This timeline of ceratopsian research is a chronological listing of events in the history of paleontology focused on the ceratopsians, a group of herbivorous marginocephalian dinosaurs that evolved parrot-like beaks, bony frills, and, later, spectacular horns. The first scientifically documented ceratopsian fossils were described by Edward Drinker Cope starting in the 1870s; however, the remains were poorly preserved and their true nature was not recognized. Over the next several decades, Cope named several such genera and species. Cope's hated rival, Othniel Charles Marsh, also described ceratopsian remains. In 1887, Marsh mistook a Triceratops horn for one belonging to a new species of prehistoric Bison. Marsh also named the eponymous genus Ceratops in 1888. The next year, he named the most famous ceratopsian, Triceratops horridus. It was the discovery of Triceratops that illuminated the ceratopsian body plan, and he formally named the Ceratopsia in 1890.

The early 20th century was a fruitful time for ceratopsian research. In 1907, Hatcher and others published a monograph on ceratopsid anatomy that is still considered the single most significant publication on the topic to date. Many new species were being described, including Centrosaurus, Styracosaurus, and Chasmosaurus. Not long after, the Central Asiatic Expedition led by Roy Chapman Andrews of the American Museum of Natural History discovered the primitive ceratopsians Psittacosaurus and Protoceratops in Mongolia. Protoceratops gained notoriety as the supposed parent of the first fossil dinosaur eggs known to science. One of these supposed Protoceratops nests preserved the skeleton of a new kind of theropod dinosaur, Oviraptor. It was thought to have been preserved after being killed in the act of raiding the Protoceratops nest. This narrative would last until the 1990s, when the "Protoceratops" eggs were determined to belong to Oviraptor itself.

Throughout the rest of the century, paleontologists would be occupied with several controversies regarding ceratopsian paleobiology. One concerned the stance of the ceratopsid forelimbs. When Marsh first reconstructed the ceratopsid forelimb, he portrayed it in an erect posture. However, when later researchers like Sternberg and Osborn tried to mount the skeletons, they found that the forelimb bones apparently sprawled despite the hindlimbs standing straight up and down. Later researchers like Robert T. Bakker and Gregory S. Paul attempted to revive the erect reconstruction, but continuing research in the 1990s by researchers like John Ostrom, Peter Dodson, and James Farlow found an intermediate value to be better supported.

The original use of the ceratopsids' horns and frills was another long-running controversy in ceratopsian paleontology. Early researchers like Richard Swann Lull thought that bony frills served as the attachment site for enlarged jaw muscles. This explanation was followed by researchers like Russell, Haas, and Ostrom. Sternberg thought the horns of ceratopsians helped defend against predators. In 1961, Davitashvili proposed that ceratopsids used their horns and frills to compete over mates. Farlow and Dodson arrived at the same conclusion in the 1970s, and were followed by Ralph Molnar. Ostrom, who had previously followed the jaw musculature interpretation, came to support this view in 1986. The idea gained further support in the 1990s from researchers like Forster and Sampson.

19th century

1870s

1872 Edward Drinker Cope described the new genus and species Agathaumas sylvestris. Cope described the new genus and species Polyonax mortuarius.

1876 Cope described the new genus and species Monoclonius crassus, Dysganus bicarinatus, D. encaustus, D. haydenianus, and Dysganus peiganus. He also described the new species Monoclonius fissus.

1878 William Edmund Cutler was born in England.

1880s

1887 Despite the description of several ceratopsid taxa by Cope, science still had no concept of what these animals were like due to the scrappy quality of the fossils. Othniel Charles Marsh described the new species Bison alticornis based on horn cores from the animal he would later name Triceratops, not recognizing their dinosaurian origins.

1888 Marsh described the new genus species Ceratops montanus.

1889 Marsh described the new species Ceratops horridus. Marsh erected the new genus Triceratops to house the species Ceratops horridus. The fossils included the first complete ceratopsid skull to be scientifically documented. Marsh described the new species Triceratops flabellatus. Marsh described the new species Triceratops galeus. Cope described the new species Monoclonius recurvicornis and M. sphenocerus.

1890s

1890 Marsh named the Ceratopsia. He also named the Ceratopsidae. Marsh described the new species Triceratops prorsus.

Marsh described the new species Triceratops serratus. Marsh described the new species Triceratops sulcatus. Marsh described the new genus and species Torosaurus latus.

1891 Marsh described the new species Torosaurus gladius. Marsh described the new species Triceratops elatus. Marsh erected the new genus Sterrholophus. Marsh reconstructed Triceratops with both its fore and hindlimbs held with erect posture.

1896 Barnum Brown discovered a Triceratops skull in Wyoming. It was the first dinosaur fossil Brown ever discovered.

1898 Marsh described the new species Triceratops calicornis. Marsh described the new species Triceratops obtusus.

20th century

1900s

1901 William Temple Hornaday discovered some Triceratops fossils in Montana. These were the first Triceratops fossils to ever be discovered in the Hell Creek Formation.

1902 Lawrence Lambe described the new species Monoclonius dawsoni. Lambe described the new species Monoclonius belli. Lambe described the new species Monoclonius canadensis. Barnum Brown and Richard Swann Lull set out to excavate the Triceratops discovered by Hornaday.

1904 Lambe described the new genus and species Centrosaurus apertus. A skeletal mount for Triceratops was designed for the United States National Museum of Natural History. This was the first skeletal mounts of any ceratopsid constructed for a museum.

1905 Richard Swann Lull described the new genus and species Diceratops hatcheri. John Bell Hatcher described the new species Triceratops brevicornus.

1907 Hatcher and others published a monograph on ceratopsids. This publication has been regarded as the first comprehensive study on ceratopsids and was still regarded as "the most valuable single reference on ceratopsid anatomy" nearly a century later. The researchers classified ceratopsids into two main groups. One consisted of Monoclonius, Triceratops, and their relatives and the other consisted of Ceratops, Torosaurus and their relatives.

1908 Lull interpreted ceratopsid frills as sites for the attachment of enlarged jaw muscles.

1910s

1910 An expedition led by Barnum Brown on behalf of the American Museum of Natural History discovered an isolated brainscase in the Horseshoe Canyon Formation. This find represented the first non-ceratopsid neoceratopsian remains discovered in the unit. Field photos suggest that the discovery occurred near the AMNH 5245 "Ankylosaurus" quarry.

1913 Lambe described the new genus and species Styracosaurus albertensis. The frill of Styracosaurus bore three pairs of long, bony spikes, giving it a spectacular and formidable appearance.

1914 Brown described the new genus and species Leptoceratops gracilis.

Brown described the new genus and species Anchiceratops ornatus. Brown described the new species Monoclonius flexus. Charles Whitney Gilmore described the new species Brachyceratops montanensis.

Lambe described the new genus and species Chasmosaurus belli. Lambe described the new genus Protorosaurus. Lambe reported the presence of fossilized skin in C. belli.

1915 Lambe divided the Ceratopsidae into the Centrosaurinae, Chasmosaurinae, and Eoceratopsinae. Lambe erected the new genus Eoceratops to house the species Monoclonius canadensis. Lull described the new species Triceratops ingens.

1917 Brown described the new species Monoclonius cutleri. Brown described the new species Monoclonius nasicornis. Brown reported fossilized skin in Monoclonius cutleri and Monoclonius nasicornis. Sternberg argued that ceratopsids used their horns and frills to protect themselves from predators like tyrannosaurids.

1918 Tapia described the new genus and species Notoceratops bonarelli.

1920s

1922 17 April: The Central Asiatic Expedition, led by Andrews, departed from Peking toward Mongolia.

1923 Henry Fairfield Osborn named the new genus and species Psittacosaurus mongoliensis and Protiguanodon mongoliensis as well as the new family Psittacosauridae. Osborn named the new genus and species Pentaceratops sternbergii. 13 July: George Olsen, a member of the Central Asiatic Expedition led by Roy Chapman Andrews discovered fossil dinosaur eggshell at Iren Debasu, Mongolia. Expedition member Walter W. Granger realized that they must have been laid by dinosaurs. They were mistakenly thought to be the first scientifically documented dinosaur egg fossils. They attributed these eggs to the locally abundant primitive ceratopsian that they would name "Protoceratops".

Walter W. Granger and William King Gregory described the new genus and species Protoceratops andrewsi. A Triceratops skeletal mount was created for the American Museum of Natural History. It was the second ceratopsid skeletal mount ever created.

1924 Osborn described the new non-ceratopsian theropod dinosaur genus and species Oviraptor philoceratops. Since a specimen was found preserved on top of a nest of eggs presumed to belong to Protoceratops and its short toothless beak seemed adapted to cracking open eggs, Osborn thought that it was smothered by a sandstorm while in the act of raiding the nest.

1925 William Arthur Parks described the new genus and species Arrhinoceratops brachyops.

Charles Mortram Sternberg described the fossilized skin of Chasmosaurus belli. The skin was preserved as an impression of skin covering the right side of the animal's pelvic region. C. belli had skin covered in small "nonimbricating" polygonal scales interspersed with rows of larger rounded plates up to 5.5 cm across spaced between 5 and 10 cm across.

1928 Tait and Barnum Brown interpreted ceratopsids as low browsers than fed on herbaceous plants.

1927 A Chasmosaurus skeletal mount was created for the National Museum of Canada. It was the first skeletal mount of Chasmosaurus ever created and the third skeletal mount of any ceratopsid. Sternberg argued that while the hindlimbs of Triceratops stood straight up and down, its forelimbs sprawled.

1929 Sternberg described the species Anchiceratops longirostris. Richard Lull mounted a Centrosaurus apertus skeleton for the Yale Peabody Museum.

1930s

1930 Carl Wiman described the species Pentaceratops fenestratus. Gilmore described the species Styracosaurus ovatus.

1931 Yang Zhongjian ("C.C. Young") described the species Psittacosaurus osborni and P. tingi.

1933 Brown described the species Chasmosaurus kaiseni. Brown described the species Triceratops maximus. Lull described the species Chasmosaurus brevirostris. Lull described the fossilized skin of Monoclonius cutleri. The skin was preserved as an impression of skin near the far end of the animal's thigh. The skin of M. cutleri was similar to that of Chasmosaurus belli, which had skin covered in small "nonimbricating" polygonal scales interspersed with rows of larger rounded plates up to 5.5 cm across. The larger plate-like scales of M. cutleri, however, were more widely spaced than the 5–10 cm intervals seen in C. belli.