Worth a Thousand Words

Large sharks don’t have much to worry about as far as being a target for predators – they are top predators themselves. But their young are still small and thus potentially vulnerable. This is why sharks protect their young by hatching them in nurseries where there is plenty of food and shelter and where perhaps large adults can protect the youngsters until they are big anough to safely fend for themselves.

Megalodon is the biggest shark that ever lived (and I have a special attachment to it) but we did not know – that is, until yesterday’s article in PLoS ONE – that they also used the same strategy to protect their young. In the article Ancient Nursery Area for the Extinct Giant Shark Megalodon from the Miocene of Panama, Catalina Pimiento, Dana J. Ehret, Bruce J. MacFadden and Gordon Hubbell report their finding of a Megalodon nursery. How did they figure out that the teeth really belonged to the young, small individuals and were not just small front teeth of large adults? Fortunately, the smaller front teeth and the larger back teeth also differ in shape and sharpness. Thus, it is possible to figure out if the tooth was front or back, and thus if it belonged to a small or large individual. The differences are stark:

From the Abstract:

Background

As we know from modern species, nursery areas are essential shark habitats for vulnerable young. Nurseries are typically highly productive, shallow-water habitats that are characterized by the presence of juveniles and neonates. It has been suggested that in these areas, sharks can find ample food resources and protection from predators. Based on the fossil record, we know that the extinct Carcharocles megalodon was the biggest shark that ever lived. Previous proposed paleo-nursery areas for this species were based on the anecdotal presence of juvenile fossil teeth accompanied by fossil marine mammals. We now present the first definitive evidence of ancient nurseries for C. megalodon from the late Miocene of Panama, about 10 million years ago.

Methodology/Principal Findings

We collected and measured fossil shark teeth of C. megalodon, within the highly productive, shallow marine Gatun Formation from the Miocene of Panama. Surprisingly, and in contrast to other fossil accumulations, the majority of the teeth from Gatun are very small. Here we compare the tooth sizes from the Gatun with specimens from different, but analogous localities. In addition we calculate the total length of the individuals found in Gatun. These comparisons and estimates suggest that the small size of Gatun’s C. megalodon is neither related to a small population of this species nor the tooth position within the jaw. Thus, the individuals from Gatun were mostly juveniles and neonates, with estimated body lengths between 2 and 10.5 meters.

Conclusions/Significance

We propose that the Miocene Gatun Formation represents the first documented paleo-nursery area for C. megalodon from the Neotropics, and one of the few recorded in the fossil record for an extinct selachian. We therefore show that sharks have used nursery areas at least for 10 millions of years as an adaptive strategy during their life histories.

A couple of good discussions of the paper can be found on Laelaps and Discovery News.