BRONTOTHERIIDAE MARSH, 1873
Microtitan Granger and Gregory, 1943
Two species of
Microtitan
,
M. mongoliensis
and M.? elongatus, have been reported from the Ulan Shireh Formation at North Mesa and the Arshanto Formation at Daoteyin Obo, respectively ( Granger and Gregory, 1943; Qi, 1987).
Microtitan mongoliensis
is known from a mandible with p2–m3 (AMNH FM 22099) and a maxilla with C–M3 (AMNH FM 21611).
Microtitan mongoliensis
initially was assigned to “
Metarhinus
?” by Osborn (1925) based a fragmentary mandible with p4–m1 (AMNH FM 20167), lacking diagnostic characters except for its small size. AMNH FM 20167 was discovered in the Irdin Manha Formation on the Irdin Manha escarpment ( Osborn, 1925). Later, Granger and Gregory (1943) erected a new genus
Microtitan
for “
Metarhinus
?”
mongoliensis
and selected AMNH FM 22099 as a neotype. Mihlbachler (2008) further pointed out that AMNH FM 20167 actually was made up of multiple individuals.
Microtitan
? elongatus was erected by Qi (1987) based on P3–M3 (IVPP V 5767) from the Arshanto Formation at Daoteyin Obo. However, Mihlbachler (2008) considered the species a nomen dubium. Qi (1987) further referred a M2 (IVPP V 5768) to
Microtitan sp.
from the Arshanto Formation at Huheboerhe. It is noteworthy that, based on our fieldwork over the past decade, no brontotheres have been found in the Arshanto Formation in the Huheboerhe area. Consequently, the horizon bearing
Microtitan
? elongatus and
Desmatotitan sp.
(as discussed below) recorded as the Arshanto Formations is questionable.
Desmatotitan Granger and Gregory, 1943
Only one species of
Desmatotitan
,
D. tukhumensis
, has been reported from the Ulan Shireh Formation at Wulantaolegai ( Granger and Gregory, 1943). The species is known only from the type AMNH FM 21606, which is composed of a mandible with i1–c and p2–m3.
Desmatotitan tukhumensis
is probably allied either with
Metatelmatherium
or
Microtitan mongoliensis
( Granger and Gregory, 1943; Mihlbachler, 2008).
Qi (1987) referred a single m3 (IVPP V 5769) to
Desmatotitan sp.
from the upper part of Arshanto Formation at Huheboerhe.
Acrotitan Ye, 1983
Ye (1983) erected a new genus and species
Acrotitan ulanshirehensis
from the Ulan Shireh Formation at Wulanhuxiu. The species is known from a fragmentary mandible with p3–4 (IVPP V 6686), and is characterized by two pairs of lower incisors ( Mihlbachler, 2008).
Epimanteoceras Granger and Gregory, 1943
Only one species of
Epimanteoceras
,
E. formosus
, has been reported from the Ulan Shireh Formation at Wulantaolegai ( Granger and Gregory, 1943; Mihlbachler, 2008). The type of
E. formosus
is known from a complete skull with complete dentition (AMNH FM 21613). Granger and Gregory (1943) erected a new genus and species
Dolichorhinoides angustidens
based on a partial skull with P1–M3 (AMNH FM 21607) from the Ulan Shireh Formation at Wulanhuxiu. However, Mihlbachler (2008) considered the species a junior synonym of
E. formosus
.
Hyotitan Granger and Gregory, 1943
Only one species of
Hyotitan
,
H. thomsoni
, was discovered in the Erlian Basin. The type of
H. thomsoni
, known from a mandible (AMNH FM 26401), was collected from the “Houldjin gravels” at Camp Margetts. However, Mihlbachler (2008) proposed that
H. thomsoni
could be a synonym of Qufutitian zhoui.
Metatelmatherium Granger and Gregory, 1938 Two species
of
Metatelmatherium
,
M. ultimum
and
M. parvum
, have been reported from the Erlian Basin. Granger and Gregory (1943) erected a new species
Metatelmatherium cristatum
based on a skull and mandible (AMNH FM 26411) from the “Irdin Manha Formation” at Camp Margetts. Mihlbachler (2008) considered
M. cristatum
a junior synonym of the Uintan
M. ultimum
from North America, but Mader (1989, 1998) regarded them as two different species. Furthermore, Bai et al. (2017) pointed out that the horizon bearing AMNH FM 26411 is actually in the Irdin Manha rather than the Arshanto Formation.
Metatelmatherium parvum
, known from a fragmentary mandible with p3–4 (AMNH FM 20168), was found in the Irdin Manha Formation at Irdin Manha ( Granger and Gregory, 1943). However, Mihlbachler (2008) considered the species a nomen dubium because it lacks diagnostic characters.
Protitan Granger and Gregory, 1943
The genus
Protitan
was erected by Granger and Gregory (1943) and originally included six species:
P. grangeri
,
P. robustus
,
P. minor
,
P. bellus
,
P. obliquidens
, and P.? cingulatus. Granger and Gregory (1943) further considered
Dolichorhinus olseni
and “
Manteoceras
?” irdinensis named by Osborn (1925) as junior synonyms of
P. grangeri
. However, Mihlbachler (2008) synonymized
P. robustus
,
P. bellus
, and
P. obliquidens
with
P. grangeri
, and considered P.? cingulatus a nomen dubium. Thus, according to the revision by Mihlbachler (2008), only two species of
Protitan
,
P. grangeri
and
P.minor
, are valid species.
The type of
Protitan grangeri
, known from a complete skull and mandible (AMNH FM 20103), is from the Irdin Manha Formation at Irdin Manha ( fig. 2G
View FIG
). The species is also known from the following horizons and localities: Irdin Manha Formation at Irdin Manha (AMNH FM 19179, 20104 [holotype of P. “
robustus
], 20108, 20109 [holotype of “
Dolichorhinus olseni
”], 20111 [holotype of “
Manteoceras
? irdinensis ”], 20112–20114, 20119, 20120, 20123, 20125 [holotype of P. “
obliquidens
”], and 20126); “Houldjin gravels” at Camp Margetts (AMNH FM 26421); and “lower red bed” at Spring Camp of East Mesa, Shara Murun region (AMNH FM 26104 [holotype of
P. bellus
]).
The type of
Protitan minor
, a skull (AMNH FM 26416), probably is from the top of “Irdin Manha” at 0.5 mi west of Camp Margetts. Mihlbachler (2008) also referred a partial skull (AMNH FM 26417) to
P.minor
from “?Irdin Manha beds,” 1 mi west of Camp Margetts. However, Bai et al. (2017) have pointed out that the horizon bearing AMNH FM 26416 is indeed within the Irdin Manha Formation.
Four mandibles (AMNH FM 26410, 26415, 26418, and 26408) initially assigned to
P.minor
or
P. grangeri
were considered to represent a new species (Camp Margetts “taxa A”) by Mihlbachler (2008). These specimens derive from the “Houldjin gravels” or ““Irdin Manha beds” in the Camp Margetts area.
The type of “
Protitan
?” cingulatus, composed of a mandible with p1–m3 ( AMNH
FM 26412
), was unearthed from the “Houldjin gravels” at Chaganboerhe. Mihlbachler (2008) also referred AMNH
FM 26403
from the “Houldjin gravels” at Camp Margetts and AMNH
FM 20110
from the Irdin Manha Formation at Irdin Manha to the species
.
Qi et al. (1992) referred a single m3 and some postcrania (IVPP
V 10104
View Materials
) to
Protitan sp.
from the so-called “Tukhum Formation” at Erden Obo. However, the horizon is equivalent to the “Low Red” bed.
Gnathotitan Granger and Gregory, 1943
Only one species of Gnathotita n,
G. berkeyi
, has been reported from the Erlian Basin ( Granger and Gregory, 1943; Mihlbachler, 2008). Gnathotita n
berkeyi
was assigned initially to
Telmatherium
by Osborn (1925), and later Granger and Gregory (1943) erected the genus Gnathotita n for the species. The species is characterized by its disproportionately large and deep mandible ( Mihlbachler, 2008). The type of
G. berkeyi
is known from a mandible with c–m3 (AMNH FM 20106) from the Irdin Manha Formation at Irdin Manha. Mihlbachler (2008) also referred the following specimens to
G. berkeyi
from the Irdin Manha Formation at Irdin Manha: AMNH FM 20107, 20115, 20121, and 141231 (formerly part of AMNH FM 20106). As noted by Mihlbachler (2008), two specimens (AMNH FM 20124, 20127) originally referred to
G. berkeyi
by Osborn (1925) were sent to the Chinese Geological Survey in October 1928 and are unfortunately lost. Both specimens were from the Irdin Manha Formation at Irdin Manha.
Rhinotitan Granger and Gregory, 1943
Two species of
Rhinotitan
,
R. kaiseni
and
R. andrewsi
, have been recognized from the Shara Murun Formation at Ula Usu ( Granger and Gregory, 1943; Wang, 1982; Mihlbachler, 2008). Osborn (1923b, 1925) named three new brontothere species from Ula Usu:
Protitanotherium mongoliensis
,
Protitanotherium andrewsi
, and
Dolichorhinus kaiseni
, but Granger and Gregory (1943) later erected a new genus
Rhinotitan
for these three species. Wang (1982) further considered
R. andrewsi
as a junior synonym of
R. mongoliensis ( Takai, 1939)
. However, Mihlbachler (2008) treated
R. mongoliensis
as a nomen dubium.
The type of
R. kaiseni
, known from a skull and mandible (AMNH FM 20252), was unearthed from the Shara Murun Formation at Ula Usu. AMNH FM 20257 and FMNH P 14048 (formerly AMNH FM 20260) were referred to
R. kaiseni
from the same horizon and locality. The type of
R. andrewsi
, known from a skull (AMNH FM 20271), is from the Shara Murun Formation at Ula Usu. AMNH FM 20254, 20261, 20263, IVPP V 3254-1, 3254-2, PIN 2198-3, 2198-5, and 7130-3 have been assigned to
R. andrewsi
from the same horizon and locality as the holotype. Mihlbachler (2008) further referred many specimens to
Rhinotitan sp.
from the Shara Murun Formation at Ula Usu, 4 mi north of Baron Sog Lamasery.
Pachytitan Granger and Gregory, 1943
Only one species of
Pachytitan
,
P. ajax
(AMNH FM 21612), is known from the Shara Murun Formation (gray beds), 4 mi north of Baron Sog Lamasery in the Shara Murun region ( Granger and Gregory, 1943; Mihlbachler, 2008). AMNH FM 21612 is a fragmentary skull with left I3, C, and P2–M3.
Pachytitan ajax
is very close to
Rhinotitan
, but is more advanced than the latter in having more molarized premolars that resemble those of
Embolotherium
or
Parabrontops
from the Erlian Basin ( Granger and Gregory, 1943; Mihlbachler, 2008). Cranially,
Pachytitan
most resemble
Rhinotitan andrewsi
and
Diplacodon elatus ( Mihlbachler, 2008)
.
Titanodectes Granger and Gregory, 1943 Granger and Gregory (1943)
erected a new genus,
Titanodectes
, comprising
T. minor
and
T. ingens
, from the Erlian Basin. However, Mihlbachler (2008) considered both of them syn- onymous with
Embolotherium grangeri
. Considering that the horizons and localities bearing
Titanodectes
and
Embolotherium
are different, and that none of the reliable lower dentition of
E. grangeri
has been reported, we still regard
Titanodectes
as a valid genus. The type of
T. minor
, known from an incomplete mandible with front teeth and p2–m1 (AMNH FM 26132), is from the “Shara Murun Formation” at Spring Camp in the East Mesa. Granger and Gregory (1943) further referred AMNH FM 26021 from the “Lower White” of Erden Obo, AMNH FM 26012 from the “Ulan Gochu beds” at Twin Obos, and AMNH FM 21600 from the Shara Murun Formation (gray beds), 4 mi north of Baron Sog Lamasery to the species. However, Mihlbachler (2008) referred AMNH FM 26021 to
Parabrontops
cf.
P. gobiensis
. The type of
Titanodectes ingens
, known from a mandible (AMNH FM 26005), is from the “Ulan Gochu beds” at Jhama Obo.
Titanodectes
is considered to be in certain respects intermediate between
Rhinotitan
and
Embolotherium
( Granger and Gregory, 1943; Mihlbachler, 2008).
Embolotherium Osborn, 1929
Osborn (1929) erected a new genus,
Embolotherium
, which includes
E. andrewsi
,
E. grangeri
, and
E. loucksii
, from the Shara Murun region and Erden Obo.
Embolotherium
is characterized by its large, upward extended nasal horns ( Osborn, 1929). Granger and Gregory (1943) further named a new species
E. ultimum
from the Baron Sog Mesa. However, Mihlbachler (2008) considered
E. ultimum
and
E. loucksii
as a junior synonyms of
E. andrewsi
and
E. grangeri
, respectively. Thus, only two species of
Embolotherium
are recognized as valid.
The type of
Embolotherium grangeri
, known from a complete skull (AMNH FM 26002), is from the base of “Middle Red” at Erden Obo ( Osborn, 1929). Mihlbachler (2008) referred following specimens to
E. andrewsi
from the Erlian Basin: AMNH FM 26004 from the base of “Middle Red” layer at Erden Obo; AMNH FM 26040 from the base of “Ulan Gochu beds” at Twin Obos; AMNH FM 21610 (holotype of
E. louksii
) from the base of Ulan Gochu Formation, 4 mi north of Baron Sog Lamasery; and AMNH FM 26018 from the surface of a plain, 2 mi south of Baron Sog Lamasery.
The type of
Embolotherium andrewsi
, known from a nearly complete skull (AMNH FM 26001), is from the “Middle White” layer at Erden Obo ( fig. 2H
View FIG
) ( Osborn, 1929). Mihlbachler (2008) referred the following specimens to
E. andrewsi
from the Erlian Basin: those largely from the “Middle White” layer at Erden Obo (AMNH FM 26003, 26000 (presented to the Chinese Geological Survey Museum), 26011, 26006–26008, and IVPP
V 11959
View Materials
); those from the “Ulan Gochu Formation” at Jhama Obo (AMNH FM 26009 and 26010); those from East Mesa (PIN 2200-1 and 2200-2); and those from the Baron Sog Formation at Baron Sog Mesa (AMNH FM 21604 [holotype of
E. ultimum
] and AMNH FM 22114). AMNH FM 20352 actually is from the Ardyn Obo Beds at Ardyn Obo (field no. 245), instead of the “Ulan Gochu Formation” at Erden Obo as mentioned by Mihlbachler (2008).
Parabrontops Granger and Gregory, 1943
Only one species of
Parabrontops
,
P. gobiensis
, has been reported from the Erlian Basin ( Osborn, 1925; Granger and Gregory, 1943). The species
P. gobiensis
was initially assigned to
Brontops
by Osborn (1925). The type of the species, known from a distorted skull (AMNH FM 20354), is from the Ardyn Obo beds at Ardyn Obo (field no. 253) ( Osborn, 1925; Granger and Gregory, 1943), rather than the Urtyn Obo Formation at Urtyn Obo as mentioned by Mihlbachler (2008). In detail, the locality 253 is situated “near trail, 1 mi northwest of Obo point.” AMNH FM 26020, known from a partial skull, was unequivocally referred to
P. gobiensis
( Granger and Gregory, 1943; Mihlbachler, 2008) and is from the “Middle White” layer at Erden Obo. Mihlbachler (2008) referred the following specimens to
Parabrontops
cf.
P. gobiensi
s: AMNH FM 26019 (“Middle White” layer, Erden Obo); AMNH FM 26021 (“Lower Gray” layer, Erden Obo); and AMNH FM 26131 (“Shara Murun beds,” Spring Camp). However, Granger and Gregory (1943) assigned AMNH FM 26021 to
Titanodectes minor
as discussed above.
Metatitan Granger and Gregory, 1943
Granger and Gregory (1943) named three species within a new genus
Metatitan
:
M. primus
,
M. progressus
, and
M. relictus
. However, Mihlbachler (2008) erected a new genus,
Nasamplus
, for
M. progressus
, and thus only two species are included in
Metatitan
.
The type of
Metatitan primus
, known from a partial skull and mandible ( AMNH
FM 26101
), was discovered at
Big Red Draw
, 1 mi southwest of
Chimney Butte Camp
at
North Mesa. The
horizon bearing AMNH
FM 26101
is probably equivalent to the Ulan Shireh Formation at Wulanhuxiu. Mihlbachler (2008) further referred a mandible ( AMNH
FM 26102
) to the species from the middle of the upper red beds at the northwest promontory, 1 mi northwest of Chimney Butte Camp
.
The type of
Metatitan relictus
, known from a skull and mandible (AMNH FM 26391), is from the “Houldjin gravels,” 1 mi west of Camp Margetts.
Metatitan
is considered to be derived from
Rhinotitan
and to bridge the morphological gap between
Embolotherium
and most other horned brontotheres with the paired frontonasal horns ( Granger and Gregory, 1943). The following specimens from the “Houldjin gravels” in the Camp Margetts area are referred to
M. relictus
( Granger and Gregory, 1943; Mihlbachler, 2008): AMNH FM 26395–26399; AMNH FM 26402; 26404–26407; 26420; 26427; and 26429. Mihlbachler (2008) further proposed that AMNH FM 26400, originally assigned to
Metatitan relictus ( Granger and Gregory, 1943)
, probably represents a new species (Camp Margetts “taxa B”). AMNH FM 26400 is from the “Houldjin gravels,” 1 mi west of Camp Margetts.
Wang et al. (2009) referred a maxilla with P1–3 (IVPP
V 15714
View Materials
) and several isolated lower teeth to
Metatitan sp.
from the Houldjin Formation at Houldjin and near Erenhot Railway Station.
Nasamplus Mihlbachler, 2008
The genus
Nasamplus
was erected by Mihlbachler (2008) for “
Metatitan
”
progressus ( Granger and Gregory, 1943)
. The type species, known from a fragmentary skull (AMNH FM 26014), is from the “Ulan Gochu beds” at Jhama Obo.
