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Description
The famous long necked Elasmosaurids were also present in the Paleogene, although with some notable exceptions. The iconic Cretaceous Elasmosaurus and Styxsosaurus were gone before the K-PG event, leaving only the stem Elasmosaurs and the Weddelonectians to swim on into the Paleogene. Of these, the Aristonectines and relatives were the most successful and widespread, with some reaching very large sizes. The stem forms radiated out as slender, superficially Elasmosaurus-like piscivores around the time of the Paleocene-Eocene Thermal Maximum but declined significantly as the world’s oceans began to cool later in the period. The Weddelonectians were marginal creatures, possessing a near global range in the Eocene but being low in number. The major exception to this rule was the land at the bottom of the world: Antarctica. This was the stronghold of the Weddelonectians, with the group being rather diverse here; ranging from the huge cruising descendants of the Aristonectines to the much smaller, speedy Morenosaurines. Anversaurus was a member of the latter subfamily. Descended from ancestors with longer necks and small heads, Morenosaurines and their close cousins the Neoplesiosaurians began to converge on the Polycotylids more common in the Northern Hemisphere during the Paleogene, developing shorter, more robust necks and proportionally larger skulls. Anversaurus would have been a 6m long predator with a relatively fast swimming lifestyle, different from the slower cruising movement of its ancestors. While the Morenosaurines like A. bellingshauseni became extinct at the end of the Eocene, along with the larger Aristonectines and all the stem elasmosaurs, the closesly related Neoplesiosaurians would weather the worst of the extinction event. By the Oligocene, Neoplesiosaurians would begin to recover and eventually give rise to some of the strangest and most fascinating plesiosaurs to have ever evolved.

Description
The famous long necked Elasmosaurids were also present in the Paleogene, although with some notable exceptions. The iconic Cretaceous Elasmosaurus and Styxsosaurus were gone before the K-PG event, leaving only the stem Elasmosaurs and the Weddelonectians to swim on into the Paleogene. Of these, the Aristonectines and relatives were the most successful and widespread, with some reaching very large sizes. The stem forms radiated out as slender, superficially Elasmosaurus-like piscivores around the time of the Paleocene-Eocene Thermal Maximum but declined significantly as the world’s oceans began to cool later in the period. The Weddelonectians were marginal creatures, possessing a near global range in the Eocene but being low in number. The major exception to this rule was the land at the bottom of the world: Antarctica. This was the stronghold of the Weddelonectians, with the group being rather diverse here; ranging from the huge cruising descendants of the Aristonectines to the much smaller, speedy Morenosaurines. Anversaurus was a member of the latter subfamily. Descended from ancestors with longer necks and small heads, Morenosaurines and their close cousins the Neoplesiosaurians began to converge on the Polycotylids more common in the Northern Hemisphere during the Paleogene, developing shorter, more robust necks and proportionally larger skulls. Anversaurus would have been a 6m long predator with a relatively fast swimming lifestyle, different from the slower cruising movement of its ancestors. While the Morenosaurines like A. bellingshauseni became extinct at the end of the Eocene, along with the larger Aristonectines and all the stem elasmosaurs, the closesly related Neoplesiosaurians would weather the worst of the extinction event. By the Oligocene, Neoplesiosaurians would begin to recover and eventually give rise to some of the strangest and most fascinating plesiosaurs to have ever evolved.