Title: Nearctic realm
Content:  Although North America and South America are presently joined by the Isthmus of Panama, these continents were separated for about 180 million years, and evolved very different plant and animal lineages. When the ancient supercontinent of Pangaea split into two about 180 million years ago, North America remained joined to Eurasia as part of the supercontinent of Laurasia, while South America was part of the supercontinent of Gondwana. North America later split from Eurasia. North America has been joined by land bridges to both Asia and South America since then, which allowed an exchange of plant and animal species between the continents, 
Title: North America
Content:   Laurentia is an ancient craton which forms the geologic core of North America; it formed between 1.5 and 1.0 billion years ago during the Proterozoic eon. The Canadian Shield is the largest exposure of this craton. From the Late Paleozoic to Early Mesozoic eras, North America was joined with the other modern-day continents as part of the supercontinent Pangaea, with Eurasia to its east. One of the results of the formation of Pangaea was the Appalachian Mountains, which formed some 480 million years ago, making it among the oldest mountain ranges in the world. When Pangaea began to rift around 200 million years ago, North America became part of Laurasia, before it separated from Eurasia as its own continent during the mid-Cretaceous period. The Rockies and other western mountain ranges began forming around this time from a period of mountain building called the Laramide orogeny, between 
Title: Americas
Content:  South America broke off from the west of the supercontinent Gondwana around 135 million years ago, forming its own continent. Around 15 million years ago, the collision of the Caribbean Plate and the Pacific Plate resulted in the emergence of a series of volcanoes along the border that created a number of islands. The gaps in the archipelago of Central America filled in with material eroded off North America and South America, plus new land created by continued volcanism. By three million years ago, the continents of North America and South America were linked by the Isthmus of Panama, thereby forming the single landmass of the Americas. The Great American Interchange resulted in many species being spread across the Americas, such as the cougar, porcupine, opossums, armadillos and hummingbirds.
Title: Laurentia
Content:  Baltica, forming the landmass Euramerica. ; In the Permian (298.9 ± 0.8 to 252.17 ±0.4 Ma), all major continents collided against each other, forming the supercontinent Pangaea. ; In the Jurassic (201.3 ± 0.6 to 145 ±4 Ma), Pangaea rifted into two landmasses: Laurasia and Gondwana. Laurentia was part of the landmass Laurasia. ; In the Cretaceous (145 ± 4 to 66 Ma), Laurentia was an independent continent called North America. ; In the Neogene (23.03 ± 0.05 Ma until today or ending 2.588 Ma), Laurentia, in the form of North America, collided with South America, forming the landmass America. 
Title: Geography of North America
Content:  center of the Proterozoic supercontinent Rodinia in most models, and was also part of the later Laurussia, Pangea, and Laurasia supercontinents. Roughly 3 million years ago (Ma), the volcanic Isthmus of Panama formed between the North and South American continents creating a bridge over what was the Central American Seaway and allowing the migration of flora and fauna between the two landmasses in the Great American Interchange. Starting 2.58 Ma, the Quaternary glaciation covered much of the continent with ice, centered west of Hudson Bay, the floor of which is slowly rebounding after being depressed by the great weight of the ice. Glaciers descended the slopes 
Title: Geology of the United States
Content:  about 300 million years ago (Pennsylvanian Period) Africa was approaching North American craton. The collisional belt spread into the Ozark-Ouachita region and through the Marathon Mountains of Texas. Continent vs. continent collision raised the Appalachian-Ouachita chain to lofty, Himalayan-scale ranges. The massive bulk of Pangea was completed near the end of the Paleozoic Era (Permian Period) when Africa (Gondwana) plowed into the continental agglomeration, with the Appalachian-Ouachita mountains near the core. From about 280-230 million years ago, (Late Paleozoic Era until the Late Triassic) the continent we now know as North America was continuous with Africa, South America, and Europe. During the Late Triassic, Pangea began to 
Title: North America
Content:  and 55 million years ago. The formation of the Isthmus of Panama that connected the continent to South America arguably occurred approximately 12 to 15 million years ago, and the Great Lakes (as well as many other northern freshwater lakes and rivers) were carved by receding glaciers about 10,000 years ago. North America is the source of much of what humanity knows about geologic time periods. The geographic area that would later become the United States has been the source of more varieties of dinosaurs than any other modern country. According to paleontologist Peter Dodson, this is primarily due to stratigraphy, climate and geography, human resources, and history. Much of the Mesozoic Era is represented by exposed outcrops in the many arid regions of the continent. The most significant Late Jurassic dinosaur-bearing fossil deposit in North America is the Morrison Formation of the western United States.
Title: Rise of the Continents
Content:  200 million years ago North and South America were carved from Pangaea, and pushed westwards as separate island continents. The episode explains how subduction has created the longest continual mountain range in the world - the Andes, and how 300 million years ago New York was at the heart of a huge mountain range. Using llama as an example, Iain explains how most of South America's wildlife originated in North America, and only came south when the two island continents of North and South America joined three million years ago.
Title: South American land mammal age
Content:  ; 34–9 Ma – Tinguirirican to Chasicoan - South America had no land connections to any other continent. ; 9–3 Ma – Huayquerian to Chapadmalalan - islands formed between South and North America. A complete Isthmus of Panama most likely formed near the end of this interval, leading to the Great American Biotic Interchange (GABI). ; 3 Ma to present – Uquian to Holocene - the land connection between South and North America is established and migration between the formerly separated continents occurs. The main migrational route is from north to south, rather than the opposite way. This led to much higher extinction levels 
Title: Prehistory of the United States
Content:  The eastern United States was part of Pangaea's interior for most of the Triassic Period of the Mesozoic era. At the time, the area lay close to the equator and was connected to western Europe and Africa. The union of all of Earth's continents into a single land mass changed the way the atmosphere and oceans circulated. This left what is now the eastern US with a hot climate and pronounced seasons. Much of the country was located at about 30 latitudinal degrees North, where there tends to be high atmospheric pressures and little precipitation. The western United States were largely 

Question: what land mass was north america a part of about 300 million years ago?
Answer: Pangaea.
Pangaea or Pangea.