北美發(fā)現(xiàn)暴龍家族新成員：體重僅78公斤
北美發(fā)現(xiàn)的新種恐龍Moros intrepidus的復(fù)原圖。圖源：Jorge Gonzalez；版權(quán)： Lindsay Zanno
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2月底，《通訊-生物學(xué)》在線發(fā)表的一篇論文Diminutive fleet-footed tyrannosauroid narrows the 70-million-year gap in the North American fossil record報道了一個暴龍超科的新種恐龍。該恐龍屬于白堊紀(jì)時期同類中體型最小的一種，它的發(fā)現(xiàn)幫助填補了北美化石記錄中長到7000萬年的空白。
著名的君王暴龍（也稱霸王龍，Tyrannosaurus rex）是一種大型的頂級掠食者。但是，其它已知的暴龍超科動物在1億年的演化歷史中，大部分時候都是小型的次級掠食者。雖然亞洲的化石記錄較為完整，但是北美的化石記錄卻相對匱乏，這限制了我們對君王暴龍以及其它大型暴龍超科動物的主要演化事件的理解。
Moros intrepidus化石及其發(fā)現(xiàn)地。圖源：Zanno等
美國北卡羅萊納州自然科學(xué)博物館的Lindsay Zanno及其同事在美國猶他州埃默里縣發(fā)現(xiàn)了屬于一個體型異常之小的暴龍超科的化石。這個被命名為Moros intrepidus的新物種，將北美的化石記錄延長了1500萬年，填補了此前跨越侏羅-白堊紀(jì)之交和白堊紀(jì)大部分時期的7000萬年的化石記錄空白。
研究人員估計成年M. Intrepdius 的體重僅為78千克，肢體長1.2米。作者對M. intrepidus及其亞洲近親的分析結(jié)果顯示，暴龍超科在約1500萬年間一直體型較小，之后在不到1600萬年的時間內(nèi)演化形成像君王暴龍這樣的大型恐龍。
摘要
To date, eco-evolutionary dynamics in the ascent of tyrannosauroids to top predator roles have been obscured by a 70-million-year gap in the North American (NA) record. Here we report discovery of the oldest Cretaceous NA tyrannosauroid, extending the lineage by ~15 million years. The new taxon—Moros intrepidus gen. et sp. nov.—is represented by a hind limb from an individual nearing skeletal maturity at 6–7?years. With a ~1.2-m limb length and 78-kg mass, M. intrepidus ranks among the smallest Cretaceous tyrannosauroids, restricting the window for rapid mass increases preceding the appearance of colossal eutyrannosaurs. Phylogenetic affinity with Asian taxa supports transcontinental interchange as the means by which iconic biotas of the terminal Cretaceous were established in NA. The unexpectedly diminutive and highly cursorial bauplan of NA’s earliest Cretaceous tyrannosauroids reveals an evolutionary strategy reliant on speed and small size during their prolonged stint as marginal predators.
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期刊介紹：Communications Biology(https://www.nature.com/commsbio/) is an open access journal from Nature Research publishing high-quality research, reviews and commentary in all areas of the biological sciences. Research papers published by the journal represent significant advances bringing new biological insight to a specialized area of research.
