Meet The Dinosaurs

FAS Astronomers Blog, Volume 31, Number 14.

In this article, we’ll focus on several individual dinosaurs and tell you a little more about them. As noted in An Introduction to Dinosaurs and The Classification of Dinosaurs, not all dinosaurs are the same. They came in all sizes and shapes. Some were meat-eaters (carnivores) and some plant-eaters (herbivores). Some lived during the Jurassic period and others during the Cretaceous period.

Most dinosaur groupings preserve the “bird hipped” vs. “lizard hipped” distinction developed in 1887 By Harry Seeley (Seeley 1887).

• Ornithischians had “bird like hips” with the pubic bone pointing backward. They were typically smaller plant-eating dinosaurs (e.g., Stegosaurus and Triceratops) grouped in several ways (e.g., bird feet, fringe headed, horned face, thick headed, spiked, and armored). Please try and avoid any name calling.
• Saurischians had “lizard like hips” with the pubic bone pointing down and forward. They were the large meat-eating Theropods (e.g., rex) and the large plant-eating Sauropods (e.g., Brontosaurus).

Ornithischians

A group of these smaller plant-eating dinosaurs were classified as Thyreophorans. One of the more famous, Stegosaurus, and the less well known Kentrosaurus, were Stegosaurs that lived during the Jurassic period. Stegosaurus is best known for its spikes and its small (“walnut sized”) brain. Ankylosaurs such as Ankylosaurus were similar but appeared later during the Cretaceous period and had armor plating rather than spikes.

Triceratops, part of the subgroup Ceratopsians, also came later during the Cretaceous period. It was the size of an elephant and had three menacing horns and a shield-like appendage on its forehead.

Other Ornithischian dinosaurs, including Iguanodontians (e.g., Iguanodon) and hadrosaurs (large duckbilled dinosaurs such as Hadrosaurus and Edmontosaurus), fell into a subgroup called Ornithopods for their “bird feet”.

Theropods

These large meat-eating dinosaurs are probably the best known. The most famous, Tyrannosaurus rex (T. rex), is familiar to most dinosaur enthusiasts as the “King of the Dinosaurs.” There was also Albertosaurus and Gorgosaurus, smaller cousins of T. rex discovered in Alberta and Allosaurus, a smaller dinosaur similar to T. rex that lived much earlier. T. rex was not, however, the largest of these Theropods. Giganotosaurus, initially found in Argentina, is thought to be slightly larger than T. rex. Spinosaurus (“spine lizard”), discovered in North Africa with its long spine, was larger than both.

In addition to the large theropods such as T. rex, there were also smaller meat-eating theropods called raptors. Some of them are in the family dromaeosaurid (raptors). You might remember one from the movie Jurassic Park. Or maybe not. More on this in The Case of the Velociraptor (coming soon).

Sauropods

These large, long-necked plant-eating dinosaurs are also well known. Most were found during the Jurassic period. The most famous is Brontosaurus, or maybe it is Apatosaurus, or maybe still Brontosaurus. More on this in The Case of the Brontosaurus (coming soon).

Brontosaurus wasn’t the only long-necked Sauropod that lived during the later Jurassic.

Another large Sauropod was Brachiosaurus altihorax, which was discovered by Elmer Riggs in 1900 and named in 1903 (Riggs 1903). At the time, Riggs thought it to be the longest of the Sauropods. It was similar in appearance to the Brontosaurus, sorry Apatosaurus, but with a protruding appendage on its forehead and more of an upright (giraffe-like) stance. It might not be as famous as Brontosaurus/Apatosaurus, but it appeared in the movie Jurassic Park, and is showing up in plastic dinosaur collections.

Brachiosaurus has a history of mistaken identity.

• A Sauropod skull from the Felch Quarry in Colorado was sent to Othniel C. Marsh in 1883. Marsh assumed it belonged to a Brontosaurus and mounted it on a Brontosaurus Many years later, Kenneth Carpenter and Virginia Tidwell (Carpenter and Tidwell, 1998) determined that the skull was, in fact, from a Brachiosaurus.
• In 1914, Werner Janensch thought he had discovered another species, Brachiosaurs bracai. However, much later in 2009, Michael Taylor (Taylor 2009) showed that this dinosaur was unique and renamed it Giraffatitan bracai.

The record for the longest of these Jurassic Sauropods might go to Diplodocus, which was discovered by Earl Douglas and Samuel W. Williston in 1877.

Most of the long-necked dinosaurs died off by the end of the Jurassic period. However, a group known as Titanosaurs continued on through the Cretaceous. Titanosaurs were defined originally by Titanosaurus, although there is now some doubt that this namesake actually fits into the group. Three Titanosaurs, Argentinosaurus, Puertasaurus, and Patagotitan, might vie for the record as the longest dinosaur at over 100 feet.

Marine “Dinosaurs”

Dinosaurs lived on the land. However, giant reptiles that resembled dinosaurs were found in the oceans of the Earth.

Ichthyosaurs were large (6-10 ft) dolphin-like reptiles that appeared during the late Triassic period. They prospered during the Jurassic but were displaced by other large marine reptiles later in the period. The larger (15 ft) long-necked Plesiosaurs were next – appearing early in the Jurassic period. They were followed by the even larger whale-sized (40 ft) Pliosaurs. Appearing during the Cretaceous period was the smaller, more agile Mosasaurs that eventually became the dominant marine reptile.

Flying “Dinosaurs”

The so called “flying dinosaurs” are known as Pterosaurs (Pterosauria) and are distinct from Dinosaurs (Dinosauria). Pterodactyl (technically Pterodactylus), with up to an 8-foot wingspan, is one of the well-known Jurassic Pterosaurs. Pteranodon with a wingspan of over 20 feet, and Quetzalcoatlus with a wingspan of over 30 feet, were much larger and came later during the Cretaceous period.

Archaeopteryx was a flying dinosaur. This small pigeon-sized animal has sometimes been called the first bird, although others think it is more of a link between dinosaurs and birds. Modern birds probably evolved from the Theropods of the late Cretaceous period and not directly from Archaeopteryx.