Evolving By Shrinking: How Dinosaurs Became Birds. Most dinosaurs went extinct 65 million years ago but one dinosaur lineage survived and lives on today – we call these the birds and they rule the skies the way they once ruled land. An international team, led by scientists from Oxford University and the Royal Ontario Museum, estimated the body mass of 426 dinosaur species based on the thickness of their leg bones. The team found that dinosaurs showed rapid changes in body size shortly after their origins, around 220 million years ago. However, these soon slowed: only the evolutionary line leading to birds continued to change size at this rate, and did so for a further 170 million years, producing new ecological diversity not seen in other dinosaur lineages. The study suggests that shrinking their bodies may have helped this group to continue exploiting new ecological niches throughout their evolution, and to become such a diverse and widespread group of animals today.
CLICK FOR LARGER SIZE. "How do you weigh a dinosaur? No evidence for directional evolution of body mass in herbivorous theropod dinosaurs | Proceedings of the Royal Society of London B: Biological Sciences. Abstract The correlation between large body size and digestive efficiency has been hypothesized to have driven trends of increasing mass in herbivorous clades by means of directional selection. Yet, to date, few studies have investigated this relationship from a phylogenetic perspective, and none, to our knowledge, with regard to trophic shifts. Here, we reconstruct body mass in the three major subclades of non-avian theropod dinosaurs whose ecomorphology is correlated with extrinsic evidence of at least facultative herbivory in the fossil record—all of which also achieve relative gigantism (more than 3000 kg).
Ordinary least-squares regressions on natural log-transformed mean mass recover significant correlations between increasing mass and geological time. 1. The ability of herbivores to subsist on a high-fibre diet requires a complex interplay of anatomical and physiological adaptations [1–4]. Figure 1. 2. (a) Mass estimates and trees (b) Trend analyses 3. (a) Body mass estimates 4. 「雷龍」要回來了嗎？ 長長的脖子、龐大的身軀，在草原中緩慢行走，悠哉地吃著樹葉，是大家對雷龍的印象。 可是「雷龍」（Brontosaurus）這個名稱，早在1903年就不再被科學界所用，因為當時的科學家認為牠與迷惑龍（Apatosaurus）是同一種生物，所以其實「雷龍」並不存在。 BUT！ 科學就是這一個BUT……最近古生物學家針對幾種同屬梁龍科（Diplodocidae）的恐龍骨骼研究，發現雷龍與迷惑龍骨骼之間的差異其實很大，足以區分為兩個不同屬的生物。 所以「雷龍」又回來了。 發現與消失 西元1877年，地質學家Arthur Lakes將一些骨頭的化石寄給了耶魯大學的古生物學家Othneil Charles Marsh，Marsh將它命名為埃阿斯迷惑龍（Apatosaurus ajax），屬於蜥腳下目，認為牠生活在晚侏儸紀。 此時科學界出現了不同的意見，1903年古生物學家Elmer Riggs的研究認為，埃阿斯迷惑龍（A.ajax）和秀麗雷龍（B.excelsus）之間的關係遠比Marsh想像中的親近，近到兩者應該是同一種生物，而迷惑龍（Apatosaurus）是先被命名的，所以應該優先保留這個名字。 直到1990年代，休士頓自然史博物館古生物館的館長Bob Bakker重新爭取調整秀麗迷惑龍（A. excelsus）的名稱，他引用了秀麗迷惑龍（A. excelsus）的肩胛骨、頭部和頸部等與其他迷惑龍不同的地方，並將結果發表在2004年的《National Science Museum Monographs》。
重新討論 起初，葡萄牙古生物學家Emanuel Tschopp只是想要鑑定一些從瑞士的博物館來的幾份骨頭標本，卻發現既有的分類必須要修改，因為分類的特徵都不足以將這批骨頭標本歸類。 研究團隊中的Mateus教授在接受期刊訪問時也說：「這是一個科學研究過程的典型範例，特別是如果當初的假說是建立在一些比較零碎的化石上時，那新的發現就很可能推翻過去多年的研究成果」。 參考資料： 研究文獻： Once were dinosaurs. The male and female of the oviraptosaur Avimimus, which may have used its feathered forelimbs for display. Credit: Peter Schouten: Zhao Chang and Xing Lida IF YOU COULD step back to the late Jurassic, 160 million years ago, and conceal yourself in the prehistoric foliage of Mongolia, you would see something remarkable. Between the tree ferns and cycads, an unusual looking bird would appear. It tidies up a clearing – removing leaves, sticks and other debris. Then, with a dramatic flourish, the pigeon-sized creature stands on tip toes, puffs-up its strikingly coloured plumage, and starts to jerkily dance from side to side, all the while producing clicks and shrill little calls.
Most conspicuous are its four long tail feathers, which flick and waft as it shimmies to an internal beat. This is actually a courtship ritual, very much like the kind played out by birds of paradise today in New Guinea. “Did they use feathers in complex mating rituals? Not everyone agrees. The Institute for Creation Research. "A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit. " (Matthew 7:18) Evolutionists have expended great effort in trying to establish that birds evolved from dinosaurs. Some skeletal similarities do exist—encouraging them to minimize the differences and to champion any possible clue (like hints of feathers in theropod dinosaurs) that the two classes might be related. Now it appears that some would even resort to fraud to establish such a lineage.
Wings: The proposed ancestors of birds are thought to have walked on their hind legs. Feathers: Feathers are not at all similar to scales. Bones: Birds have delicate, hollow bones to lighten their weight while dinosaurs had solid bones. Warm blooded: Birds are warmblooded with exceptionally high metabolism and food demands. Lungs: Birds are unique among land-dwelling vertebrates in that they don't breathe in and out.
Cite this article: John D. The Pterosaur Heresies | There's something very wrong with our pterosaurs. Humans, not climate, to blame for Ice Age-era disappearance of large mammals, study concludes -- ScienceDaily. Was it humankind or climate change that caused the extinction of a considerable number of large mammals about the time of the last Ice Age? Researchers at Aarhus University have carried out the first global analysis of the extinction of the large animals, and the conclusion is clear -- humans are to blame. A new study unequivocally points to humans as the cause of the mass extinction of large animals all over the world during the course of the last 100,000 years.
"Our results strongly underline the fact that human expansion throughout the world has meant an enormous loss of large animals," says Postdoctoral Fellow Søren Faurby, Aarhus University. Was it due to climate change? For almost 50 years, scientists have been discussing what led to the mass extinction of large animals (also known as megafauna) during and immediately after the last Ice Age. One of two leading theories states that the large animals became extinct as a result of climate change. Theory of overkill First global mapping. Dinosaurs. Great Dinosaur Pictures. Dinosaur Extinction Theories. 【每日酷知識】恐龍時代 – 國家地理雜誌-中文網.
恐龍生活在什麼時代？ 我們的地球已經45億歲了。 但就我們所知，在這漫長的地球歲月中，生物存在於地球上的時間，其實只是短短的一剎那。 而恐龍又是生長在什麼樣的時代中呢？ 地質時間 地球已經很老很老了，所以研究史前生物和岩石的科學家——也就是古生物學家和地質學家——有他們自己專用的時序表。 因為每個地質時期都有不一樣的氣候狀態和地質活動，像是火山噴發、生長的動植物類型也不一樣，因此會形成不同類型的岩石和化石。 圖片取自：《那時候魚兒還有腳，鯊魚剛長牙，蟲子到處爬》 恐龍時代的結束 大約在6500萬年前，地球上將近90%的生物都死亡了。 圖片取自：《國家地理》數位雜誌互動版 2014.10月號 延伸閱讀： 《國家地理》數位雜誌互動版 2014.10月號 霸王龍，讓開！ 小心，恐龍出沒中！ 持續追蹤，每日小知識，讓您跟孩子分享這世界，每天發現的美好與奇妙。 【恐龍酷知識】不要學《侏羅紀公園》亂混DNA！ – 國家地理雜誌-中文網. 關於恐龍跟蚊子的DNA…. 人類對恐龍實在太著迷了，因此催生了好幾部賣座電影。 不過，冒險電影常常把科幻小說與科學事實混為一談。 不要亂混DNA 最有名的恐龍電影應該就屬《侏羅紀公園》了。 這是第一部《侏羅紀公園》裡的一幕，人類受到霸王龍的威脅。 這個想法很有創意，不過請記住，DNA是會隨著時間而劣化的，因此，無論保存得多完好，都不太可能歷經數百萬年而無損。 圖片取自：《國家地理》EVERYTHING小百科系列 – 恐龍 另外，科學家在取得恐龍的DNA時，也可能會不小心取到一些蚊子的DNA，而把這兩種DNA混在一起。 Photograph by Darlyne A. 這樣一來，科學家就會創造出來真正的大怪物——霸蚊龍！ 延伸閱讀： 《國家地理》雜誌互動數位版 2014.10月號 霸王龍，讓開！ 小心，恐龍出沒中！ 持續追蹤，每日小知識，讓您跟孩子分享這世界，每天發現的美好與奇妙。 【恐龍酷知識】 恐龍的小知識！(二) – 國家地理雜誌-中文網. 跟恐龍有關的知識 ①. 電影《侏羅紀公園》裡的科學家讓滅絕的恐龍再度復活。 目前這還是無法實現的。 圖片取自：《國家地理EVERYTHING系列》-恐龍 ②.1842年，英文的恐龍（Dinosaur）一詞出現了。 ③.連續不斷的恐龍足跡化石稱為恐龍行跡。
④.尼日龍（Nigersaurus）的嘴裡有大約500顆多的牙齒。 圖片取自：《怪異恐龍總動員》 ⑤.科學家已經發現了近1000種恐龍的遺骸。 延伸閱讀： 《國家地理》數位雜誌互動版 2014.10月號 霸王龍，讓開！ 小心，恐龍出沒中！ 持續追蹤，每日小知識，讓您跟孩子分享這世界，每天發現的美好與奇妙。