Even though marsupial mammals give birth to live young, an eggshell forms briefly early in their development. This is evidence that:
a. Marsupials share a common ancestor with some egg-laying species
b. Marsupials are not really mammals
c. All animals arose from a common ancestor.
d. Marsupial mammals were separately created by God
e. The fossil record of marsupial mammals is incorrect

Verified step by step guidance

1. Step 1: Begin by analyzing the biological significance of the eggshell formation in marsupial mammals. The presence of an eggshell briefly during development suggests a connection to ancestral traits found in egg-laying species.
2. Step 2: Understand the concept of shared ancestry in evolutionary biology. Traits like eggshell formation can be considered vestigial, meaning they are remnants of features that were present in a common ancestor but have been reduced or modified in descendants.
3. Step 3: Evaluate the options provided in the question. Consider which option aligns with the evidence of shared traits and evolutionary relationships. For example, option (a) suggests a common ancestor with egg-laying species, which is consistent with evolutionary theory.
4. Step 4: Eliminate options that contradict established scientific principles. For instance, options (b), (d), and (e) are not supported by evolutionary biology or empirical evidence. Option (c) is overly broad and does not specifically address the eggshell formation in marsupials.
5. Step 5: Conclude that the most scientifically supported answer is option (a), as it aligns with the evidence of shared ancestry and evolutionary relationships between marsupials and egg-laying species.

Key Concepts

Common Ancestry

Common ancestry refers to the idea that different species share a common ancestor from which they evolved. This concept is fundamental in evolutionary biology, as it explains the similarities and differences among species. The presence of shared traits, such as the temporary formation of an eggshell in marsupials, supports the notion that marsupials and egg-laying species diverged from a common lineage.

Evolutionary Development

Evolutionary development, or evolutionary developmental biology (evo-devo), studies how developmental processes evolve and how they contribute to the diversity of life. The brief formation of an eggshell in marsupials indicates that certain developmental traits can be retained from ancestral species, even as organisms adapt to different reproductive strategies. This concept helps explain the evolutionary significance of developmental similarities.

Mammalian Classification

Mammalian classification categorizes animals based on shared characteristics, such as mammary glands and live birth in most species. Marsupials, a subgroup of mammals, exhibit unique reproductive traits, including giving birth to underdeveloped young that continue to develop in a pouch. Understanding this classification is essential for recognizing the evolutionary relationships among different mammalian groups and their reproductive adaptations.