The Siamese crocodile (Crocodylus siamensis) is a medium-sized freshwater crocodile native to Indonesia (Borneo and possibly Java), Brunei, East Malaysia, Laos, Cambodia, Myanmar, Thailand and Vietnam. The species is critically endangered and already extirpated from many regions. Its other common names include Siamese freshwater crocodile, Singapore small-grain, and soft-belly.
Phylogeny
Below is a cladogram based on a 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data, as revised by the 2021 Hekkala et al. paleogenomics study using DNA extracted from the extinct Voay.
Characteristics
The Siamese crocodile is a medium-sized, freshwater crocodilian, with a relatively broad, smooth snout and an elevated, bony crest behind each eye. Overall, it is olive-green, with some variation to dark-green. Young individuals measure and weigh , growing to a length of and a weight of as an adult. Three individuals measuring and weighing had bite force of . Large male individuals reach and in weight.
Distribution and habitat
Siamese crocodiles occur in a wide range of freshwater habitats, including slow-moving rivers and streams, lakes, seasonal oxbow lakes, marshes and swamps.
Behaviour and ecology
Despite conservation concerns, many aspects of C. siamensis life history in the wild remain unknown, particularly regarding its reproductive biology.
Adults feed mainly on fish and snakes, but also eat amphibians and small mammals.
Very little is known about the natural history of this species in the wild, but females build mound-nests constructed from scraped-up plant debris mixed with mud. In captivity, these crocodiles breed during the wet season (April to May), laying between 15 and 50 eggs, which are then guarded until they hatch. After incubation, the female will assist her young as they break out of their eggs and then carry the hatchlings to the water in her jaws.
Pure, unhybridised examples of this species are generally unaggressive towards humans, and there are only four confirmed attacks, none of them fatal. One was defending its young, another was probably defending itself, one was provoked, and the reason for the last is unclear. A fifth attack in 1928 that was probably done by a Siamese crocodile was fatal, with the victim being a child.
Threats
Siamese crocodiles are under threat from human disturbance and habitat occupation, which is forcing remaining populations to the edges of their former range. Extinct from 99% of its original range, the Siamese crocodile is considered one of the least studied and most critically endangered crocodilians in the world. Although few wild populations remain, more than 700,000 C. Siamese are held on commercial crocodile farms in Southeast Asia.
In 1992, it was believed to be extremely close to or fully extinct in the wild until 2000 when scientists from Fauna and Flora International and the Government of Cambodia's Forestry Administration confirmed the presence of Siamese crocodiles in the Cardamom Mountains in Southwest Cambodia. Since then, surveys have identified around 30 sites in Cambodia that contain wild Siamese crocodiles (conservatively estimated to number between 200 and 400 individuals in total), a tiny population in Thailand (possibly as few as two individuals, discounting recent reintroductions), a small population in Vietnam (possibly fewer than 100 individuals), Cat Tien National Park has about 200, and a more sizeable population in Laos. In March 2005, conservationists found a nest containing juvenile Siamese crocodiles in the southern Lao province of Savannakhet. There are no recent records from Malaysia, Burma or Brunei. A small but important population of the crocodiles is also known to live in East Kalimantan, Indonesia.
Habitat degradation
Factors causing loss of habitat include: conversion of wetlands for agriculture, chemical fertilisers use, use of pesticides in rice production, and an increase in the population of cattle. The effects of warfare stemming from the conflicts in Vietnam, Laos, and Cambodia during the Vietnam War (from land mines to aerial bombardment) have also been factored.