What is a Parasagittal gait?
The parasagittal stance: the erect posture with the hindlimbs positioned directly underneath the body rather than sprawling to the sides In this posture, the muscles running from the femur to the tail are still the main source of propulsion, but that motion is limited to front-to-back motion.
Are crocodiles archosaurs?
Crocodilians and birds are the two extant clades of archosaurs, a group that includes the extinct dinosaurs and pterosaurs. Fossils suggest that living crocodilians (alligators, crocodiles, and gharials) have a most recent common ancestor 80 to 100 million years ago.
Are all reptiles archosaurs?
Archosaurs are broadly classified as reptiles, in the cladistic sense of term which includes birds. Extinct archosaurs include non-avian dinosaurs, pterosaurs, and extinct relatives of crocodilians….Archosauria.
| Crurotarsi | † Parasuchia † Ornithosuchidae Suchia |
|---|---|
| Ornithodira | †?Scleromochlus † Pterosauria Dinosauromorpha |
What are the two major groups of archosaurs?
The true archosaurs are divided into two branches. The Pseudosuchia branch includes crocodiles and all other archosaurs more closely related to crocodiles than to birds. Pseudosuchians comprise mostly extinct Triassic groups such as phytosaurs, aetosaurs, prestosuchids, rauisuchids, and poposaurs.
What is an AM ankle?
The Pseudosuchia have what is called a crurotarsal, or “crocodile-normal” ankle. This is a very flexible arrangement in which the astragalus (medial proximal ankle bone) bears a peg that fits into a socket in the calcaneum (lateral proximal ankle bone).
What gait does birds and most mammals have?
Birds and nearly all mammals have the Fully Erect Gait- the proximal limb segments operate in nearly vertical, parasagittal planes, and the body weight can be supported with less emphasis on muscle power and more on direct transmission of forces through bone and joints than in the Sprawling Gait.
Are turtles archosaurs?
“We show that turtles share a more recent common ancestor with birds and crocodilians — a group known as archosaurs — than with lizards and snakes.” Field and collaborators report their findings May 5 in the journal Evolution and Development. Reptiles comprise a vast animal group of more than 20,000 species.
Is Ostrich an Archosaur?
Living archosaurs comprise birds (dinosaurs), and their sister group, the crocodilians. Archosaurs appeared in fossil record sometime in the Triassic and are thought to have evolved ears sensitive to airborne sound sometime later. Palaeognaths are generally flightless and include such birds as the ostrich.
Do birds have a mandibular Fenestra?
Among extant archosaurs, birds still possess antorbital fenestrae, whereas crocodylians have lost them.
What is the Synapomorphy for archosaurs?
Distinguishing characteristics. The simplest and most widely-agreed synapomorphies of archosaurs are: Teeth set in sockets, which makes them less likely to be torn loose during feeding. This feature is responsible for the name “thecodonts” (“socket teeth”), which paleontologists used to apply to all or most archosaurs.
Do any animals have three legs?
Apart from the parrot conjecture, there are no known species where three legs are standard, although the movement of some macropods such as kangaroos, which can alternate between resting their weight on their muscular tails and their two hind legs and hop on all three, may be an example of tripedal locomotion in …
When did dinosaurs diverge from their archosaur ancestors?
Dinosaurs diverged from their archosaur ancestors during the middle to late Triassic period, roughly 20 million years after the Permian–Triassic extinction event wiped out an estimated 95% of all life on Earth.
Why did Dinosaurs stand with their hind limbs erect?
Dinosaurs stand with their hind limbs erect in a manner similar to most modern mammals, but distinct from most other reptiles, whose limbs sprawl out to either side. This posture is due to the development of a laterally facing recess in the pelvis (usually an open socket) and a corresponding inwardly facing distinct head on the femur.
Are there any dinosaurs above the Paleogene boundary?
Non-avian dinosaur remains are occasionally found above the Cretaceous–Paleogene boundary. In 2001, paleontologists Zielinski and Budahn reported the discovery of a single hadrosaur leg-bone fossil in the San Juan Basin, New Mexico, and described it as evidence of Paleocene dinosaurs.
Which is the only dinosaur to survive the extinction event?
The fossil record shows that birds are the only extant dinosaurs on Earth, having evolved from feathered dinosaurs. Birds evolved from earlier theropods during the Late Jurassic epoch, and are the only dinosaur lineage to survive the Cretaceous–Paleogene extinction event approximately 66 million years ago.