Problem 10 - Campbell Biology

Question

This animal is a vertebrate with hair. What can you infer about its phylogeny? Identify as many key derived characters as you can that distinguish this animal from invertebrate chordates.

Step-by-Step Solution

Answer

The animal is a mammal. Key derived characters include a backbone, hair, mammary glands, three middle ear bones, and a neocortex.

Step 1 - Identify Vertebrate Characteristics

Recognize that vertebrates are animals with a backbone or spinal column. This backbone distinguishes them from invertebrates, which lack a backbone.

Step 2 - Recognize Hair as a Mammalian Trait

Identify that hair is a characteristic feature of mammals. Therefore, we can infer the animal is a mammal since it has hair.

Step 3 - Phylogeny Inference

By knowing the animal is a vertebrate and has hair, place it in the mammalian lineage of the phylogenetic tree. Mammals are a class within the phylum Chordata, which includes all vertebrates.

Step 4 - Derived Characteristics of Mammals

List key derived characters of mammals: presence of mammary glands, three middle ear bones, a neocortex region in the brain, hair or fur, and endothermy (regulating internal body temperature). Contrast these with invertebrate chordates, which lack these features.

Step 5 - Differences with Invertebrate Chordates

Understand invertebrate chordates, such as tunicates and lancelets, possess a notochord and dorsal nerve cord but lack a vertebral column (backbone) and other mammalian features such as hair and mammary glands.

Key Concepts

Vertebrates

Vertebrates are animals that possess a backbone or spinal column. This structural feature is a critical characteristic that sets them apart from invertebrates, which lack a backbone. The vertebral column provides support and protects the spinal cord. Vertebrates are part of the larger phylum known as Chordata, which also includes invertebrate chordates like tunicates and lancelets. However, only vertebrates have developed the backbone as a defining trait.

Phylogeny

Phylogeny is the study of the evolutionary history and relationships among species. In this context, knowing that an animal is a vertebrate with hair places it within the mammalian lineage of the phylogenetic tree. Mammals branch off from other vertebrates due to their unique derived characteristics. By examining these traits, scientists can map out the evolutionary pathways that led to the diversity we see today in the animal kingdom.

Mammary Glands

Mammals are distinguished by their mammary glands, which produce milk to nourish their young. This is one of the key derived characteristics that separate mammals from other vertebrates. Mammary glands allow for efficient feeding and nurturing, contributing to the survival and growth of mammalian offspring. This trait is not found in invertebrate chordates, highlighting a significant evolutionary development in mammals.

Neocortex

The neocortex is a region of the brain that is highly developed in mammals. It is responsible for higher-order brain functions such as sensory perception, cognition, and generation of motor commands. This advanced brain structure allows mammals to exhibit complex behaviors and adapt to their environments. In contrast, invertebrate chordates lack this specialized brain region, which marks another significant evolutionary advance within the mammalian lineage.

Endothermy

Endothermy refers to the ability of an organism to regulate its internal body temperature through metabolic processes. Mammals, as endotherms, can maintain a stable internal temperature regardless of external conditions. This trait is crucial for sustaining high levels of activity and survival in various environments. Invertebrate chordates do not possess this capability, relying instead on external temperatures to regulate their body heat.