Titanoceratops

Discovery and namingEdit

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, although its separation is not certain and the two binomials are treated as synonymous according to Wick & Lehman (2013). 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.

Named by Longrich, 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.

DescriptionEdit

The skull measures 1.2 m (3.9 ft) from the tip of the snout to the quadrate and its restored frill extends its total length up to 2.65 m (8.7 ft) making it a candidate for the longest skull of any terrestrial vertebrate. Titanoceratops was as large as the later triceratopsins 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. 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 certebrae, 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.

ClassificationEdit

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. However, even thought most recent studies find Titanoceratops to be valid and distinguished from Pentaceratops, one study in which Bravoceratops was described found the two genera and species to be synonymous, and therefore Titanoceratops ouranos the invalid name.

The below cladogram follows Longrich (2015), who named a new species of Pentaceratops, and included nearly all species of chasmosaurine.

Distinguishing characteristicsEdit

Titanoceratops was provided with a list of characters found by Longrich in its description that differ it from other taxa. The features below distinguish it from other Chasmosaurines: the possession of thin squamosals (Triceratops); an unsealed parietal fenestrae (Triceratops); an epijugal resembling a hornlike structure (Triceratops); a narrow median bar of the parietal (Triceratops, Torosaurus); a narial strut oriented vertically with a narrow base (Triceratops, Torosaurus); an enlarged epoccipital on the rear end of the squamosal (Triceratops, Torosaurus, Eotriceratops); an extremely enlarged premaxillary fossa (Triceratops, Torosaurus, Eotriceratops); and in lacking a narial process of the premaxilla that is dorsally inflected (Triceratops, Torosaurus, Eotriceratops).

PaleoecologyEdit

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 array 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.

BiogeographyEdit

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.