Question: How many species of dinosaurs are known to have lived during the Early Cretaceous Period?

List of North American dinosaurs

This is a list of dinosaurs whose remains have been recovered from North America. North America has a rich dinosaur fossil record with great diversity of dinosaurs.
History
The earliest record of dinosaurs in North America comes from rare, unidentified (possibly theropod) footprints and teeth in the Middle-Late Triassic Pekin Formation of North Carolina.[1] Later in the Triassic period, dinosaurs left more recognizable remains, and could thus be identified as specific genera. Examples of later Triassic North American dinosaur genera include Coelophysis, Chindesaurus, Gojirasaurus, and Tawa.  Fossils of Tawa-like dinosaurs have also been found in South America, which has important indications about paleogeography. During the Early Jurassic Period, dinosaurs such as Dilophosaurus, Anchisaurus, Coelophysis (formerly known as Megapnosaurus), and the early thyreophoran Scutellosaurus lived in North America. The latter is believed to have been the ancestor of all stegosaurs and ankylosaurs. The Middle Jurassic is the only poorly represented time period in North America, although several Middle Jurassic localities are known from Mexico. Footprints, eggshells, teeth, and fragments of bone representing theropods, sauropods, and ornithopods have been found, but none of them are diagnostic to the genus level. 

The Late Jurassic of North America, however, is the exact opposite of the Middle Jurassic. The Late Jurassic Morrison Formation is found in several U.S. states, including Colorado, Utah, Wyoming, Montana, New Mexico, Oklahoma, South Dakota, and Texas. It is notable as being the most fertile single source of dinosaur fossils in the world. The roster of dinosaurs from the Morrison is impressive. Among the theropods, Allosaurus, Saurophaganax, Torvosaurus, Ceratosaurus, Coelurus, Ornitholestes, Tanycolagreus, Stokesosaurus, and Marshosaurus are found in the Morrison. An abundance of sauropods has been found there, including Apatosaurus, Diplodocus, Barosaurus, Brachiosaurus, Camarasaurus, Brontosaurus and Amphicoelias. Three genera of stegosaurs, Alcovasaurus, Stegosaurus and Hesperosaurus, have been found there. Finally, ornithopods found in the Morrison include Dryosaurus, Camptosaurus, Drinker, Othnielia, and Othnielosaurus.
During the Early Cretaceous, new dinosaurs evolved to replace the old ones. Sauropods were still present, but they were not as diverse as they were in the Jurassic Period. Theropods from the Early Cretaceous of North America include dromaeosaurids such as Deinonychus and Utahraptor, Acrocanthosaurus, and Microvenator. Sauropods included Astrodon, Brontomerus, and Sauroposeidon. Ornithischians were more diverse than they were in the Jurassic Period. Tenontosaurus, Dakotadon, Protohadros, and Eolambia are some of the ornithopods that lived during this time period. Ankylosaurs replaced their stegosaur cousins in the Cretaceous. Ankylosaurs from the Early Cretaceous of North America include Sauropelta and Gastonia. Therizinosaurs such as Falcarius are also known from the Early Cretaceous of North America.
Finally, the Late Cretaceous Period, the greatest abundance and diversity of dinosaurs of all time lived in North America. During the early part of the Late Cretaceous, the therizinosaur Nothronychus and the ceratopsian Zuniceratops lived. During the Campanian stage of the Late Cretaceous, an enormous diversity of dinosaurs is known. Theropods included the tyrannosaurs Albertosaurus, Gorgosaurus, Daspletosaurus, Teratophoneus, Bistahieversor, and Appalachiosaurus, and the dromaeosaurids Dromaeosaurus, Saurornitholestes, Atrociraptor, and Bambiraptor. Ceratopsians, such as Pachyrhinosaurus, Styracosaurus, Centrosaurus, Monoclonius, Brachyceratops and Pentaceratops also existed. Among hadrosaurs, Hypacrosaurus, Gryposaurus, Kritosaurus, Parasaurolophus, Corythosaurus, Lambeosaurus and Prosaurolophus existed. During the latest Cretaceous, the Maastrichtian age, the diversity of dinosaurs saw a decline from the preceding Campanian stage. North American herbivorous dinosaurs from this time period include the titanosaur sauropod Alamosaurus, the ceratopsians Bravoceratops, Regaliceratops, Triceratops,  Leptoceratops, Torosaurus, Nedoceratops, Tatankaceratops (the latter two possible species of Triceratops), and Ojoceratops, the pachycephalosaurs Pachycephalosaurus, Stygimoloch, Dracorex, and Sphaerotholus, the hadrosaurs Augustynolophus, Saurolophus and Edmontosaurus, the ornithopod Thescelosaurus the ankylosaur Ankylosaurus and the nodosaurs Denversaurus, Glyptodontopelta  and Edmontonia. Predatory dinosaurs from this time period included the tyrannosaurids Tyrannosaurus, Nanotyrannus (which may just be a juvenile of the former) and Dryptosaurus, the ornithomimids Ornithomimus and Struthiomimus, the oviraptorids Anzu, Leptorhynchos and Ojoraptorsaurus, the troodontids Pectinodon, Paronychodon and Troodon, the coelurosaur Richardoestesia and the dromaeosaurs Acheroraptor and Dakotaraptor.
The only dinosaur fossil from Central America is a .,[2][3] discovered in the central part of Honduras in the year 1971 near San Luis, Comayagua Department, by Bruce Simonson and Gregory Horne. It was found in the highest part of the Valle de Angeles Redbeds. The fossil bone is in the US National Museum of Natural History in Washington (catalog number USNM PAL 181339). It was identified as ornithopod bone by John Ostrom,[3] and by Nicholas Hotton as the right femur of a small hadrosaur.[4]
There is also an older report of dinosaur fossil from Honduras documented only in US newspapers at 1933, but not scientifically documented . This report comments the discovery of a dinosaur ankle bone near the town of Olanchito, Yoro Department, Honduras; by the explorer Gregory Mason. This information is described on page 9 of The Washington Post of August 23, 1933, on page 8 of the newspaper The Norwalk Hour August 24, 1933[5] and on page 6 of Nebraska newspaper The Plattsmouth Journal of August 21 of 1933[6]
Criteria for inclusion
Inclusion criteria:
The creature must appear on the List of dinosaur genera.
Fossils of the creature must have been found in North America.
This list is a complement to Category:Dinosaurs of North America.
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Timeline
This is a timeline of selected dinosaurs from the list above.  Time is measured in Ma, megaannum, along the x-axis.

See also

List of North American birds