2.13B Evidence of Evolution FRQ

Fossils of the oldest amphibian-like vertebrate animals have been found in rocks that are approximately 370 million years old. Based on fossil evidence of early amniotes, scientists estimated that the first amniotes evolved from amphibians around 340 million years ago. In May 2025, fossilized footprints of a reptile-like creature were discovered on a rock slab in Australia dated to approximately 355 million years ago. 

Scientists are interested in finding fossils of transitional species between amphibians and amniotes to better understand how and when this transition occurred. Three rock samples are available to search for these transitional forms:

• A rock sample that is 330 million years old

• A rock sample that is 360 million years old

• A rock sample that is 380 million years old

(a) Select the most appropriate sample of rocks in which to search for a transitional species between amphibians and amniotes.

360 MYA

 (b)Justify your selection.

Fossils are typically found in the order they were placed and an organism with intermediate  characteristics between two groups should be found in a rock layer between those two groups. 330 is too recent to contain transitional fossils and 380 is older than known amphibian fossils, so is too old to contain transitional fossils

Transitional fossils are found between 370 MYA (when the earliest amphibians lived) and when amniotes appeared, at least 340 MYA

(c )Using the data in the table, create a phylogenetic tree on the template provided to reflect the evolutionary relationships of the organisms (1pt)

(d) Identify whether morphological data or amino acid sequence data are more likely to accurately represent the true evolutionary relationships among the species, and provide reasoning for your answer.

Amino acid sequence (or molecular) data are more likely to accurately represent true evolutionary relationships because morphologies may be similar due to convergent evolution (analogous structures) and may not reflect common ancestry (homologous structures).

Molecular data directly reflect genetic changes that accumulate as species diverge from common ancestors at a relatively steady rate and can be compared across many species to determine when they last shared a common ancestor