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Description

A selection of basal forms of proboscideans, to scale.

Along with horses (equids) and apes (hominids), elephants have a long evolutionary history scattered with numerous fossils. Living elephants are just the final remnant of a vast range of species, some of which have been discussed in previous posts: Hoe-tuskers - Deinotheres , Not elephants 1 - Mastodons and Not elephants 2 - Gomphotheres . The earliest members of the Proboscidea were smaller and show less of the derived features that are familiar in later species.

One notable feature which changed was the decrease in the number of incisors with later groups. Early forms had up to three pairs in the upper jaw and two in the latter, while later species (deinotheres and elephantiforms) only had a maximum of a single pair of tusks in either jaw. There is some argument as to whether the tusks of later groups are derived from incisors, but this seems to be the most logical conclusion. Other adaptations to the skull saw a shortening of the face and a retraction of the nasal opening. As proboscideans grew larger their stance also changed to a graviportal one supported by columnar legs. Early forms had more angular legs and plantigrade feet.

Living only 5 million years after the K-Pg extinction event was the oldest, smallest and most primitive proboscidean. Eritherium stood only 20 cms at the shoulder. Structurally it's teeth were similar to the distantly related manatees and embrithopods, and uniquely among proboscideans Eritherium had a full set of teeth including canines. The orbits were placed forward in the skull, a feature which shifted towards the rear in later forms.

Phosphatherium had the typical low skull of other proboscideans but lacked the structures for any trunk. Teeth and jaw musculature are markedly different between males and females. Scratch marks on the teeth indicated that Phosphatherium had a broad diet of rough vegetation which may also included animal matter.

Some of the best skeletal material is known from Numidotherium. Unlike the low slung body shape of other basal forms, this proboscidean was more terrestrial with relatively long limbs and would have most resembled a tapir. An elongated nasal opening shows that Numidotherium had a short trunk while the enlarged incisors protruded forwards.

The first large-sized proboscideans appeared during the Late Eocene. Standing 2 metres at the shoulder. Barytherium was a graviportal species that evidently spent alot of time in water. Unlike later proboscideans it retained the plantigrade feet. There were four short tusks in both jaws with the upper ones being vertical and pointed outwards, while the lower tusks projected forwards. They were likely used to shear vegetation. Barytherium probably had a small proboscis as the attachment points on the skull are not strongly defined.

Now considered a side branch of proboscidean evolution, the familiar Moeritherium was once believed to be 'the' ancestral elephant. There are several species known and all are extremely elongate with short limbs for a semi-aquatic life in estuarine wetlands. Moeritherium had a long cranium, high placed eyes and long tusk-like second incisors. Being low to the ground, a trunk would have been a very unlikely feature. Two early elephantiforms, Phiomia and Palaeomastodon lived alongside Moeritherium in the Eocene Fayum Formation. This was the lineage that would go on to produce mastodons, gomphotheres and true elephants.

Description

A selection of basal forms of proboscideans, to scale.

Along with horses (equids) and apes (hominids), elephants have a long evolutionary history scattered with numerous fossils. Living elephants are just the final remnant of a vast range of species, some of which have been discussed in previous posts: Hoe-tuskers - Deinotheres , Not elephants 1 - Mastodons and Not elephants 2 - Gomphotheres . The earliest members of the Proboscidea were smaller and show less of the derived features that are familiar in later species.

One notable feature which changed was the decrease in the number of incisors with later groups. Early forms had up to three pairs in the upper jaw and two in the latter, while later species (deinotheres and elephantiforms) only had a maximum of a single pair of tusks in either jaw. There is some argument as to whether the tusks of later groups are derived from incisors, but this seems to be the most logical conclusion. Other adaptations to the skull saw a shortening of the face and a retraction of the nasal opening. As proboscideans grew larger their stance also changed to a graviportal one supported by columnar legs. Early forms had more angular legs and plantigrade feet.

Living only 5 million years after the K-Pg extinction event was the oldest, smallest and most primitive proboscidean. Eritherium stood only 20 cms at the shoulder. Structurally it's teeth were similar to the distantly related manatees and embrithopods, and uniquely among proboscideans Eritherium had a full set of teeth including canines. The orbits were placed forward in the skull, a feature which shifted towards the rear in later forms.

Phosphatherium had the typical low skull of other proboscideans but lacked the structures for any trunk. Teeth and jaw musculature are markedly different between males and females. Scratch marks on the teeth indicated that Phosphatherium had a broad diet of rough vegetation which may also included animal matter.

Some of the best skeletal material is known from Numidotherium. Unlike the low slung body shape of other basal forms, this proboscidean was more terrestrial with relatively long limbs and would have most resembled a tapir. An elongated nasal opening shows that Numidotherium had a short trunk while the enlarged incisors protruded forwards.

The first large-sized proboscideans appeared during the Late Eocene. Standing 2 metres at the shoulder. Barytherium was a graviportal species that evidently spent alot of time in water. Unlike later proboscideans it retained the plantigrade feet. There were four short tusks in both jaws with the upper ones being vertical and pointed outwards, while the lower tusks projected forwards. They were likely used to shear vegetation. Barytherium probably had a small proboscis as the attachment points on the skull are not strongly defined.

Now considered a side branch of proboscidean evolution, the familiar Moeritherium was once believed to be 'the' ancestral elephant. There are several species known and all are extremely elongate with short limbs for a semi-aquatic life in estuarine wetlands. Moeritherium had a long cranium, high placed eyes and long tusk-like second incisors. Being low to the ground, a trunk would have been a very unlikely feature. Two early elephantiforms, Phiomia and Palaeomastodon lived alongside Moeritherium in the Eocene Fayum Formation. This was the lineage that would go on to produce mastodons, gomphotheres and true elephants.