Chapter 1. Mirror Experiment Activity for Fig. 23.20: Does the fossil record contain an intermediate between asymmetrical and symmetrical fish?

The asymmetric location of eye orbitals in modern-day flatfish and in fossils of Heteronectes and Amphistium has been referred to as a synapomorphy. Which of the following statements is true of synapomorphies?

When you think of data collection, you may think of scientists collecting information on the size and shape of living organisms, on the behavior of bacterial cells in culture, or on the genetic sequences of patients. However, scientists can also collect data from fossils and non-living specimens, as Friedman did when he examined Heteronectes and Amphistium fossils. Imagine that Friedman classified his fossils into three groups: 1) those with eye orbitals on both sides of the head in equivalent positions; 2) those with eye orbitals on both sides of the head but in unequal positions (that is, one eye orbital further up the head than the other); and 3) specimens with eye orbitals located only on one side of the head. In this scenario, what type of data would Friedman have collected?

If Friedman had carefully measured the position of the eye orbitals in his fossil specimens, and noted the distance of the orbital from the uppermost and lowermost point of the cranium, he would have collected which of the following types of data?

Figure 1 illustrates two examples of living, or extant, fish — Trachinotus and Citharus — with different morphologies. Two extinct types of fish — Amphistium and Heteronectes — are also depicted. Which of the following characteristics present in Amphistium and Heteronectes could be considered “intermediate” traits, between those of Trachinotus and Citharus?

Given the position of the right eye orbital seen in Heteronectes and Amphistium, what could Friedman have concluded about the evolutionary relationship between asymmetrical and symmetrical fishes?

According to Figure 1, which of the following statements is likely true regarding Trachinotus, Amphistium, Heteronectes and Citharus?

Within his paper, Friedman noted that the skulls, or craniums, of both the Heteronectes and Amphistium specimens he examined were derived from adult organisms. Why was this fact of special interest?

Fossils can be rare finds. How could researchers be sure that the asymmetrical placement of the eye orbitals in Heteronectes and Amphistium fossils was due to evolution, and not the result of damage to these structures?

As we discuss in later chapters (especially Chapter 44), the embryonic development of organisms can be used to predict evolutionary relationships among different species. For example, although certain marine worms and mollusks have very different adult body plans, they both demonstrate a unique embryonic stage characterized by a particular larval shape. Thus, these organisms are thought to share a common ancestor. In his paper, Friedman mentions that the larvae of modern flatfish initially develop with symmetrical eyes — one located on either side of the head. However, one of these eyes “migrates” to the other side of the head during embryogenesis. Modern symmetrical fish also develop from larvae having rudimentary eyes located on both sides of the head; however, these eyes do not migrate, resulting in an adult with symmetrical morphology. What does this tell you about the evolutionary origins of flatfish?