Atractosteus grandei lived less than 1,500-2,500 years after the Chicxulub asteroid impact, an event that is widely accepted as a major cause behind the end-Cretaceous mass extinction that eradicated roughly 75% of the animal and plant species on Earth, including whole groups like non-avian dinosaurs and ammonites.
Skull (a) and partial skeleton (b) of Atractosteus grandei in dorsal view. Scale bars – 4 cm. Image credit: Chase Doran Brownstein & Tyler R. Lyson, doi: 10.1098/rsbl.2022.0118.
Gars are a primitive group of euryhaline fishes in the family Lepisosteidae. There are seven living species of gars in two genera: Atractosteus and Lepisosteus.
These fishes first appeared during the Late Jurassic epoch, approximately 150 million years ago.
They have slender torpedo-shaped bodies, ganoid scales, long snouts, and numerous teeth.
Gars occur in eastern North America, as far west as Montana in the United States; as far north as Montana and southern Quebec, Canada; and as far south as Central America and Cuba.
They are primarily freshwater fishes, although some have been known to swim into saltwater areas near the ocean shore.
The newly-identified species belongs to the genus Atractosteus, which also includes the giant alligator gar (Atractosteus spatula).
“When we estimate the size of Atractosteus grandei, we get about 1.4-1.5 m (4.6-4.9 feet), which is in the size range of the largest gars and holosteans,” said Chase Doran Brownstein, a paleontologist with Yale University and the Stamford Museum and Nature Center.
An alligator gar (Atractosteus spatula), about 3 m (10 feet) long, caught in Moon Lake, Mississippi, in March 1910. Image credit: D. Franklin / American Museum of Natural History.
Atractosteus grandei lived in what is now North Dakota, the United States, some 66 million years ago.
“Atractosteus grandei is the oldest known definite crown-group gar from the Americas,” Brownstein noted.
The fossilized remains of this ancient fish were found in the lowest-most portion of the Fort Union Formation in Bowman County, North Dakota.
“The specimen is preserved in a light tan, highly friable, silty mudstone unit that overlies the 8 cm (3.15 inches) thick formational contact lignite, interpreted to be a ponded water depositional environment,” Brownstein and his colleague, Denver Museum of Nature and Science’s Dr. Tyler Lyson, explained.
“The specimen consists of an articulated skull and in place lower jaws, as well as a series of mostly articulated precaudal vertebrae, ribs, and associated ganoid scales.”
“The specimen was found ‘belly up,’ with the front portion of the skull and lower jaws pointing up.”
The discovery of Atractosteus grandei suggests healthy freshwater ecosystems existed in North America within thousands of years of the Chicxulub asteroid impact.
“The end-Cretaceous mass extinction was responsible for the destruction of global ecosystems and loss of approximately three-quarters of species diversity 66 million years ago,” the paleontologists said.
“Large-bodied land vertebrates suffered high extinction rates, whereas small-bodied vertebrates living in freshwater ecosystems were buffered from the worst effects.”
“The presence of this freshwater macropredator approximately 1,500-2,500 years after the asteroid impact suggests the rapid recovery and reassembly of North American freshwater food webs and ecosystems after the mass extinction.”
A paper describing the discovery was published in the June 2022 issue of the journal Biology Letters.
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Chase Doran Brownstein & Tyler R. Lyson. 2022. Giant gar from directly above the Cretaceous-Palaeogene boundary suggests healthy freshwater ecosystems existed within thousands of years of the asteroid impact. Biol. Lett 18 (6): 20220118; doi: 10.1098/rsbl.2022.0118
Source link: https://www.sci.news/paleontology/atractosteus-grandei-11103.html
