All About Theropods: The Beast Foots


Photo: chaiyapruek2520 via Getty Images

The Theropoda dinosaurs (which means "beast-footed") were a suborder of the Saurischian dinos.

The first theropods evolved 230 million years ago in the Triassic epoch, eventually branching into numerous subgroups. One of the bloodlines gave rise to the first birds somewhere during the Jurassic period, if not earlier. Although birds (technically a form of Theropod dinosaur) have persisted to the current day, all other non-avian dinosaurs became extinct after the Cretaceous period, some 65 million years ago.

All theropod dinosaurs walked with two legs. Their ability to rotate or "pronate" their forearms such that their palms turned backward or down towards the ground was severely limited, as was their general range of motion. Numerous herbivorous theropod species evolved during the Cretaceous, but the vast majority of theropods were carnivores.

In many ways, theropods stood in stark contrast to sauropods. The sauropods were lumbering and sluggish, but the theropods were swift and agile. Theropods had similar characteristics to birds, including three toes on each foot, hollow bones, feathers, and egg-laying nests.

The Biggest Therapods To Exist

Spinosaurus aegyptiacus

This bizarre animal's skull resembled a modern crocodilian whose conical teeth were both straight and unarmed. Its towering neural spines generated its distinctive sail-like back structure, some of which reached a length of 1.65 meters (5.4 ft).

It was the best swimmer of all the gigantic theropod dinosaurs thanks to characteristics like its enormous tail fin and low center of gravity. The maximum length for this beast was 14 meters (49 feet), and its maximum weight was 4 tons (4.4 short tons).

According to the available evidence, Spinosaurus probably ate fish most of the time. Experts think it hunted similarly to a modern heron or stork by walking into the water and poking its head under the surface to catch fish. Likely, it occasionally hunted land mammals, too.

About 99 to 93.5 million years ago, Spinosaurus inhabited the area that is now North Africa. The enormous theropod Carcharodontosaurus was one of its neighbors.

Tyrannosaurus rex

Tyrannosaurus rex is the most well-known dinosaur, a prehistoric classic, and a pop culture beast frequently featured in the media. The enormous size, terrifying jaws, and enormous teeth of the T. rex are just a few of the many reasons why this dinosaur immediately captures our interest.

Despite this, evolution over hundreds of millions of years created some other carnivorous dinosaurs that were just as terrifying and had a similar impact on their environments. Even though they are terrifying, these animals are often neglected in favor of the "tyrant lizard king" in popular media.

Giganotosaurus carolinii

It's safe to assume that anything whose given name begins with "Giga" is massive in stature. Here, we're not just dealing with a massive creature; it's also a dangerous predator.

It is estimated that the maximum length of a Giganotosaurus was between 12 and 13 meters (39 to 43 ft). Its gigantic head was accompanied by a lengthy tail, robust arms with three clawed fingers, and sturdy legs.

The 'giant southern lizard' belonged to a group of carcharodontosaurids that included Carcharodontosaurus, Mapusaurus, and Tyranotitan. These enormous predators were the largest allosauroids ever to evolve, and all of them were comparable in size to Tyrannosaurus rex.

The Smallest Therapods To Exist

Parvicursor remotus

Alvarezsaurian dinosaur Parvicursor remotus was relatively small. It's the tiniest dinosaur ever discovered, measuring in at a size slightly smaller than a chicken. It could run fast thanks to its long, lean legs. Its forelimbs were small and stocky, and its hands had almost fully fused into a single large claw, probably adapted for breaching stubborn termite mounds.

The claw's lack of length and flexibility make it improbable that it would have been effective as a defensive weapon.

Only a single, mostly intact skeleton has been found, missing only the skull, jaw, and front legs. There is still no sign of a skull. It has been given its own family by its discoverers, the Parvicursoridae, and is located in the same region of the cladogram as the Mononykus and Alvarezsaurus.

Ceratonykus oculatus

Ceratonykus is yet another alvarezsaur on our list. It is known only from incomplete remains. Thus we don't know much about it.

It existed during the Campanian period of the Late Cretaceous, from 83.6 to 72.1 million years ago, and was probably about 1.5 meters in length. Thus, it is among the bigger alvarezsaurs.

It was discovered in Mongolia's Barun Goyot Formation. Its robust bust and biceps indicated it may have foraged for termites.

Ligabueino andesi

Ligabueino is only known from pieces (femur, ilium, pubis, phalanx, and vertebrae). It was originally presented as an adult specimen, but subsequent studies proved it to be a juvenile.

It has been documented in Patagonia, Argentina, as far back as the Barremian period of the Early Cretaceous (about 125 Ma). Its phylogenetic status is up for discussion. Though it has been assigned to the Noasauridae by some, its incompleteness makes it hard to tell if it really is a Noasaur and instead places it squarely in the Abelisauroidea.

For one, it has some odd foot morphology with Noasaurus, which could lend credence to the former location; on the other hand, if it isn't a Noasaur, this would indicate that the foot structure may have evolved independently twice.

What Did Theropods Evolve Into?

There is mounting evidence that birds evolved from theropod dinosaurs and, more specifically, birds belong to the theropod group known as Maniraptora, which also includes dromaeosaurs and oviraptorids. As more and more non-avian theropods closely related to birds are uncovered, the once apparent demarcation between non-birds and birds becomes less so.

Several small theropod dinosaurs were discovered in Liaoning Province, such as the compsognathid Sinosauropteryx and the microraptorian dromaeosaurid Sinornithosaurus in northeast China, proving that these dinosaurs did possess feathers. Because of this, it's been difficult to determine precisely where the line is between birds and reptiles.

The 2002 dromaeosaurid Cryptovolans (perhaps a junior synonym of Microraptor) could fly under its power, as it had uncinate processes on its ribs and a sternal keel. If you want a "bird" with some characteristics of modern birds, Cryptovolans is a better choice than Archaeopteryx.

Because of the powered flight of some of the family's more primitive members, such as the Microraptor, some paleontologists have hypothesized that dromaeosaurids evolved from a flying ancestor and that the bigger members became flightless only later, like contemporary paleognaths like the ostrich.

The discovery of further basal dromaeosaurids, such as Xiaotingia, possibly capable of powered flight, adds more weight to the theory that early dromaeosaurids, rather than later Aves, originated flight in the bird line.

If the dinosaurian origin theory holds, then birds did not originate from the ornithischian (bird-hipped) dinosaurs as is commonly believed but rather from the saurischian (lizard-hipped) dinosaurs. This means that they individually developed the condition of their hip structure. The Therizinosauridae were an odd family of theropods that evolved a hip structure similar to birds for the third time.

A minority of scientists, most notably Larry Martin and Alan Feduccia, have proposed an alternative theory to the dinosaurian origin of birds, which holds that birds (including maniraptoran "dinosaurs") developed from early archosaurs like Longisquama. Most other paleontologists and experts on the evolution of feathers disagree with this view.



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