Artist’s concept of Ikaria wariootia. Image via Sohail Wasif/ UCR.
Geologists
say they have discovered a fossil of the first ancestor on the family
tree that contains most animals today, including humans. The fossil of
the extinct worm-like creature was discovered in deposits in Nilpena in
South Australia belonging to the Ediacaran Period, an interval of geological time ranging 635 to 541 million years ago.
The tiny creature, called Ikaria wariootia, lived about 555 million years ago and was about the size of a grain of rice. According to the study, published March 23, 2020, in the peer-reviewed journal Proceedings of the National Academy of Sciences, it is the earliest bilaterian, or organism with a front and back, two symmetrical sides, and openings at either end connected by a gut.
The development of bilateral symmetry, scientists say,
was a critical step in the evolution of animal life, giving organisms
the ability to move purposefully and a common, yet successful, way to
organize their bodies. A multitude of animals, from worms to insects to
dinosaurs to humans, are organized around this same basic bilaterian
body plan.
Ikaria wariootia impressions in stone. Image via Droser Lab/ UCR.
For the new research, University of California/Riverside scientists Scott Evans and Mary Droser
used a 3-D laser scanner to analyze miniscule oval impressions near
fossilized burrows found in 555 million-year-old Ediacaran Period
deposits in Nilpena, South Australia. Their research revealed the
regular, consistent shape of a cylindrical body with a distinct head and
tail and faintly grooved musculature. The animal ranged between 2-7
millimeters (up to about a quarter of an inch) long and about 1-2.5
millimeters (up to about a tenth of an inch) wide, just the right size
to have made the burrows. Evans said in a statement:
We thought these animals should have existed during this interval, but always understood they would be difficult to recognize. Once we had the 3-D scans, we knew that we had made an important discovery.
A 3-D laser scan of an Ikaria wariootia impression. Image via Droser Lab/ UCR.
According to a statement from the researchers:
In spite of its relatively simple shape, Ikaria was complex compared to other fossils from this period. It burrowed in thin layers of well-oxygenated sand on the ocean floor in search of organic matter, indicating rudimentary sensory abilities. The depth and curvature of Ikaria represent clearly distinct front and rear ends, supporting the directed movement found in the burrows.
The burrows also preserve crosswise, “V”-shaped ridges, suggesting Ikaria moved by contracting muscles across its body like a worm, known as peristaltic locomotion. Evidence of sediment displacement in the burrows and signs the organism fed on buried organic matter reveal Ikaria probably had a mouth, anus, and gut.
Bottom line: Geologists have discovered the
fossil of a worm-like creature that they say is the first ancestor on
the family tree that contains most animals today, including humans.
Artist’s concept of Ikaria wariootia. Image via Sohail Wasif/ UCR.
Geologists
say they have discovered a fossil of the first ancestor on the family
tree that contains most animals today, including humans. The fossil of
the extinct worm-like creature was discovered in deposits in Nilpena in
South Australia belonging to the Ediacaran Period, an interval of geological time ranging 635 to 541 million years ago.
The tiny creature, called Ikaria wariootia, lived about 555 million years ago and was about the size of a grain of rice. According to the study, published March 23, 2020, in the peer-reviewed journal Proceedings of the National Academy of Sciences, it is the earliest bilaterian, or organism with a front and back, two symmetrical sides, and openings at either end connected by a gut.
The development of bilateral symmetry, scientists say,
was a critical step in the evolution of animal life, giving organisms
the ability to move purposefully and a common, yet successful, way to
organize their bodies. A multitude of animals, from worms to insects to
dinosaurs to humans, are organized around this same basic bilaterian
body plan.
Ikaria wariootia impressions in stone. Image via Droser Lab/ UCR.
For the new research, University of California/Riverside scientists Scott Evans and Mary Droser
used a 3-D laser scanner to analyze miniscule oval impressions near
fossilized burrows found in 555 million-year-old Ediacaran Period
deposits in Nilpena, South Australia. Their research revealed the
regular, consistent shape of a cylindrical body with a distinct head and
tail and faintly grooved musculature. The animal ranged between 2-7
millimeters (up to about a quarter of an inch) long and about 1-2.5
millimeters (up to about a tenth of an inch) wide, just the right size
to have made the burrows. Evans said in a statement:
We thought these animals should have existed during this interval, but always understood they would be difficult to recognize. Once we had the 3-D scans, we knew that we had made an important discovery.
A 3-D laser scan of an Ikaria wariootia impression. Image via Droser Lab/ UCR.
According to a statement from the researchers:
In spite of its relatively simple shape, Ikaria was complex compared to other fossils from this period. It burrowed in thin layers of well-oxygenated sand on the ocean floor in search of organic matter, indicating rudimentary sensory abilities. The depth and curvature of Ikaria represent clearly distinct front and rear ends, supporting the directed movement found in the burrows.
The burrows also preserve crosswise, “V”-shaped ridges, suggesting Ikaria moved by contracting muscles across its body like a worm, known as peristaltic locomotion. Evidence of sediment displacement in the burrows and signs the organism fed on buried organic matter reveal Ikaria probably had a mouth, anus, and gut.
Bottom line: Geologists have discovered the
fossil of a worm-like creature that they say is the first ancestor on
the family tree that contains most animals today, including humans.
Aucun commentaire:
Enregistrer un commentaire