Hypsilophodontidae Temporal range: Early Cretaceous, | |
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Hypsilophodon skeleton | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | † Ornithischia |
Clade: | † Clypeodonta |
Family: | † Hypsilophodontidae Dollo, 1882 [1] |
Subgroups [2] | |
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Synonyms | |
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Hypsilophodontidae (or Hypsilophodontia) is a traditionally used family of ornithopod dinosaurs, generally considered invalid today. It historically included many small bodied bipedal neornithischian taxa from around the world, and spanning from the Middle Jurassic until the Late Cretaceous. This inclusive status was supported by some phylogenetic analyses from the 1990s and mid 2000s, [3] [4] although there have also been many finding that the family is an unnatural grouping which should only include the type genus, Hypsilophodon , with the other genera being within clades like Thescelosauridae and Elasmaria. [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] A 2014 analysis by Norman recovered a grouping of Hypsilophodon, Rhabdodontidae and Tenontosaurus , which he referred to as Hypsilophodontia. [2] All other analyses from around the same time have instead found these latter taxa to be within Iguanodontia. [12] [16]
Hypsilophodontidae was named originally in 1882 by Louis Dollo, as a family to include Hypsilophodon and other small ornithopods with a single row of teeth, four pedal digits, and a rhomboid sternum. For several decades after its naming the family only included Hypsilophodon. [4] In 1911 Karl von Zittel published a textbook on vertebrate classifications, in which he included multiple genera in "Hypsilophodontidae" (sic for Hypsilophodontidae [17] ), including Hypsilophodon, Nanosaurus , Laosaurus and Dryosaurus . Zittel considered the family to unite all taxa that lacked premaxilla teeth, had a single row of maxilla teeth, neck vertebrae which have flat articulations or a flat front and round back, fused sacral vertebrae, a femur shorter than the tibia, 5 fingered manus' and 4 toed peds. [18] Thescelosaurus was named in 1913 by Charles Gilmore, and its skeleton was described in detail by the same author in 1915. Gilmore had originally classified Thescelosaurus within Camptosauridae, but in the 1915 description he determined that it shared far more features with Hypsilophodontidae. He reclassified Laosaurus, Nanosaurus and Dryosaurus in the family Laosauridae, leaving only Thescelosaurus and Hypsilophodon in Hypsilophodontidae. The characteristics of the family were also re-analysed, and Gilmore showed that the premaxilla actually had teeth, a characteristic of the family; the 3rd manus digit had 4 phalanges; the femur was either shorter or longer than the tibia; and dorsal ribs had only a single articulation point. [17]
The first expansive analysis on the relationships of Hypsilophodontidae was that of Swinton in 1936, during a redescription of Hypsilophodon from new specimens. The possible hypsilophodonts Geranosaurus and Stenopelix were removed from the clade (then the subfamily Hypsilophodontinae), and considered to be intermediate basal ornithopods, as there were no features linking them to Hypsilophodon. Thescelosaurus was considered within the family, because of the large number of shared features, as well as Dysalotosaurus , from the Kimmeridgian of Tanzania. Laosaurus and Dryosaurus were not considered hypsilophodonts because of their lack of distinguishable features, as Swinton concluded that they were probably in the family Laosauridae, intermediate between Hypsilophodontidae and Iguanodontidae, and were probably synonyms of each other as well. [19] Charles M. Sternberg (1940) considered there to be multiple genera within the family, all sharing fully enamelled teeth, divided into two subfamilies, Hypsilophodontinae and Thescelosaurinae. Within Hypsilophodontinae–grouped by a longer scapula, thinner forelimb and femora shorter than tibiae–Sternberg included Hypsilophodon, Dysalotosaurus, and Parksosaurus (renaming of Thescelosaurus warreni). Only Thescelosaurus was included in Thescelosaurinae, as it had a tibia shorter than the femur. [20]
Peter M. Galton in 1972 re-studied the relationships of taxa within Ornithischia. Thescelosaurus was removed from Hypsilophodontidae because of its short limbs, meaning it was probably not cursorial, unlike all other hypsilophodonts. The presence of premaxilla teeth, once used to diagnose the group, was found to be present in unrelated taxa like Heterodontosaurus , Protoceratops and Silvisaurus . Galton made Hypsilophodontidae paraphyletic, as he considered Thescelosaurus to be a hypsilophodont, but excluded it from the family Hypsilophodontidae. The phylogenetic hypothesis of Galton is shown below. Taxa considered hypsilophodontids are enclosed by green. [21]
In 1992 David Weishampel and Ronald Heinrich reviewed the systematics and phylogenetics of Hypsilophodontidae. Hypsilophodontidae was supported as a monophyletic clade that encompassed "thescelosaurids", Hypsilophodon and Yandusaurus . The family was diagnosed by the absence of ridges that end as denticles in teeth (reversed in Hypsilophodon); presence of a single central ridge on dentary teeth; ossified sternal plates on torso ribs; and a straight and unexpanded shape of the prepubis. Their resulting cladogram is reproduced below: [4]
The following cladogram of hypsilophodont relationships depicts the paraphyletic hypotheses; the "natural Hypsilophodontidae" hypothesis has been falling out of favor since the mid-late 1990s. It is after Brown et al. (2013), the most recent analysis of hypsilophodonts. [16] Ornithischia, Ornithopoda, and Iguanodontia were not designated in their result, and so are left out here. Additional ornithopods beyond Tenontosaurus are omitted. Dinosaurs traditionally described as hypsilophodonts are found from Agilisaurus or Hexinlusaurus to Hypsilophodon or Gasparinisaura.
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A more recent alternate phylogeny, by Norman in 2014, resolved a monophyletic Hypsilophodontia (the family Hypsilophodontidae was not used because of its history). Hypsilophodon grouped with Rhabdodontidae and Tenontosaurus . [2]
In one analysis in her 2022 review of iguanodontian phylogenetic relationships, Karen E. Poole recovered a large Hypsilophodontidae as the sister taxon of Iguanodontia, which consisted of several "traditional" hypsilophodontids, as well as Thescelosauridae. The Bayesian topology of her phylogenetic analyses is shown in the cladogram below: [22]
In 2023, Longrich et al. described Vectidromeus as a new genus of hypsilophodontid. Although they did not perform a phylogenetic analysis, they suggested that, since other taxa previously assigned to Hypsilophodontidae had subsequently been moved to other groups, Vectidromeus and Hypsilophodon remained as the only members of the clade. [23]
Ornithischia is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name Ornithischia, or "bird-hipped", reflects this similarity and is derived from the Greek stem ornith- (ὀρνιθ-), meaning "bird", and ischion (ἴσχιον), meaning "hip". However, birds are only distantly related to this group as birds are theropod dinosaurs. Ornithischians with well known anatomical adaptations include the ceratopsians or "horn-faced" dinosaurs, the pachycephalosaurs or "thick-headed" dinosaurs, the armored dinosaurs (Thyreophora) such as stegosaurs and ankylosaurs, and the ornithopods. There is strong evidence that certain groups of ornithischians lived in herds, often segregated by age group, with juveniles forming their own flocks separate from adults. Some were at least partially covered in filamentous pelts, and there is much debate over whether these filaments found in specimens of Tianyulong, Psittacosaurus, and Kulindadromeus may have been primitive feathers.
Hypsilophodon is a neornithischian dinosaur genus from the Early Cretaceous period of England. It has traditionally been considered an early member of the group Ornithopoda, but recent research has put this into question.
Ornithopoda is a clade of ornithischian dinosaurs, called ornithopods. They represent one of the most successful groups of herbivorous dinosaurs during the Cretaceous. The most primitive members of the group were bipedal and relatively small-sized, while advanced members of the subgroup Iguanodontia became quadrupedal and developed large body size. Their major evolutionary advantage was the progressive development of a chewing apparatus that became the most sophisticated ever developed by a non-avian dinosaur, rivaling that of modern mammals such as the domestic cow. They reached their apex of diversity and ecological dominance in the hadrosaurids, before they were wiped out by the Cretaceous–Paleogene extinction event along with all other non-avian dinosaurs. Members are known worldwide.
Valdosaurus is a genus of bipedal herbivorous iguanodont ornithopod dinosaur found on the Isle of Wight and elsewhere in England, Spain and possibly also Romania. It lived during the Early Cretaceous.
Thescelosaurus was a genus of neornithischian dinosaur that appeared at the very end of the Late Cretaceous period in North America. It was a member of the last dinosaurian fauna before the Cretaceous–Paleogene extinction event around 66 million years ago. The preservation and completeness of many of its specimens indicate that it may have preferred to live near streams.
Callovosaurus is a genus of iguanodontian dinosaur known from most of a left thigh bone discovered in Middle Jurassic-age rocks of England. At times, it has been considered dubious or a valid genus of basal iguanodontian, perhaps a dryosaurid.
Notohypsilophodon is a genus of ornithopod dinosaur from the Late Cretaceous of Argentina. It was described as the only "hypsilophodont" known from South America, although this assessment is not universally supported, and Gasparinisaura is now believed to have been a basal euornithopod as well.
Parksosaurus is a genus of neornithischian dinosaur from the early Maastrichtian-age Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada. It is based on most of a partially articulated skeleton and partial skull, showing it to have been a small, bipedal, herbivorous dinosaur. It is one of the few described non-hadrosaurid ornithopods from the end of the Cretaceous in North America, existing around 70 million years ago.
Alocodon is a genus of ornithischian dinosaur known from multiple teeth from the Middle or Late Jurassic Cabaços Formation of Portugal, and also the Forest Marble and Chipping Norton Formations of England. A single species is known, A. kuehnei.
Zephyrosaurus is a genus of orodromine ornithischian dinosaur. It is based on a partial skull and postcranial fragments discovered in the Aptian-Albian-age Lower Cretaceous Cloverly Formation of Carbon County, Montana, USA. New remains are under description, and tracks from Maryland and Virginia, also in the US, have been attributed to animals similar to Zephyrosaurus. It lived approximately 113 mya.
Fulgurotherium is a dubious genus of ornithischian dinosaur from the Late Cretaceous (Cenomanian) Griman Creek Formation. It lived in what is now Australia.
Neornithischia is a clade of the dinosaur order Ornithischia. It is the sister group of the Thyreophora within the clade Genasauria. Neornithischians are united by having a thicker layer of asymmetrical enamel on the inside of their lower teeth. The teeth wore unevenly with chewing and developed sharp ridges that allowed neornithischians to break down tougher plant food than other dinosaurs. Neornithischians include a variety of basal forms historically known as "hypsilophodonts", including the Parksosauridae; in addition, there are derived forms classified in the groups Marginocephalia and Ornithopoda. The former includes clades Pachycephalosauria and Ceratopsia, while the latter typically includes Hypsilophodon and the more derived Iguanodontia.
Talenkauen is a genus of basal iguanodont dinosaur from the Campanian or Maastrichtian age of the Late Cretaceous Cerro Fortaleza Formation, formerly known as the Pari Aike Formation of Patagonian Lake Viedma, in the Austral Basin of Santa Cruz, Argentina. It is based on MPM-10001A, a partial articulated skeleton missing the rear part of the skull, the tail, and the hands. The type and only species is Talenkauen santacrucensis.
Kangnasaurus is a genus of iguanodontian ornithopod dinosaur found in supposedly Early Cretaceous rocks of South Africa. It is known from a tooth and possibly some postcranial remains found in the early-Aptian Kalahari Deposits Formation. It was probably similar to Dryosaurus.
Laosaurus is a genus of neornithischian dinosaur. The type species, Laosaurus celer, was first described by O.C. Marsh in 1878 from remains from the Oxfordian-Tithonian-age Upper Jurassic Morrison Formation of Wyoming. The validity of this genus is doubtful because it is based on fragmentary fossils. A second species from the Morrison Formation, L. gracilis, and a species from the late Cretaceous Allison Formation of Alberta, Canada, Laosaurus minimus, are also considered dubious.
Nanosaurus is the name given to a genus of neornithischian dinosaur that lived about 155 to 148 million years ago, during the Late Jurassic-age. Its fossils are known from the Morrison Formation of the south-western United States. The type and only species, Nanosaurus agilis, was described and named by Othniel Charles Marsh in 1877. The taxon has a complicated taxonomic history, largely the work of Marsh and Peter M. Galton, involving the genera Laosaurus, Hallopus, Drinker, Othnielia, and Othnielosaurus, the latter three now being considered to be synonyms of Nanosaurus. It had historically been classified as a hypsilophodont or fabrosaur, types of generalized small bipedal herbivore, but more recent research has abandoned these groupings as paraphyletic and Nanosaurus is today considered a basal member of Neornithischia.
Phyllodon was a genus of small ornithischian dinosaur from the Kimmeridgian-aged Upper Jurassic Camadas de Guimarota Formation of Leiria, Portugal and possibly also the Bathonian-aged Chipping Norton Limestone of England. It may have been closely related to contemporaneous dinosaurs in North America.
Dryosauridae was a family of primitive iguanodonts, first proposed by Milner & Norman in 1984. They are known from Middle Jurassic to Early Cretaceous rocks of Africa, Europe, and North America.
Thescelosauridae is a clade of neornithischians from the Cretaceous of Asia, North America and possibly South America. The group was originally used as a name by Charles M. Sternberg in 1937, but was not formally defined until 2013, where it was used by Brown and colleagues as the group uniting Thescelosaurus and Orodromeus, based on their phylogenetic results. During a phylogenetic revision of neornithischians by Clint Boyd in 2015, the authorship of Thescelosauridae was given to Brown and colleagues, which meant that the similar name Parksosauridae, informally defined in 2002 by Buchholz, would have had priority over Thescelosauridae. The two clades had slightly different definitions, with Parksosauridae referring to all animals closer to Parksosaurus than Hypsilophodon, but they contained the same taxa so Boyd used Parksosauridae under the assumption it had priority. However, in formalizing the clade following the regulations of the PhyloCode, Madzia, Boyd, and colleagues identified in 2021 that Sternberg was the proper authority for Thescelosauridae, giving it priority over Parksosauridae. As well, they gave Thescelosauridae the definition of the largest clade containing Thescelosaurus neglectus but not Iguanodon bernissartensis, as long as Hypsilophodon foxii was not in the group, modifying previous definitions for Thescelosauridae in order to maintain its modern use, so that the clade was not applied if Thescelosaurus fell within Hypsilophodontidae, a family that has not been recently used but may be revived if the systematic position of Hypsilophodon was solidified at some point in the future. Madzia et al. identified the analysis of Madzia et al. in 2018 as the reference analysis for the name Thescelosauridae, an analysis based on a revised version of the 2015 Boyd analysis.