Sauropsida

I really like the Paleozoic. Many important events in evolution occurred during this era, and the spread of land vertebrates is by far the most important of them. Now I want to share some thoughts about what was happening in the late Paleozoic. As you all know, from the Cambrian to the beginning of the Middle Devonian, mollusks and arthropods were the dominant animals in ecosystems (mollusks most likely until the end of the Ludlow epoch of the Silurian). But then noticeable changes occur: vertebrates become the dominant group, first in the seas, and then on land.

The number of trilobites steadily decreased from the Silurian to the Permian, chasmataspidids became extinct in the Devonian, eurypterids moved from the ocean to rivers and lakes from the mid-Devonian, large myriapods and insects became extinct by the middle of the Permian period, and large arachnids even earlier. Why did this happen? I haven't seen any reputable research on this topic, but it seems to me that the whole point is that vertebrates beat the competition with arthropods thanks to their jaws. The jaws of vertebrates turned out to be the best weapon in the fight for survival, since they made it possible to effectively hunt arthropods that were vulnerable, especially during molting.

If we consider this issue in more detail, then... In the Silurian and Early Devonian, many eurypterids lived in the seas. But after the number of jawed fishes increased and large fishes appeared, the giant eurypterids disappeared, and their relatives began to seek salvation in fresh waters. Scorpions, their relatives, have long occupied the safe land and have been apex predators there for at least 30 million years. But after the first amphibians began to walk on land, large scorpions also began to decrease in number. The last giant scorpions are known from Mississippian (Early Carboniferous) deposits. It can be assumed that some of them also lived in the Pennsylvanian period ("late Carboniferous), hiding in deserts from vertebrates that could not yet move far from water. As far as I know, there were no longer any large species among the Mississippian marine arthropods, since cartilaginous shark-like fishes became widespread during that time, and in the Pennsylvanian eugeneodontiforms appeared with teeth ideally suited for chewing shells and carapaces. Large myriapods and insects lived in swampy forests, but there were no aquatic forms among them. The only possible exception is griffinflies. They probably spent the first part of their lives in water, where they risked becoming prey to numerous amphibians. The end of the Carboniferous and beginning of the Permian is characterized not only by the drying of the climate, but also by the appearance of large terrestrial vertebrates, each of which had muscular jaws. And soon after that, large land arthropods also disappeared. In my opinion, the conclusion suggests itself that large arthropods appeared not because of the high concentration of oxygen in the atmosphere, but due to the absence of terrestrial predators. When these predators appeared, large arthropods disappeared. And mostly small species remained, unable to compete with large vertebrates. My conclusion is that our Paleozoic ancestors, beginning in the Devonian period, became dangerous animals. More dangerous than arthropods. And they became like that thanks to their jaws. What do you think about this?

Aftoktoniasaurus

Taxonomic Classification

Domain: Eukarya

Kingdom: Animalia

Phylum: Chordata

Class: Sauropsida

Clade: Dinosauria

Order: Saurischia

Suborder: Theropoda

Family: †Carcharodontosauridae

Subfamily: †Aftoktoniasaurinae

Genus: †Afoktoniasaurus (Morrison et al, 2007)

Species: †Aftoktoniasaurus morrisunis (Morrison et al, 2007)

Synonyms: †Ceratosaurus maximus? (Dalman, 2012)

Basic Information

Height: 4.2 meters

Length: 12.8 meters

Weight: 7.5 tons

Temporal Range: Mid-Jurassic - Early Cretaceous (169.5 MYA - 100.5 MYA)

Region: North America (Oklahoma, United States)

Formation: Morrison Formation

Diet: Carnivore

Prey: Sauropoda, Stegosauria, Allosaurinae

Predators: None

Discovery

Aftoktoniasaurus morrisunis (quad modo (q.m) “Suicide Lizard of Morrison”) is an extinct species of large carnivorous theropod from Jurassic-Cretaceous Oklahoma. It was found in 2002 but was only considered a valid species in 2007. It is identifiable by the large horn on its muzzle.

While in the Dead Zone of the Oklahoman panhandle, Morrison and his group searched for Allosaurus fossils to further research for the Morrison Museum of Natural History. Morrison eventually found a fragment of a maxilla, which he classified as an Allosaurus fragilis. However, when he dug deeper into the Earth, he found a nearly preserved theropod skull, aside from small dents and cracks. At first, Morrison thought it was a specimen of Allosaurus jimmadseni, but it had a horn. Not a horn-like Ceratosaurus or the now-inaccurate reconstruction of Ornitholestes, but a full, five-foot-long, forward-facing, separated horn. It puzzled him until he concluded that it was the thagomizer spike of a Stegosaurid, likely Stegosaurus. Morrison’s claim was challenged when one of the paleontologists on the team, Matthew Sachar, pointed out that the horn was flat, and showed no signs of forced entry. Morrison then came up with the idea that this dinosaur had a horn used to hunt. As he and his team dug around the skull, they eventually struck gold. 12 meters away, Morrison found a small clutch of tail vertebrae. He used the tail vertebrae and skull size, ratioed them to other theropods that shared similarities, and found the animal was likely around 12-14 meters long. This claim was backed up by the discovery of another specimen only 58 meters away. It was a nearly complete specimen.

This specimen showed large claws, and two, barbed canines, and the skull had a thick layer of hardened osteoderms, coined as the “Boss”. Morrison reexamined the specimen’s head he found, and the remnants of the osteoderms were there; the same species. The cervical vertebrae showed points for thick muscles, meaning two things, the reptile had thick neck fat and a powerful neck. It had curved brows, similar to that of the Albertosaurus sarcophagus. Morrison released a press report detailing the discoveries, which was where he first coined the term “The Suicide Lizard of Morrison”, which, after many misconceptions, he clarified as being named after the Morrison Formation, not the discoverer.

In 2012, Brandon Dalman found a nasal of a theropod skull, which showed signs of a horn. Dalman immediately thought it was a Ceratosaurus, and its ratio compared to other specimens made him publish his findings as Ceratosaurus maximus. Other paleontologists, such as Matthew Sachar and Steven Janiski pointed out Dalman’s errors, correctly classifying the specimen as a male Aftoktoniasaurus.

Paleobiology

Aftoktoniasaurus morrisunis was a large species of apex predator in its home. While it was found in Oklahoma, other specimens showed it went as far southwest as Arizona and New Mexico. Its most famous feature, the horn, measured a heavy 5 feet. It’s likely the horn caused the adaptation of a stronger neck to support its large horn. Additionally, some specimens have been found with no horn. While some associated this with a new subspecies or even a new species, it’s now thought that this was likely sexual dimorphism, with males being horned. It had a deep skull, similar to that of Teratophoneus curriei and Tyrannosaurus rex, which meant it could deliver powerful bites, reinforced by their thick neck. The ribcage is smooth and elongated, which suggests a speed-based build, similar to that of Giganotosaurus carolinii or Carcharodontosaurus saharicus, which resulted in its classification under Carcharodontosauridae.

Male specimens measured at an average of 4.2 meters tall, and 12.8 meters long, with females being slightly smaller, at 4.1 meters tall and 11.3 meters long. Thanks to their build, weights have been estimated around 7.5 tons for males, and 5.6 tons for females. A unique feature in the arms showed a thumb. Or, at least, a way smaller finger off the side of the index finger, which had a larger claw than the rest of the fingers. The initial thought was that Aftoktoniasaurus was partially piscivorous, but the claw was shaped to slice, not impale. Its arms were long and robust, comparable to that of Spinosaurinae. Its muzzle was shaped oddly, with the maxilla rising in the middle slightly, and the premaxilla being at this height. This proved the animal was a mix of a wrestler and a chaser. This helped identify its prey. One specimen of Allosaurus jimmadseni showed bite marks in the ribs, and a large tooth stuck in the neck, which matched the upscaled barbed canine found in Aftoktoniasaurus. It also was shown to directly live in packs, with a fossil site showing a specimen of Diplodocus carnegii being killed by 4 specimens of male Aftoktoniasaurus.

Due to its similarity to Allosaurus and Carcharodontosaurus, it was seen as the missing link. Allosaurus and any genera under Allosauridea were put under Allosaurinae, which was classed under Carcharodontosauridae, along with Carcharodontosaurinae, Aftoktoniasaurinae, and Concavenatinae, the latter containing genera such as Concavenator and Altispinax.

Trivia

• Aftoktoniasaurus' working name was Kavalarisaurus (q.m "The Horny Lizard")

• Aftoktoniasuaurus was originally meant to be a genus of Therizinosauridae.

Let's say that dinosaurs had somehow survived into the present and humanity evolved anyways, much like in Ken Ham's warped perception of history. How do you think Linnean taxonomy would classify dinosaurs? We now know birds are just very specialized reptiles, but Linnean taxonomy considers them a different class (I personally get pissed every time birds are considered to be their own class, but I digress).

I think dinosaurs like Stegosaurus, Triceratops, Brachiosaurus, and Spinosaurus would be classified as "reptiles" while Velociraptor would be classified as a "bird" (Deinocheirus would probably be considered to be an extremely large bird), but how would dinosaurs like Tyrannosaurus and Yutyrannus fare? Share your thoughts down below, and you can mention any dinosaur you want.

Pretty much what the title says. I do need this for school(and light reading ig), so PLEASE make it accurate(and it HAS to be peer reviewed-assignment says so)!

I would've just asked for dinosaurs in the title, but archosaurs as a whole has other cool creatures.

Also, NO EVOLUTION OF BIRDS! I'm working on reptiles only, so birds can be mentioned as a side option, but can't be the main focus of a paper. Non-avian dinosaurs are fine though

Also, if you guys can, link other papers on the evolution of venom in reptiles(something I'd like to talk about), and just general reptile and diapsid papers(including archosaurs!)

Yeah that's about it guys. please give papers!

Also which Sauropod is your favorite?