The significance of this particular hadrosaur taxon is that it is a transitional species between the genera Acristavus and Brachylophosaurus evolving from a crestless ancestor (the former genus) to its crested descendant (the latter genus) while changing the morphology of its nasal bones.
Freedman Fowler & Horner, 2015
Freedman Fowler & Horner, 2015
In 1981 and 1994, Mark Goodwin of the University of California Museum of Paleontology excavated limb bones and a vertebra near Rudyard in the north of Montana, at a site originally discovered by Kyoko Kishi. After a school class found some more bones, in 2007 and 2008 a team of the Museum of the Rockies secured the remainder of a hadrosaur skeleton, among which the skull. The fossil was donated to the Museum of the Rockies by land owners Nolan and Cheryl Fladstol; and John and Claire Wendland. In 2009, 2010 and 2011, the find was reported in the scientific literature as a possible new species of Brachylophosaurus.
In 2015, the type species Probrachylophosaurus bergei was named and described by Elizabeth A. Freedman Fowler and Jack Horner. The generic name is a combination of Latin pro, "before", and Brachylophosaurus and refers to the genus being situated in a lower position in the stratification than its relative Brachylophosaurus. The specific name honours Sam Berge, one of the landowners, and his friends who have supported the research. Probrachylophosaurus was one of eighteen dinosaur taxa from 2015 to be described in open access or free-to-read journals.
The holotype, MOR 2919, was found in a layer of the Judith River Formation dating from the Campanian and being between 79.8 and 79.5 million years old, plus or minus two hundred thousand years. It consists of a partial skeleton with skull, of an adult individual. It contains the right premaxilla, both maxillae, the left jugal, a part of the right lacrimal, the rear of a left nasal bone, the middle part of a right nasal bone, the skull roof from the frontal bones to the exoccipitals, both squamosals, both quadrate bones, the predentary of the lower jaws, both dentaries, a right surangular, eleven neck vertebrae, eleven back vertebrae, twenty-nine tail vertebrae, nineteen chevron bones, nineteen ribs, the entire pelvis, both lower legs, a right second metatarsal and a right fourth metatarsal. The bones have not been found in articulation.
Specimen MOR 1097, a fragmentary skull of a subadult individual, was referred to the species. It had been found at a kilometre distance from the holotype.
Probrachylophosaurus is a large hadrosaurid. Its holotype is the largest brachysaurolophin specimen known. Because of this size the fossil has been nicknamed "Super-Duck". Its length has been estimated at nine metres, its weight at over five tonnes.
In 2015, several distinguishing traits were established. Two of these are autapomorphies, unique derived characters. The skull crest is made of massive bone and is entirely formed by the nasal bones which, in adult individuals, overhang the supratemporal fenestrae over a distance of less than two centimetres. This crest is at its midline extremely thickened, resulting at the position of the rear frontals bones it overgrowths, in a pointed strongly triangular transverse cross-section, the upper angle of which in rear view is less than 130°. Additionally, these autapomorphies form a unique combination with traits that in themselves are not unique. The rear lacrimal bone is transversely wide as in Acristavus but not Brachylophosaurus. Of the front branch of the jugal, the lower corner is positioned behind the level of the upper corner, as with Acristavus but not Brachylophosaurus. The squamosals touch each other at the skull midline as with Acristavus but not Brachylophosaurus. The nasal bone skull crest is massive and almost horizontally oriented to the rear as in Brachylophosaurus but different from Acristavus.
Probrachylophosaurus was, within the Hadrosaurinae, placed in the Brachylophosaurini by the describing authors. Adding the traits of Probrachylophosaurus to two earlier datasets of cladistic analyses, resulted in slightly conflicting positions. In one analysis it was recovered as the sister species of Brachylophosaurus; in the other as a sister species of a clade consisting of Brachylophosaurus and Maiasaura. In both evolutionary trees Acristavus was in a more basal position. The authors suggested that Acristavus might have been a direct ancestor of Probrachylophosaurus and the latter, in view of its intermediate smaller crest form, again an ancestor of Brachylophosaurus that lived about 1.5 million years later.
The revised analysis of Albert Prieto-Márquez resulted in the following evolutionary tree:
The describing article also published the result of histological research of the bone structure of the left shinbone of the type specimen. This bone showed fourteen LAGs, lines of arrested growth, that likely represented yearly seasons of low food intake. The age of the holotype would thus be about fourteen years. The distance between the lines indicated this individual had not yet reached its maximum size, but closely approached it, proof that it was not simply a subadult Brachylophosaurus specimen with a small crest.
The lines also showed a general slowing of the growth after the fifth year. This could have been an indication sexual maturity was reached at that age. If so, the onset of maturity was about two years later than with Maiasaura.
Aquilarhinus (meaning "eagle snout" after the unusual beak morphology) is a genus of hadrosaurid ornithopod dinosaur from the Aguja Formation from Texas in the United States. The type and only species is Aquilarhinus palimentus. Due to its unusual dentary, it has been inferred to have had shovel-like beak morphology, different from the beaks of other hadrosaurs. It was originally classified as a Kritosaurus sp. before being reclassified as a new genus in 2019.Aralosaurini
Aralosaurini is a tribe of basal lambeosaurine hadrosaurs endemic to Eurasia. It currently contains Aralosaurus (from the Aral sea of Kazakhstan) and Canardia (from Toulouse, Southern France).Brachylophosaurini
Brachylophosaurini is a tribe of saurolophine hadrosaurs with known material being from N. America and potentially Asia. It contains at least four taxa; Acristavus (from Montana and Utah), Brachylophosaurus (from Montana and Alberta), Maiasaura (also from Montana), and Probrachylophosaurus (also from Montana). A hadrosaur from the Amur river, Wulagasaurus, might be a member of this tribe, but this is disputed. The group was defined by Terry A. Gates and colleagues in 2011.The clade Brachylophosaurini was defined as "Hadrosaurine ornithopods more closely related to Brachylophosaurus, Maiasaura, or Acristavus than to Gryposaurus or Saurolophus".Canardia
Canardia is an extinct genus of aralosaurin lambeosaurine dinosaur known from the Late Cretaceous Marnes d’Auzas Formation (late Maastrichtian stage) of Toulouse, Haute-Garonne Department, southern France. The type species Canardia garonnensis was first described and named by Albert Prieto-Márquez, Fabio M. Dalla Vecchia, Rodrigo Gaete and Àngel Galobart in 2013.Choyrodon
Choyrodon is a genus of hadrosauroid dinosaur from the Early Cretaceous Albian-age Khuren Dukh Formation of Mongolia. The type and only species is Choyrodon barsboldi. The generic name is derived from the city of Choyr, and -odon, from Greek for tooth; the specific name barsboldi honours paleontologist Rinchen Barsbold. The material consists of a holotype partial skull and cervical ribs, with two other partial skulls both with associated postcranial material. It was found to be the sister taxon of Eolambia.Elasmaria
Elasmaria is a clade of iguanodont ornithopods known from Cretaceous deposits in South America, Antarctica, and Australia.Iguanodontia
Iguanodontia (the iguanodonts) is a clade of herbivorous dinosaurs that lived from the Middle Jurassic to Late Cretaceous. Some members include Camptosaurus, Dryosaurus, Iguanodon, Tenontosaurus, and the hadrosaurids or "duck-billed dinosaurs". Iguanodontians were one of the first groups of dinosaurs to be found. They are among the best known of the dinosaurs, and were among the most diverse and widespread herbivorous dinosaur groups of the Cretaceous period.Jaxartosaurus
Jaxartosaurus is a genus of hadrosaurid dinosaur similar to Corythosaurus which lived during the Late Cretaceous. Its fossils were found in Kazakhstan.Jeyawati
Jeyawati is a genus of hadrosauroid dinosaur which lived during the Turonian stage of the Late Cretaceous. The type species, J. rugoculus, was described in 2010, based on fossils recovered in the U.S. state of New Mexico.The holotype, MSM P4166, was discovered in the Moreno Hill Formation. A cladistic analysis indicates that Jeyawati was more plesiomorphic (ancestral) than Shuangmiaosaurus, Telmatosaurus, and Bactrosaurus, but more derived (less like the common ancestor) than Eolambia, Probactrosaurus, and Protohadros.Koshisaurus
Koshisaurus is a monospecific genus of basal hadrosauroid from the Kitadani Formation in Japan. The discovery of the genus suggests that hadrosauroids had higher diversity along the eastern margin of Asia in the Early Cretaceous. "Koshi" means an old Japanese regional name including Fukui prefecture where fossils of the genus were discovered.Laiyangosaurus
Laiyangosaurus ("Laiyang lizard") is a genus of saurolophine hadrosaurid from the Late Cretaceous of China. It is known from one species, L.youngi, found in the Laiyang Basin within the province of Shandong.Lapampasaurus
Lapampasaurus is an extinct genus of hadrosaurid known from the Late Cretaceous Allen Formation (late Campanian or early Maastrichtian stage) of La Pampa Province, Argentina. It contains a single species, Lapampasaurus cholinoi.The generic name refers to the Argentine province of La Pampa. The specific name honours the late collector José Cholino. The material includes cervical, dorsal, sacral and caudal vertebrae, the forelimb girdle, and the partial hindlimb.Osmakasaurus
Osmakasaurus is a genus of herbivorous iguanodontian dinosaur. It is a basal iguanodontian which lived during the lower Cretaceous period (Valanginian age) in what is now Buffalo Gap of South Dakota, United States. It is known from the Chilson Member of the Lakota Formation. This genus was named by Andrew T. McDonald in 2011 and the type species is Osmakasaurus depressus. O. depressus was previously referred to as Camptosaurus depressus, and was first described in 1909 by Charles W. Gilmore.Parasaurolophini
Parasaurolophini is a tribe of derived lambeosaurine hadrosaurids that are native to Asia, N. America, and probably Europe. It is defined as everything closer to Parasaurolophus walkeri than to Lambeosaurus lambei. It currently contains Charonosaurus (from China), Parasaurolophus (from Utah, New Mexico, China and Alberta), and possibly Blasisaurus and Arenysaurus (both from Spain)Penelopognathus
Penelopognathus ("wild duck jaw") is a genus of dinosaur which lived during the Early Cretaceous. It was an iguanodont ancestral to hadrosaurids. Fossils have been found in the Bayin-Gobi Formation in what is now China. The type species, Penelopognathus weishampeli, was described by Godefroit, Li, and Shang in 2005, based on fragmentary jaw fossils.Plesiohadros
Plesiohadros is an extinct genus of hadrosauroid dinosaur. It is known from a partial skeleton including the skull collected at Alag Teg locality, from the Campanian Djadochta Formation of southern Mongolia. The type species is Plesiohadros djadokhtaensis.Rhabdodontomorpha
Rhabdodontomorpha is a clade of basal iguanodont dinosaurs. This group was named in 2016 in the context of the description, based on Spanish findings, of an early member of the Rhabdodontidae. A cladistic analysis was conducted in which it was found that Muttaburrasaurus was the sister species of the Rhabdodontidae sensu Weishampel. Therefore, Paul-Emile Dieudonné, Thierry Tortosa, Fidel Torcida Fernández-Baldor, José Ignacio Canudo and Ignacio Díaz-Martínez defined Rhabdodontomorpha as a nodal clade: the group consisting of the last common ancestor of Rhabdodon priscus Matheron, 1869 and Muttaburrasaurus langdoni Bartholomai and Molnar, 1981; and all its descendants. Within the clade are included also Zalmoxes and Mochlodon.The group consists of small to large plant eaters from Europe and Gondwana. It must have split from other iguanodont groups during the Middle Jurassic.Sahaliyania
Sahaliyania (from "black" in Manchu, a reference to the Amur/Heilongjiang River) is a genus of lambeosaurine hadrosaurid dinosaur (crested duckbilled dinosaur) from the Late Cretaceous of Heilongjiang, China.Xuwulong
Xuwulong is a genus of hadrosauroid dinosaur from the Early Cretaceous period. It lived during the early Cretaceous period (Aptian-Albian age) in what is now Yujingzi Basin in the Jiuquan area, Gansu Province of northwestern China. It is known from the holotype – GSGM F00001, an articulated specimen including a complete cranium, almost complete axial skeleton, and complete left pelvic girdle from Xinminpu Group. Xuwulong was named by You Hailu, Li Daqing and Liu Weichang in 2011 and the type species is Xuwulong yueluni.