Abstract
Despite the superb fossil record of the saber-toothed cat, Smilodon fatalis, ontogenetic age determination for this and other ancient species remains a challenge. The present study utilizes a new technique, a combination of data from stable oxygen isotope analyses and micro-computed tomography, to establish the eruption rate for the permanent upper canines in Smilodon fatalis. The results imply an eruption rate of 6.0 millimeters per month, which is similar to a previously published average enamel growth rate of the S. fatalis upper canines (5.8 millimeters per month). Utilizing the upper canine growth rate, the upper canine eruption rate, and a previously published tooth replacement sequence, this study calculates absolute ontogenetic age ranges of tooth development and eruption in S. fatalis. The timing of tooth eruption is compared between S. fatalis and several extant conical-toothed felids, such as the African lion (Panthera leo). Results suggest that the permanent dentition of S. fatalis, except for the upper canines, was fully erupted by 14 to 22 months, and that the upper canines finished erupting at about 34 to 41 months. Based on these developmental age calculations, S. fatalis individuals less than 4 to 7 months of age were not typically preserved at Rancho La Brea. On the whole, S. fatalis appears to have had delayed dental development compared to dental development in similar-sized extant felids. This technique for absolute ontogenetic age determination can be replicated in other ancient species, including non-saber-toothed taxa, as long as the timing of growth initiation and growth rate can be determined for a specific feature, such as a tooth, and that growth period overlaps with the development of the other features under investigation.
Highlights
Timing of development is critical in vertebrate ecology and evolution [1,2,3,4,5,6]
S. fatalis differs from P. leo in aspects of the relative timing of tooth development, such as the timing of permanent carnassial eruption relative to permanent incisor eruption, which makes P. leo less suitable as a modern analog for ontogenetic age estimates of S. fatalis than for ontogenetic age estimates of H. serum [13, 20]
Utilizing the absolute ontogenetic age of C1 growth initiation, the C1 growth rate range previously calculated from stable oxygen isotope values [19] and the previously determined lengths of C1 associated with particular developmental stages [13], absolute ontogenetic age doi:10.1371/journal.pone.0129847.g002
Summary
Timing of development is critical in vertebrate ecology and evolution [1,2,3,4,5,6]. Changes in the timing of life history events can have major effects on fitness and changes in the timing of development of morphological features (i.e., heterochrony) can yield major changes to the vertebrate bauplan [1,2,3,4, 7]. Based on the concept that species of comparable skeletal dimensions share similar growth rates, estimates of ontogenetic age have been assigned to stages of dental development in another machairodontine, Homotherium serum, utilizing the extant Panthera leo as a modern analog [18]. These ontogenetic age estimates are supported by stable oxygen isotope analyses that indicate similar permanent upper canine (C1) enamel growth rates for H. serum and P. leo [19]. S. fatalis differs from P. leo in aspects of the relative timing of tooth development, such as the timing of permanent carnassial eruption relative to permanent incisor eruption, which makes P. leo less suitable as a modern analog for ontogenetic age estimates of S. fatalis than for ontogenetic age estimates of H. serum [13, 20]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
