剑齿虎的犬齿需要多年时间才能长出

New research shows that the fearsome teeth of the saber-toothed cat Smilodon fatalis fully ¹ emerged at a later age than those of modern big cats, but grew at a rate about double that of their living relatives. The findings, published today in the journal PLOS ONE and based on a new technique that combines isotopic ² analysis and x-ray imaging, for the first time provide specific ages for developmental events in Smilodon, notably ³ in their teeth. The study estimates that the eruption ⁴ rate of S. fatalis's permanent upper canines ⁵ was 6 millimeters per month--double the growth rate of an African lion's teeth. But the extinct cat's dagger-like canines weren't fully developed until about three years of age. "For predators ⁶ such as big cats, an important determinant of an individual's full hunting ability is the time required to grow their weapons--their teeth," said Z. Jack ⁷ Tseng, a National Science Foundation and Frick Postdoctoral Fellow in the American Museum of Natural History's Division of Paleontology and a coauthor on the new paper. "This is especially crucial for understanding sabertoothed predators such as Smilodon.", ,S. fatalis lived in North and South America until going extinct about 10,000 years ago. About the size of a modern tiger or lion but more solidly built, the cats are famous for their protruding ⁸ canines, which could grow to be 18 centimeters (about 7 inches) long. Although well-preserved fossils of S. fatalis are available to researchers, very little is known about the absolute ages at which the animals reached key developmental stages., ," Timing ⁹ of development is critical for many aspects of vertebrate ecology and evolution," said Robert Feranec, curator of Pleistocene vertebrate paleontology at the New York State Museum and the corresponding author on the paper. "Changes in the timing of life-history events can have major effects on an organism's adult features and final appearance. For extinct species, we can usually only determine the relative sequence of developmental events. This technique will permit the determination of absolute developmental age not only for Smilodon, but other extinct species."