The birth of a large group of modern animals: the proboscideans

Phosphatherium, Moeritherium and Phiomia form an exceptional ancient evolutionary series of a single modern order of mammals. The series illustrates the very beginning of the proboscideans (the order of the elephants) at the dawn of the Cenozoic, between 55 and 33 million years ago, in the African cradle. Such evolutionary fossil series, bearing witness to the origin and evolution of major lineages, are rarely found in modern mammals.

Phosphatherium, Moeritherium and Phiomia succeed each other chronologically and show a progressive evolution in the morphology and size of the proboscideans from an extraordinarily primitive stage. The most emblematic characteristics of elephants such as their gigantic size, trunk and tusks are still absent, or barely developed, in Phosphatherium, the oldest of the three. 

The typical proboscidean characters evolved very gradually in Phosphatherium, Moeritherium and then Phiomia: we observe an increase in the size of the body and tusks and recession of the nasal cavities linked to the development of the trunk in Phiomia. In Phosphatherium, the incisors are just beginning to enlarge, the molars have two long crests (bilophodonty) and the orbit is open within the maxillary bone like in modern elephants. 

These very first proboscideans are amongst the most striking fossil evidence for Darwin’s theory of evolution and descent with modification. The three extant species of elephant are just the relics of the very rich and long evolutionary history of a group that spans 60 million years and encompasses almost 200 known fossil species across five continents.

Phosphatherium escuilliei
Gheerbrant, Sudre et Cappetta, 1996
MNHN.F.MOC213
Mammalia, Proboscidea, Phosphatheriidae
Early Eocene, 55 million years ago
Ouled Abdoun phosphate basin, Morocco

Reconstruction of a skull and mandible from a deformed skull discovered in Morocco in 2001. The species Phosphatherium escuilliei was discovered in 1996 in Morocco by French palaeontologists. It is the oldest and most primitive of the known proboscideans along with Eritherium, found more recently in 2009 within the oldest layers (60 million years old) of the same fossiliferous sites. This ancestral proboscidean was the size of a fox.

Cast from the original by D. Visset, MNHN.

Moeritherium lyonsi
Andrews, 1901
MNHN.F.LBE
Mammalia, Proboscidea, Moeritheriidae
Late Eocene, 35 million years ago
Faiyum, Egypt

Reconstruction of a skull and mandible. Discovered at the beginning of the 20th century, Moeritherium was for a long time the oldest known proboscidean, before the discovery of Numidotherium in 1984 and Phosphatherium in 1996.

It represents an extinct offshoot of proboscideans, which separated before the origin of the modern elephantine-like proboscideans (Elephantiforms), and which became specialized in the particular ecological niche of amphibious mammals. The same size as a tapir, it fed on aquatic plants.

Donated by R. Damon (Weymouth) made after a reconstruction owned by the Natural History Museum of London.

Phiomia serridens
Andrews & Beadnell, 1902
MNHN.F.LBE
Mammalia, Proboscidea, Phiomiidae
Early Oligocene, 34 million years ago
Faiyum, Egypt

Reconstruction of a skull and mandible. Phiomia is one of the first modern proboscideans (Elephantiforms). It was large in size and had an elephantine appearance, a large skull, tusks and a small trunk. The geochemical composition of its teeth indicates that it ate mangrove plants.

Donated by Andrews (Natural History Museum of London)