Iguanodontidae

Iguanodontidae is a family of iguanodontians belonging to Styracosterna, a derived clade within Ankylopollexia.

Characterized by their elongated maxillae, they were herbivorous and typically large in size. This family exhibited locomotive dynamism; there exists evidence for both bipedalism and quadrupedalism within iguanodontid species, supporting the idea that individual organisms were capable of both locomoting exclusively with their hind limbs and locomoting quadrupedally.[1] Iguanodontids possess hoof-like second, third, and fourth digits, and in some cases, a specialized thumb spike and an opposable fifth digit.[2] Their skull construction allows for a strong chewing mechanism called a transverse power stroke.[3] This, paired with their bilateral dental occlusion, made them extremely effective as herbivores.[4] Members of Iguanodontidae are thought to have had a diet that consisted of both gymnosperms and angiosperms, the latter of which co-evolved with the iguanodontids in the Cretaceous period.[5]

There is no consensus on the phylogeny of the group. Iguanodontidae is most frequently characterized as paraphyletic with respect to Hadrosauridae,[6][7] although some researchers advocate for a monophyletic view of the family.[8][9]

Iguanodontidae
Temporal range: Early Cretaceous
Iguanodon de Bernissart IRSNB 01
Iguanodon bernissartensis mounted in modern quadrupedal posture, Royal Belgian Institute of Natural Sciences, Brussels
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Ornithischia
Suborder: Ornithopoda
Clade: Hadrosauriformes
Family: Iguanodontidae
Cope, 1869
Subgroups

Description

Skull and Mandible

The upper surface of a typical iguanodontid skull has a convex curve that extends from the snout to just past the orbit, where the skull flattens out to form a roughly level plane directly above the braincase.[3] The antorbital fenestra, an opening in the skull anterior to the eye sockets, is reduced in size in iguanodontids. Their maxillae are roughly triangular, fairly flat, and sport thickened bony walls. An elongated maxilla is characteristic of the family.[10] Iguanodontid dentaries are very long as well, and become increasingly thick towards the back of the skull. A pair of bony processes extending from the maxilla insert into the jugal and lacrimal, respectively. The iguanodontid jugal has particularly deep crevices that serve to mediate this contact. The lacrimal process constitutes the rostral margin of the reduced antorbital fenestra.[3]

Teeth

Iguanodontids are generally limited to the possession of single replacement tooth at each position, although exceptions exist. The most primitive example bears positions for 13 maxillary and 14 dentary teeth. More derived forms have a larger number of positions per row. For example, I. bernissartensis is able to accommodate up to 29 maxillary and 25 dentary teeth. Iguanodontids exhibit contact between maxillary and dentary teeth upon closure of the jaw.[4] They have a thick layer of enamel over the lip-facing (labial) surface of the crown, a robust primary ridge beginning at the base of the crown, and a denticulate margin. Most members of the family have maxillary tooth crowns lanceolate in shape. The labial surface of the teeth has some grooves, while the tongue-facing (lingual) surface is smooth. Iguanodontids have lost their premaxillary teeth.[3]

Manus and Pes

Iguanodon manus 1 NHM
Hand with spike

The second, third, and fourth digits of the iguanodontid forelimb are close together. In some cases, it is possible that digits three and four were bound into a single structure by layers of skin, a specialized adaptation for quadruped locomotion.[2] In addition, the wrist bones are fused into a block, and the thumb bones are fused into a spike-like point. In Iguanodon, the fifth digit is long, flexible, and opposable. On the hind limb, digits two, three, and four are wide and short, with blunt claws that resemble hooves.[3]

Body

All of the cervical vertebrae have ribs attached. The initial set are linear; the rest are two-headed. Tendons along the neural arches were ossified, limiting mobility in the backbone in exchange for reinforcement. A similar ossification is seen in the tail.[10] Iguanodontids have a rod-shaped pubis that extends parallel to the ischium. The paired sternal bones are often hatchet-shaped. The humerus has a shallow curve, in contrast to the straight ulna and radius. The ilium is thinner at the anterior end than it is at the posterior. Evidence suggests that these dinosaurs do not have plated, armored skin.[3]

Classification

In the past, Iguanodontidae became a waste-basket for any ornithopod that did not belong in either Camptosauridae, Hadrosauridae, or the now defunct Hypsilophodontidae. A number of studies suggest that Iguanodontidae as traditionally defined is paraphyletic with respect to Hadrosauridae.[11] That is, iguanodontids represent successive steps in the acquisition of advanced hadrosaurian characteristics, and in this view cannot be defined as a single distinct clade.[12] Nevertheless, some researchers have found support for a monophyletic Iguanodontidae consisting of a handful of genera.[8][9] Some other studies, however, fail to recover the group.[6] The left cladogram was recovered in a 2015 analysis that supports a monophyletic Iguanodontidae,[9] whereas the right cladogram from 2012 study finds the group to be paraphyletic:[7]

Camptosaurus

Batyrosaurus

Ouranosaurus

Hadrosauroidea

Iguanodontidae

Barilium

Mantellisaurus

Iguanodon

Proa

Jinzhousaurus

Bolong

Camptosaurus

Uteodon

Hippodraco

Theiophytalia

Iguanacolossus

Lanzhousaurus

Kukufeldia

Barilium

Iguanodon

Mantellisaurus

Hadrosauroidea

Palaeobiology

Locomotion

Mantellisaurus atherfieldensis Steveoc
Mantellisaurus in quadrupedal posture

Fossilized footprints provide evidence for both quadrupedality and bipedality within iguanodontids. It is thought that iguanodontids were primarily quadrupedal but could optionally walk on two limbs. The ossification of tendons along the neural arches may have played a role in facilitating the dynamic pedality of iguanodontids, as the ossified tendons could help withstand the additional stress incurred on the backbone by standing upright.[10] Some research suggests that organism size plays a role in the determination of pedality, where larger organisms are more likely to choose to walk on all fours than their smaller counterparts.[1]

Diet

Iguanodontids are low-browsing herbivores that fed extensively on gymnosperms like ferns and horsetails, especially during the early Cretaceous period. These dinosaurs were very effective as herbivores due in part to their combination of bilateral dental occlusion with the transverse power stroke of their chewing mechanism. Additionally, iguanodontids lack a rigid secondary palate, which helps to mitigate torsional stresses during occlusion, a feature that enhanced their ability to break down plant matter.[3] Additionally, the iguanodontids co-evolved with the radiation of angiosperms in the Cretaceous period. Angiosperms typically develop more rapidly and lower to the ground than gymnosperms; their proliferation provided a wealth of easily accessible food for the members of Iguanodontidae.[5]

References

  1. ^ a b Galton, Peter (1976). "The Dinosaur Vectisaurus valdensis (Ornithischia: Iguanodontidae) from the Lower Cretaceous of England". Journal of Paleontology. 50 (5): 976–984.
  2. ^ a b Moratalla, J.J. (1992). "A Quadrupedal Ornithopod Trackway from the Lower Cretaceous of La Rioja (Spain): Inferences on Gait and Hand Structure". Journal of Vertebrate Paleontology. 12 (2): 150–157. doi:10.1080/02724634.1992.10011445. JSTOR 4523436.
  3. ^ a b c d e f g Godefroit, Pascal (2012). Bernissart Dinosaurs and Early Cretaceous Terrestrial Ecosystems.
  4. ^ a b Weishampel, David (2012). Evolution of Jaw Mechanisms in Ornithopod Dinosaurs.
  5. ^ a b Barrett, P.M. (2001). "Did Dinosaurs invent flowers? Dinosaur-angiosperm coevolution revisited". Biol. Revs. 76: 411–447. doi:10.1017/s1464793101005735.
  6. ^ a b McDonald, A.T.; Kirkland, J.I.; DeBlieux, D.D.; Madsen, S.K.; Cavin, J.; Milner, A.R.C.; Panzarin, L. (2010). Farke, Andrew Allen (ed.). "New Basal Iguanodontians from the Cedar Mountain Formation of Utah and the Evolution of Thumb-Spiked Dinosaurs". PLoS ONE. 5 (11): e14075. doi:10.1371/journal.pone.0014075. PMC 2989904. PMID 21124919.
  7. ^ a b Mcdonald, Andrew (2012). "Phylogeny of Basal Iguanodonts (Dinosauria: Ornithischia): An Update". PLoS ONE. 7: e36745. doi:10.1371/journal.pone.0036745. PMC 3358318.
  8. ^ a b Godefroit P, Escuillié F, Bolotsky YL, Lauters P. 2012. A new basal hadrosauroid dinosaur from the Upper Cretaceous of Kazakhstan. In: Godefroit P, ed. Bernissart dinosaurs and Early Cretaceous terrestrial ecosystems. Bloomington & Indianapolis: Indiana University Press, 335–358.
  9. ^ a b c Norman, D. B. (2015). "On the history, osteology, and systematic position of the Wealden (Hastings group) dinosaur Hypselospinus fittoni (Iguanodontia: Styracosterna)". Zoological Journal of the Linnean Society. 173: 92–189. doi:10.1111/zoj.12193.
  10. ^ a b c Lucas, Spencer (1998). Lower and Middle Cretaceous Terrestrial Ecosystems: Bulletin 14.
  11. ^ Sereno, Paul. "Phylogeny of the bird-hipped dinosaurs". national geographic research. 2: 234–256.
  12. ^ Wang, Xaolin (2001). "A new iguanodontid (Jin- zhousaurus yangi gen. et sp. nov.) from the Yixian For- mation of western Liaoning, China". Chinese Science Bulletin. 46 (19). doi:10.1007/bf02900633.
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).

Burianosaurus

Burianosaurus is a genus of ornithopod dinosaur that lived in what is now the Czech Republic (it was found in 2003 near the city of Kutná Hora), being the first validly named dinosaur from that country. It was named B. augustai in 2017; the genus name honours the Czech palaeoartist Zdeněk Burian, and the species name honours the Czech palaeontologist Josef Augusta. The holotype specimen is a femur discovered in 2003, which was described as possibly belonging to an iguanodont in 2005.

Callovosaurus

Callovosaurus (meaning "Callovian lizard") 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.

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.

Dryosauridae

Dryosaurids were primitive iguanodonts. They are known from Middle Jurassic to Early Cretaceous rocks of Africa, Europe, and North America.

Elasmaria

Elasmaria is a clade of iguanodont ornithopods known from Cretaceous deposits in South America, Antarctica, and Australia.

Gongpoquansaurus

Gongpoquansaurus (meaning "Gongpoquan reptile") is an extinct genus of basal hadrosauroid dinosaur that was not formally named until 2014, while the name was a nomen nudum for many years previously. It is known from IVPP V.11333, a partial skull and postcranial skeleton. It was collected in 1992 at locality IVPP 9208–21, from the Barremian Zhonggou Formation (Xinminpu Group), in Mazongshan, Gansu Province, China. The specimen was first described and named by Lü Junchang in 1997 as the third species of Probactrosaurus, Probactrosaurus mazongshanensis. Following its description, several studies found it to be less derived than the type species of Probactrosaurus in relation to Hadrosauridae. Therefore, "Gongpoquansaurus" had been suggested, yet informally, as a replacement generic name. In 2014, the species was formally redescribed, and the describers erected Gongpoquansaurus.

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.

Iguanodon

Iguanodon ( i-GWAH-nə-don; meaning "iguana-tooth") is a genus of ornithopod dinosaur that existed roughly halfway between the first of the swift bipedal hypsilophodontids of the mid-Jurassic and the duck-billed dinosaurs of the late Cretaceous. While many species have been classified in the genus Iguanodon, dating from the late Jurassic Period to the early Cretaceous Period of Asia, Europe, and North America, research in the first decade of the 21st century suggests that there is only one well-substantiated species: I. bernissartensis, which lived from the late Barremian to the earliest Aptian ages (Early Cretaceous) in Belgium, Spain, England and possibly elsewhere in Europe, between about 126 and 113 million years ago. Iguanodon were large, bulky herbivores. Distinctive features include large thumb spikes, which were possibly used for defense against predators, combined with long prehensile fifth fingers able to forage for food.

The genus was named in 1825 by English geologist Gideon Mantell but discovered by William Harding Bensted, based on fossil specimens found in England, some of which were subsequently assigned to Mantellodon. Iguanodon was the second type of dinosaur formally named based on fossil specimens, after Megalosaurus. Together with Megalosaurus and Hylaeosaurus, it was one of the three genera originally used to define Dinosauria. The genus Iguanodon belongs to the larger group Iguanodontia, along with the duck-billed hadrosaurs. The taxonomy of this genus continues to be a topic of study as new species are named or long-standing ones reassigned to other genera.

Scientific understanding of Iguanodon has evolved over time as new information has been obtained from fossils. The numerous specimens of this genus, including nearly complete skeletons from two well-known bone beds, have allowed researchers to make informed hypotheses regarding many aspects of the living animal, including feeding, movement, and social behaviour. As one of the first scientifically well-known dinosaurs, Iguanodon has occupied a small but notable place in the public's perception of dinosaurs, its artistic representation changing significantly in response to new interpretations of its remains.

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.

Jinzhousaurus

Jinzhousaurus is a genus of hadrosauroid dinosaur of the Early Cretaceous of China. The type species is Jinzhousaurus yangi. The generic name refers to the town Jinzhou. The specific name honours Yang Zhongjian as the founder of Chinese paleontology. It was first described by Wang Xiao-lin and Xu Xing in 2001.

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.

Muttaburrasaurus

Muttaburrasaurus was a genus of herbivorous ornithopod dinosaur, which lived in what is now northeastern Australia sometime between 112 and 99.6 million years ago during the early Cretaceous Period. It has been recovered in some analyses as a member of the iguanodontian family Rhabdodontidae. After Kunbarrasaurus, it is Australia's most completely known dinosaur from skeletal remains. It was named after Muttaburra, the site in Queensland, Australia, where it was found.

Orcauichnites

Orcauichnites is an ichnogenus of dinosaur footprint.

Ornithopoda

Ornithopods () or members of the clade Ornithopoda ( or ) are a group of ornithischian dinosaurs that started out as small, bipedal running grazers, and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world, and dominated the North American landscape. 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 in the duck-bills (hadrosaurs), before they were wiped out by the Cretaceous–Paleogene extinction event along with all other non-avian dinosaurs. Members are known from all seven continents, though they are generally rare in the Southern Hemisphere.

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.

Proa valdearinnoensis

Proa is a genus of basal styracosternan iguanodont known from the Early Cretaceous Escucha Formation (lower Albian stage) of Teruel Province, Spain.

Probactrosaurus

Probactrosaurus (meaning "before Bactrosaurus") is an early herbivorous hadrosauroid iguanodont dinosaur. It lived in Mongolia and China during the Late Cretaceous period.

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