The mugger crocodile (Crocodylus palustris) is a medium-sized broad-snouted crocodile, also known as mugger and marsh crocodile. It is native to freshwater habitats from south-eastern Iran to the Indian subcontinent, where it inhabits marshes, lakes, rivers and artificial ponds. It rarely reaches a body length of and is a powerful swimmer, but also walks on land in search of suitable waterbodies during the hot season. Both young and adult mugger crocodiles dig burrows to which they retreat when the ambient temperature drops below or exceeds . Females dig holes in the sand as nesting sites and lay up to 46 eggs during the dry season. The sex of hatchlings depends on temperature during incubation. Both parents protect the young for up to one year. They feed on insects, and adults prey on fish, reptiles, birds and mammals.
The mugger crocodile evolved at least and has been a symbol for the fructifying and destructive powers of the rivers since the Vedic period. It was first scientifically described in 1831 and is protected by law in Iran, India and Sri Lanka. Since 1982, it has been listed as Vulnerable on the IUCN Red List. Outside protected areas, it is threatened by conversion of natural habitats, gets entangled in fishing nets and is killed in human–wildlife conflict situations and in traffic accidents.
Taxonomy Crocodilus palustris was the scientific name proposed by René Lesson in 1831 who scientifically described the type specimen from the Gangetic plains. In subsequent years, several naturalists and curators of natural history museums described zoological specimens and proposed different names, including: C. bombifrons by John Edward Gray in 1844 for a specimen sent by the Museum of the Royal Asiatic Society of Bengal to the British Museum of Natural History. C. trigonops also by Gray in 1844 for a young mugger specimen from India.
Evolution Phylogenetic analysis of 23 crocodilian species indicated that the genus Crocodylus most likely originated in Australasia about . The freshwater crocodile (C. johnstoni) is thought to have been the first species that genetically diverged from the common ancestor of the genus about . The sister group comprising saltwater crocodile (C. porosus), Siamese crocodile (C. siamensis) and mugger crocodile diverged about . The latter diverged from this group about . A paleogenomics analysis indicated that Crocodylus likely originated in Africa and radiated towards Southeast Asia and the Americas, diverging from its closest recent relative, the extinct Voay of Madagascar, around near the Oligocene/Miocene boundary. Within Crocodylus, the mugger crocodile's closest living relatives are the Siamese crocodile and the saltwater crocodile.
Fossil crocodile specimens excavated in the Sivalik Hills closely resemble the mugger crocodile in the shortness of the premaxillae and in the form of the nasal openings. In Andhra Pradesh's Prakasam district, a long fossilized skull of a mugger crocodile was found in a volcanic ash bed that probably dates to the late Pleistocene. Crocodylus palaeindicus from late Pliocene sediments in the Sivalik Hills is thought to be an ancestor of the mugger crocodile. Fossil remains of C. palaeindicus were also excavated in the vicinity of Bagan in central Myanmar.
Below cladogram is from a tip dating study, for which morphological, molecular DNA sequencing and stratigraphic fossil age data were simultaneously used to establish the inter-relationships within Crocodylidae. This cladogram was revised in a paleogenomics study.
Characteristics
Mugger crocodile hatchlings are pale olive with black spots. Adults are dark olive to grey or brown. The head is rough without any ridges and large scutes around the neck that is well separated from the back; the scutes usually form four, rarely six longitudinal series and 16 or 17 transverse series. The limbs have keeled scales with serrated fringes on the outer edges, and outer toes are extensively webbed. The snout is slightly longer than broad with 19 upper teeth on each side. The symphysis of the lower jaw extends to the level of the fourth or fifth tooth. The premaxillary suture on the palate is nearly straight or curved forwards, and the nasal bones separate the premaxilla above.
The mugger crocodile is considered a medium-sized crocodilian, but has the broadest snout among living crocodiles. It has a powerful tail and webbed feet. Its visual, hearing and smelling senses are acute. Adult female muggers are on average; males usually measure , but rarely reach a length of . The two largest known muggers measured and were killed in Sri Lanka. One male mugger caught in Pakistan of about weighed .
One individual weighing had a bite force of .
Distribution and habitat
The mugger crocodile occurs in southern Iran, Pakistan, Nepal, India and Sri Lanka up to an elevation of . It inhabits freshwater lakes, rivers and marshes, prefers slow-moving, shallow water bodies, and also thrives in artificial reservoirs and irrigation canals.
In Iran, the mugger occurs along rivers in Sistan and Baluchestan Province along the Iran–Pakistan border. A population of around 200 mugger crocodiles lives on the Iranian Makran coast near Chabahar. Due to human activity and a long drought in the late 1990s and early 2000s, it had been pushed to the brink of extinction. Following several tropical cyclones in 2007 and 2010, much of the habitat of the mugger crocodiles has been restored as formerly dry lakes and hamuns were flooded again.
In Pakistan, a small population lives in 21 ponds around Dasht River; in the winter of 2007–08, 99 individuals were counted. By 2017, the population had declined to 25 individuals. In Sindh Province, small mugger populations occur in wetlands of Deh Akro-2 and Nara Desert Wildlife Sanctuary, near Chotiari Dam, in the Nara Canal and around Haleji lake.
In Nepal's Terai, it occurs in the wetlands of Shuklaphanta and Bardia National Parks, Ghodaghodi Tal, Chitwan National Park and Koshi Tappu Wildlife Reserve. In the Rapti River, it was mostly observed basking on sandy banks with slopes of 15–25°.
In India, it occurs in: Rajasthan along the Chambal, Ken and Son Rivers, and in Ranthambore National Park Gujarat along the Vishwamitri River and several reservoirs and lakes in Kutch Madhya Pradesh's National Chambal Sanctuary Uttarakhand's Rajaji National Park, Corbett Tiger Reserve and Lansdowne Forest Division Uttar Pradesh's Katarniaghat and Kishanpur Wildlife Sanctuaries Odisha's Simlipal National Park and along Mahanadi and Sabari Rivers In 2019, 82 individuals were recorded in the river systems of Simlipal National Park. Telangana's Manjira Wildlife Sanctuary Maharashtra's Kadavi and Warna Rivers, and Savitri River in Raigad District. Goa's Salaulim Reservoir, Zuari River and in small lakes Karnataka along Kaveri and Kabini Rivers, in Ranganthittu Bird Sanctuary, Nagarhole National Park and Tungabhadra Reservoir Kerala's Parambikulam Reservoir and Neyyar Wildlife Sanctuary Tamil Nadu's Amaravathi Reservoir, Moyar and Kaveri rivers.
In Sri Lanka, it occurs in Wilpattu, Yala and Bundala National Parks. Between 1991 and 1996, it was recorded in another 102 localities.
In Bangladesh, it was historically present in the northern parts of the Sundarbans, where four to five captive individuals survived in an artificial pond by the 1980s. It is possibly locally extinct in the country. In Bhutan, it became extinct in the late 1960s, but a few captive-bred individuals were released in the Manas River in the late 1990s. It is considered locally extinct in Myanmar.
Behaviour and ecology
The mugger crocodile is a powerful swimmer that uses its tail and hind feet to move forward, change direction and submerge. It belly-walks, with its belly touching ground, at the bottom of waterbodies and on land. During the hot dry season, it walks over land at night to find suitable wetlands and spends most of the day submerged in water. During the cold season it basks on riverbanks, individuals are tolerant of others during this period. Territorial behaviour increases during the mating season.
Like all crocodilians, the mugger crocodile is a thermoconformer and has an optimal body temperature of and risks dying of freezing or hyperthermia when exposed to temperatures below or above , respectively. It digs burrows to retreat from extreme temperatures and other harsh climatic conditions. Burrows are between deep, with entrances above the water level and a chamber at the end that is big enough to allow the mugger to turn around. Temperatures inside remains constant at , depending on region.
Hunting and diet The mugger crocodile preys on fish, snakes, turtles, birds and mammals including monkeys, squirrels, rodents, otters and dogs. It also scavenges on dead animals. During dry seasons, muggers walk many kilometers over land in search of water and prey. Hatchlings feed mainly on insects such as beetles, but also on crabs and shrimp and on vertebrates later on. It seizes and drags potential prey approaching watersides into the water, when the opportunity arises. Adult muggers were observed feeding on a flapshell turtle and a tortoise. Subadult and adult muggers favour fish, but also prey on small to medium-sized ungulates up to the size of chital (Axis axis). At the Chambal River, muggers have attacked water buffaloes, cattle and goats. In Bardia National Park, a mugger was observed caching a chital kill beneath the roots of a tree and returning to its basking site; a part of the deer was still wedged among the roots on the next day. In the same national park, a mugger caught a brown fish owl (Ketupa zeylonensis); several instances of water bird feathers in mugger dung have been reported. Muggers have also been observed preying and feeding on pythons. In Yala National Park, a mugger killed a large Indian pangolin (Manis crassicaudata) and devoured pieces over several hours.
Tool use Mugger crocodiles have been documented using lures to hunt birds. This means they are among the first reptiles recorded to use tools. By balancing sticks and branches on their heads, they lure birds that are looking for nesting material. This strategy is particularly effective during the nesting season.
Reproduction Female muggers obtain sexual maturity at a body length of around at the age of about 6.5 years, and males at around body length. The reproduction cycle starts earliest in November at the onset of the cold season with courtship and mating. Between February and June, females dig deep holes for nesting between away from the waterside. They lay up to two clutches with 8 –46 eggs each. Eggs weigh on average. Laying of one clutch usually takes less than half an hour. Thereafter, females scrape sand over the nest to close it. Males have been observed to assist females in digging and protecting nest sites. Hatching season is two months later, between April and June in south India, and in Sri Lanka between August and September. Then females excavate the young, pick them up in their snouts and take them to the water. Both females and males protect the young for up to one year.
Healthy hatchlings develop at a temperature range of . Sex ratio of hatched eggs depends on incubation temperature and exposure of nests to sunshine. Only females develop at constant temperatures of , and only males at . Percentage of females in a clutch decreases at constant temperatures between , and of males between . Temperature in natural nests is not constant but varies between nights and days. Foremost females hatch in natural early nests when initial temperature inside nests ranges between . The percentage of male hatchlings increases in late nests located in sunny sites. Hatchlings are long and weigh on average when one month old. They grow about per month and reach a body length of when two years old.
Sympatric predators