Titanoceratops (meaning "titanic horned face") is a controversial genus of chasmosaurine ceratopsian dinosaur that lived in the Late Cretaceous period (Campanian stage, about 75 million years ago) in what is now New Mexico. Titanoceratops was named for its large size, being one of the largest known horned dinosaurs and the type species was named T. ouranos, after Uranus (Ouranos), the father of the Greek titans. It was named in 2011 by Nicholas R. Longrich for a specimen previously referred to Pentaceratops. Longrich believed that unique features found in the skull reveal it to have been a close relative of Triceratops, classified within the subgroup Triceratopsini. However, other researchers have expressed skepticism, and believe Titanoceratops to simply be an unusually large, old specimen of Pentaceratops. The holotype specimen is OMNH 10165, a partial skeleton including a mostly complete skull and jaws, and much of the skeleton. It was found in either the upper Fruitland Formation or the lower Kirtland Formation. The original quarry is lost, so it is not known which formation the fossil was excavated from. The formations are both late Campanian in age. The skull is incomplete, but as currently reconstructed it measures 2.65 metres (8.7 ft) long, making it a candidate for the longest skull of any land animal. With an estimated weight of 6.55 tonnes (6.45 long tons; 7.22 short tons) and length of 6.8 metres (22 ft), Titanoceratops was comparable in size with the largest ceratopsians, Torosaurus and Triceratops, and was likely the largest animal in its ecosystem, if not in North America, at the time.
Description
The skull measures 1.2 m (3.9 ft) from the tip of the snout to the quadrate, and the restored frill extends its length up to 2.65 m (8.7 ft) making it a candidate for the longest skull of any land animal. Titanoceratops was as large as the later triceratopsins Triceratops and Torosaurus, with an estimated weight of 6.55 tonnes (7.22 short tons) and a mounted skeleton measuring 6.8 metres (22.3 ft) long and 2.5 metres (8.2 ft) tall at the back. In 2016 Gregory S. Paul gave a lower estimation of 6.5 meters (21.3 ft) and 4.5 tonnes (4.9 short tons). Tom Holtz (2012) noted that it is extremely similar to its closely related contemporaries Eotriceratops and Ojoceratops, which may all be synonymous. The holotype skeleton of Titanoceratops consists of a partial skull with jaws, syncervical, cervical, dorsal, and sacral vertebrae, caudal vertebrae, ribs, humeri, a right radius, femora, tibiae, a right fibula, both ilia, both ischia, and ossified tendons. In total, the amount of material assigned to Titanoceratops means it is quite well known, along with genera like Triceratops, Vagaceratops, Pentaceratops, Chasmosaurus, Centrosaurus, Styracosaurus, and Anchiceratops.
History of study
The holotype of Titanoceratops was collected from the upper Fruitland Formation or the lower Kirtland Formation in July 1941, by a field crew consisting J. Willis Stovall, his student Wann Langston Jr., and Donald E. Savage. The precise location of the quarry is no longer known. The holotype specimen consists of most of the fore and hindlimbs, some vertebrae, a fairly complete skull with only one small section of the frill, and partial lower jaws. The bones, being preserved in a fine-grained shale, were crushed and fragile, and so the skeleton was initially considered unsuitable for mounting. Later, however, the fossils were prepared and the skeleton put on display at the Oklahoma Museum of Natural History. In 1998, the specimen was described by Thomas Lehman as an aberrant and unusually large individual of Pentaceratops sternbergii, previously described from the same area. The specimen was later reinterpreted as a member of the Triceratopsini, the group including Triceratops, by Nicholas R. Longrich and given the name Titanoceratops ouranos in 2011. The name Titanoceratops is derived from the Greek Titan, a mythical race of giants, keras (κέρας), meaning "horn", and ops (ὤψ), "face". The species name ouranos, refers to Uranus, the father of the Titan race. Longrich's re-interpretation would have major implications for the evolutionary history and biogeography of chasmosaurine dinosaurs. Previously, the origins of Triceratops were poorly known. Until the Longrich's re-interpretation of Titanoceratops, Eotriceratops was thought to be the oldest known triceratopsin, and only dated to 68 million years old, from the uppermost region of the Horseshoe Canyon Formation. No Campanian triceratopsins were known, so it appeared as if the group evolved in the Maastrichtian. If Titanoceratops is a member of this group, it would demonstrate that they evolved millions of years earlier than previously thought, and it would imply a five million year long gap in the fossil record and ghost lineage leading to Eotriceratops. However, several subsequent studies have cast doubt on the hypothesis that Titanoceratops is a triceratopsin.
Classification
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