Our Ancient Relatives Were Not So Simple

Author: University of Nottingham
Published: 12 Nov 2022 - Updated: 29 Apr 2023
Peer Reviewed Publication: Yes

Contents: Synopsis - Introduction - Main - Related Publications

Synopsis: A new study reveals that our ancient ancestors were a lot more complex than we originally thought.

Introduction

"Filtering Artifactual Signal Increases Support for Xenacoelomorpha and Ambulacraria Sister Relationship in the Animal Tree of Life" - Current Biology.

Researchers at the University of Nottingham have solved an important piece of the animal evolution puzzle after a new study revealed that our ancient ancestors were more complex than originally thought.

Main Content

In our distant evolutionary history, animals underwent a major innovation. They evolved to have a left and right side and two gut openings. This brought about many significant advantages in propelling themselves directly forward at increased speed through the early seas, from finding food and extracting nutrients to avoiding being eaten. It was such a successful strategy that, today, we share our planet with a huge diversity of other animals with bilateral symmetry and two gut openings just like us humans. They include animals as diverse as starfish, sea cucumbers, elephants, crickets, and snails. They also include an enigmatic group of very simple marine worms called Xenacoelomorphs, who lack many of the complex features of their fancier-looking cousins.

For years, scientists have debated who is more closely related to who in this diverse collection of bilaterally symmetrical animals. Some experts argue that Xenacoelomorphs mark the first group to branch in that major jump in innovation from animals with circular body plans (e.g., jellyfish and corals) to bilateral symmetry. The first bilaterian was also a straightforward animal if this was the case. Others argued for different placements of Xenacoelomorphs on the family tree.

However, a research team led by Dr. Mary O'Connell at the University of Nottingham found that Xenacoelomorphs branch much later. They are not the earliest branch on the bilaterian family tree, and their closest relatives are far more complex animals, like starfish. This means that Xenacoelomorphs have lost many of the complex features of their closest relatives, challenging the idea that evolution leads to ever more complex and intricate forms. Instead, the new study shows that the loss of features is important in driving evolution.

Dr. Mary O'Connell, Associate Professor in Life Sciences at the University of Nottingham, says:

"There are many fundamental questions about the evolution of animals that need to be answered. Many parts of this family tree still need to be discovered or resolved. But what an exciting time to be an evolutionary biologist with the availability of exquisite genome data from the beautiful diversity of species we currently have on our planet, allowing us to unlock secrets of our most distant past."

The paper, titled 'Filtering artifactual signal increases support for Xenacoelomorpha and Ambulacraria sister relationship in the animal tree of life' has been published in the peer-reviewed journal Current Biology. It details the application of a special phylogenetic technique to help extract signal from noise over deep time, showing increased support for Xenacoelomorphs being sister to ambulacraria (e.g., starfish) rather than being the deepest diverging of the bilateria.

The research team at the University of Nottingham will now explore other challenging family trees and other connections between genome changes and phenotypic diversity.

Also see: Research by Texas A&M Redefines Mammalian Tree of Life

Attribution/Source(s): This peer reviewed publication was selected for publishing by the editors of Disabled World (DW) due to its relevance to the disability community. Originally authored by University of Nottingham and published on 12 Nov 2022, this content may have been edited for style, clarity, or brevity.