The sprawling waters of Londolozi are home to some of the most ancient and formidable creatures on earth – crocodiles. The dry season provides many great opportunities for guests to marvel at sightings of some particularly large crocodiles basking on riverbanks and gliding through the waters. Their size and prehistoric appearance often lead to two common questions:

 “How old is that crocodile?”

and “Are they related to dinosaurs?”

Crocodiles share a heritage with dinosaurs as part of a group known as archosaurs or “ruling reptiles”, who date back to the Early Triassic period. They have since evolved into 23 different species in three distinct families: crocodiles, alligators or caimans and gharials.

These questions highlight the timeless fascination with these predators. Prehistoric crocodiles, known as archosaurs, originated over 250 million years ago, while the crocodilians we know evolved around 95 million years ago. So despite their resemblance to dinosaurs, they are not directly related but share an ancient family member. This ancestral link and their impressive size, longevity, and resilience make them fascinating, not just for their fearsome appearance but also for their unique biological traits, including their ability to resist ageing, a phenomenon known as negligible senescence.

This crocodile’s sheer size and majestic presence show he is well into the later years of his life. Likely 50-60 years if not older.

Understanding Negligible Senescence in Crocodiles

Before exploring the methods of ageing crocodiles, it’s important to understand the concept of negligible senescence. Unlike most animals, which show clear signs of ageing like declining reproductive capacity, increasing mortality rate, and loss of physiological functions, some species exhibit negligible senescence. Crocodiles are prime examples, maintaining robust health and reproductive capability well into old age. This rare trait makes them a subject of great interest in ageing and longevity studies.

Patiently awaiting any unsuspecting prey to wash down into its jaws.

How to Age a Crocodile

Determining the age of a crocodile is no simple task, given their slow and steady growth throughout their lives. For starters, we know that they can live for an average of 70-100 years in the wild. However, there are a few methods researchers use to estimate their age:

• Size and Growth Rings: Similar to trees, crocodiles have growth rings in their bones and teeth. By examining these rings under a microscope, scientists can estimate the age of a crocodile. This method involves taking a small sample from a bone or tooth and counting the growth rings, each of which typically represents one year of life.

Since we won’t be taking any teeth or bone samples while out on a game drive, the next best option is:

• Size Measurement: Although not as precise as growth ring analysis, measuring the length and weight of a crocodile can provide a rough estimate of its age. Crocodiles grow rapidly during their early years, about 30cm (1ft) per year and then more slowly as they age. By comparing the size of a crocodile to known growth charts, researchers can approximate its age. Here are some general size references for the Nile crocodile seen here at Londolozi:
  • Hatchlings: Approximately 25-30cm (10-12 inches)
  • Juveniles (1-3 years): Around 1-1.5m (3.3-5 ft)
  • Sub-adults (4-7 years): About 2-3m (6.5-10ft)
  • Adults (8+ years): Males can reach lengths of 4-5.5m (13-18ft), while females are typically smaller, averaging 3-3.5m (10-11.5ft)

As a grey heron flies over this crocodile, it acts as a good size reference. Grey herons stand up to 1m (40in) and have a wingspan of 155-195cm (61-77in), while I would say this crocodile is roughly 2.5-3m in length, suggesting it is in the early stages of adulthood.

How to Identify the Gender of Crocodiles

While I was diving into the ageing topic, I thought it would be worth looking at a few tips on how to sex a crocodile as a physical examination is certainly not an option.

• Size and Shape: Generally, male crocodiles are larger and more robust than females, especially in their head and body shape. Males tend to have broader heads and thicker necks compared to the more slender and streamlined females. However, size alone is not a definitive indicator, especially in younger crocodiles.
• Behavioural Observation: During the breeding season, which typically occurs in late spring to early summer, males exhibit distinct behaviours such as bellowing, head-slapping, and territorial displays to attract females. Observing these behaviours can provide clues about the sex of the crocodiles in a given area. Males are often more aggressive and active during this time, making it easier to distinguish them from females.

An epic display as this crocodile thrashes an Egyptian goose around – is it just a meal or part of a mating display?

While figuring out the exact age of a crocodile can be intriguing, many guests find them captivating because of their link to dinosaurs and their impressive longevity. Next time you pass by one of these ruling reptiles, even if you aren’t sure exactly how old it is, you can marvel at their connection to the prehistoric world.