite.gif&w=252&h=166&ei=ucM_UfDAOsfLmgW5zYCIAw&zoom=1&ved=1t:3588,r:45,s:0,i:223&iact=rc&dur=288&page=3&tbnh=132&tbnw=201&start=29&ndsp=18&tx=83&ty=58 The Late Triassic Mass Extinction event occurred at the end of the Triassic Period [251 million to 199.6 million years ago]. The cause of the late Triassic Mass Extinction is an topic of heated debate. Many believe it was caused by climate change. Theory #1 The active volcanoes, caused from the rifting of the supercontinent Pangea released widespread carbon dioxide. Rising sea levels also occurred because of the sudden release of large amounts of carbon dioxide. This strengthened the global greenhouse effect, which then raised the average air temperature around the globe. Theory #2 This theory suggests that the minor heating caused by the rise in carbon dioxide in the atmosphere allowed the methane trapped in permafrost and undersea ice to escape. This is what then caused the Earth’s atmosphere to warm significantly. Theory #3 Others however, state that the mass extinction was caused by the impact of an asteroid or a comet. One other theory argues that the mass extinction was the product not of a single major event, but instead a “prolonged turnover of species across a considerable amount of time”. This concludes by saying that the event should not be classified as a mass extinction at all. Theory #4 76% of all marine and terrestrial species and 20% of all taxonomic families were wiped out during the Late Triassic Mass Extinction. This was important as ammonoids and conodonts are now seen as important index fossils. The dinosaurs soon became the most common and dominant land animals on Earth. This was because most large amphibians and mammal-like reptiles had been wiped out. Much of the vertebrate fauna became extinct also. Many families of brachiopods, gastropods, bivalves and marine reptiles also died out. The only species of ammonoids that were able to survive were the phylloceratid ammonoids. The conodonts and many Triassic ceratitid ammonoids became extinct. The dinosaurs, pterosaurs, crocodiles, turtles, mammals, and fish suffered very little at all. http://www.google.com.au/imgres?hl=en&safe=active&biw=1229&bih=507&tbm=isch&tbnid=iJx8OGzokQsIRM:&imgrefurl=http://pubs.usgs.gov/circ/2004/1264/html/trip3/pl1.html&docid=0tqD8TZBwzGlWM&imgurl=http://pubs.usgs.gov/circ/2004/1264/graphics/trip3/plate.jpg&w=600&h=735&ei=1IxLUb33D4nnkAWvyYGoBw&zoom=1&ved=1t:3588,r:0,s:0,i:81&iact=rc&dur=1129&page=1&tbnh=188&tbnw=153&start=0&ndsp=13&tx=83&ty=102 http://www.google.com.au/imgres?hl=en&safe=active&biw=1229&bih=507&tbm=isch&tbnid=OHbc1RePn6BtjM:&imgrefurl=http://www.sciencedirect.com/science/article/pii/S0031018209002296&docid=eyBiiqmpUpXjlM&imgurl=http://ars.els-cdn.com/content/image/1-s2.0-S0031018209002296-gr6.jpg&w=756&h=1057&ei=_oxLUcC4B8rwkQXypoHYAw&zoom=1&ved=1t:3588,r:4,s:0,i:92&iact=rc&dur=5&page=1&tbnh=195&tbnw=139&start=0&ndsp=12&tx=85&ty=90 http://www.google.com.au/imgres?hl=en&safe=active&biw=1229&bih=507&tbm=isch&tbnid=zeW2zF27UQZ2lM:&imgrefurl=http://www.ucmp.berkeley.edu/brachiopoda/brachiopoda.html&docid=CWYoUmXWk9LWMM&imgurl=http://www.ucmp.berkeley.edu/brachiopoda/strophex.jpg&w=230&h=165&ei=w41LUa2JDcjRkwXW_YH4Ag&zoom=1&ved=1t:3588,r:0,s:0,i:78&iact=rc&dur=663&page=1&tbnh=132&tbnw=182&start=0&ndsp=11&tx=89&ty=66 http://www.google.com.au/imgres?hl=en&safe=active&biw=1229&bih=507&tbm=isch&tbnid=4XfUaAhvqACUcM:&imgrefurl=http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/gastropoda.php&docid=nmox7gTRv9YVgM&imgurl=http://www.ucmp.berkeley.edu/images/taxa/inverts/shell_morph.jpg&w=625&h=241&ei=-o5LUYfaAYuXkQWflYD4Dw&zoom=1&ved=1t:3588,r:2,s:0,i:84&iact=rc&dur=590&page=1&tbnh=132&tbnw=300&start=0&ndsp=11&tx=74&ty=58 http://www.google.com.au/imgres?hl=en&safe=active&biw=1229&bih=507&tbm=isch&tbnid=RHF5p_ydU72T9M:&imgrefurl=http://www.arcodiv.org/seabottom/Bivalves.html&docid=EzwBdQQHMzMkfM&imgurl=http://www.arcodiv.org/seabottom/bivalves/Astarte_borealis/Astarte_borealis2_400x300.jpg&w=400&h=300&ei=QpBLUfiiEcnNkwXjvoDQAw&zoom=1&ved=1t:3588,r:5,s:0,i:93&iact=rc&dur=6&page=1&tbnh=173&tbnw=164&start=0&ndsp=10&tx=98&ty=84 conodonts Ceratitid Ammonoids Brachiopod Gastropods Bivalves Mammal-like reptiles such as Thrinaxodon thrived during the Early Triassic. They were however, not excluded in the mass extinction. Mammal-like reptiles reached their end in the Late Triassic Mass Extinction. As the warm, shallow seas decreased, the reefs died. This caused other marine organisms to be faced with increased competition in less space. On land, the lack of water led to more extreme temperatures and seasons. When deep water spread back over the continents, it was low in oxygen. This resulted in further marine extinctions. Flying reptiles, such as the pterosaurs, diversified after the mass extinction. In the sea, other reptiles such as ichthyosaurs, mosasaurs and plesiosaurs, grew to whale-like proportions. Flowering plants appeared. The earliest birds evolved from a group of meat-eating dinosaurs, the theropods. The Late Permian Mass Extinction occurred about 248 million years ago. The Late Permian was the greatest mass extinction ever recorded in Earth’s history. Theory #1:
A huge meteorite or comet over 10 kilometres in diameter that impacted with the Earth. Evidence, such as extra-terrestrial helium and argon in rocks from the Permo-Triassic boundary in China and Japan, has been discovered. When looking closely at the helium and argon that has been found, isotope ratios like nothing else on Earth, but similar to those found in meteorites, has been uncovered. Although not definite, evidence has been found in the form of sediment grains located in the Permo-Triassic boundary sections in China. These grains show evidence of compression by impact, as well as geochemical shifts that also suggest this. Evidence for an impact is limited; many geologists do not accept the impact theory for the mass extinction at the end of the Permian. Theory #2:
A massive and prolonged volcanic eruption. This theory suggests that there were massive volcanic eruptions, which were sustained over a period of half-a-million years or more. This caused catastrophic environmental deterioration such as poison gas, global warming, the stripping of soils and plants from the landscape, the eruption of gases from their frozen locations deep in the oceans, large ash clouds that encompassed the world and mass deoxygenation. The Late Permian housed huge volcanic eruptions, this is a fact; the remains of these are preserved in the Siberian Traps. The combination of sulphates in the atmosphere and the ejection of ash clouds may have lowered global climatic conditions. The age of the lava flows has been dated to be in the interval in which the Permian mass extinction occurred. Theory #3: Glaciation. The rapid warming and severe climatic variations produced by simultaneous glaciation events on the north and south poles may have resulted in a mass extinction. This would have resulted in global widespread cooling and/or worldwide lowering of sea levels. Theory #4:
The Formation of Pangea The reduction of shallow continental shelves due to the formation of the super-continent Pangea may have resulted in ecological competition for space. However, the formation of Pangea occurred in the early and middle Permian, and the mass extinction did not occur until the late Permian. Life on Earth was almost completely wiped out by the Late Permian Mass Extinction All over the world complete, complex ecosystems were destroyed. Only 5% of species survived the catastrophe. It eliminated more than 95% of all marine species and more than 70% of all terrestrial species. In the sea, coral reefs, fishes, shellfish, trilobites, plankton, and many other groups disappeared. On land, gorgonopsian reptiles with their sabre-teeth, and the dinocephalians and pareiasaurs, their rhinoceros-sized prey, were wiped out forever. Groups that were significantly reduced were the bryozoans, the brachiopods, the ammonoids, the sharks, the bony fish, the crinoids, the eurypterids, the ostracodes and the echinoderms. For the next 500,000 years life itself hovered on the brink of extinction. It took 50 million years or more for full ecosystem complexity to recover. When oxygen levels fall, plants and photosynthesising plankton in the sea normally replenish it by absorbing excess CO2 and generating oxygen. However, the oxygen levels were too low and so much plant life had died, so this was made impossible. It took 20 to 30 million years for coral reefs to re-establish themselves and for the forests to regrow. A trilobite. http://www.google.com.au/imgres?hl=en&safe=active&biw=1229&bih=507&tbm=isch&tbnid=sjCE1Zv2WJ30jM:&imgrefurl=http://www.trilobites.info/trilobite.htm&docid=k5i7hX8qByFRFM&imgurl=http://www.trilobites.info/cepthopyg.gif&w=274&h=325&ei=S8ZOUceFMoymkwWtioGABg&zoom=1&ved=1t:3588,r:5,s:0,i:93&iact=rc&dur=555&page=1&tbnh=191&tbnw=161&start=0&ndsp=10&tx=40&ty=118 A Gorgonopsian reptile. http://www.google.com.au/imgres?hl=en&safe=active&biw=1229&bih=507&tbm=isch&tbnid=aU9LPh2QwJD-cM:&imgrefurl=http://palaeo.gly.bris.ac.uk/Russia/russia-tetrapods.html&docid=-t91TjktWz3sgM&imgurl=http://palaeo.gly.bris.ac.uk/Russia/images/gorgonopsian.jpg&w=740&h=552&ei=F8lOUfLuKseykAXYz4GgAQ&zoom=1&ved=1t:3588,r:2,s:0,i:86&iact=rc&dur=868&page=1&tbnh=178&tbnw=260&start=0&ndsp=9&tx=100&ty=64 A Dinocephalian. http://www.google.com.au/imgres?hl=en&safe=active&biw=1229&bih=507&tbm=isch&tbnid=GHmwQXaJQJ-fLM:&imgrefurl=http://eonsepochsetc.com/Mesozoic/Triassic/Tri_Animals/reptile_groups.html&docid=qov6Sz_csiHcPM&imgurl=http://eonsepochsetc.com/Mesozoic/Triassic/Tri_Animals/Images/Moschops.jpg&w=800&h=568&ei=ncpOUbbwL4PykQXYxYHwBg&zoom=1&ved=1t:3588,r:4,s:0,i:90&iact=rc&dur=11&page=1&tbnh=189&tbnw=267&start=0&ndsp=9&tx=186&ty=71 The Late Devonian Mass Extinction occurred at the Frasnian - Famennian boundary. Theory #1:
Glaciation. Evidence suggests that warm water marine species were the most severely affected in this extinction event. This evidence has led many palaeontologists to say that the Devonian extinction occurred because of global cooling. According to this theory, the mass extinction was triggered by another glaciation event on Gondwana, which is supported by evidence such as glacial deposits in northern Brazil. Low oxygen levels in the ocean, global cooling and widespread lowering of the sea-level may have triggered the Late Devonian Mass Extinction. Theory #2:
Impact. Meteorite impacts at the Frasnian-Famennian boundary have also been suggested as the cause for the Late Devonian Mass Extinction. Currently, the data surrounding a possible extra-terrestrial impact remains uncertain, and the mechanisms which produced the mass extinction are still under debate. The Late Devonian Mass Extinction is believed to have occurred in either two main phases; the first lasting about 2 million years and the second about 1 million years; or several pulses of extinctions that spread across 15 to 20 million years. Some scientists think that the increased diversity and amount of plant cover on land triggered the global cooling. 22% of all marine families, 57% of all genera became extinct; an estimated 79-87% of all species. The mass extinction primarily affected the marine community, having very little impact on the terrestrial flora. The most important group to be affected were the major reef-builders which included the stromatoporoids, the rugose, and the tabulate corals. The severely affected groups included the brachiopods, the trilobites, the conodonts, and the acritarchs, as well as all the jawless fish, and the placoderms. Armoured fish such as ostracoderms and placoderms vanished completely. Plants and insects suffered very little. Shallow tropical oceans were particularly affected badly. Reef ecosystems came to an end and no new ones were built for the next 100 million years. This Late Devonian Mass Extinction affected specific organisms so severely that reef-building was relatively uncommon until the evolution of the modern corals in the Mesozoic era. With the disappearance of the heavily armoured fish and placoderms, sharks filled the ecological gap. Vast swamps grew and enhanced the evolution of new marine and terrestrial species. Amphibians appeared and were soon followed by the first reptiles. Ostracoderms http://www.google.com.au/imgres?hl=en&safe=active&biw=1229&bih=507&tbm=isch&tbnid=u3eMDJ-UemzTgM:&imgrefurl=http://en.wikipedia.org/wiki/Ostracoderm&docid=Hq-CaRQ0pcYsNM&imgurl=http://upload.wikimedia.org/wikipedia/commons/thumb/6/6e/Osteostraci_Janvier.gif/260px-Osteostraci_Janvier.gif&w=260&h=224&ei=uelOUcj6H6mWiQevi4DQCA&zoom=1&ved=1t:3588,r:2,s:0,i:84&iact=rc&dur=544&page=1&tbnh=179&tbnw=208&start=0&ndsp=10&tx=94&ty=87 A Placoderm http://www.google.com.au/imgres?hl=en&safe=active&biw=1229&bih=507&tbm=isch&tbnid=DxzVKMBGBJAf4M:&imgrefurl=http://www.dinosaurjungle.com/prehistoric_animals_placoderms.php&docid=OfxbopzvN17I7M&imgurl=http://www.dinosaurjungle.com/focus_placoderm.jpg&w=467&h=311&ei=R-tOUe3CAoe6iQeC1YCgAg&zoom=1&ved=1t:3588,r:1,s:0,i:81&iact=rc&dur=7&page=1&tbnh=183&tbnw=243&start=0&ndsp=9&tx=183&ty=54 The Late Ordovician Mass Extinction was the second most devastating mass extinction in Earth’s history. The Late Ordovician Mass Extinction occurred about 440-450 million years ago. Theory #1: Glaciation and Sea-Level Lowering Hypothesis. It is said to be the result of a single event: the glaciation of the continent Gondwana. Evidence for this can be found in glacial deposits in the Saharan Desert. The cause of this glaciation is that when Gondwana passed over the North Pole during the Ordovician, global climatic cooling occurred. This happened to such a degree that there was widespread glaciation on a global scale. This also caused the sea level to lower worldwide as large amounts of water became tied up in ice sheets. A combination of this [lowering of the sea-level], the reduction of ecospace on continental shelves and the cooling caused by the glaciation itself are the most likely cause for the Late Ordovician Mass Extinction. This extinction is listed as the second most devastating extinction to affect marine communities in Earth’s history. It caused the disappearance of one third of all brachiopod and bryozoan families, as well as numerous groups of conodonts, trilobites, and graptolites. Much of the reef-building fauna was also annihilated. In total, more than 100 families of marine invertebrates became extinct. The greatest extinctions occurred in the tropical oceans because if the oceans had cooled, those organisms that lived in the warmer waters would not be adapted, and therefore would die. After the Late Ordovician Mass Extinction, the diversity of many of the affected marine invertebrate groups increased again. Fish became a major part of marine and freshwater fauna. On land, plants continued to spread and expand. By the time the Devonian period came about, the first forests had appeared, as well as primitive insects and the ancestors of amphibians. A Brachiopod. http://www.google.com.au/imgres?hl=en&safe=active&biw=1229&bih=507&tbm=isch&tbnid=erQJReCEXUrPPM:&imgrefurl=http://paleo.cortland.edu/tutorial/Brachiopods/brachmorph.htm&docid=EjcrnK7qFOOCoM&imgurl=http://paleo.cortland.edu/tutorial/Brachiopods/Brachiopod%252520Images/brachdraw2.GIF&w=395&h=363&ei=3gJPUeCcFquRiQfi0IDACg&zoom=1&ved=1t:3588,r:1,s:0,i:81&iact=rc&dur=510&page=1&tbnh=177&tbnw=192&start=0&ndsp=10&tx=144&ty=67 A bryozoan. http://www.google.com.au/imgres?hl=en&safe=active&biw=1229&bih=507&tbm=isch&tbnid=k0apcGfDpBP45M:&imgrefurl=http://members.wolfram.com/jeffb/Fossils/Bryozoa.shtml&docid=08kVcK4lYIgJFM&imgurl=http://members.wolfram.com/jeffb/Fossils/bryozoan2.jpg&w=2832&h=2288&ei=XAVPUabLFquYiAfhsIFY&zoom=1&ved=1t:3588,r:0,s:0,i:78&iact=rc&dur=225&page=1&tbnh=186&tbnw=244&start=0&ndsp=11&tx=142&ty=43 The megafauna went extinct between about 51,000 and 40,000 years ago. Theory #1: Hunting Many argue that the megafauna went extinct because they were hunted by humans. However, in Australia there has been very little evidence found of large scale hunting of megafauna. Although evidence has been found to suggest that the Aborigines were eating the megafauna animals. The Aboriginal’s tools and weapons at that time were not strong enough to take own a fully grown, adult megafauna. This has led to the suggestion that the people may have been eating dead or dying animals that had been trapped in the mud around the water's edge. It was also suggested that the Aborigines probably hunted juvenile megafauna animals because of their limited weapons. Juveniles would provide less food than adults, so the hunters would have needed to kill more individuals than if they hunted the adults. At some locations, such as Coral Bay in Western Australia, there is evidence of harvesting of Genyornis eggs. But the evidence does not point to large-scale plundering of the eggs. There has not been evidence found that indicates that the aborigines were extinguishing the megafauna the way the Ica Age hunters did in other parts of the world. Theory #2: Climate change. Some argue that humans did not have the numbers in population nor the technology to efficiently wipe out the megafauna. They believe that the megafauna were wiped out by climate change. A harsh climate changed happened 40-50,000 years ago in the Darling Down's region. Evidence has been found that suggests a very severe drought occurred around 40-50,000 years ago; this may have caused the megafauna to die. It has been suggested that although they could survive the hard times, once human hunting, and habitat change was added to the mix, it may have been enough to tip the balance against them. One feature of the changing Australian climate that may have affected the megafauna more than glaciation and its accompanying dry conditions was the progressive change of the Australian continent that had been progressing in stages since the Middle Miocene. Theory # 3: non extinction There are those who believe that rather than becoming extinct, they simply down-sized. For example: the Diprotodon, evolving into the Eastern Grey Kangaroo. Some believe that the unproductive nature of Australian ecosystems led to smaller sizes of the Australian megafauna. This suggests that the herbivores of the megafauna evolved to cope with the vegetation that survived on impoverished soils and low, erratic rainfall, which resulted in smaller sizes. Theory # 4: food The plants that Genyornis depended on were mostly gone, so it is likely that hunting alone didn't kill them off, though it would have been an added stress. It has been suggested that the extinction of the Diprotodon and other large herbivores may have been caused by a sudden lack in suitable vegetation. They had survived dry periods, but the relentless spread of arid conditions, even before the arrival of humans, may have been pushing the megafauna past their ability to adapt. At the time the megafauna went extinct the vegetation of the continent was changing on a large scale, and it occurred continent-wide. As their food sources became more and more scarce, they would have found it difficult to find enough to survive. Eventually they would have reached the point where they were either dying of starvation, or being weakened so much that they became easy prey for disease as well as their predators, human or animal. Once the herbivores were gone the predators would follow. Many animals went extinct, examples include the
Zaglossus hacketti, a sheep-sized echidna
Obdurodon dicksoni, a platypus up to 60 cm in total length
Megalibgwilia ramsayi, a large, long-beaked echidna with powerful forelimbs for digging.
The diprotodon, a hippopotamus-sized marsupial, most closely related to the wombat.
And the Procoptodon goliah (the giant short-faced kangaroo) is the largest kangaroo to have ever lived.
Propleopus oscillans was a carnivorous kangaroo.
The Family Dromornithidae: this group of birds was more closely related to waterfowl.
Varanus priscus was a giant, carnivorous goanna.
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