牙齒研究顯示暴龍是溫血動物，體溫近似人類

作者：Will DunhamBy Will Dunham

華盛頓，9月16日（路透）——科學家利用暴龍牙齒中的化學線索證實，這種巨大掠食者是溫血動物，體溫接近人類。研究人員表示，這項發現應促使外界對這種知名恐龍的認知出現根本改變。WASHINGTON, Sept 16 (Reuters) - Using chemical clues in Tyrannosaurus rex teeth, scientists have shown that this massive predator was warm-blooded — with a body temperature close to that of a person — in a finding they said should prompt a fundamental change in the perception of the celebrity dinosaur.

研究人員發現，在蒙大拿州出土的三顆暴龍牙齒，其琺瑯質化學組成顯示，這種恐龍的體溫為華氏97.3度（攝氏36.3度），誤差範圍正負華氏4.5度（攝氏2.5度）。人類的平均體溫為華氏98.6度（攝氏37度）。The chemical makeup of the enamel in three T. rex teeth unearthed in Montana indicated that the dinosaur had a body temperature of 97.3 degrees Fahrenheit (36.3 degrees Celsius), plus or minus 4.5 F (2.5 C), the researchers found. For humans, the average body temperature is 98.6 F (37 C).

更貼切的比較對象或許是現存最大陸生動物大象，其平均體溫約華氏97度（攝氏36度）；以及現存最大鳥類鴕鳥，體溫約華氏102度（攝氏39度）。暴龍是體型最龐大的肉食性恐龍之一。More apt comparisons may be the average body temperature of the elephant, the most massive extant land animal, of around 97 F (36 C), and the ostrich, the largest extant bird, at roughly 102 F (39 C). Tyrannosaurus was among the most massive meat-eating dinosaurs.

這項新研究提出暴龍是溫血動物的證據，駁斥了暴龍是行動遲緩蠻獸的過時觀念。The new study's evidence that Tyrannosaurus was warm-blooded rebuts the obsolete notion of a sluggish brute.

加州大學洛杉磯分校地球科學家、週三發表於期刊《科學進展》（Science Advances）的這項研究資深作者阿拉德娜・特里帕蒂說：「牠不再是人們想像中那種爬蟲類。體溫攝氏36度的動物不會等著太陽把身體曬暖。牠在體溫上獨立於周遭環境；就這一點而言，牠比起鱷魚，更接近大象或鴕鳥。」"It stops being a reptile in the way people picture reptiles. An animal at 36 degrees Celsius is not waiting for the sun to warm up. It is thermally independent of its surroundings, and in that respect closer to an elephant or an ostrich than to a crocodile," said UCLA geoscientist Aradhna Tripati, senior author of the research published on Wednesday in the journal Science Advances.

暴龍約在6600萬年前、恐龍時代末期的白堊紀，漫遊於北美洲西部。已知暴龍化石的分布，北至加拿大亞伯達省與薩斯喀徹溫省，向南經過美國蒙大拿州、懷俄明州與達科他地區，並延伸至新墨西哥州與德州。Tyrannosaurus roamed western North America during the Cretaceous Period about 66 million years ago at the end of the age of dinosaurs. Its fossils are known from as far north as the Canadian provinces of Alberta and Saskatchewan, then south through the U.S. states of Montana, Wyoming and the Dakotas, and into New Mexico and Texas.

特里帕蒂表示，氣候模型顯示暴龍原本能夠棲息於這片大陸的大部分地區，「包括寒冷環境，在那裡牠會經歷結冰溫度。這是一種遠比人們想像中更具移動能力、也更能適應環境的動物。」Tripati said climate modeling indicates Tyrannosaurus would have been able to inhabit most of the continent, "including cold environments where it would have experienced freezing. That is a far more mobile and adaptable animal than the one people picture."

「多得多的食物」'SIGNIFICANTLY MORE FOOD'

溫血性也稱為內溫性，指動物能夠產生並保存體內代謝熱。這帶來若干生理優勢，例如持續的能量與耐力，以及在溫暖與寒冷氣候中都能繁盛生存的能力。冷血性或外溫性，則使動物依賴外部熱源來讓身體升溫，例如鱷魚與蛇。Warm-bloodedness, also called endothermy, involves the ability of an animal to generate and conserve internal metabolic heat. This provides certain physiological advantages such as sustained energy and stamina, as well as the ability to thrive in warm and cold climes. Cold-bloodedness, or ectothermy, makes animals dependent upon external heat sources to warm up their bodies, like crocs and snakes.

UCLA地球生物學家、研究共同作者羅伯特・伊格爾說：「內溫性常見於大型動物，甚至也見於部分魚類。不過，這是有代價的。」"Endothermy is common in large animals and even some fish. It comes at a cost, though," UCLA geobiologist and study co-author Robert Eagle said.

伊格爾說：「較高的代謝率意味著需要更多食物，也可能需要更積極獵食以取得食物。具有內溫性的暴龍必須取得多得多的食物，才能維持較高代謝率；但牠也會有能力進行更持久的活動，以尋找食物、遷徙，並生活在較寒冷的環境。」"Higher metabolic rates mean higher food requirements and potentially more active hunting to acquire it. An endothermic T. rex would have had to acquire significantly more food to sustain its higher metabolic rate, but would also be capable of more sustained activity to find food and migrate, and live in colder environments," Eagle said.

鳥類與哺乳類都是內溫動物。所有肉食性恐龍都屬於獸腳類這一演化支。鳥類也是這個演化支的一部分，由小型有羽毛恐龍演化而來。現今的小型飛鳥體溫約華氏107度（攝氏42度）。Birds and mammals are endotherms. All meat-eating dinosaurs are part of a lineage called theropods. Birds are part of this lineage, having evolved from small feathered dinosaurs. Small flying birds today have a body temperature around 107 F (42 C).

特里帕蒂說：「我們測得的暴龍體溫，落在內溫動物範圍的低端。」"Our temperature for T. rex sits at the low end of the endotherm range," Tripati said.

牙齒是這項研究的關鍵。Teeth were the key to the study.

特里帕蒂說：「牙齒琺瑯質是在動物體內、以其體溫形成，因此琺瑯質化學組成就是一支溫度計。」"Tooth enamel forms inside the animal at body temperature, so the enamel chemistry is a thermometer," Tripati said.

琺瑯質中碳與氧的某些形式，也就是同位素的比例，可以透過稱為「團簇同位素」的方法揭示體溫。The ratio of certain forms, or isotopes, of carbon and oxygen present in the enamel can reveal body temperature, through a method called "clumped isotopes."

研究人員採用破壞性極低的技術，使用配有碳化鎢鑽頭的低速旋轉鑽，從每顆牙齒取下約5毫克琺瑯質粉末，少於一小撮鹽的量。The researchers used a minimally destructive technique using a low-speed rotary drill with a tungsten carbide bit to take about 5 milligrams of enamel powder, less than a pinch of salt, from each tooth.

這些牙齒由洛杉磯郡自然史博物館提供，其中兩顆來自一具保存良好、暱稱「湯瑪斯」（Thomas）的年輕成體標本，另一顆則是來自第二隻暴龍的單獨局部牙齒；兩者均出自蒙大拿州卡特郡同一地點。The Natural History Museum of Los Angeles County provided the teeth, two from a well-preserved young adult specimen nicknamed Thomas and the other an isolated partial tooth from a second Tyrannosaurus, both from the same locale in Montana's Carter County.

研究人員也將這項技術應用於同一岩層中5顆年代相近的鱷形類牙齒，發現其平均體溫為華氏87.6度（攝氏30.9度），與現代鱷魚相符，且低於暴龍。The researchers also applied the technique to five similarly old crocodilian teeth from the same rock formation, finding average body temperatures of 87.6 F (30.9 C), in line with modern crocs and lower than in Tyrannosaurus.

伊格爾說：「一般認為許多恐龍是溫血動物，但不一定全部都是。不過，即使在溫血生物之間，也存在程度上的問題。牠們可能像樹懶或食蟻獸那樣，屬於低程度內溫；也可能像現代大型哺乳動物；或像鳥類那樣具有內溫性，而鳥類通常比哺乳類有更高的代謝率。」"It's thought that many dinosaurs, but not necessarily all, were warm-blooded," Eagle said. "However even amongst warm-blooded organisms, there are questions of the degree. They can be warm-blooded like sloths or anteaters, with low-level endothermy; modern large mammals; or avian (bird) endotherms, which typically have higher metabolic rates than mammals."

談到其他恐龍是否具有內溫性時，特里帕蒂說：「對於其他恐龍，我會謹慎看待是否能一概而論。這只是一個物種，而跨恐龍類群的證據顯示，牠們採取的是一系列策略，而不是單一答案。」"On other dinosaurs, I would be cautious about generalizing," Tripati said, regarding endothermy. "This is one species, and the evidence across dinosaurs points to a range of strategies rather than a single answer."

（Will Dunham報導；Daniel Wallis編輯）(Reporting by Will Dunham; Editing by Daniel Wallis)