Gary Byrd, a part-time palaeontologist, discovered some remains of this euornithopod (ribs and an ungual) during early 1994 at Flower Mound, Denton County, north-central Texas, which was a part of the Appalachian continent at the time. He informed professional palaeontologist Yuong-Nam Lee of the find, who arranged for the entire preserved fossil to be excavated. It was first reported upon in 1996 by Jason Head of the Dedman College of Humanities and Sciences, Southern Methodist University. The type species Protohadros byrdi was described and named by Head in 1998. The genus name is derived from Greek πρῶτος, protos, "first", en ἁδρός, hadros, "thick", a reference to the fact that Head considered the species the oldest known hadrosaur. The specific name honours Byrd.
The holotype, specimen SMU 7458e Cenomanian. It consists of a partial skull, pieces of ribs, a hand ungual and a [[neur2, of Protohadros, was found in the Woodbine Formation, which dates to the middlal arch]]. In 1997 Lee named possible tracks of Protohadros as the ichnospecies Caririchnium protohadrosaurichnos.
Due to the paucity of the remains, much of the reconstruction of this dinosaur is speculative. The skull is about seventy centimetres long. From this Head estimated the length of the type specimen of Protohadros at seven to eight metres. He pointed out that this specimen was that of a subadult and that fully-grown individuals could have been longer. Protohadros had a massive, very deep set of lower jaws, and the snout was strongly turned down at the front, which according to Head suggested a habit of grazing on low-growing plants, rather than browsing from bushes or overhanging branches. Its diet would then have consisted of the swamp plants which grew in the delta streams in its habitat, scooped up by the broad, down-turned mouth. In some respects Protohadros was intermediate in morphology to more derived hadrosaurids. Like these, it did have pleurokinesis, a cranial joint system that produced the food-grinding action, but only partially in that the quadrate at the back of the skull was still relatively immobile.
Protohadros' rear legs were probably longer than the front pair, and it could move on all fours or walk and run on its hind legs only.
Protohadros was first described as the most basal member of the Hadrosauridae, hence its generic name. However, scientific opinion has since changed and it is now regarded as a non-hadrosaurid iguanodontian, a basal member of the Hadrosauroidea, though one closely related to the Hadrosauridae. The dinosaur's discovery conflicted with the idea that hadrosaurids evolved in Asia, but its reassessment as a less-derived iguanodontian has rendered this discrepancy less problematic.
Altirhinus (; "high snout") is a genus of iguanodontian ornithopod dinosaur from the Early Cretaceous Period of Mongolia.Aquilarhinus
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).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.Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding age. Both age and stage bear the same name.
As a unit of geologic time measure, the Cenomanian age spans the time between 100.5 ± 0.9 Ma and 93.9 ± 0.8 Ma (million years ago). In the geologic timescale it is preceded by the Albian and is followed by the Turonian. The Upper Cenomanian starts approximately at 95 M.a.
The Cenomanian is coeval with the Woodbinian of the regional timescale of the Gulf of Mexico and the early part of the Eaglefordian of the regional timescale of the East Coast of the United States.
At the end of the Cenomanian an anoxic event took place, called the Cenomanian-Turonian boundary event or the "Bonarelli Event", that is associated with a minor extinction event for marine species.Elasmaria
Elasmaria is a clade of iguanodont ornithopods known from Cretaceous deposits in South America, Antarctica, and Australia.Eolambia
Eolambia (meaning "dawn lambeosaurine") is a genus of herbivorous hadrosauroid dinosaur from the early Late Cretaceous of the USA. It contains a single species, E. caroljonesa, named by paleontologist James Kirkland in 1998. The type specimen of Eolambia was discovered by Carole and Ramal Jones in 1993; the species name honors Carole. Since then, hundreds of bones have been discovered from both adults and juveniles, representing nearly every element of the skeleton. All of the specimens have thus far been found in Emery County, Utah, in a layer of rock known as the Mussentuchit Member of the Cedar Mountain Formation.
Measuring up to 6 metres (20 ft) long, Eolambia is a large member of its group. While it closely approaches the Asian hadrosauroids Equijubus, Probactrosaurus, and Choyrodon, in traits of the skull, vertebrae, and limbs, it may actually be more closely related to the North American Protohadros. This grouping, based on the straightness of the quadrate bone and scapula, would represent an isolated, endemic radiation of hadrosauroids. Despite resembling hadrosaurids – lambeosaurine hadrosaurids in particular – in several features, leading to its initial identification as one of them, these similarities have been rejected as either entirely convergent or misinterpreted.
Eolambia would have lived in a forested environment at the edge of lakes in a humid floodplain environment, feeding on gymnosperms, ferns, and flowering plants. The water levels in the lakes changed over time with cyclical wet and dry spells caused by the precession of the Earth, reflected by alternating bands in the sediments of the Mussentuchit Member. As a juvenile, Eolambia would have been preyed upon by large crocodylomorphs residing in the lake waters. With increasing age, however, they became impervious to the crocodylomorphs, and mature individuals (at least eight to nine years in age) were preyed on by large theropods such as the neovenatorid Siats.Hadrosauroidea
Hadrosauroidea is a clade or superfamily of ornithischian dinosaurs that includes the "duck-billed" dinosaurs, or hadrosaurids, and all dinosaurs more closely related to them than to Iguanodon.They are from Asia, Europe and Africa. Many primitive hadrosauroids, such as the Asian Probactrosaurus and Altirhinus, have traditionally been included in a paraphyletic (unnatural grouping) "Iguanodontidae". With cladistic analysis, the traditional Iguanodontidae has been largely disbanded, and probably includes only Iguanodon and perhaps its closest relatives.Hadrosauromorpha
Hadrosauromorpha is a cohort of iguanodontian ornithopods, defined in 2014 by David B. Norman to divide Hadrosauroidea into the basal taxa with compressed manual bones and a pollex, and the derived taxa that lack them. The clade is defined as all the taxa closer to Edmontosaurus regalis than Probactrosaurus gobiensis. This results in different taxon inclusion depending on the analysis.Huehuecanauhtlus
Huehuecanauhtlus is an extinct genus of hadrosauroid dinosaur known from the Late Cretaceous (Santonian stage) of Michoacán, western Mexico. It contains a single species, Huehuecanauhtlus tiquichensis.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.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.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.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.Yunganglong
Yunganglong is an extinct genus of basal hadrosauroid dinosaur known from the early Late Cretaceous lower Zhumapu Formation of Zuoyun County, Shanxi Province of northeastern China. It contains a single species, Yunganglong datongensis.Zuoyunlong
Zuoyunlong is an extinct genus of herbivorous ornithischian dinosaur belonging to the Hadrosauroidea, that lived during the Late Cretaceous in the area of present China.In 2015 the type species Zuoyunlong huangi was named and described by Wang Runfu, You Hailu, Wang Suozhu, Shichao Xu, Yi Jian, Xie Lijuan, Jia and Lei Xing Hai. The generic name refers to the prefecture of Zuoyun with the Chinese word long, "dragon". The specific name honors the Chinese paleontologist Huang Weilong.The holotype, SXMG V 00 004, was found by the team of the Shanxi Regional Geological Survey in a layer of the Zhumapu Formation in the province of Shanxi which dates from the Cenomanian, roughly ninety-five million years old. It consists of two bones from the right-hand half of the pelvis, a partial right ilium with the field number ZY004-001 to which the cover sheet is missing, and the lower end of the shaft of the right ischium, field number ZY004-002. Additional specimens are unassigned.The descriptors established a unique feature derived, or autapomorphy for this taxon: the back sheet of the ilium has only half the length of the main body. The ilium has a preserved length of sixty-two centimeter indicating a body length of about eight meters. The shaft of the buttock ends in a side view in large "foot" the tip of which points obliquely downwards and forwards. The shaft is much higher than transverse width.A cladistic analysis found that Zuoyunlong had a basal position in the Hadrosauroidea, as sister taxon of Probactrosaurus. Zuoyulong was thus in 2015 the most basal hadrosauroid known from the Upper Cretaceous. As the oldest known hadrosauroid outside Asia, Eolambia and Protohadros from North America, also date from the Cenomanian, the descriptors considered that is likely that Zuoyunlong was close to the separation between the Asian and North American hadrosauroids.