East america fossil dating

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Paleognath birds (ratites and South American tinamous) may have migrated by this route around the same time, more likely in the direction from South America to Australia/New Zealand.Other taxa that may have dispersed by the same route (if not by flying or floating across the ocean) are parrots, chelid turtles and (extinct) meiolaniid turtles.The pyrotheres and astrapotheres were also strange but were less diverse and disappeared earlier, well before the interchange.

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Sparassodonts and giant opossums shared the ecological niches for large predators with fearsome flightless "terror birds" (phorusrhacids), whose closest extant relatives are the seriemas.

Marsupials present in South America included didelphimorphs (opossums) and several other small groups; larger predatory relatives of these also existed, like the borhyaenids and the sabertooth Thylacosmilus (sparassodont metatherians which are no longer considered to be true marsupials).

After the extinction of sparassodonts, and before the arrival of carnivorans, giant opossums like Thylophorops represented true marsupial macropredators.

The interchange is visible from observation of both biostratigraphy and nature (neontology).

Its most dramatic effect is on the zoogeography of mammals but it also gave an opportunity for reptiles, amphibians, arthropods, weak-flying or flightless birds, and even freshwater fish to migrate.

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