Introduction

For the next 365 days, I will post a dead bird lizard (colloquially known as "dinosaurs") every day. These will not be in any particular order and do not represent every known genus or species. Megalosaurus will be the first, however, since it was the first to be scientifically described.

Some things to remember: Late Triassic (237 million years ago - 201 million years ago) / Early Jurassic (201 million years ago - 174 million years ago) / Middle Jurassic (174 million years ago - 161 million years ago) / Late Jurassic (161 million years ago - 143 million years ago) / Early Cretaceous (143 million years ago - 100 million years ago) / Late Cretaceous (100 million years ago - 66 million years ago)

• "Basal" = primitive animal or trait in comparison to derived animals or traits. More similar to shared ancestors.
• "Derived" = advanced animal or trait in comparison to basal animals or traits. More removed from shared ancestors.
• "Theropod" = bipedal and mostly, though not always, carnivorous dead bird lizards. Live bird non-lizards of today belong to this group.
• "Sauropod" = quadrupedal, long-necked herbivorous dead bird lizards.
• "Ornithopod" = ancestrally bipedal, later both quadrupedal and bipedal herbivorous dead bird lizards. "duck-billed" hadrosaurs belong to them.
• "Thyreophoran" = quadrupedal, heavily armored dead bird lizards (ankylosaurs and stegosaurs).
• "Ceratopsian" = originally bipedal, later mostly quadrupedal, large-headed and horned dead bird lizards (Triceratops and kin).

Despite calling them "dead bird lizards", dead bird lizards aren't true lizards. True lizards belong to the order Squamata, which they share with snakes. Dinosaurs belong to a group called the Archosauria, which they share with modern crocodiles. The pigeon who shit on my head when I was a child is closer phylogenetically to crocodiles than crocodiles are to my pet iguana Devin and I tried to exhume after its death.

Megalosaurus

Name Meaning: "large lizard" / Location: United Kingdom (England) / Time Period: c. 166 million years ago (Middle Jurassic) / Length: 20 - 25 ft (6 - 7.5 m) / Weight: 1 ton (950 kg) / Locomotion: Biped / Diet: Carnivore / Described: 1824 (Buckland) / Geological Formation(s): Taynton Limestone / Valid Species: Megalosaurus bucklandii (type)

Phylogeny: Dinosauria > Saurischia > Theropoda > Neotheropoda > Tetanurae > Megalosauroidea (?) > Megalosauridae > Megalosaurinae

Overview: Fossil remains later attributed to Megalosaurus had been known to English academics since the 1600's, but were scant and mistaken for remains of Roman war elephants or giant humans. More fossils would be uncovered, leading to its 1824 description, published by the theologian and naturalist William Buckland. Its name, meaning "great" or "large lizard" of course refers to its size, though we know today there were many far larger theropod dinosaurs. Megalosaurus is considered to be the first validly described non-avian dinosaur genus. Indeed, it was named before the concept of the Dinosauria even existed. In 1842, the famed naturalist Richard Owen used Megalosaurus (along with Iguanodon and Hylaeosaurus) to establish dinosaurs as a taxonomic clade, distinguishing them from other large prehistoric reptile groups like the mosasaurs or plesiosaurs.

Early restorations of Megalosaurus depicted it as a bulky, quadrupedal creature. Its remains were incomplete and scientists had yet to learn that theropod dinosaurs were bipeds. Modern depictions restore it as a largely "stereotypical" large-bodied theropod. It had a large head with fairly long jaws. The arms weren't overly long, but were probably quite powerful, each hand equipped with three large claws. Megalosaurus appears to have been the largest predator in its local environment. Potential food sources included long-necked sauropods like Cetiosaurus. This genus acts as the namesake of the larger family Megalosauridae, which also contained notable dinosaurs like Torvosaurus and Eustreptospondylus. These animals saw their greatest success during the Middle to Late Jurassic. Known fossils include parts of the jaw and skull, the pelvis, limb bones and some vertebrae.

Iguanodon

Name Meaning: "iguana tooth" / Location: Belgium, United Kingdom (England), Spain, Germany / Time Period: c. 125 million years ago (Early Cretaceous) / Length: 33 ft (10 m) / Weight: 5 tons (4,500 kg) / Locomotion: Quadruped & Biped / Diet: Herbivore / Described: 1825 (Mantell) / Geological Formation(s): Sainte-Barbe Clays, Camarillas, etc. / Valid Species: Iguanodon bernissartensis (type)

Phylogeny: Dinosauria > Ornithischia > Genasauria > Neornithischia > Cerapoda > Ornithopoda > Iguanodontia > Ankylopollexia > Styracosterna > Hadrosauriformes > Iguanodontidae

Overview: In the 1820's, an English physician by the name of Gideon Mantell came to possess a set of scattered fossils, clearly belonging to an enormous reptile. These consisted of teeth and some other bones. One of Mantell's associates pointed out similarities between the creature's teeth and those of modern iguanas, so when Mantell officially described the animal in 1825, it was named for this fact. In 1842, along with Megalosaurus and Hylaeosaurus, Iguanodon was one of the taxa used to establish the Dinosauria as a distinct clade. Early restorations depicted Iguanodon as a massively scaled-up iguana or, in some later depictions, as an elephant-like reptile walking on all fours. One bony spike associated with the find was interpreted as a large nasal horn. Decades later, in the 1870's, far more complete fossils were found deep within a Belgian coal mine, consisting of many complete skeletons. These were used as the basis for a new species - Iguanodon bernissartensis. One of these specimens was so complete that it was designated as the new type specimen for the genus Iguanodon.

The Belgian specimens revealed Iguanodon to be quite different than previously imagined. It was not an entirely quadrupedal animal, as it retained the ability to walk up on its hind limbs (bipedal locomotion being the ancestral state of ornithopods), though much of its time would've been spent down on all fours as it grazed. Like other iguanodonts, it possessed both a beak and a set of grinding teeth. Its supposed horn was actually a set of thumb-spikes, likely used for both foraging and defense against predators. Iguanodon possessed long and quite muscular arms, which in addition to its overall bulk, would've made it dangerous prey for most of the predators in its environment. Changing the type specimen of the genus to that of I. bernissartensis has caused a bit of an issue in recent years. It turns out that the genus described by Mantell and that from Belgium may not have been the same taxon, but as the type specimen was changed, the generic name of Iguanodon is now fixed to the latter. Mantell's specimens have since been referred to a new related genus called Mantellisaurus. Mantellisaurus may belong to the same iguanodontid family, though this is debated. Both animals were relatives of the famous “duck-billed” dinosaurs, though a fair bit more basal in comparison, retaining traits of their ancestors.