Apex predators in many of the world’s most complex freshwater systems, crocodiles are some of the largest, semi-aquatic reptiles. They belong to the Crocodylidae family under the order Crocodilia, which includes ancestors that first appeared as far back as 100 million years ago. Given their seemingly conserved morphology, they are known as living fossils. Nonetheless, herpetologists would be quick to remind us that these dinosaur-like reptiles have complex evolutionary backgrounds.
Crocodiles are often confused with alligators and caimans, which likewise belong to the order Crocodilia but are grouped under the Alligatoridae family. Compared to their scaley and similarly ferocious relatives, crocodiles have a more V-shaped snout. When their massive mouths are closed, their sharp teeth remain visible as they fall into exterior depressions around the upper jaw. Moreover, crocodiles have distinctly webbed toes on their hind feet.
Aggressive, carnivorous, and stealthy, crocodiles feed on a wide range of vertebrates in swamps, rivers, and many wetland habitats. Some freshwater species are able to venture into estuarine or coastal areas as they are equipped with specialized salt glands. Most of today’s extant species are restricted to tropical areas, where they can comfortably hunt and rest in warm waters. While some are critically endangered, others are productive enough to become invasive species.
1) Nile crocodile (Crocodylus niloticus)
The largest freshwater crocodile in Africa, C. niloticus is present in a wide range of habitats throughout more than 20 of the continent’s tropical countries. This enormous reptile, which can grow to a maximum size of about 16 feet (5 meters), can weigh as much as 1,650 pounds (748 kg). True behemoths that far exceed these measurements have been recorded in lakes, river systems, marshes, and murky swamps. It is unsafe for humans to swim in the freshwater systems they occupy.
A social reptile, the Nile crocodile is often found close to more of its kind. They may collectively bask in brightly lit shorelines, especially those close to productive parts of rivers or along zones where terrestrial mammals may gather for a drink. With jaws that are equipped with as many as 68 pointy teeth, this agile swimmer kills its prey items by tightly gripping their flesh. It can overpower larger animals by thrashing forcefully and pulling them into water.
2) Australian freshwater crocodile (Crocodylus johnstoni)
Unlike the aggressive Nile crocodile, the Australian freshwater crocodile is not known for being a man-eater. Relatively small for a full-fledged crocodilian, its largest males rarely measure more than 10 feet (3 meters) long. With a mature weight averaging around 150 pounds (68 kg) for males and 88 pounds (40 kg) for females, this freshwater reptile is quite slender. Typically, its adult specimens are light brown and have thick, dark bands running across their back and tail.
C. johnstoni is found in billabongs (i.e. oxbow lakes), creeks, river systems, and other freshwater wetlands. They remain in these habitats even through dry periods. As they have small mouths, insects tend to make up the highest percentage of their prey items. They also feed on wetland birds, fishes, snakes, frogs, and small mammals. Though they have teeth, they prefer to swallow their prey whole. Their stomach’s gizzard and digestive enzymes are responsible for grinding up and thoroughly breaking down food.
3) Orinoco crocodile (Crocodylus intermedius)
Found only in the Orinoco River Basin, C. intermedius is now a critically endangered crocodile. It is estimated that there are less than 1,500 individuals left. In an effort to aid in their recovery, captive-breeding programs have intentionally bred them and released hatchlings in a handful of Venezuela’s national parks. Unfortunately, though some of these programs continue to be operational, they are affected by poor funding and local conflicts.
One of the largest predators of South America, the Orinoco crocodile looks quite similar to the brackish American crocodile (C. acutus). Males, which seem to be able to grow in size throughout their entire lifespan, may attain lengths of 13 – 16 feet (4 – 5 meters). Females, on the other hand, tend to max out at just less than 11 feet (3.4 feet) long. Unfortunately, due to having been hunted for skins throughout much of the last century, larger specimens are now exceedingly rare.
4) Mugger crocodile (Crocodylus palustris)
The mugger or marsh crocodile is a freshwater reptile that inhabits slow-moving lakes, rivers, shallow marshes, canals, and reservoirs. With populations that were once declared near-extinct due to prolonged droughts throughout their native range, many clusters have recovered as their dry habitats became flooded once more. Protected under India’s Wildlife Protection Act and listed as Vulnerable on the IUCN’s Red List, this species is highly sensitive to both climatic and anthropogenic disturbances.
Symbolic of both the power and mystery of South Asia’s river systems, the mugger crocodile is an apex predator wherever it is found. A mighty foe, even for terrestrial beasts, it may occasionally compete with Bengal tigers for prey. Medium-sized yet powerful for a crocodile, it grows to a full length of about 9 – 12 feet (2.7 – 3.7 meters). Its heftiest males boast a weight of about 1,000 pounds (454 kg)!
5) Cuban crocodile (Crocodylus rhombifer)
Among freshwater crocodiles, the Cuban crocodile is unique due to its tendency to remain in terrestrial environments for relatively long periods of time. It is also extremely territorial despite its small size as a crocodile. Its adults grow to an average maximum length of about 7.5 feet (2.3 meters), though they do have the potential to measure as much as 475 pounds (215 kg) in protected areas with abundant prey. Interestingly, they show a level of intelligence that rivals those of animals known to hunt in packs.
Critically endangered, wild Cuban crocodiles are now restricted to limited ranges within Isla de la Juventud and the Zapata Swamp. Once found in freshwater systems throughout the Caribbean, it is unfortunately heavily hunted by humans. Additionally, due to its propensity to resort to cannibalism for food, many young specimens cannot reach adulthood.
6) Philippine crocodile (Crocodylus mindorensis)
Yet another critically endangered crocodile, the Philippine crocodile has been heavily victimized by destructive fishing techniques. This freshwater reptile is fairly small compared to its close relatives. Nowadays, it’s near-impossible to find males measuring more than 8 feet (2.4 meters) long. Specimens weighing more than 200 pounds (91 kg) are considered exceptional.
Golden-brown and increasingly dark with age, Philippine crocodiles expertly blend in with the murky waters of their wild habitats. Though this species was once an apex predator in wetlands dotting the entirety of the Philippine archipelago, its remaining populations are now concentrated in northern Luzon and central Mindanao. Habitat destruction has severely diminished its numbers. Once important as predators that both balanced local fish populations and produced nutrient-rich waste, they are valued by indigenous communities.
7) West African crocodile (Crocodylus suchus)
As the West African crocodile shares a portion of its natural range with the Nile crocodile, both species may be confused with one another. The former is less aggressive than the latter and is typically smaller in terms of average length and weight. Males of this species range from 6.5 – 10 feet (2 – 3 meters) long in the wild. They have distinctly stout muzzles and may be brown to olive green. Their juveniles have black bands along the length of their tails.
Also called the desert crocodile due to its capacity to survive in dry conditions, C. suchus is able to enter a dormant period (i.e. aestivation). In the Sahara and Sahel desert regions, it remains in cool caves or burrows through the hottest months. Once rainfall is abundant enough to create seasonal pockets of water, known as “gueltas”, they exit their caves. Outside of these desert regions, this croc remains in lagoons and forested wetlands.
8) Morelet’s crocodile (Crocodylus moreletii)
Morelet’s crocodile, also commonly referred to as the Belize crocodile, is typically found in lagoons, marshes, ponds, lakes, and rivers throughout its native range. It may occasionally venture into coastal areas or estuaries in search of prey or more reliably productive habitats. Once readily confused with the American crocodile due to their many shared characteristics and overlapping range, Morelet’s crocodile has been deemed to be generally darker and smaller.
Morphologically, this species has evolved to move more efficiently in water than on land. Its four short legs, coupled with its lengthy tail and webbed hind feet, allow it to deftly maneuver through isolated and heavily forested freshwater systems. To keep cool during seasonal dry periods, they may dig out burrows. When floods occur, their distribution naturally expands as they can easily move from one water feature to another.
9) New Guinea crocodile (Crocodylus novaeguineae)
Found in the swamps, freshwater lakes, and shallow marshes of the northern region of New Guinea, C. novaeguineae is a nocturnal and principally aquatic reptile. Throughout most of the day, it remains submerged with just its nostrils and eyes situated above the water’s surface. At night, it energetically explores its habitat for prey. The size of its prey increases relative to the size of its own body. While juveniles stick to smaller fish, insects, tadpoles, and spiders, adults may feed on small mammals, larger fish, and various amphibians.
New Guinea crocodiles are known for actively communicating with one another, even as juveniles. They yelp, grunt, growl, and roar to signal a wide range of warnings. Evidently intelligent as reptiles, they are seemingly protective of their young. Once heavily hunted for their hide, their wild populations are now kept in check by conservation measures.
10) Hall’s New Guinea crocodile (Crocodylus halli)
Once grouped with C. novaeguineae under a single taxon, C. halli is now considered a wholly separate species. Endemic to the southern region of the island of New Guinea, its populations are geographically isolated from the crocodiles in northern freshwater systems. The island’s central highlands likely caused these two species to separate from one another and eventually develop major differences in their genetic code.
One of the key behavioral differences between the two species is their nesting period. While Hall’s New Guinea crocodile prefers to nest in November – April, which is during the wet season, C. novaeguineae nests during the dry season. Though seemingly minor, this simple variation in reproductive strategies can effectively prevent both species from re-converging.
11) Siamese crocodile (Crocodylus siamensis)
Extensive populations of the Siamese crocodile have now been extirpated from much of their natural range. This critically endangered species unfortunately continues to be elusive. Little is known about its reproductive biology and its general life history. Data on its breeding behavior has largely been obtained by observing captive specimens. In the wild, it is estimated to have just 500 – 1,000 mature individuals left.
A medium-sized, freshwater reptile, the Siamese crocodile grows to a full length of about 9.8 feet (3 meters). It is typically found in oxbow lakes, swamps, marshes, and slow-moving rivers and streams. Its adults subsist on a varied diet of fish, small mammals, amphibians, and snakes. Its habitats are now severely threatened by anthropogenic disturbances. The construction of dams, for example, has resulted in major losses of natural water features.
12) Dwarf crocodile (Osteolaemus tetraspis)
The smallest living crocodilian, the dwarf crocodile grows to an average length of just 1.5 meters (4.9 feet). Its adults have dark-colored backs and tails, but their undersides are distinctly yellowish and speckled. Its juveniles may have lighter crosswise bands running the length of their backs and tails. Its cave-dwelling conspecifics may possess bright orange patches due to exposure to guano.
Dwarf crocodiles are found in swamps, small rivers, pools, streams, and patches of mangroves in estuaries. They usually avoid the larger and more exposed sections of rivers, where they may need to expend more energy to swim against currents or search for prey. As a generalist and nocturnal predator, it forages for small fish, bats, lizards, crabs, frogs, and shrews close to the shoreline.
13) Osborn’s dwarf crocodile (Osteolaemus osborni)
Once grouped with O. tetraspis as a single taxon, recent anatomical and genetic research has revealed that O. osborni is distinct enough to be its own species. Endemic to the Democratic Republic of Congo, its populations are likely restricted to the Congo Basin and possibly its tributaries. Little is known about the ecology and life history of this species other than that it favors closed-canopy environments and prefers to feed at night.
14) West African slender-snouted crocodile (Mecistops cataphractus)
The West African slender-snouted crocodile favors heavily forested bodies of freshwater in regions that are distantly located from any human settlements. It favors pristine waters with minimal input from any anthropogenic sources. A poorly known species, it has unfortunately been deemed to be critically endangered. Its illegal consumption as an exotic bush meat, coupled with the fragmentation of its wild habitat, has led to its widespread extirpation.
As suggested by its common name, M. cataphractus is distinguished by a narrow snout. This helps it feed on small fish, crabs, and other aquatic invertebrates. Its males can grow to quite a hefty size if they are left to thrive in undisturbed areas. Typically measuring 10 – 13 feet (3 – 4 meters) long, they can out-measure the large males of other massive species.
Is the American Crocodile (Crocodylus acutus) a Freshwater Species?
Though the American crocodile is found in freshwater environments, it mainly occupies brackish or saltwater environments. Its presence in inland areas may be facilitated by the existence of lengthy canal systems or by the connectivity of freshwater swamps with estuaries. Some of its well-established populations can be found in islets and cays with no access to freshwater.
A principal component of the Everglades’ megafauna, the American crocodile may rely on south-flowing freshwater to create a comfortable environment for its juveniles. Once these have matured, they are likely to explore biologically active, brackish-water habitats. Here, they may feed on coastal birds, the juveniles of many marine fish, and a high diversity of aquatic and marine invertebrates.
