Based on common features such as the presence of a notochord and a dorsal hollow neural system at some stage of life, animals like fishes, amphibians, reptiles, birds and mammals are all included in which phylum?

Introduction / Context:
Animal classification groups organisms into hierarchical categories such as phylum, class, order and family based on shared characteristics. One of the most significant phyla in the animal kingdom is Chordata, which includes familiar vertebrates such as fishes, amphibians, reptiles, birds and mammals. This question asks you to identify the phylum that unites these varied groups based on features like notochord and dorsal hollow nerve cord.

Given Data / Assumptions:

• The animals listed include fishes, amphibians, reptiles, birds and mammals.
• Common features mentioned are presence of notochord and a dorsal hollow neural system at some stage.
• Options include Mammalia, Chordata, Primata and Insecta.
• We assume standard zoological hierarchy where phylum is a higher rank than class or order.

Concept / Approach:
The defining characteristics of phylum Chordata include the presence of a notochord, a dorsal hollow nerve cord, pharyngeal slits and a post anal tail at some stage of development. Vertebrates are a subphylum within Chordata and include fishes, amphibians, reptiles, birds and mammals. Mammalia is only one class within Chordata, Primata is an order within Mammalia, and Insecta is a class in a completely different phylum, Arthropoda. Therefore, the correct phylum that groups all the listed animals is Chordata.

Step-by-Step Solution:
Step 1: Note that fishes, amphibians, reptiles, birds and mammals all possess a backbone in their adult form, making them vertebrates.Step 2: Recall that vertebrates belong to the subphylum Vertebrata under the phylum Chordata.Step 3: Recognize that the key chordate features, such as notochord and dorsal hollow nerve cord, are present during some stage in their life cycle.Step 4: Evaluate option B, Chordata, which matches the description of a phylum characterized by these features and which contains all the listed classes of animals.Step 5: Exclude option A, Mammalia, because it includes only mammals and not fishes, amphibians, reptiles or birds.Step 6: Exclude option C, Primata, because it is only an order inside Mammalia and does not cover all vertebrates.Step 7: Exclude option D, Insecta, because insects are arthropods and do not have a notochord or dorsal hollow nerve cord.Step 8: Conclude that Chordata is the correct answer.

Verification / Alternative check:
You can verify this by consulting standard classification tables where phylum Chordata is shown to contain subphyla such as Vertebrata, Urochordata and Cephalochordata. Within Vertebrata, the classes Pisces (fishes), Amphibia, Reptilia, Aves (birds) and Mammalia are all listed. This means that all these animals share chordate features and are grouped under Chordata. Insects, by contrast, appear under phylum Arthropoda and do not show chordate features.

Why Other Options Are Wrong:
Option A is wrong because Mammalia includes only warm blooded animals with hair and mammary glands and does not include fishes, amphibians, reptiles or birds. Option C is wrong because Primata is limited to primates such as monkeys and humans. Option D is wrong because Insecta is a class under Arthropoda and includes organisms like houseflies and butterflies, which lack a notochord and dorsal hollow nerve cord.

Common Pitfalls:
Students sometimes confuse class, order and phylum when they memorize classification ranks. A common mistake is to select Mammalia because it seems familiar and includes humans. To avoid this, remember that phylum is a broader category than class, and Chordata is the phylum that unites all animals with chordate characteristics, including humans. Visualizing the hierarchy with Chordata at the top and classes like Mammalia and Aves under it can help you quickly choose the correct phylum in exam questions.

Final Answer:
Chordata, the phylum characterized by notochord and dorsal nerve cord.