Tuesday, December 15, 2015

A Lamniform Shark From Albian Cretaceous Texas Grew 6.3m (20+ ft) in 18 Years

Ontogeny and life history of a large lamniform shark from the Early Cretaceous of North America


Frederickson et al


Due to an incomplete fossil record, little is known about lamniform shark life history from the Early Cretaceous of North America. Recent discoveries have shown that during this time, some lamniformes reached gigantic sizes (greater than 6–8 m in total length) not seen in earlier species. Given the importance of life history to understand how organisms reach such sizes, we conducted an ontogenetic analysis on three very large shark vertebrae, representing a single individual from the Lower Cretaceous (Albian) Duck Creek Formation of Texas. Using three different techniques (computed tomography, histological sectioning, and surface texture analysis), we were able to show that this individual was born at a relatively small size and subsequently grew at rapid rate, achieving a total length of over 6.3 m in approximately 18 years; a rate not observed in any other Cretaceous species. Comparison of the different aging techniques yielded complementary results; however, surface texture analysis produced the most complete ontogenetic record for this specimen. More work is needed to determine broad patterns in the life history evolution of giant Early Cretaceous lamniform sharks.

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