Sirenians

The dugong is a marine mammal belonging to the order of the sirenians and is the only representative of the Dugongidae family. With its split caudal fin, the dugong can surpass 3 metres in length and 400 kilograms. It has a pronounced muzzle with two long incisors that can measure up to 18 centimetres. This herbivore principally feeds on seagrass.

Until the middle of the 20^th century, large herds of dugongs inhabited the coastal waters stretching from East Africa to the islands of the western Pacific Ocean. This is no longer the case today. The species survives but its distribution is fragmented and in decline due to human activity. The dugong is often caught in fishing nets, injured by boats or hunted for its meat. It also suffers from water pollution and the effects of climate change, which lead to the disappearance of seagrass meadows. The latter are both its principal source of food and a vital space for other animals that are essential to the economy of local human populations.

The expedition of the Astrolabe and Zélée

This skull was collected off the eastern coast of Indonesia by surgeon Jacques Hombron (1798-1852) and zoologist Honoré Jacquinot (1815-1887). It comes from the French circumnavigation expedition of the Astrolabe and Zélée, led by Captain Jules Dumont d'Urville (1790-1842). The two corvettes left Toulon in 1837 in the direction of South America, then descended as far as the Antarctic continent. They then headed towards the Pacific Ocean and Oceania. From Tasmania, the captain once again set his sights on Antarctica and in doing so discovered new territories, including Adélie Land, named in honour of his wife Adèle Pépin (1798-1842). After three years of exploring and collecting, the ships sailed back to France.

This skeleton is that of a Steller’s sea cow, an extinct marine mammal belonging to the sirenian order. The specimen on display is 6 metres long, but the largest individuals could reach 8 metres and weigh 10 tonnes. The Steller’s sea cow lived around the western Aleutian Islands, in the cold waters of the Bering Sea. Its considerable mass and thick skin, featuring a 20-plus centimetre layer of fat, allowed it to endure the low temperatures. It principally ate brown seaweeds (kelp). The Steller’s sea cow did not have teeth and instead used keratinous grinding plates to chew its food.

Discovery and extinction

Previously known and hunted by the Aleuts, Steller’s sea cow was discovered by Europeans in 1741 during the last expedition of Captain Vitus Bering (1681-1741). Commissioned to find a passage between Russia and the American continent, Bering’s voyage was abruptly interrupted by bad weather which forced the crew to take refuge on one of the Komandorski Islands. The sailors owed their survival in this hostile environment to the unexpected discovery of a giant animal. Relatively easy to capture, the Steller’s sea cow became their principal source of food. The on-board naturalist, Georg Wilhelm Steller (1709-1746), took the opportunity to study the animal in detail; he is in fact the only scientist to have observed it alive. The existence of Steller’ sea cow was revealed when the sailors returned. From then on, it became a sought-after resource for fur hunters who exploited its meat, blubber, leather and milk to resupply their expeditions. Relentlessly hunted, the species became extinct in 1768, just 27 years after its discovery.

There are three species of manatee living in shallow coastal and river waters: the Caribbean manatee, the West African manatee and the Amazonian manatee. Contrary to the dugong, these streamlined sirenians have a flattened caudal fin. They have large prehensile lips, which allow them to grasp aquatic plants, and long sensory hairs on the head, called vibrissae, that help them perceive their environment. The Caribbean manatee is the largest species, measuring up to 4 meters and weighing a ton.

The skeleton displayed behind the glass case is that of an African manatee. This species is the least well known of the three. It has a wide distribution, from the coastal zones between Mauritania and Angola to humid environments further inland. These animals are capable of swimming up rivers, like the Senegal, navigating through the murky waters of mangrove swamps. They are therefore threatened by the presence of river dams but also by pollution, habitat loss and hunting.

Account of an expedition to the Amazon

The Amazonian manatee skull in the glass case was collected during an expedition in South America led by Francis de Castelnau (1810-1880) between 1843 and 1847. Accompanied by the Museum’s specimen preparator, Émile Deville (1824-1853), Castelnau travelled across the continent studying and collecting numerous animal and plant species. While travelling up the Amazon in Peru, the explorers noticed large numbers of manatees. The local population regularly ate their meat and used the skin for craft works. These findings led Castelnau to reflect upon the potential domestication of the species for farming purposes. He also observed the progressive encroachment of man on the manatee's habitat, a subject still relevant today.