dinosauromorph
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What is a dinosauromorph?
A dinosauromorph is any archosaurian reptile more closely related to dinosaurs than to pterosaurs. Dinosauromorpha includes all dinosaurs (including birds) plus some dinosaur-like reptiles that possess some, but not all, of the features of dinosaurs.
Dinosauromorphs that are not considered to be true dinosaurs are the most basal members of the group and have generally primitive features compared with the dinosaurs. The basal dinosauromorphs lived in the Middle and Late Triassic periods (about 246 million to 200 million years ago). They were relatively small (1 metre [3.3 feet] in length), and most were bipedal.
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How are dinosauromorphs related to dinosaurs?
Dinosauromorphs are a group of archosaurian reptiles that include dinosaurs and all reptiles more closely related to dinosaurs than to pterosaurs. Dinosauromorpha includes all dinosaurs plus some dinosaur-like reptiles that possess some, but not all, of the features of dinosaurs.
Those dinosauromorphs that are not considered to be true dinosaurs are the most basal members of the group and have generally primitive features compared with the dinosaurs. Research has revealed that dinosaurs and basal dinosauromorphs coexisted in faunas for at least 20 million years during the Late Triassic.
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When did dinosauromorphs first appear on Earth?
Dinosauromorphs, a group of archosaurian reptiles more closely related to dinosaurs than to pterosaurs, appeared in the Middle Triassic period, roughly 246 million to 200 million years ago. These basal dinosauromorphs exhibited primitive features compared to true dinosaurs, such as more uniform backbones and simpler hip girdles. However, they shared key traits with dinosaurs and pterosaurs, including a bowed femur, a hingelike knee, and an erect stance.
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What are some examples of early dinosauromorphs?
Dinosauromorphs are archosaurian reptiles closely related to dinosaurs. They include dinosaurs and reptiles sharing a more recent evolutionary link to dinosaurs than to pterosaurs. Basal dinosauromorphs, those not considered true dinosaurs, exhibit primitive traits like uniform backbones and simple hip girdles.
Examples of early dinosauromorphs include:
* Lagerpeton and Dromomeron: Lagerpeton, from the Middle Triassic, was a small, rabbit-like creature known from a hind limb discovered in Argentina. Dromomeron, a related, more complete form, existed in the Late Triassic of Arizona, New Mexico, and Texas.
* Marasuchus: A lightly built, bipedal animal from the Middle Triassic of Argentina, measuring approximately 30ā40 cm in length.
* Silesaurids: Represented by Silesaurus and Eucoelophysis, with Silesaurus being a quadrupedal plant eater.3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How do scientists study dinosauromorph fossils?
Scientists study dinosauromorph fossils using various methods to understand their evolution, relationships, and lifestyles. These methods include:
- Cladistics Comparing dinosauromorph fossils with other known dinosaurs to classify new finds and develop hypotheses about evolutionary relationships.
- Phylogenetic analyses Analyzing relationships by using the methods of cladistics, which dispenses with the traditional taxonomic hierarchy in favour of "phylogenetic trees" that are more explicit about evolutionary relationships.
- Functional anatomic studies Using analogous traits of present-day animals, along with mechanical and theoretical models, to visualize certain aspects of extinct animals.
- Analysis of trackways Estimating walking and running speeds based on the analysis of trackways, combined with biomechanical examination of the legs and joints and reconstruction of limb musculature.
- Paleoecology Determining the environmental conditions under which a fossil organism lived, including the type of biological community and food chain.
- Radiometric dating Measuring how much the radioactive elements in a rock or fossil have disintegrated to reveal its age.
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What features distinguish dinosauromorphs from other prehistoric reptiles?
Dinosauromorphs are archosaurian reptiles that include dinosaurs and reptiles more closely related to dinosaurs than to pterosaurs. Dinosauromorphs that are not true dinosaurs have primitive features such as uniform backbones with fewer distinct segments, more robust shoulder girdles, and simple, triangular hip girdles.
However, dinosauromorphs share features with dinosaurs and pterosaurs, including a bowed femur, a hingelike knee, a strong straight tibia, a reduced fibula, a hingelike ankle, and a long foot with long toe bones. Unlike dinosaurs and pterosaurs, the head of the femur in basal dinosauromorphs is not well offset from the shaft.
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dinosauromorph, any of a group of archosaurian reptiles that includes dinosaurs and all other reptiles bearing a closer evolutionary relationship to dinosaurs than to pterosaurs. Dinosaurs include birds and other theropods, sauropodomorphs, and ornithischiansāfamiliar animals that embody the concept of āDinosauriaā erected by British anatomist and paleontologist Richard Owen in 1842, long before the present diversity and relationships of dinosaurs were known. In contrast, the clade Dinosauromorpha includes all these dinosaurs plus some other dinosaur-like reptiles that possess some, but not all, of the features of dinosaurs.
In the 1980s it was discovered that dinosaurs and the Pterosauria, a group containing flying reptiles called pterosaurs, shared some important features of the skull, vertebral column, and limbs that indicated a close common ancestry. In short, these two major groups of archosaurs from the Mesozoic Era are often regarded as each otherās closest relatives. It was discovered, however, that some nondinosaurian reptiles were more closely related to dinosaurs than to pterosaurs. Such reptiles are included with the dinosaurs in the Dinosauromorpha. Likewise, those archosaurs that include pterosaurs and other animals closer to them than to dinosaurs are considered to be part of the Pterosauromorpha.
Basal forms
Those dinosauromorphs that are not considered to be true dinosaurs are the most basal members of the group, and they have generally primitive features compared with the dinosaurs. For example, the backbones of the basal dinosauromorphs are more uniform and divided into fewer distinct segments along the vertebral column. Their shoulder girdles tend to be more robust, and their hip girdles are simple and triangular. Their limbs share with dinosaurs and pterosaurs a bowed femur (thighbone), a hingelike knee, a strong straight tibia (shin bone) and a reduced fibula (side bone to the tibia), a hingelike ankle, and a long foot with long toe bones. The head of the femur in basal dinosauromorphs, however, is not as well offset from the shaft as it is in dinosaurs and pterosaurs. Similar to dinosaurs and pterosaurs, the other features of the leg indicate that these forms stood erect and walked with a parasagittal gait (swinging the limbs fore and aft as opposed to rotating them). The basal dinosauropmorphs lived in the Middle and Late Triassic periods (about 246 million to 200 million years ago). They were relatively small (1 metre [3.3 feet] in length), and most were bipedal. One group, the silesaurids, grew to about 2 metres (7 feet) in length and reverted to quadrupedality.
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There are three main groups of nondinosaurian dinosauromorphs. None of these groups, however, are particularly diverse. First are the Lagerpetonidae, named for Lagerpeton, a Middle Triassic, small, rabbitlike, long-legged form known mainly from a hind limb discovered in Argentina in the 1960s. In 2007 a related and much more complete form dated to the Late Triassic of Arizona, New Mexico, and Texas was discovered and named Dromomeron. Two species of Dromomeron (D. romeri and D. gregorii) are known but not yet fully described. The second group is represented by Marasuchus (originally named Lagosuchus), another long-legged form from the Middle Triassic of Argentina. It is represented by material that allows a nearly complete skeletonal restoration and shows a lightly built bipedal animal perhaps 40 cm (16 inches) in total length. The third group contains the silesaurids, represented by Silesaurus and Eucoelophysis. Silesaurus is much better known; it was an unusual secondarily quadrupedal plant eater.
Possible replacement by dinosaurs
When the first nondinosaurian dinosauromorphs, such as Marasuchus and Lagerpeton, were found in rocks in Argentina dated to the Middle Triassic, it was thought that they had been quickly replaced when dinosaurs evolved, because fossils of the two groups were never found together in later-formed rocks in which only dinosaurs persisted. Research has shown, however, that in high latitudes dinosaurs and basal dinosauromorphs lived together in faunas for at least 20 million years during the Late Triassic. Thus, at least in some places there was not a rapid ecological replacement by dinosaurs, as had long been thought.