The Lancian was a North American faunal stage of the Late Cretaceous . It was the final stage of the Cretaceous period in North America, lasting from approximately 70.6 to 66 million years ago.
26-519: Terrestrial sedimentary strata from the Judithian to the Lancian are generally regressive throughout the entire sequence, so the preserved changes in fossil communities represent not only phylogenetic changes but ecological zones from the submontane habitats to near-sea level coastal habitats. By the Lancian, the crested hadrosaurs are no longer the dominant inhabitant of any province of western North America;
52-452: A change in the ecosystems' flora was "the most immediate cause...though perhaps not the ultimate one." The rapid expansion of land and drying of inland climate accompanying a drop in sea level could explain some of the environmental changes occurring Late Cretaceous western North America. The wetland habitat enjoyed by many dinosaurs would have shrunk and fragmented. Since many species had very limited geographic ranges its plausible that some of
78-703: A few dinosaur generalists." The appearance or reappearance of basal neoceratopsians could be explained by immigration from Asia. Dinosaurs like Nodocephalosaurus resembled Asian forms, and some like Saurolophus co-occurred in Asia as well as North America. Potential Asian immigrants were especially common in upland environments. The appearance of Alamosaurus may have represented an immigration event from South America. Some taxa may have co-occurred on both continents, including Kritosaurus and Avisaurus . Alamosaurus appears and achieves dominance in its environment very abruptly. Some scientists speculated that Alamosaurus
104-489: A rise in sea level during the Bearpaw Transgression created selective pressure as coastal lowlands were swallowed up the sea, resulting in anagenesis . If the geographic range of some dinosaur species were truly as limited as the fossil record suggests, then a rapid rise and in sea level could cause intense pressure even the event was local. Additionally, a rapid drop in sea level could allow for "rapid colonization by
130-625: Is by far the largest LIP in Earth's history. The Ontong Java Plateau today covers an area of 1,860,000 km . In the Indian Ocean another LIP began to form at c. 120 Ma, the Kerguelen Plateau – Broken Ridge , together covering 2,300,000 km . Another LIP on the Liaodong Peninsula , China, c. 131–117 Ma, lasted for 10 million years. It was the result of the subduction of
156-633: The Canada Basin in the Arctic Ocean. With the opening of the Labrador Sea , Greenland became a separate tectonic plate and Laurentia became North America . The Proto-Caribbean Sea continued to grow and the Paraná-Etendeka LIP began to break Africa into three pieces. The Falkland Plateau broke off from southern Africa at 132 Ma and Madagascar ceased to move independently c. 120 Ma. In
182-776: The Kula and Pacific plates, which was probably caused by a superplume . During the opening of the South Atlantic the Paraná–Etendeka LIP produced 1.5 million km of basalts and rhyolites , beginning 133 Ma and lasting for a million years. The opening of the Central Atlantic continued as the Mid-Atlantic Ridge spread north to separate the Iberian Peninsula from the banks of Newfoundland and to connect to
208-637: The Late Jurassic continued to persist. Angiosperms (flowering plants) appeared for the first time during the Early Cretaceous; Archaefructaceae , one of the oldest fossil families (124.6 Ma) was found in the Yixian Formation , China. This time also saw the evolution of the first members of the Neornithes (modern birds). Sinodelphys , a 125 Ma-old boreosphenidan mammal found in
234-757: The Panthalassic Ocean the Pacific Plate continued to grow; the Arctic Alaska-Chukotka terrane formed the Bering Strait. Continued rifting opened new basins in the Indian Ocean, separating India, Antarctica, and Australia. By 110 Ma the Mid-Atlantic Ridge reached south into the Proto-Caribbean and South Atlantic, effectively separating South America from Africa, and continued rifting in
260-553: The Miocene to the present primarily effected large herbivores and occurred over roughly the same length of time as the Late Cretaceous changes, and so may be parallel. They have many commonalities, including the replacement of diverse with single species environments ( caribou in the north, bison to the south). The most spectacular and specialized forms became extinct. The mammalian turnover was preceded by an episode of immigration, and
286-564: The Yixian Formation, China, is one of the oldest mammal fossils found. The fossil location indicates early mammals began to diversify from Asia during the Early Cretaceous. Sinodelphys was more closely related to metatherians (marsupials) than eutherians (placentals) and had feet adapted for climbing trees. Steropodon is the oldest monotreme (egg-lying mammal) discovered. It lived in Gondwana (now Australia) at 105 Ma. Oil in
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#1732869863419312-455: The base of a mountain range , higher hill range or an upland area. They are a transition zone between plains and low relief hills and the adjacent topographically higher mountains , hills, and uplands. Frequently foothills consist of alluvial fans , coalesced alluvial fans , and dissected plateaus . Foothills primarily border mountains, especially those which are reached through low ridges that increase in size closer and closer to
338-464: The defining early Aptian Oceanic Anoxic Event 1a (OAE1a) was carbon isotope dated to 123.1±0.3 Ma, limiting the possible range for the boundary to c. 122–121 Ma. There is a possible link between this anoxic event and a series of Early Cretaceous large igneous provinces (LIP). The Ontong Java - Manihiki - Hikurangi large igneous province, emplaced in the South Pacific at c. 120 Ma,
364-544: The disappearing forms anyway. Lehman described the evidence for immigration as a driving force in Lancian dinosaur faunal turnovers as "not particularly compelling." The faunal turnover may be explained by the descent of more primitive forms existing in upland refugia characterized by conifer -dominated flora into areas that were formerly coastal lowlands as the seas retreated and conditions became more arid. The decline of mammal diversity in Western North America from
390-479: The expansion of its preferred habitat rather than an immigration event. Early Cretaceous deposits in North America reveal that basal neoceratopsians were already present on the continent before their apparent reemergence in the Lancian, so an immigration event from Asia is unnecessary to explain their appearance. The major potential immigrants represent archaic forms that probably wouldn't have directly competed with
416-534: The fragments would be smaller than the area needed to support the species. However, there's no direct evidence for the shrinking of wetland environments. Lehman contends that the actual area of coastal lowlands within 150m of the shoreline must have actually increased significantly. Further, dinosaurs that inhabited inland or arid environments were among the most prevalent in the Lancian. The Alamosaurus - Quetzalcoatlus association probably represent semi-arid inland plains. In previous research Jack Horner speculated that
442-688: The higher montane ecosystems . Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous ( chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous . It is usually considered to stretch from 145 Ma to 100.5 Ma. Proposals for the exact age of the Barremian–Aptian boundary ranged from 126 to 117 Ma until recently (as of 2019), but based on drillholes in Svalbard
468-607: The mountain, but can also border uplands and higher hills. Areas where foothills exist, or areas commonly referred to as the foothills, include the: Another word for a foothill region is "piedmont", derived from "foot of the mount" in Romance languages . The Piedmont region of Italy lies in the foothills of the Alps , and several other foothills in other parts of the world are called "piedmont" , and include: Ecosystems of piedmonts (foothills) are often known as submontane zones, relating to
494-589: The northern end completed the longitudinal extent of the Atlantic. In Panthalassa the Ontong-Java Mega-LIP resulted in the formation of new tectonic plates and in the Indian Ocean the Kerguelen LIP began to push India northward. During this time many new types of dinosaur appeared or came into prominence, including ceratopsians , spinosaurids , carcharodontosaurids and coelurosaurs , while survivors from
520-467: The only remaining species was Hypacrosaurus . Lehman records three surviving chasmosaurs, Triceratops , Torosaurus and Nedoceratops , with the possibility of the recently discovered Ojoceratops , Regaliceratops and Bravoceratops . It has recently been suggested that Triceratops and Torosaurus may be synonymous, though this is still up for debate. Saurolophine dinosaurs like Edmontosaurus , Kritosaurus , Saurolophus as well as
546-418: The recently discovered Augustynolophus were some of the known surviving hadrosaurs. All lacked the elaborate ornamentation of their predecessors, the lambeosaurs . The ankylosaurs had been reduced to down to a handful of species, with ankylosaurs like Anodontosaurus and Ankylosaurus , as well as nodosaurs like Denversaurus , Edmontonia and Glyptodontopelta being the only known survivors. In
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#1732869863419572-454: The south the transition to the Lancian is even more dramatic, which Lehman describes as "the abrupt reemergence of a fauna with a superficially "Jurassic" aspect." These faunas are dominated by Alamosaurus and feature abundant Quetzalcoatlus , Bravoceratops and Ojoceratops in Texas. The extreme changes occurring in the make-up of herbivore communities during the faunal turnover suggests that
598-480: The very least, Lehman argues, the altitudinal life zones would shift, and a change in the distribution of vegetation utilized by herbivorous dinosaurs would have probably resulted. By the end of the Judithian, North America had 7.7 million km of land area, but by the end of the Lancian it had reached 17.9 million km, nearly the modern value of 22.5 million km. Submontane Foothills or piedmont are geographically defined as gradual increases in elevation at
624-407: Was an immigrant from Asia. Inhabitants of upland environment are more likely to be endemic than coastal species, and tend to have less of an ability to cross bodies of water. Further, early Cretaceous titanosaurs were already known, so North American potential ancestors for Alamosaurus already existed. Quetzalcoatlus also had precursors in North America and its apparent range expansion may represent
650-445: Was associated with the rapid expansion of terrestrial habitat due to melting glaciers . In the mammalian turnover, the newly emerging dominant fauna were clearly Old World immigrants, the cervids and bovids . In the southern biome, by Lancian time sauropods had replaced both hadrosaurs and ceratopsians. In the north, both were still present although hadrosaurs were demoted to a "subordinate" role in dinosaur ecosystems. Edmontosaurus
676-529: Was the dominant northern hadrosaurid. At the end of the Cretaceous, most ecosystems were dominated by a single herbivore. The northern biome was dominated by Triceratops and the southern biome by Alamosaurus . This faunal turnover coincides with the Laramide orogeny and the uplift of the central Rockies. Strata exhibit changes in lithology and the direction of paleocurrents, and a severe drop in relative sea level. At
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