Researchers have discovered in Montana the remains of two newly identified species of birds from the Cretaceous period, dating back to about 67 million years ago, that show anatomical features similar to today’s birds of prey. Specifically, they have a leg bone built in a way that allowed them to capture, subdue and transport prey, just as hawks, owls and eagles do today, notes Reuters.
The fossils were discovered in the same stretch of rock in the Hell Creek Formation, which spans four US states, where many dinosaurs have been discovered over the years, including T. rex, Triceratops and Edmontosaurus.
The two are known only from the tarsometatarsus, the leg bone between the ankle and the toes. Based on its size, the larger of the two birds, named Avisaurus darwini, may have been the size of a large falcon, with a wingspan of perhaps 1.3 meters. The other, slightly smaller one, is also part of the Avisaurus genus, but its species name has not been coined.
The similarities of the tarsometatarsus to modern birds of prey “suggest that it may have functioned similarly and may have occupied an ecology not too different from what we see today,” said Alex Clark, a PhD student in evolutionary biology at the University of Chicago and the Field Museum in Chicago and lead author of the study published Wednesday in the journal PLOS ONE.
“When we refer to a bird of prey, we are specifically discussing extant birds that primarily use their legs and feet to subdue or incapacitate prey,” Clark added.
The two species may have hunted small mammals, lizards and other birds, just as a hawk would today.
The first birds appeared about 150 million years ago, during the Jurassic period, evolving from small feathered dinosaurs. The two newly identified species were part of the enantiornithines, one of the four main groups of birds that lived during the age of the dinosaurs. This group disappeared in the mass extinction 66 million years ago caused by an asteroid strike that doomed the dinosaurs, except for some of their avian descendants.
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These newly identified birds of prey are not ancestral to any living today, but rather evolved with the same anatomical features.
“The morphology that would equip an animal for raptorial-type behavior probably evolved multiple times,” Clark said.
To date, the oldest known birds of prey date from millions of years after the beginning of the Cenozoic period, which followed the extinction of the dinosaurs and saw the rise of mammals.
The incomplete nature of the Avisaurus fossils discovered leaves a mystery as to what these birds looked like.
“Would these enantiornithines have had teeth or hooked beaks like many modern raptors? Both are possible, and only future discoveries will tell,” said Jingmai O’Connor, a paleontologist at the Field Museum and co-author of the study.
A feature seen on their tarsometatarsus was a robust muscle attachment point, similar to that of hawks and owls.
“This indicates strong leg muscles and legs that could catch and possibly carry relatively large prey,” Clark said.
Another feature—grooves on the tarsometatars, called trochleae, which indicate potentially powerful toes—is a feature present in modern birds of prey that is useful in subduing prey to be carried in flight.
The researchers also discovered the remains of a third new bird species dating from the same period, called Magnusavis ekalakaensis, but its lifestyle remains unclear.
The discovery of these new species deepens the understanding of ecosystems at the end of the age of dinosaurs and fills some gaps in the knowledge of the evolution of birds during this crucial period for life on Earth.
“You have an ecosystem that can support a tyrant like Tyrannosaurus rex, but then you have enough diversity of small vertebrates to support several species of likely birds of prey,” Clark said.
(source: AFP)
Source: jurnalul.ro
