Apesteguía Sebastián, Novas Fernando E
Museo Argentino de Ciencias Naturales Bernardino Rivadavia, Av. Angel Gallardo 470, Buenos Aires (1405), Argentina.
Nature. 2003 Oct 9;425(6958):609-12. doi: 10.1038/nature01995.
Sphenodontian reptiles successfully radiated during Triassic and Jurassic times, but were driven almost to extinction during the Cretaceous period. The sparse Early Cretaceous record of sphenodontians has been interpreted as reflecting the decline of the group in favour of lizards, their suspected ecological successors. However, recent discoveries in Late Cretaceous beds in Patagonia partially modify this interpretation. Numerous skeletons of a new sphenodontian, Priosphenodon avelasi gen. et sp. nov., were collected from a single locality in the Cenomanian-Turonian Candeleros Formation, where it is more abundant than any other tetrapod group recorded in the quarry (for example, Crocodyliformes, Serpentes, Dinosauria and Mammalia). Adult specimens of Priosphenodon reached one metre in length, larger than any previously known terrestrial sphenodontian. Here we propose, using available evidence, that sphenodontians were not a minor component of the Cretaceous terrestrial ecosystems of South America, and that their ecological replacement by squamates was delayed until the early Tertiary. The new discovery helps to bridge the considerable gap in the fossil record (around 120 million years) that separates the Early Cretaceous sphenodontians from their living relatives (Sphenodon).
喙头目爬行动物在三叠纪和侏罗纪时期成功地广泛分布，但在白垩纪时期几乎濒临灭绝。早期白垩纪稀少的喙头目动物记录被解释为反映了该类群的衰落，有利于蜥蜴，它们被怀疑是生态上的后继者。然而，最近在巴塔哥尼亚晚白垩世地层的发现部分修正了这一解释。从森诺曼阶-土伦阶坎德列罗斯组的一个地点采集到了大量新的喙头目动物——阿韦拉西原喙龙（Priosphenodon avelasi）的骨骼，在那里它比采石场记录的任何其他四足动物类群都更丰富（例如鳄形目、蛇目、恐龙和哺乳动物）。原喙龙的成年标本长度达到一米，比任何先前已知的陆地喙头目动物都要大。在这里，我们利用现有证据提出，喙头目动物并非南美洲白垩纪陆地生态系统的次要组成部分，它们被有鳞目动物的生态替代直到第三纪早期才发生。这一新发现有助于弥合化石记录中（约1.2亿年）将早白垩世喙头目动物与其现存亲属（楔齿蜥）分隔开来的巨大差距。
