GOMPHOTHERES: AN INTERESTING EXTINCT LAND MAMMAL WITH A CONFUSING TAXONOMIC HISTORY

The genus name “gomphothere” and its family name “Gomphotheriidae” are derived from ancient Greek and mean “wedge beast,” in reference to the teeth of this animal. The root of these names does not help to understand as to what kind of “beast” the animal actually was. In fact, until about 20 years ago, before modern scientific techniques (e.g., cladistics and collagen studies) became widely used, the only thing that most vertebrate paleontologists could agree on about gomphotheres was that they belonged to a group of extinct proboscideans that included mastodons, mammoths, and elephants. Classification of gomphotheres is still unsettled, and ongoing research is trying to clarify their evolutionary history (which is a formibable task to say the least, as I discovered while working on this blog post). There is also the confusing problem of having gomphotheres with Latinized names including with the suffix “mastodon” (e.g., Notiomastodon, Sinomastodon, Stegomastodon, etc.).

Gomphothere bodies tend to have long, low-sloping foreheads with tapered trunk areas. Their molar teeth are distinctive: moderately tall and with bun-like tops = bunodont teeth. The majority of gomphotheres have four tusks (incisors): two upper and two lower. They curve upward and outward. Some gomphotheres have only two tusks.

Two views (side and head-on) of a plastic model of Gomphotherium with four tusks.

Gomphotherium skull, side view.

In this post, I recognize the following nine genera of gomphotheres. The number of tusks each genus had is given in parentheses [note: the tusks of Cuvieronius were long (up to three meters) and very sharp]. 

Gomphotherium (4)

Gnathabelodon  (4)

Eubelodon (4)

Blancotherium (4)

Rhynchotherium (4)

Cuvieronius (2) Its two tusks were very long (3 m) and sharp.

Notiomastodon (2)

Sinomastodon (2)

Stegomaston (2)

The diagram shown above depicts the paleobiogeographic distribution of gomphotheres through time. Some of the nine genera names are plotted on this chart, but no attempt was made to include all of them because a few are not well studied.  New age-dating techniques combined with current thinking on plate tectonics reveal that gomphotheres originated in Africa and spread to Eurasia during the early Miocene (19 m.y. ago) and reached North America during the early Miocene (16 m.y. ago). 

Gomphotheres had widespread distribution. They migrated into North America from Asia several times during middle Miocene time via the land bridge Beringia 2. Their peak diversity was in the late Miocene (7-10 mya). Remains of two genera of gomphotheres, Gomphotherium and Stegomastodon, have been found in Miocene (about 9 mya) rocks in the Anza-Borrego Park area in southern California. Also, Gomphotherium remains are found Miocene strata at Redrock Canyon, Mojave Desert, south-central California and in strata at Mint Canyon, southern California.

About 2.7 mya, gomphotheres migrated from North America to South America via the Panama Isthmus land bridge event (GABI). They went extinct in the Pleistocene.

Gomphotheres preferred savannah habitats over forests and grasslands. Thus, when grasslands became more plentiful during the middle Cenozoic, gomphopheres, like other non-grass-eating land mammals, went into decline because they could no longer successfully compete.

References Used:

en.wikipedia.org

Savage, R.J.G. and M.R. Long. 1986. Mammal evolution an illustrated guide. British Museum of Natural History. Chapter 10 of this very informative book needs updating becaue it confusingly regards some gomphopheres as matodons. New information, which is utilized in this current blog post, has clarified some of this confusion but not all of it. 

McDaniel, G.E. 2006. Mammoths and their relatives. Pp. 217-233. In Fossil Treasures of the Anza-Borrego Desert. The last seven million years. G.T. Jefferson and L. Lindsay (eds.).Sunset Publications, San Diego, California.

UCMP.berkeley.edu   =  (University of California Museum of Paleontology) website.