To explain relationships in life, you need a ‘Tree of Death’

Phylogenetics seeks to explain the relationships between organisms today, effectively drawing up a phylogeny, like a family tree. That means pulling together information on the past history of a group, and so botanists use fossils as snapshots of how a family looked in the past.

Diagram of a partially dead phylogeny.
Not every organism went on to provide offspring in the modern world. Image: Canva.

Selena Smith and colleagues point out that the problem with constructing a past ‘tree of life’ connecting species is that a lot of the tree is dead. Instead, they argue that scientists should build a ‘tree of death’, which they describe as, “a tree of life that includes both extant and extinct taxa to resolve overall patterns of phylogenetic relationships.” The authors use the Zingiberales, an order of plants that includes banana and ginger, to show how to integrate fossils into the phylogeny.

Writing in AmJBot, the authors say: “Extinct species record different combinations of characters than seen in extant taxa. What may seem like incongruence between morphological and molecular data sets in inferring phylogenetic relationships is better understood with incorporation of fossil data. The fact that the familial affinities of Spirematospermum have been debated for over two decades (largely based on study of Spire. wetzleri) but not quantitatively tested points to the need to incorporate fossils in phylogenetic analyses not only to place the fossils, but also to better understand morphological evolution, homoplasy, and apparent conflicts in the data.”

They argue that this is a study where citizen science could have a significant input. While fruits and seeds are widely studied in fossils, Smith and colleagues state that stems and leaves are unstudied. They think there could be a lot of data where the public’s eyes could contribute to classifying fossils and help place the fossils into the right place in the family tree. Getting this right could lead to techniques in studying other plants and getting a better understanding of the evolution of major crops.

Reference List

Smith, S. Y., Iles, W. J. D., Benedict, J. C., & Specht, C. D. (2018). Building the monocot tree of death: Progress and challenges emerging from the macrofossil-rich Zingiberales. American Journal of Botany. https://doi.org/10.1002/ajb2.1123