Birgeria

Birgeria is a group of ancient carnivorous fish that lived in the oceans during the Triassic period. These fish have been found all over the world. Fossils have been discovered in places like Madagascar, Spitsbergen, Germany, Switzerland, Italy, Slovenia, China, Russia, Canada, and Nevada in the United States. The earliest fossils of Birgeria come from rock layers in East Greenland. These rocks date to the very start of the Triassic period, right after a big event called the Permian-Triassic mass extinction. Birgeria lived until the end of the Triassic period. They went extinct during another big event known as the Triassic-Jurassic mass extinction.

At first, scientists thought one of these fish belonged to a different group called Saurichthys. After studying it more, a scientist named Erik Stensiö decided it was different enough to deserve its own group. He named this new group after his friend Birger Sjöström. Birger had gone with Erik on a trip to the Arctic island of Spitsbergen (Svalbard) in 1915.

Systematics

Birgeria is the only genus of the family Birgeriidae and order Birgeriformes. Other fish like Psilichthys, Ohmdenia and Brazilichthys were once thought to be related, but they are not. This family was first described in 1937. These fish lived in the very early Triassic period in Greenland and disappeared by the late Triassic period. They were most common during the early to middle Triassic.

In many studies, Birgeria is closely related to the Saurichthyiformes. Together, they are often linked to groups like sturgeons and paddlefish. However, some studies suggest they might not be closely related to these fish. With around eight known species, Birgeria was less common than another fish group called Saurichthys. Fossils of unknown species have been found in Canada, Bolivia, Luxembourg, and Saudi Arabia.

Appearance

Birgeria had very few scales, mostly only on the top of its tail fin and the back of its tail. The scales that it had were small and diamond-shaped.

Its tail fin was large and split deeply in the middle. The top and bottom fins were placed near the back of its body. The eyes were at the front of its head, and it had long jaws with many sharp teeth.

Ecology

Birgeria was a top hunter among fish from the Triassic period, living together with another fish called Saurichthys.

Most Birgeria fish grew longer than 1 meter (about 3.3 feet), with some reaching up to 2 meters (about 6.6 feet) or more. Some of the biggest types lived in the early Triassic, such as Birgeria aldingeri from Spitsbergen and Birgeria americana from Nevada, United States. They were among the first large hunters to appear after a big event called the Permian-Triassic mass extinction.

Scientists once thought a Birgeria fossil from Madagascar might have carried baby fish inside, but this idea was later dropped. It now seems more likely that these were actually small fish that Birgeria had eaten. Unlike Saurichthys, Birgeria probably did not give birth to live young. This idea is supported because no fossils showing special organs for this have been found.

From its body shape, scientists believe Birgeria was a fast swimmer in the open ocean. Because there are not many fossils of it, it likely lived far from shore.