Brontotheriidae

Brontotheres; Temporal range: 56–34 Ma PreꞒ Ꞓ O S D C P T J K Pg N Eocene
	Megacerops skeleton at the ; National Museum of Natural History, Washington, DC
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Perissodactyla
Suborder:	Hippomorpha
Family:	†Brontotheriidae; Marsh, 1873
Genera
	See text
Synonyms
	Menodontidae; Titanotheriidae;

Brontotheriidae is a family of extinct mammals belonging to the order Perissodactyla, the order that includes horses, rhinoceroses, and tapirs. Superficially, they looked rather like rhinos, although they were actually more closely related to horses; Equidae and Brontotheriidae make up the suborder Hippomorpha. They lived around 56–34 million years ago, until the very close of the Eocene.

Characteristics and evolution[]

Life reconstruction of Megacerops

Life reconstruction of Protitanops curryi

Skull of Rhinotitan

Brontotheres retain four toes on their front feet and three toes on their hind feet. Their teeth are adapted to shearing (cutting) relatively nonabrasive vegetation. Their molars have a characteristic W-shaped (outer shearing blade).

The evolutionary history of this group is well known due to an excellent fossil record in North America.^[1] The earliest brontotheres, such as Eotitanops, were rather small, no more than a meter in height, and hornless.

Brontotheres evolved massive bodies, although some small species such as Nanotitanops did persist through the Eocene. Some genera, such as Dolichorhinus, evolved highly elongated skulls. Later brontotheres were massive, up to 2.5 m (8.2 ft) tall with horn-like skull appendages. The North American brontothere Megacerops, for example, evolved large sexually dimorphic paired horns above their noses. The sexually dimorphic horns suggest that brontotheres were highly gregarious (social) and males may have performed some sort of head-clashing behavior in competition for mates. Unlike rhinoceros, in which the horns are made of keratin, however, the horns of brontotheres are composed of bone (the frontal bone and nasal bone) and were placed side-to-side rather than front-to-back.

Brontotheres probably became extinct because they could not adapt to drier conditions and tougher vegetation (such as grasses) that spread during the Oligocene.^[1]

Classification[]

Classification for Brontotheriidae after Mihlbachler 2008^[2] and Mader 2010^[3]

Brontotheriidae

Two classification systems for Brontotheriidae are presented below. The first contains 43 genera and 8 subfamilies, and although it is based on a 1997 publication by McKenna and Bell, it summarizes research that was conducted before 1920 and is badly outdated. The second classification is based on 2004 and 2005 research by Mihlbachler et al., which indicates that many of the previous subfamily names are invalid. Several more recently discovered brontotheres are included in the newer classification.

Although Lambdotherium and were previously included in Brontotheriidae, they are no longer considered members of this family. Lambdotherium, though excluded, may be the closest known relative to brontotheres. Xenicohippus is now thought to be an early member of the horse family, Equidae.

Old classification (summarized by McKenna and Bell, 1997)	New classification (Mihlbachler et al., 2004a, 2004b; Mihlbachler, 2005)
Family Brontotheriidae Pakotitanops incertae sedis, from Pakistan Nanotitanops incertae sedis, from Asia Subfamily Lambdotheriinae Lambdotherium, from North America , from North America Subfamily Palaeosyopinae Palaeosyops (including Eotitanops), from North America, 0.5 m tall Mulkrajanops, from Pakistan, 1.25 m tall Subfamily Dolichorhininae Metarhinus, from North America, 1 m tall Sphenocoelus, from North America, 1.25 m tall Mesatirhinus, from North America, 1 m tall Subfamily Brontotheriinae Duchesneodus, from North America Brontotherium, from North America Megacerops, from North America, 2.5 m tall Subfamily Embolotheriinae Titanodectes, from Asia Embolotherium, from Mongolia, 2.5 m tall , from Outer Mongolia, 2 m tall Subfamily Brontopinae Brachydiastematherium, from Eastern Europe, 2 m tall , from Inner Mongolia, 2 m tall , from China, 2 m tall , from Inner Mongolia, 2.5 m tall , from Inner Mongolia, 0.75 m tall , from Inner Mongolia, 2 m tall , from Inner Mongolia, 2 m tall Rhinotitan, from Inner Mongolia, 2.5 m tall , from Mongolia, 1.5 m tall Protitanotherium, from North America, 2 m tall , from Mongolia, 2 m tall Oreinotherium, from North America Brontops, from North America Protitanops, from North America, 2 m tall , from China, 0.5 m tall Subfamily Telmatheriinae , from Inner Mongolia, 0.3 m tall , from Inner Mongolia, 1.25 m tall , from China , from Inner Mongolia, 2.2 m tall Sthenodectes, from North America, 1.25 m tall Telmatherium (including Metatelmatherium), from North America and Inner Mongolia, 1.5 m tall , from Asia and Europe Subfamily Menodontinae Diplacodon, from North America, 2 m tall Eotitanotherium, from North America Notiotitanops, from North America, 2 m tall Menodus, from Europe and North America Ateleodon, from North America	Family Brontotheriidae Pakotitanops incertae sedis, from Pakistan Mulkrajanops incertae sedis, from Pakistan, 1.25 m tall Eotitanops, from North America, 0.5 m tall Palaeosyops, from North America, 1 m tall Subfamily Brontotheriinae , from Asia Mesatirhinus, from North America, 1 m tall Dolichorhinus, from North America, 1.25 m tall Sphenocoelus, from North America, 1.25 m tall , from Inner Mongolia, 1.25 m tall , from North America Metarhinus, from North America, 1 m tall , from Inner Mongolia, 0.75 m tall Sthenodectes, from North America, 1.25 m tall Telmatherium, from North America, 1.25 m tall Metatelmatherium, from North America and Inner Mongolia, 1.25 m tall , from Inner Mongolia, 2 m tall incertae sedis, from Inner Mongolia, 2.2 m tall Nanotitanops incertae sedis, from Asia incertae sedis, from China, 0.5 m tall incertae sedis, from Inner Mongolia, 0.3 m tall incertae sedis, from China incertae sedis, from China Tribe Brontotheriini , from Inner Mongolia, 2 m tall Protitanotherium, from North America, 2 m tall Rhinotitan, from Inner Mongolia, 2.5 m tall Diplacodon (including Eotitanotherium), from North America, 2 m tall , from Inner Mongolia, 2 m tall Brachydiastematherium, from Eastern Europe, 2 m tall , from Asia and Europe Subtribe Embolotheriina , from Inner Mongolia, 2.5 m tall , from Kazakhstan, 2.5 m tall , from Mongolia, 1.5 m tall , from Inner Mongolia , from Outer Mongolia, 2 m tall Embolotherium (including Titanodectes), from Mongolia, 2.5 m tall Subtribe Brontotheriina , from Mongolia, 2 m tall Protitanops, from North America, 2 m tall Notiotitanops, from North America, 2 m tall , from China, 2 m tall Duchesneodus, from North America Megacerops (including Menodus, Brontotherium, Brontops, Menops, Titanotherium, Ateleodon, and Oreinotherium), from North America, 2.5 m tall

References[]

^ ^a ^b Titanotherium
^ Mihlbachler, Matthew C. "Species taxonomy, phylogeny and biogeography of the Brontotheriidae (Mammalia, Perissodactyla)". Bulletin of the American Museum of Natural History. American Museum of Natural History (311). hdl:2246/5913. Retrieved 4 September 2013.
^ Mader, Bryn J. "A species-level revision of the North American brontotheres Eotitanops and Palaeosyops (Mammalia, Perissodactyla)" (PDF). Department of Biological Sciences and Geology, Queensborough Community College. Retrieved 4 September 2013.

External links[]

Brontotheroidea at Mikko's Phylogeny Archive

[Titanotherium_keltationsart-1] Titanotherium

[Mihlbachler_2008-2] Mihlbachler, Matthew C. "Species taxonomy, phylogeny and biogeography of the Brontotheriidae (Mammalia, Perissodactyla)". Bulletin of the American Museum of Natural History. American Museum of Natural History (311). hdl:2246/5913. Retrieved 4 September 2013.

[Mader_2010-3] Mader, Bryn J. "A species-level revision of the North American brontotheres Eotitanops and Palaeosyops (Mammalia, Perissodactyla)" (PDF). Department of Biological Sciences and Geology, Queensborough Community College. Retrieved 4 September 2013.

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Brontotheriidae

Contents

Characteristics and evolution[]

Classification[]

References[]

Further reading[]

External links[]

Brontotheres Temporal range: 56–34 Ma PreꞒ Ꞓ O S D C P T J K Pg N Eocene

Megacerops skeleton at the National Museum of Natural History, Washington, DC
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Perissodactyla
Suborder:	Hippomorpha
Family:	†Brontotheriidae Marsh, 1873
Genera
See text
Synonyms
Menodontidae Titanotheriidae