Temporal range: Late Cretaceous, 74.73–72.79Ma
|Holotype erroneously labeled as and frill restored after Pentaceratops|
Titanoceratops (// meaning "titanic horn face") is a genus of herbivorous ceratopsian dinosaur. It was a giant chasmosaurine ceratopsian which lived during the Late Cretaceous period (late Campanian, 74.7–73.3 Ma) in what is now New Mexico, and the earliest known triceratopsin. It was named in 2011 by Nicholas R. Longrich for a specimen previously thought to belong to Pentaceratops. Titanoceratops was named for its giant skull, and the type species was named T. ouranos, after the father of the Greek titans.
It is known solely from the holotype OMNH 10165, a partial skeleton including a mostly complete skull and jaws. The skeleton has a reconstructed skull measuring 2.65 metres (8.7 ft) long, which makes it an easy candidate for the longest skull of any land vertebrate. With an estimated weight of 6.55 tonnes (6.45 long tons) and length of 9 metres (30 ft), Titanoceratops can compare to the giant sizes of Torosaurus and Triceratops.
The holotype skeleton, OMNH 10165, was found in the upper layers of the Fruitland Formation, or the lower layers of the Kirtland Formation. The border between the two formations is very bold, but the location of the original quarry has been lost, so it is not certainly known whether of not Titanoceratops is known from either formation. Either way, the formations are both from the Kirtlandian land-vertebrate age. The age of the lowest ash-filled section of the Fruitland Formation dates to 74.7 million years ago, and the date of the two ash-filled layers of the Kirtland Formation, which are in the upper section, date to 73.4 and 72.8 million years ago. Therefore, Titanoceratops lived in the Campanian, and as it was found in the lower region of the Kirtland, or the upper region of the Fruitland, it probably dates closer to 74 than 73 million years ago. Many dinosaurs existed in the two formations, and might have coexisted with Titanoceratops in the Hunter Wash local fauna. The possible contemporaries from the two formations include Bistahieversor sealeyi, "Saurornitholestes" robustus, Kritosaurus navajovius, Naashoibitosaurus ostromi, Anasazisaurus horneri, Parasaurolophus tubicen, Parasaurolophus cyrtocristatus, Sphaerotholus goodwini, Stegoceras validum, Nodocephalosaurus kirtlandensis, Pentaceratops sternbergii, an unnamed ornithomimid, and a indeterminate centrosaurine.
Before the assignment of Titanoceratops to Triceratopsini, the origins of triceratopsins were poorly known. Until the naming of Titanoceratops, Eotriceratops was the oldest certain triceratopsin. Eotriceratops comes from the uppermost section of the Horseshoe Canyon Formation, and dates to 68 million years ago. The identification of Titanoceratops as a triceratopsin suggests that there is a five million year ghost lineage leading the more derived chasmosaurines such as Eotriceratops.
Discovery and naming
The holotype of Titanoceratops is thought to come from the upper Fruitland Formation or the lower Kirtland Formation based on field notes and the lithology of the matrix surrounding the fossils, but unfortunately the precise location of the quarry is no longer known. Because the location of the quarry is no longer known, the bold border between the formations can not be discriminated. The species was formally named by Nicholas R. Longrich in 2011 and the type species is Titanoceratops ouranos. Previously, its fossils were assigned to Pentaceratops. The holotype specimen consists of most of the fore and himdlimbs, some vertebrae, a fairly complete skull with only one small section of the frill, and partial lower jaws.
Named by Longrich, Titanoceratops is derived from the Greek titan, a mythical race of giants, ceras, meaning "horned", and ops, "face". Ouranos, the specific name, refers to Ouranos, the father of the titan race.
The skull is estimated to be 2.65 m (8.7 ft) long when complete, making it a candidate for the longest skull of any terrestrial vertebrate. Longrich found that Titanoceratops was one of the largest triceratopsins, and estimated its weight to be 6.55 tonnes (6.45 long tons). Tom Holtz (2010) noted that it is extremely similar to its closely related contemporaries Eotriceratops and Ojoceratops, which may all be synonymous. He also found that Titanoceratops was 9 metres (30 ft) long, the same size as Triceratops and Torosaurus. The skull of Titanoceratops is possibly the longest of any chasmosaurine known, and measures 1.2 metres (3.9 ft) in length. The holotype skeleton of Titanoceratops consists of a partial skull with jaws, syncervical, cervical, dorsal, and sacral vertebrae, caudal certebrae, ribs, humeri, a right radius, femora, tibiae, a right fibula, both ilia, both ischia, and ossified tendons.
Titanoceratops was provided with a list of characters found by Longrich in its description that differ it from other taxa. The features below differ it from Triceratops:
- it has thin squamosals;
- open parietal fenestrae;
- a hornlike epijugal;
- the possession of a narrow parietal median bar;
- a vertical narial strut with a narrow base;
- an enlarged epoccipital on the caudal end of the squamosal
- an extremely large premaxillary fossa
- and in lacking a dorsally inflected narial process of the premaxilla.
It differs from Torosaurus in the fact it has:
- a narrow parietal median bar;
- a vertical narial strut with a narrow base;
- an enlarged epoccipital on the caudal and of the squamosal;
- an extremely large premaxillary fossa;
- and it lacks a dorsally inflected narial process on the premaxilla.
Longrich found it also differed from Eotriceratops in the fact it has:
- an enlarged epoccipital on the caudal end of the squamosal;
- an extremely enlarged premaxillary fossa;
- in lacking a dorsally inflected narial process of the premaxilla;
- and a premaxilla that is elongate relative to its height.
Originally assigned to Pentaceratops, Titanoceratops was found by Longrich in its description to not be closely related to it, and instead found it to share characteristics with triceratopsins. The skeleton has many derived features that are shared between Triceratops and its closest relatives.
Titanoceratops is known from OMNH 10165, a skeleton from the lowermost Fruitland Formation, or from the uppermost Kirtland Formation. The Fruitland Formation is about 100 metres (330 ft) thick, and consists of sandstones, mudstones, and coals deposited in a coastal floodplain. The Kirtland Formation, which it is overlain comfortably by, is approximately 600 metres (2,000 ft) thick, and is made up of sandstone, siltstone, mudstone, and shale. Both formation are last Campanian in age, with the Fossil Forest Member of the Fruitland being 74.11 ± 0.62 million years old, and the Hunter Wash Member of the Kirtland being between 73.37 ± 0.18 and 73.04 ± 0.25 million years in age. The two member combined make up the Hunter Wash local fauna. Therefore, Titanoceratops dates between 74 and 73 million years ago, in the Hunter Wash local fauna, although the specimen was probably found closer to the Fossil Forest Member with an age of 74 million years ago, based on the fact the tops of the Kirtland Formation is 73 million years old. The age Titanoceratops lived in is called the Kirtlandian land-vertebrate age, and it is characterized by the appearance of Pentaceratops sternbergii.
A moderately diverse amount of fauna are known from the Kirtland and Fruitland formations. Among the dinosauria fauna from the Fruitland and Kirtland Formations are the theropods Bistahieversor sealeyi (previously Daspletosaurus and Albertosaurus sp.), "Saurornitholestes" robustus, Paronychodon lacustris, and an indeterminate ornithomimid (previously Ornithomimus antiquus); the hadrosaurids Anasazisaurus horneri and Parasaurolophus cyrtocristatus; the pachycephalosaur Stegoceras novomexicanum (previously S. validum); the ankylosaur Nodocephalosaurus kirtlandensis; and the ceratopsians Pentaceratops sternbergii and an unidentified centrosaurine.
Non-dinosaurian fauna include the fishes Myledaphus bypartitus, and Melvius chauliodous; the turtles Denazinemys ornata, Denazinemys nodosa, Boremys grandis, Neurankylus baeuri, Adocus bossi, Adocus kirtlandicus, Basilemys nobilis, Asperideretes ovatus, "Plastomenus" robustus, and Bothremydidae n. gen., barberl; the crocodylians Denazinosuchus kirtlandicus, Brachychampsa montana, Deinosuchus rugosus, and Leidyosuchus sp.; and the mammalians Paracimexomys judithae, Mesodma senecta, Mesodma sp., Cimexomys sp., Cinemoxys antiquus, Kimbetohia campi, Cimolodon electus, Meniscoessus intermedius, Essonodon sp., Alphadon marshi, Alphadon wilsoni, Alphadon sp. A, Alphadon sp. B, Alphadon? sp., Pediomys cooki; Gypsonictops sp., Cimolestes sp., and an indeterminate eucosmodontid.
Previously, the origins of Triceratops were poorly known. Until the description of Titanoceratops, Eotriceratops was 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 before, so it appeared as if the group suddenly diversified in the Maastrichtian. Titanoceratops shows that large-bodied ceratopsians evolved earlier than thought. Based on the age of Titanoceratops, there must have been a five million year ghost lineage leading to Eotriceratops.
- Nicholas R. Longrich (2011). "Titanoceratops ouranos, a giant horned dinosaur from the Late Campanian of New Mexico". Cretaceous Research 32 (3): 264–276. doi:10.1016/j.cretres.2010.12.007.
- Holtz, Thomas R. Jr. (2012). Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages. Random House Books for Young Readers. p. 432. ISBN 978-0-375-82419-7.
- Sullivan, R.M. & Lucas, S.G. (2006). The Kirtlandian Land-Vertebrate "Age"-Faunal Composition, Temporal Position, and Biostratigraphic Correlation in the Nonmarine Upper Cretaceous of Western North America. In Lucas, S.G. & Sullivan, R.M. "Late Cretaceous vertebrates from the Western Interior". New Mexico Museum of Natural History and Science Bulletin 35: 7–23.
- Jasinski, S.E. & Sullivan, R.M. (2011). "Re-evaluation of the Pachycephalosaurids from the Fruitland-Kirtland Transition (Kirtlandian, Late Campanian), San Juan Basin, New Mexico, with a Description of a New Species of Stegoceras and a Reassesment of Texacephale langstoni". New Mexico Museum of Natural History and Science, Bulletin 53: 202–213.