Which animal listed here has the shortest gestation period among mammals?

Introduction / Context:
Gestation period is the time between conception and birth in mammals. It varies widely among species and often reflects body size, developmental strategy and evolutionary history. This question asks you to identify which animal from the given list has the shortest gestation period, a fact commonly used in comparative biology and general knowledge questions.

Given Data / Assumptions:

Options include elephant, meadow vole, mouse, opossum and cow. We are looking for the smallest gestation time, not the largest. We assume typical values reported in biology and GK sources.

Concept / Approach:
In general, larger mammals have longer gestation periods and smaller mammals have shorter ones. Elephants, for example, have one of the longest gestation periods of all mammals, lasting around 20 to 22 months. Cows also have long gestations of around nine months. Mice and voles have relatively short gestation periods measured in weeks. However, some small marsupials such as opossums have extremely short gestation periods, often less than two weeks, because they give birth to very underdeveloped young that continue growing in a pouch. Among the listed options, the opossum is therefore the animal with the shortest gestation period.

Step-by-Step Solution:
Step 1: Eliminate elephant and cow immediately because they are large mammals with long gestation periods of many months. Step 2: Compare the smaller mammals. Mice usually have gestation periods of about three weeks. Step 3: Meadow voles have gestation periods roughly in the same short range of a few weeks. Step 4: Opossums, being marsupials, give birth after a very brief pregnancy of around 12 to 13 days in some species. Step 5: Therefore, among the given options, opossum has the shortest gestation period.

Verification / Alternative check:
To verify, recall that marsupials differ from placental mammals because their young are born at a much earlier developmental stage and then continue growing in a pouch. This results in much shorter internal gestation times. Many GK books highlight this by specifically referring to the opossum or some other small marsupial as having one of the shortest mammalian pregnancies. Elephants, in contrast, are often mentioned as having the longest pregnancy, which helps you immediately place them at the opposite end of the scale.

Why Other Options Are Wrong:
Elephant and cow are clearly wrong because they have very long gestation periods. Mouse and meadow vole do have short gestations, but these are still longer than the extremely short gestation of some opossum species. They provide distractor options that may mislead candidates who know only that small animals have shorter pregnancies without recognizing the special case of marsupials.

Common Pitfalls:
Students may quickly choose mouse because they remember that mice reproduce rapidly, or they might pick the smallest sounding animal without recalling the special biology of marsupials. To avoid this, associate the term shortest gestation period with opossum and other marsupials in your long term memory. At the same time, connect longest gestation period with elephant. This simple pair of associations is tested frequently in multiple choice exams.

Final Answer:
Among the animals listed, the opossum has the shortest gestation period.