Laurasia

The name Laurasia was coined in German geological literature in 1928 and entered English usage by 1931. It is a portmanteau of 'Laurentia'—the geologists' name for the ancient continental core of North America, derived from the Laurentian Mountains near the St. Lawrence River in eastern Canada—and 'Eurasia.' The Laurentian geological term was first used by William E. Logan and T. Sterry Hunt in 1854 to describe granite strata in Quebec.

South African geologist Alexander du Toit formalized the concept in his 1937 book Our Wandering Continents. Where Alfred Wegener had proposed a single supercontinent (Pangaea), du Toit argued for two primordial landmasses: Laurasia in the north and Gondwana in the south, separated by the Tethys Sea. Du Toit marshalled extensive geological and paleontological evidence—including matching glacial deposits, the distribution of the Glossopteris flora, and the freshwater reptile Mesosaurus found only in South America and southern Africa—to support continental drift. His two-continent refinement proved more consistent with observed geological data than Wegener's original single-continent model, and it was later validated by the plate tectonics revolution of the 1960s.

Laurasia's component continental blocks had a complex pre-Pangaean history. Around 400 million years ago (Silurian–Devonian), Laurentia, Avalonia, and Baltica collided during the Caledonian Orogeny to form a continent known as Laurussia (or Euramerica). During the Late Carboniferous (approximately 300–290 Ma), Kazakhstania and Siberia were added to Laurussia, completing the northern portion of the assembling supercontinent. The collision of Laurussia with Gondwana during the Carboniferous–Permian (the Variscan/Hercynian Orogeny in western Europe and the Alleghanian Orogeny in eastern North America) completed the formation of Pangaea. The Ural Mountains mark the suture zone where Siberia docked with the rest of Laurasia.

The breakup of Pangaea commenced in the Late Triassic, approximately 215–200 million years ago, with rifting between eastern North America and northwestern Africa. This was accompanied by the eruption of the Central Atlantic Magmatic Province (CAMP), one of the largest flood basalt events in Earth's history, around 201 Ma. The proto-Central Atlantic Ocean began to form as a result. By the Middle Jurassic (approximately 175 Ma), the separation between Laurasia and Gondwana was well established, with the Tethys Sea widening between them. However, the separation was not complete everywhere simultaneously: intermittent land connections persisted between northwestern Africa and southern Europe for extended periods, facilitating faunal exchange.

Laurasia did not persist as a unified continent. A series of tectonic and eustatic events progressively divided it into smaller blocks.

During the late Callovian–early Kimmeridgian (approximately 163–152 Ma), the Uralian epicontinental sea separated Europe from Central and East Asia, isolating Chinese dinosaur faunas (e.g., mamenchisaurid sauropods) from their western counterparts. In the late Kimmeridgian–early Tithonian (approximately 152–147 Ma), land connections existed between North America and western Europe, creating a shared 'Euramerican' dinosaur fauna that included genera such as Allosaurus and Stegosaurus.

During the Aptian–Albian (approximately 121–100 Ma), marine regressions removed the Uralian Sea barrier and the Bering Strait land bridge formed between Asia and North America, briefly reconstituting a coherent Laurasian landmass and enabling wide-ranging geodispersal. In the late Albian–Campanian (approximately 105–72 Ma), the Western Interior Seaway flooded central North America, dividing the continent into the western sub-continent of Laramidia and the eastern sub-continent of Appalachia.

The final breakup of Laurasia occurred in the Paleogene. Seafloor spreading in the Labrador Sea began around 67 Ma, separating Greenland from Canada. The Norwegian–Greenland Sea opened around 60–56 Ma, splitting Greenland–North America (Laurentia) from Eurasia. Britannica dates Laurasia's fragmentation into the present continents of North America, Europe, and Asia to the interval from approximately 66 to 30 million years ago.

Laurasia was the evolutionary stage for many of the most iconic dinosaur lineages. By the Middle Jurassic, key groups that would later dominate Laurasian ecosystems—including coelurosaurs (ancestors of tyrannosaurids), neosauropods, stegosaurs, ankylosaurs, and ornithopods—had already originated and achieved wide distributions before Pangaean fragmentation commenced.

The Late Cretaceous Asiamerican fauna is one of the most well-documented examples of inter-continental biotic exchange within Laurasia. The Bering Strait land bridge, which was intermittently present during the Aptian–Albian and again during the Campanian (approximately 84–72 Ma), facilitated repeated geodispersal between East Asia and western North America (Laramidia). The groups that participated in this exchange include tyrannosaurids, ceratopsids, ankylosaurids, ornithomimids, alvarezsaurids, dromaeosaurids, and later-branching hadrosaurids. The ancestors of Tyrannosaurus rex are widely held to have originated in Asia and dispersed across the Bering Strait into Laramidia during the Campanian.

By contrast, Gondwanan faunas were dominated by abelisaurid theropods (the large predator niche occupied by tyrannosaurids in Laurasia), titanosaurian sauropods, and carcharodontosaurids. This Laurasia–Gondwana faunal dichotomy is a direct consequence of the Tethyan marine barrier. Phylogenetic network analyses by Kubo (2011) confirmed that Gondwanan areas shared more faunal similarities with each other than with Laurasian areas, and vice versa, particularly during the Late Cretaceous.

The biogeographic history of Laurasia and Gondwana was not a simple branching (vicariance) pattern but a reticulate one, with repeated connections and disconnections creating a palimpsest of overprinted biogeographic signals (Upchurch & Chiarenza, 2024).

The Apulian land bridge (approximately 123–100 Ma) connected Europe with North Africa, enabling exchange of abelisauroid, spinosaurid, and carcharodontosaurid theropods as well as rebbachisaurid and titanosaurian sauropods. This created a distinctive 'Euro-Gondwana' biogeographic pattern in the Early Cretaceous, where European faunas bore stronger resemblances to African than to East Asian faunas. During the Campanian–Maastrichtian (approximately 84–66 Ma), exchange between North and South America occurred via land bridges or island-hopping, with titanosaurs dispersing north and hadrosaurs and ankylosaurs dispersing south. In the Maastrichtian (approximately 72–66 Ma), the De Geer land bridge may have connected Greenland to northwestern Europe, allowing leptoceratopsids and lambeosaurine hadrosaurs to disperse from North America into Europe.

Laurasia's climate underwent dramatic changes over its existence. During the Late Triassic and Early Jurassic, a pronounced arid belt at low paleolatitudes acted as a dispersal barrier for early dinosaurs, particularly large-bodied herbivorous sauropodomorphs. By the Late Jurassic and Cretaceous, warm greenhouse conditions prevailed globally, and even high-latitude Laurasian regions (approximately 70° N and above) supported diverse dinosaur communities. The Cenomanian–Turonian thermal maximum (approximately 94–91 Ma) extended subtropical conditions to high latitudes, favoring large-bodied herbivores and coinciding with peak sauropod body masses. Recent evidence from the Prince Creek Formation of Alaska and equivalent high-latitude localities suggests that theropods and ornithischians at paleolatitudes of 70°+ N were year-round residents, equipped with feathery insulation and elevated metabolic rates that enabled them to cope with polar winters.

The fragmentation of Laurasia produced the Atlantic Ocean, the Arctic Ocean, and the Norwegian Sea, and determined the current configuration of Northern Hemisphere continents. The collision of the Indian plate (originally part of Gondwana) with the Eurasian portion of Laurasia generated the Himalayan mountain chain. In modern biology, the mammalian superorder Laurasiatheria—which includes carnivorans, ungulates, bats, and certain insectivores—is named for its inferred origin on Laurasia and subsequent radiation following the K–Pg mass extinction. This nomenclature reflects the enduring influence of Mesozoic continental configurations on modern biodiversity patterns.