Ornithopoda () is a
clade
In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
of
ornithischia
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 ...
n
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
s, called ornithopods (). They represent one of the most successful groups of
herbivorous dinosaurs during the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
. 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
Chewing or mastication is the process by which food is crushed and ground by the teeth. It is the first step in the process of digestion, allowing a greater surface area for digestive enzymes to break down the foods.
During the mastication proc ...
apparatus that became the most sophisticated ever developed by a non-avian dinosaur, rivaling that of modern
mammal
A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
s such as the domestic
cow. They reached their apex of diversity and ecological dominance in the
hadrosaurids (colloquially known as 'duck-bills'), before they were wiped out by the
Cretaceous–Paleogene extinction event
The Cretaceous–Paleogene (K–Pg) extinction event, also known as the K–T extinction, was the extinction event, mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event cau ...
along with all other non-
avian dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
s. Members are known worldwide.
History of research
In 1870,
Thomas Henry Huxley listed
Iguanodontidae (coined by
Edward Drinker Cope
Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontology, paleontologist, comparative anatomy, comparative anatomist, herpetology, herpetologist, and ichthyology, ichthyologist. Born to a wealthy Quaker fam ...
a year earlier
) as one of his three families of dinosaurs (alongside
Megalosauridae
Megalosauridae is a monophyletic Family (taxonomy), family of Carnivore, carnivorous theropod dinosaurs within the group Megalosauroidea. Appearing in the Middle Jurassic, megalosaurids were among the first major radiation of large theropod dino ...
and
Scelidosauridae), including within it the genera ''
Iguanodon
''Iguanodon'' ( ; meaning 'iguana-tooth'), named in 1825, is a genus of iguanodontian dinosaur. While many species found worldwide have been classified in the genus ''Iguanodon'', dating from the Late Jurassic to Early Cretaceous, Taxonomy (bi ...
'', ''
Hypsilophodon
''Hypsilophodon'' (; meaning "high-crested tooth") 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 ...
'', and ''
Hadrosaurus'', in addition to ''
Cetiosaurus
''Cetiosaurus'' ( meaning 'whale lizard', from the Greek '/ meaning 'sea monster' (later, 'whale') and '/ meaning 'lizard'), is a genus of herbivorous sauropod dinosaur from the Middle Jurassic Period, living about 171 to 165 million years ago ...
'' and tentatively ''
Stenopelix''.
The term Ornithopoda was erected by
Othniel Charles Marsh
Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of paleontology. A prolific fossil collector, Marsh was one of the preeminent paleontologists of the nineteenth century. Among his legacies are the discovery or ...
in 1881 as part of his then still ongoing investigation of the classification of Dinosauria. It was considered one of the four definite
orders of dinosaurs, the others being
,
Sauropoda
Sauropoda (), whose members are known as sauropods (; from ''wikt:sauro-, sauro-'' + ''wikt:-pod, -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative t ...
, and
Stegosauria
Stegosauria is a group of Herbivore, herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous Period (geology), periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere (North America, Europe a ...
(
Hallopoda was considered a possible fifth). He subdivided the order into three families:
Camptonotidae,
Iguanodontidae, and
Hadrosauridae
Hadrosaurids (), also hadrosaurs or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod fam ...
; the former was a new name, whereas the latter two were carried over from the nomenclatures of Huxley and
Edward Drinker Cope
Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontology, paleontologist, comparative anatomy, comparative anatomist, herpetology, herpetologist, and ichthyology, ichthyologist. Born to a wealthy Quaker fam ...
respectively. Within Camptonotidae he included the European ''
Hypsilophodon
''Hypsilophodon'' (; meaning "high-crested tooth") 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 ...
'' and three American taxa he named himself, ''
Camptonotus'', ''
Laosaurus'', and ''
Nanosaurus''.
[ ''Camptonotus'' was in 1885 renamed to ''Camptosaurus'', as the original name was pre-occupied by a cricket; the associated family followed suit, becoming Camptosauridae.] In Iguanodontidae, only found in Europe, he included ''Iguanodon
''Iguanodon'' ( ; meaning 'iguana-tooth'), named in 1825, is a genus of iguanodontian dinosaur. While many species found worldwide have been classified in the genus ''Iguanodon'', dating from the Late Jurassic to Early Cretaceous, Taxonomy (bi ...
'' and '' Vectisaurus''. In Hadrosauridae, he included '' Hadrosaurus'', ''Cionodon
''Cionodon'' (meaning 'column tooth') is a dubious genus of hadrosauridae, hadrosauridJ. R. Horner, D. B. Weishampel, and C. A. Forster. 2004. Hadrosauridae. In D. B. Weishampel, H. Osmolska, and P. Dodson (eds.), ''The Dinosauria'' (2nd edition ...
'', and tentatively '' Agathaumas''.
Description
''Ornithopoda'' means "bird feet", from the Greek
Greek may refer to:
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group
*Greek language, a branch of the Indo-European language family
**Proto-Greek language, the assumed last common ancestor of all kno ...
''ornithos'', ''ornis'' ("bird") and ''pous'', ''podos'' ("feet"); this is in reference to members’ characteristic birdlike feet. They were also characterized as lacking in body armour, not developing a horny beak
The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for pecking, grasping, and holding (in probing for food, eating, manipulating and ...
, having an elongated pubis (that eventually extended past the ilium), and having a missing hole in the lower jaw (a Mandibular fenestra). A variety of ornithopods, and related ornithischia
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 ...
ns, had thin cartilaginous
Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...
plates along the outside of the ribs; in some cases, these plates mineralized and were fossilized. The function of these intercostal plates is unknown. They have been found with ''Hypsilophodon
''Hypsilophodon'' (; meaning "high-crested tooth") 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 ...
'', '' Nanosaurus'', ''Parksosaurus
''Parksosaurus'' (meaning "William Parks (paleontologist), William Parks's lizard") is a genus of neornithischian dinosaur from the Maastrichtian, early Maastrichtian-age Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada. It is based ...
'', ''Talenkauen
''Talenkauen'' is a genus of Basal (phylogenetics), 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 Ma ...
'', '' Thescelosaurus'', and '' Macrogryphosaurus'' to date.
The early ornithopods were only about 1 metre (3 feet) long, but probably very fast. They had a stiff tail, like the theropods, to help them balance as they ran on their hind legs. Later ornithopods became more adapted to grazing on all fours; their spines curved, and came to resemble the spines of modern ground-feeders, such as the bison
A bison (: bison) is a large bovine in the genus ''Bison'' (from Greek, meaning 'wild ox') within the tribe Bovini. Two extant taxon, extant and numerous extinction, extinct species are recognised.
Of the two surviving species, the American ...
. As they became more adapted to eating while bent over, they became facultative quadrupeds; still running on two legs, and comfortable reaching up into trees, but spending most of their time walking or grazing on all fours. The taxonomy of dinosaurs previously ascribed to the ''Hypsilophodontidae'' is problematic. The group previously consisted of all non- iguanodontian bipedal ornithischians, but a phylogenetic reappraisal has shown such species to be paraphyletic
Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
. As such, the hypsilophodont family is currently represented only by ''Hypsilophodon
''Hypsilophodon'' (; meaning "high-crested tooth") 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 ...
''.
Later ornithopods became larger, but never rivalled the incredible size of the long-necked, long-tailed sauropod
Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...
s. The very largest, such as '' Shantungosaurus'', were as heavy as medium-sized sauropods (up to 23 metric ton
The tonne ( or ; symbol: t) is a unit of mass equal to 1,000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton in the United States to distinguish it from the non-metric units of the sh ...
s/25 short ton
The short ton (abbreviation: tn
or st), also known as the US ton, is a measurement unit equal to . It is commonly used in the United States, where it is known simply as a ton; however, the term is ambiguous, the single word "ton" being variously ...
s), but never grew much beyond 15 metres (50 feet).
Based on evidence derived from examination of dental microwear Dental microwear analysis is a method to infer diet and behavior in extinct animals, especially in fossil specimens. It has been used on a variety of taxa, including hominids, victoriapithecids, amphicyonids, canids, ursids, hyaenids, hyaenodont ...
, early ornithopods were mainly browsers or frugivores, whereas larger, more derived iguanodontians were bulk feeders that fed on tougher, less nutritious vegetation and were able to subsist on it due to their long gut passage time.
Classification
Historically, most indeterminate ornithischian biped
Bipedalism is a form of terrestrial locomotion where an animal moves by means of its two rear (or lower) limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' ' ...
s were lumped in as ornithopods. Most have since been reclassified.
Taxonomy
Ornithopoda is usually given the rank of Suborder, within the order Ornithischia. While ranked taxonomy has largely fallen out of favour among dinosaur paleontologists, some researchers have continued to employ such a classification, though sources have differed on what its rank should be. Benton (2004) placed it as an infraorder within the suborder Cerapoda
Neornithischia ("new ornithischians") 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 ins ...
(originally named as an unranked clade
In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
), while others, such as Ibiricu ''et al.'' 2010, have retained it at its traditional ranking of suborder.
Iguanodontia is often listed as an infraorder within a suborder Ornithopoda, though Benton (2004) lists Ornithopoda as an infraorder and does not rank Iguanodontia. Traditionally, iguanodontians were grouped into the superfamily Iguanodontoidea and family Iguanodontidae. However, phylogenetic
In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
studies show that the traditional "iguanodontids" are a paraphyletic
Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
grade leading up to the hadrosaurs (duck-billed dinosaurs). Groups like Iguanodontoidea are sometimes still used as unranked clade
In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
s in the scientific literature, though many traditional "iguanodontids" are now included in the more inclusive group Hadrosauroidea. Iguanodontia was originally phylogenetically defined, by Paul Sereno
Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago who has discovered several new dinosaur species on several continents, including at sites in Inner Mongolia, Argentina, Morocco and Niger. ...
, in 1998, as the most inclusive group containing '' Parasaurolophus walkeri'' but not ''Hypsilophodon foxii
''Hypsilophodon'' (; meaning "high-crested tooth") is a neornithischian dinosaur genus from the Early Cretaceous Period (geology), period of England. It has traditionally been considered an early member of the group Ornithopoda, but recent resear ...
''. Later, in 2005, he amended the definition to include '' Thescelosaurus neglectus'' as a secondary external specifier, alongside ''Hypsilophodon'', accounting for the paraphyletic nature of Hypsilophodontidae. A 2017 study which named and described '' Burianosaurus'' noted that the type species '' Iguanodon bernissartensis'' must be part of the definition, and that the 2005 definition would, in their analysis, include a far larger group than intended (including Marginocephalia). They proposed an entirely new, node-based definition: the last common ancestor of ''Iguanodon bernissartensis'', '' Dryosaurus altus'', '' Rhabdodon priscus'', and '' Tenontosaurus tilletti''.
In 2021, Iguanodontia was given a formal definition under the PhyloCode
The ''International Code of Phylogenetic Nomenclature'', known as the ''PhyloCode'' for short, is a formal set of rules governing phylogenetic nomenclature. Its current version is specifically designed to regulate the naming of clades, leaving the ...
: "The smallest clade containing '' Dryosaurus altus'', '' Iguanodon bernissartensis'', '' Rhabdodon priscus'', and '' Tenontosaurus tilletti'', provided that it does not include ''Hypsilophodon foxii
''Hypsilophodon'' (; meaning "high-crested tooth") is a neornithischian dinosaur genus from the Early Cretaceous Period (geology), period of England. It has traditionally been considered an early member of the group Ornithopoda, but recent resear ...
''." Under this revised definition, Iguanodontia is limited to its traditionally included species, and if it were found to include hypsilophodonts, which were not traditionally considered iguanodontians, it would become an invalid grouping.
The slightly less inclusive clade Dryomorpha was named by Paul Sereno in 1986 and given a formal definition in the ''PhyloCode
The ''International Code of Phylogenetic Nomenclature'', known as the ''PhyloCode'' for short, is a formal set of rules governing phylogenetic nomenclature. Its current version is specifically designed to regulate the naming of clades, leaving the ...
'' as "the smallest clade containing '' Dryosaurus altus'' and '' Iguanodon bernissartensis''". This group includes basal members such as '' Hesperonyx'', members of the family Dryosauridae, and the derived clade Ankylopollexia.
Phylogeny
In 2021, Ornithopoda was given a formal definition under the PhyloCode
The ''International Code of Phylogenetic Nomenclature'', known as the ''PhyloCode'' for short, is a formal set of rules governing phylogenetic nomenclature. Its current version is specifically designed to regulate the naming of clades, leaving the ...
: "The largest clade containing '' Iguanodon bernissartensis'' but not '' Pachycephalosaurus wyomingensis'' and ''Triceratops horridus
''Triceratops'' ( ; ) is a genus of Chasmosaurinae, chasmosaurine Ceratopsia, ceratopsian dinosaur that lived during the late Maastrichtian age of the Late Cretaceous Period (geology), period, about 68 to 66 million years ago on the island ...
''."
The cladogram
A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
below follows a 2024 analysis of Fonseca ''et al.''
References
External links
GEOL 104 dinosaurs: a Natural history, ornithopoda: beaks, bills & crests
by Thomas R. Holtz Jr.
{{Taxonbar, from=Q467430
Dinosaur clades