Abstract
Trophic position is a fundamental characteristic of animals, yet it is unknown in many extinct species. In this study, we ground-truth the
15
N/
14
N ratio of enameloid-bound organic matter (δ
15
N
EB
) as a trophic level proxy by comparison to dentin collagen δ
15
N and apply this method to the fossil record to reconstruct the trophic level of the megatooth sharks (genus
Otodus
). These sharks evolved in the Cenozoic, culminating in
Otodus megalodon
, a shark with a maximum body size of more than 15 m, which went extinct 3.5 million years ago. Very high δ
15
N
EB
values (22.9 ± 4.4‰) of
O. megalodon
from the Miocene and Pliocene show that it occupied a higher trophic level than is known for any marine species, extinct or extant. δ
15
N
EB
also indicates a dietary shift in sharks of the megatooth lineage as they evolved toward the gigantic
O. megalodon
, with the highest trophic level apparently reached earlier than peak size.
Nitrogen isotope ratios in fossil teeth place extinct megatooth sharks at the top of the marine food web.
