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Humans share genes with headless creatures

Headless ocean creatures from 555 million years ago share genes with animals today, including humans

The first multicellular organisms had no head or limbs, and according to a study by the University of California, Riverside, share genes with modern animals, including humans.

One of the authors of the research, Mary Droser, explains that the oceanic creatures of 555 million years ago, from the Ediacaran period, had neither a head nor a skeleton. Many of them probably looked like three-dimensional bath mats on the seafloor, with round discs sticking out. These animals are so rare and so different that it is difficult to assign them to modern categories of living organisms.

The well-preserved fossil records made it possible to relate the appearance and behaviors of these animals to the genetic analysis of current living beings.


Dickinsonia fossil, an animal from the Ediacaran period. Source: Mary Droser

Ediacaran period animals

For their analysis, the researchers analyzed four animals representative of the more than 40 recognized species that have been identified since the Ediacaran period. These creatures ranged in size from a few millimeters to nearly a meter in length.

All four animals were multicellular, with cells of different types. Most were symmetrical, and their nervous systems and musculature were not centralized. One of those four were the Kimberella, teardrop-shaped creatures with a wide, rounded end and a narrow end that likely scraped the seafloor in search of food. Additionally, they could move using a muscular foot like today’s snails, according to the authors.

The Ikaria, animals recently discovered by a team in which Mary Droser also participated, were also observed. They were approximately the size and shape of a grain of rice and represent the first bilaterians, that is, organisms with a front, back and openings at each end connected by an intestine.

Furthermore, it appears that these animals can repair damaged body parts through a process known as apoptosis, or programmed cell death. The same genes involved are key elements of the human immune system, helping to eliminate precancerous and virus-infected cells. The account indicates that these animals likely already possessed the instructions responsible for the head and sensory organs normally found there. However, the necessary complexity in the interaction between these genes that would later give rise to these characteristics had not yet been achieved.

Droser’s team said their work is a way to put these animals on the tree of life and show that they are genetically linked to current animals and to ourselves. In the future, they plan to investigate muscle development and functional studies to better understand the animals’ early evolution.


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