它們看起來就像是遠古哺乳動物的腦袋，然而這些在東非發(fā)現(xiàn)的1億年前的化石遺骸卻屬于鱷魚家族中的一位成員。
美國俄亥俄大學的Patrick M. O’Connor與同事，在坦桑尼亞西南Rukwa Rift盆地的白堊紀沉積物中發(fā)現(xiàn)了一種新的、體型較小的鱷形動物化石,，顯示了關(guān)于趨同性形態(tài)演化的進一步證據(jù)。
研究人員將這種遠古鱷魚命名為Pakasuchus,。他們注意到,，它們的牙齒是最不像鱷魚的,，倒與那些溫血的食肉動物牙齒非常相像——同樣具有突出的犬齒、鋒利的前磨牙以及扁平的臼齒,。
研究人員指出,，所有這些特征使得這些史前鱷魚能夠咬傷、撕裂并咀嚼它的獵物,。與此形成對照的是,，現(xiàn)代鱷魚用來捉住并吞噬獵物的牙齒都是均勻的錐形。Pakasuchus具有能夠進行牙冠至牙冠接觸——這種接觸是咀嚼的特征——的牙系,， 并且具有幾乎全部被認為屬于哺乳動物的牙齒特點,。
根據(jù)對新發(fā)現(xiàn)的鱷魚化石的其他部分進行的分析，包括長而直的四肢,，科學家斷定,，這條鱷魚生前曾在非洲的稀樹大草原上游蕩，以大型昆蟲,，例如蜻蜓,，或新孵化的恐龍幼崽為食。
研究人員指出,，在哺乳動物的祖先紛紛開拓北方大陸時,，這種鱷魚很有可能填補了南半球的小生境。這意味著Pakasuchus能夠像最近在非洲發(fā)現(xiàn)的其他遠古鱷魚一樣,，在離開水后找到一種非常安逸的生活方式,。
研究人員在8月5日出版的《自然》雜志上報告了這一發(fā)現(xiàn)。（生物谷Bioon.com）
生物谷推薦原文出處：
Nature doi:10.1038/nature09061
The evolution of mammal-like crocodyliforms in the Cretaceous Period of Gondwana
Patrick M. O’Connor,Joseph J. W. Sertich,Nancy J. Stevens,Eric M. Roberts,Michael D. Gottfried,Tobin L. Hieronymus,Zubair A. Jinnah,Ryan Ridgely,Sifa E. Ngasala& Jesuit Temba
Fossil crocodyliforms discovered in recent years1, 2, 3, 4, 5 have revealed a level of morphological and ecological diversity not exhibited by extant members of the group. This diversity is particularly notable among taxa of the Cretaceous Period (144–65?million years ago) recovered from former Gondwanan landmasses. Here we report the discovery of a new species of Cretaceous notosuchian crocodyliform from the Rukwa Rift Basin6 of southwestern Tanzania. This small-bodied form deviates significantly from more typical crocodyliform craniodental morphologies, having a short, broad skull, robust lower jaw, and a dentition with relatively few teeth that nonetheless show marked heterodonty. The presence of morphologically complex, complementary upper and lower molariform teeth suggests a degree of crown–crown contact during jaw adduction that is unmatched among known crocodyliforms, paralleling the level of occlusal complexity seen in mammals and their extinct relatives7, 8, 9, 10, 11, 12. The presence of another small-bodied mammal-like crocodyliform in the Cretaceous of Gondwana indicates that notosuchians probably filled niches and inhabited ecomorphospace that were otherwise occupied by mammals on northern continents.
