Iguanodontidae

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Iguanodontids
Temporal range: Early Cretaceous, 126–122  Ma
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Iguanodon de Bernissart IRSNB 01.JPG
Iguanodon bernissartensis mounted in modern quadrupedal posture, Royal Belgian Institute of Natural Sciences, Brussels
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Ornithischia
Clade: Ornithopoda
Clade: Hadrosauriformes
Family: Iguanodontidae
Cope, 1869
Subgroups

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

Contents

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]

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 hand with spike Iguanodon manus 1 NHM.jpg
Iguanodon 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 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 in quadrupedal posture Mantellisaurus atherfieldensis Steveoc.jpg
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]

Related Research Articles

<i>Iguanodon</i> Ornithopod dinosaur genus from Early Cretaceous period

Iguanodon, named in 1825, is a genus of iguanodontian dinosaur. 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, taxonomic revision in the early 21st century has defined Iguanodon to be based on one well-substantiated species: I. bernissartensis, which lived from the late Barremian to the earliest Aptian ages in Belgium, Germany, England, Spain, and possibly elsewhere in Europe, between about 126 and 122 million years ago. Iguanodon was a large, bulky herbivore, measuring up to 9–11 metres (30–36 ft) in length and 4.5 metric tons in body mass. 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.

<i>Hypsilophodon</i> Extinct genus of dinosaurs

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.

<i>Muttaburrasaurus</i> Extinct genus of dinosaurs

Muttaburrasaurus was a genus of herbivorous iguanodontian ornithopod dinosaur, which lived in what is now northeastern Australia sometime between 112 and 103 million years ago during the early Cretaceous period. It has been recovered in some analyses as a member of the iguanodontian clade Rhabdodontomorpha. 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.

<span class="mw-page-title-main">Ornithopoda</span> Extinct suborder of dinosaurs

Ornithopoda is a clade of ornithischian dinosaurs, called ornithopods, 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, dominating the North American land. 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 from all seven continents, though they are generally rare in the Southern Hemisphere.

<i>Ouranosaurus</i> Extinct genus of dinosaurs

Ouranosaurus is a genus of herbivorous basal hadrosauriform dinosaur that lived during the Aptian stage of the Early Cretaceous of modern-day Niger and Cameroon. Ouranosaurus measured about 7 to 8.3 metres long. Two rather complete fossils were found in the Elrhaz Formation, Gadoufaoua deposits, Agadez, Niger, in 1965 and 1970, with a third indeterminate specimen known from the Koum Formation of Cameroon. The animal was named in 1976 by French paleontologist Philippe Taquet; the type species being Ouranosaurus nigeriensis. The generic name is a combination of ourane, a word with multiple meanings, and sauros, the Greek word for lizard. The specific epithet nigeriensis alludes to Niger, its country of discovery. And so, Ouranosaurus nigeriensis could be interpreted as "brave lizard originating from Niger".

<span class="mw-page-title-main">Hypsilophodont</span> Extinct family of dinosaurs

Hypsilophodontidae 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, 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. A 2014 analysis by Norman recovered a grouping of Hypsilophodon, Rhabdodontidae and Tenontosaurus, which he referred to as Hypsilophodontia. All other analyses from around the same time have instead found these latter taxa to be within Iguanodontia.

<span class="mw-page-title-main">Iguanodontia</span> Extinct clade of dinosaurs

Iguanodontia 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.

<i>Altirhinus</i> Extinct genus of dinosaurs

Altirhinus is a genus of hadrosauroid ornithopod dinosaur from the Early Cretaceous period of Mongolia.

Arstanosaurus is a genus of hadrosauroid dinosaur from the Santonian-Campanian-age Upper Cretaceous Bostobe Formation, Kazakhstan. It has had a confusing history, being considered both a hadrosaurid and a ceratopsid, or both at the same time (chimeric).

<i>Jinzhousaurus</i> Extinct genus of dinosaurs

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.

<i>Lurdusaurus</i> Extinct genus of dinosaurs

Lurdusaurus is a genus of massive and unusually shaped iguanodont dinosaur from the Elrhaz Formation in Niger. It contains one species, L. arenatus. The formation dates to the Early Cretaceous, roughly 112 million years ago. Lurdusaurus has a highly atypical body plan for an iguanodont, with a small skull, long neck, rotund torso, and powerful forelimbs and claws, somewhat reminiscent of a ground sloth. Its metacarpals are fused and reinforced into a large block, and the thumb spike is remarkably enormous. These would have allowed the hand to have functioned almost like a ball-and-chain flail. Lurdusaurus is estimated to have been 7–9 m (23–30 ft) long and 2 m high when on all-fours, but its stomach would have been only 70 cm off the ground. It may have weighed 2.5–5.5 t, conspicuously heavy for an iguanodontid this size.

<i>Probactrosaurus</i> Extinct genus of dinosaurs

Probactrosaurus is an early herbivorous hadrosauroid iguanodont dinosaur. It lived in China during the Late Cretaceous period.

<span class="mw-page-title-main">Hadrosauroidea</span> Extinct clade of dinosaurs

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. Their remains have been recovered in Asia, Europe, Africa and the Americas. Many primitive hadrosauroids, such as the Asian Probactrosaurus and Altirhinus, have traditionally been included in a paraphyletic "Iguanodontidae". With cladistic analysis, the traditional Iguanodontidae has been largely disbanded, and probably includes only Iguanodon and perhaps its closest relatives.

<i>Theiophytalia</i> Extinct genus of dinosaurs

Theiophytalia is a genus of herbivorous iguanodontian dinosaur from the lower Cretaceous period of Colorado, USA. It contains a single species, T. kerri.

<i>Cedrorestes</i> Extinct genus of dinosaurs

Cedrorestes is a genus of iguanodontian dinosaur from the Early Cretaceous of Utah. It is based on an incomplete skeleton which was found in the Valanginian-age Yellow Cat Member of the Cedar Mountain Formation.

<span class="mw-page-title-main">Rhabdodontidae</span> Extinct family of dinosaurs

Rhabdodontidae is a family of herbivorous iguanodontian ornithopod dinosaurs whose earliest stem members appeared in the middle of the Lower Cretaceous. The oldest dated fossils of these stem members were found in the Barremian Castrillo de la Reina Formation of Spain, dating to approximately 129.4 to 125.0 million years ago. With their deep skulls and jaws, Rhabdodontids were similar to large, robust iguanodonts. The family was first proposed by David B. Weishampel and colleagues in 2003. Rhabdodontid fossils have been mainly found in Europe in formations dating to the Late Cretaceous.

<i>Hippodraco</i> Extinct genus of dinosaurs

Hippodraco is a genus of iguanodontian ornithopod dinosaur from the Early Cretaceous Cedar Mountain Formation of Utah, United States. The genus contains a single species, H. scutodens, known from a partial skeleton belonging to an immature individual.

<i>Iguanacolossus</i> Extinct genus of dinosaurs

Iguanacolossus is a genus of iguanodontian ornithopod dinosaur that lived in North America during the Early Cretaceous period. It is known from UMNH VP 20205, the associated holotype with a large partial skeleton of a single individual.

<i>Ratchasimasaurus</i> Extinct genus of dinosaurs

Ratchasimasaurus is a genus of iguanodontian ornithopod dinosaur from Early Cretaceous Khok Kruat Formation of Nakhon Ratchasima Province in northeastern Thailand. The type and only species is R. suranareae, named after Thao Suranari, a 19th-century war heroine. It was considered by one study to be a nomen dubium, diagnosed with characters widespread in Styracosterna.

<i>Jianchangosaurus</i> Extinct genus of dinosaurs

Jianchangosaurus is a genus of therizinosaurian dinosaur that lived approximately 126 million years ago during the early part of the Cretaceous Period from the Yixian Formation in what is now China. The nearly complete juvenile specimen was missing only the distal tail. Jianchangosaurus was a small, lightly built, bipedal, ground-dwelling herbivore, that could grow up to an estimated 2 m (6.6 ft) long and was 1 m (3.3 ft) high at the hips.

References

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