''Zygolophodon'' is an extinct genus of mammutid proboscidean that lived during the

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

in Africa, Eurasia, and North America.

Description

As with other mammutids, the molars have a zygodont morphology. The fused front region of the lower jaw (the

mandibular symphysis In human anatomy, the facial skeleton of the skull the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: ''symphysis menti'') or line of junction where the two lateral ha ...

) is elongate and bears tusks/incisors. The upper tusks have enamel bands and are untwisted and downward curving, and outwardly diverge from each other. The jaws retained permanent

premolar The premolars, also called premolar Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...

teeth. Species probably reached similar sizes to the American mastodon, with a shoulder height of estimated for the species ''Z. metachinjiensis.''

Ecology

''Zygolophodon'' is suggested to have primarily had a

browsing Browsing is a kind of orienting strategy. It is supposed to identify something of relevance for the browsing organism. In context of humans, it is a metaphor taken from the animal kingdom. It is used, for example, about people browsing open sh ...

-based diet. Its teeth primarily served to vertically chew plant material.

Taxonomy

''Zygolophodon'' belongs in the family Mammutidae, whose best known member is the American mastodon (''Mammut americanum''). The genus likely originated in Africa. The oldest species is ''Z. aegyptensis,'' known from Egypt and Namibia, dating to the late Early Miocene-early Middle Miocene.Duangkrayom, J., Wang, S., Deng, T., & Jintasakul, P. (2017). The first Neogene record of Zygolophodon (Mammalia, Proboscidea) in Thailand: Implications for the mammutid evolution and dispersal in Southeast Asia. Journal of Paleontology, 91(1), 179-193. doi:10.1017/jpa.2016.143 The species ''Z. turicensis'' had a widespread distribution in both Africa (Kenya, Tunisia),

Anatolia Anatolia (), also known as Asia Minor, is a peninsula in West Asia that makes up the majority of the land area of Turkey. It is the westernmost protrusion of Asia and is geographically bounded by the Mediterranean Sea to the south, the Aegean ...

and Europe, dating to the Early-Late Miocene, with its earliest appearance in Europe being approximately 18-17 million years ago, and last appearance in the region dating to around 7-6 million years ago.'''' The youngest confirmed record of ''Zygolophodon'' in Africa dates to around 13 million years ago, based on teeth suggested to belong to ''Z. turicensis'' found in Kenya, though a possible younger record is known from the Late Miocene of Algeria. The species ''Z''. ''tapiroides'' (Desmarets, 1822) is considered invalid''.'' The taxonomy of East Asian ''Zygolophodon'' is uncertain. Tassy ''et al.'' (1988) synonymised many Chinese species with ''Z. gobiensis'' (including ''Z. lufengensis'', ''Z. chinjiensis'', ''Z. nemonguensis'', ''Z. gromovae'' and ''Z. jiningensis,'' as well as ''Miomastodon tongxiensis''), with ''Z. gobiensis'' also known from Mongolia, but other authors suggest that at least some of these species may be valid. The species ''Z. atavus'' is known from the early Middle Miocene of Kazakhstan. The oldest remains of ''Zygolophodon'' on the

Indian subcontinent The Indian subcontinent is a physiographic region of Asia below the Himalayas which projects into the Indian Ocean between the Bay of Bengal to the east and the Arabian Sea to the west. It is now divided between Bangladesh, India, and Pakista ...

are known from the Bugti Hills of Pakistan, dating to around 19-17 million years ago. The species ''Z. metachinjiensis'' is known from the mid-Late Miocene (around 13.8 to 12.4 million years ago) of Pakistan. ''Zygolophodon'' has also been reported from western India, dating to the mid Miocene, and other probable remains dating to the Late Miocene, around 10 million years old, representing the youngest mammutids on the Indian subcontinent. An indeterminate species has also been reported from Thailand, of uncertain but probably Late Miocene age. ''Zygolophodon'' entered North America during the latter part of the Early Miocene (during the late

Hemingfordian The Hemingfordian on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 20,600,000 to 16,300,000 years BP. It is usually considered to overlap the lates ...

faunal stage), with the oldest record being a partial tooth from Massacre Lake, Nevada, dating to 16.5-16.4 million years ago.Koenigswald, Widga & Göhlich (2021)
New mammutids (Proboscidea) from the Clarendonian and Hemphillian of Oregon – a survey of Mio-Pliocene mammutids from North America
/ref> Remains of ''Zygolophodon'' are known from across western and central North America during the following

Barstovian The Barstovian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 16,300,000 to 13,600,000 years BP, a period of . It is usua ...

(including Colorado, California, Montana, Oregon, Nebraska, Nevada, Wyoming and Saskatchewan). ''Z. proavus'' currently represents the only known North American species of ''Zygolophodon.'' The youngest specimens of ''Z''. ''proavus'' date to approximately 11-12 million years ago. ''

Mammut A mastodon, from Ancient Greek μαστός (''mastós''), meaning "breast", and ὀδούς (''odoús'') "tooth", is a member of the genus ''Mammut'' (German for 'mammoth'), which was endemic to North America and lived from the late Miocene to ...

'' is thought to be descended from ''Zygolophodon''. The species ''

"Mammut" borsoni ''"Mammut" borsoni'' (sometimes called Borson's mastodon) is an extinct species of mammutid proboscidean known from the Late Miocene to Early Pleistocene of Eurasia, spanning from western Europe to China. It is the last known mammutid in Eurasi ...

,'' whose relationship with North American ''Mammut'' is controversial, and sometimes placed in ''Zygolophodon'' (from which, like North American ''Mammut'', it descended from), is the youngest member of Mammutidae in Eurasia, persisting from the Late Miocene into the Earliest Pleistocene, around 2.5-2 million years ago. Some authors have suggested placing ''M. tongxinensis'', ''Z.'' ''gobiensis'' and ''Z. metachinjiensis'' within a revived ''Miomastodon'', which was originally described for the North American ''Miomastodon merriami.''Wang, S.-Q., Zhang, X.-X., and Li, C.-Y. 2020
Reappraisal of ''Serridentinus gobiensis'' Osborn and Granger and ''Miomastodon tongxinensis'' Chen: The Validity of Miomastodon
Vertebrate PalAsiatica, 58:134-158. ''Miomastodon'' is usually treated as a synonym of ''Zygolophodon'' (with ''M. merriami'' typically considered a synonym of ''Z. proavus'')'''' and other authors have reacted with caution to the proposal. Due to the conservatism of tooth morphology in ''Zygolophodon'' and the fact that most species are only or mostly known from molar teeth, is it difficult to determine the true number of valid species.

References

{{Taxonbar, from=Q2796916 Mammutidae Miocene proboscideans Pliocene proboscideans Miocene mammals of North America Miocene mammals of Asia Miocene mammals of Europe Pliocene mammals of North America Pliocene mammals of Asia Pliocene mammals of Europe Miocene mammals of Africa Pliocene mammals of Africa Prehistoric placental genera Fossil taxa described in 1877