Apply What You’ve Learned
591
Review
27.1 Land plants fall into ten major clades.
27.3 The precursors of vascular plants are extinct.
27.3 Horsetails and ferns are more closely related than previously thought.
Original Paper: Kenrick, P. and P. R. Crane. 1997. The origin and early evolution of plants on land. Nature 389: 33–
Together, phylogenetic analysis and the fossil record reinforce each other in deepening our understanding of the evolution of taxa. The figure below shows the evolution of early land plants, reflecting the fossil record and phylogenetic relationships. Use the figure to answer the questions that follow.
Questions
Question 1
About how long ago and in what geological period did the last common ancestor of ferns and seed plants live?
The last common ancestor of seed plants and ferns lived in the mid-
Question 2
Spike mosses are a group of lycophytes, some species of which are popular for cultivation. If you saw fossils of spike mosses in a geological stratum, would you expect to find plants closely related to the last common ancestor of ferns and seed plants in the same rock formation? Explain. If not, would you expect to find the last common ancestor of ferns and seed plants in a higher or lower stratum?
Spikemosses did not exist until the late Devonian. Spikemosses were not yet present when the last common ancestor of seed plants and ferns lived and thus fossils of spikemosses would not be expected in the same stratum with fossils of the common ancestors of ferns and seed plants. Because the common ancestor of ferns and seed plants lived before spikemosses did, we would expect fossils of that ancestor to be in a lower stratum.
Question 3
If you saw rhyniophyte fossils in a geological stratum, would you expect to find plants closely related to the last common ancestor of ferns and seed plants in the same stratum? Explain.
Yes, rhyniophytes existed from the late Silurian through much of the Devonian, and survived for tens of millions of years after the last common ancestor of seed plants and ferns lived. So it would not be surprising if fossils of these two lineages were in the same stratum.
Question 4
About how long ago and in what geological period did the last common ancestor of embryophytes live? What significant change in the life history of plants occurred in this lineage?
The last common ancestor of embryophytes lived in the Ordovician about 470 million years ago. This lineage was the first group of plants to live out of water and colonize land.