Large size is also favoured in males because larger males tend to be more successful at reproducing, both because of their size advantage in endurance rivalry and their advantage in sperm competition because larger males are able to produce more sperm. Large size in females leads to higher fecundity and larger offspring as a result male mate choice favours larger females. This size difference has several benefits for both sexes. murinus) have one of the most extreme size differences, where females average roughly 32 kg (70 lb) and males average only around 7 kg (15 lb). Females are larger than males in most snakes, and green anacondas ( E. Sexual size dimorphism in Eunectes is the opposite of most other vertebrates. beniensis are much less common, making the specific details of their mating systems less well understood. murinus) is the most well-studied species of Eunectes in terms of their mating system, followed by the yellow anaconda ( E. The mating seasons in Eunectes varies both between species and within species depending on locality, although the trend appears to be the dry season. This species is extinct its fossils have been found in the La Venta fauna ( Miocene) in Colombia. South America in the Departments of Beni and Pando in Bolivia Rivas and his team working in the Venezuelan llanos. Most of our knowledge comes from the work of Dr. Local communities and some European explorers have given accounts of giant anacondas, legendary snakes of much greater proportion than any confirmed specimen.Īlthough charismatic, there is little known on the biology of wild anacondas. Nevertheless, threat from anacondas is a familiar trope in comics, movies and adventure stories set in the Amazon jungle. While encounters between people and anacondas may be dangerous, they do not regularly hunt humans. Videos exist of anacondas preying on domestic animals such as goats and sometimes even jaguars that venture too close to the water. Feeding Īll four species are aquatic snakes that prey on other aquatic animals, including fish, river fowl, and caiman. The name Eunectes is derived from Ancient Greek: εὐνήκτης, romanized: eunēktēs, lit.'good swimmer'.įound in tropical South America from Ecuador, Brazil, Colombia and Venezuela south to Argentina. Fossils of recent ancestors are not known, so the living species ‘pull’ the historical range of the genus to the present. The fossil record of the this group is effected by an artifact called the Pull of the Recent. The recent fossil record of Eunectes is relatively sparse compared to other vertebrates and other genera of snakes. They are a semiaquatic group of snakes and include one of the largest snakes in the world, E. Eunectes is a genus of boas found in tropical South America commonly called anacondas.
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