Tag: gomphothere

It Came From The Wastebasket #03: The Gomphothere In The Room

The three living species of elephants are the last surviving members of the proboscidean lineage – but up until the end of the last ice age about 11,000 years ago their relatives were much more numerous and widespread, found on every continent except Australia and Antarctica. Mammoths are probably the most famous of these recently-extinct proboscideans, closely related to modern Asian elephants, but there were also the more distantly-related stegodonts and mastodons…

…And also the gomphotheres.

A cladogram showing the traditional classification of gomphotheres as a poorly-defined group evolutionarily between mastodons and modern elephants.

Traditionally any proboscideans that fell into the evolutionary grade between mastodons and elephants-and-stegodonts were all labelled as gomphotheres. As a result by the late 20th century this group ended up as a wastebasket full of elephant-like forms that didn’t easily fit anywhere else, defined more by what they weren’t rather than by any features they all had in common.

This big collection of gomphotheres was highly diverse. Some species independently evolved similar convergent features, and there was also considerable individual physical variation within species, making the actual taxonomy of these animals very difficult to figure out. But over the last few decades there’s been a lot of revision of proboscidean evolutionary relationships, and gradually the gomphothere wastebasket has been clearing up. Groups like the choerolophodontids, amebelodontids, and anancids have been split off, leaving a more defined lineage of gomphotheres that do have shared anatomical characteristics – distinctive three-lobed trefoil-shaped wear patterns on their molar teeth.

A cladogram showing a more modern classification of gomphotheres, with the gomphotheriids as just one of several different lineages originating between mastodons and modern elephants.

These gomphotheriids were widespread, found across Africa, Europe, Asia, and the Americas – and they were especially successful in the latter. They arrived in North America during the Miocene (~16 million years ago) via the Beringia land bridge, and rapidly spread across the continent and down into Central America. They went on to become the only proboscideans to disperse into South America during the Great American Biotic Interchange, with two different lineages arriving at separate times – Notiomastodon around 2.5 million years ago, and Cuvieronius around 750,000 years ago.

An illustration of Cuvieronius, an extinct elephant-like gomphothere. It has a longer flatter head than modern elephants, and its tusks have a spiral twist to them.
Cuvieronius hyodon, a 2.3m tall (7’7″) South American gomphotheriid with distinctive spiraled tusks.

The exact relationships of the gomphotheriids to other elephant-like proboscideans are still a little uncertain. Both protein sequences and mitochondrial DNA have recently been recovered from 35,000-13,000-year old Notiomastodon specimens, but these studies have given different taxonomic conclusions – with the protein results suggesting gomphotheriids were most closely related to mastodons, and the DNA results suggesting they were much closer to true elephants.

Island Weirdness #32 — Tiny Elephants On Parade Part 3: More Indonesia

It’s finally time for part 2 of the Island Weirdness series!

(If you haven’t seen the previous installments, I suggest starting back at the beginning here.)

We left off last time with the dwarf stegodontids of Flores, but other Indonesian islands also had their own populations of unusually small elephant-relatives — so here’s a few more to start off this month!

A stylized illustration of an extinct dwarf elephant. It has long straight tusks and small ears.
Sinomastodon bumiajuensis

Sinomastodon bumiajuensis lived on the island of Java during the early Pleistocene, about 2-1.5 million years ago. It stood around 2m tall at the shoulder (6’6″), less than half the size of most other Sinomastodon species from mainland Asia. Although it looked convergently similar to modern elephants it was actually a member of the gomphotheres, much more closely related to the weird “shovel-tuskers” than to any living species.

A stylized illustration of an extinct dwarf elephant. It has long gently curving tusks and proportionalyl short legs.
Stegodon semedoensis

Stegodon semedoensis, also from the early Pleistocene of Java about 1.5 million years ago, is only known from a few isolated molar teeth — but the size of those teeth suggest it was one of the smallest known pygmy stegodontids. It was probably no more than 1.2m at the shoulder (3’11”), comparable in size to its close relative Stegodon sondaari over on Flores.

A stylized illustration of an extinct dwarf elephant. It has four straight tusks, two longer ones in its upper jaw and two shorter ones in its lower jaw.
Elephas celebensis

Meanwhile on Sulawesi, Elephas celebensis (sometimes called Stegoloxodon celebensis) was an actual true elephant closely related to the modern Asian elephant. Living during the late Pliocene and early Pleistocene, between about 2.5 million and 800,000 years ago, it was only 1.5m tall (5′) and had a second set of tusks in its lower jaw, a “primitive” feature retained from the gomphothere-like ancestors of modern elephants.

A stylized illustration of an extinct dwarf elephant. It has long curving tusks and small ears.
Stegodon sompoensis

At the same time Sulawesi also had yet another small stegodontid, Stegodon sompoensis, also around 1.5m tall.

Both of these dwarfs lived alongside a larger Stegodon species, as well as giant tortoises and large-tusked pigs.

The cooling climate of the Pleistocene and dropping sea levels eventually connected the islands of western Indonesia to the Sundaland landmass of mainland Asia. Influxes of new predators and competitors — and early humans — probably drove these endemic small elephants to extinction.