Long bone histology of a eusuchian crocodyliform from the Upper Cretaceous of Spain: Implications for growth strategy in extinct crocodiles

- A Late Cretaceous crocodylian long bone has been sampled for histological study.
- The bone shows changes in bone tissue organization clearly related to changes in growth rate during ontogeny.
- Bone tissue types found indicate a determinate growth strategy.
- It is confirmed that modern crocodylian growth strategy was already in place by the Cretaceous.

The long bone histology of a Late Cretaceous eusuchian crocodyliform from the Iberian Peninsula reveals clear variations in the cortical structure which reflects changes in the speed of bone deposition (i.e., skeletal growth) related to ontogeny. The presence of secondary woven-fibred bone tissue in the perimedullar region of the cortex, and the existence of an external fundamental system in the most external periostic cortex, which is a proxy for somatic maturity and effective cessation of growth, challenges the former idea that the growth strategy of extinct crocodylians fit in the typical ectotherm condition, according to which these animals grew slowly during life under an indeterminate growth strategy. The analysed specimen lived for a minimum of 16 years and the highest preserved apposition rates took place in an advanced ontogenetic stage. The study suggests that the general aspects of the modern crocodylian growth strategy were already in place in some lineages by the Cretaceous.