Among all two legged (bipedal) creatures on Earth, which creature is known to be the fastest runner on land?

Introduction / Context:
Speed comparisons are a popular topic in general science and biology. When we talk about two legged or bipedal creatures, we include humans and several species of birds such as ostriches and emus. This question focuses on which biped is the fastest runner on land, an interesting fact that also connects to adaptations of body structure and habitat.

Given Data / Assumptions:

• The comparison is limited to two legged (bipedal) animals.
• We are concerned with maximum running speed on land, not flying speed.
• The options include humans and large flightless birds that walk and run on two legs.
• Only one option is known to achieve the highest running speeds among bipeds.

Concept / Approach:
Bipedal locomotion occurs in humans and several birds. Among them, the ostrich is famous for its exceptional running speed, adapted to open savanna and semi desert environments. Adult ostriches can run at speeds of around 60 to 70 km/h, far surpassing human sprinters and other bipedal birds. The approach is to recall approximate speed ranges and the special adaptations that allow ostriches to move so quickly on two legs.

Step-by-Step Solution:
Step 1: List the main bipedal animals in the options: humans, ostriches, emus, kangaroos, and cassowaries.Step 2: Recall that elite human sprinters reach top speeds of about 35 to 44 km/h for short distances.Step 3: Emus and cassowaries are fast birds but typically run slower than ostriches.Step 4: Kangaroos use hopping locomotion and can be fast, but average speeds in sustained running are still below the top speeds of ostriches.Step 5: Recognise that ostriches are widely cited as the fastest running birds and the fastest bipedal animals, and select Ostrich as the answer.

Verification / Alternative check:
Reference materials on animal records and biology consistently mention the ostrich as the fastest running bird and the fastest biped, with speeds that can exceed 60 km/h. No other bipedal creature in the options is recorded with higher land sprint speeds. This information provides a clear confirmation that ostrich is the correct answer.

Why Other Options Are Wrong:
Option A: Human beings are fast compared to many animals but do not reach ostrich level speeds.Option C: Emus are quick but slower than ostriches and not recognised as the fastest biped.Option D: Kangaroos can move rapidly using jumps but still fall short of ostrich running speeds.Option E: Cassowaries are powerful and potentially dangerous birds but are not recorded as the fastest bipedal runners.

Common Pitfalls:
A common misconception is to assume humans must be the fastest among bipeds because of sprinting records, or to guess kangaroos due to their impressive jumping ability. Others may confuse flight speed with running speed. To avoid such mistakes, remember that ostriches are specialised for high speed running in open terrains, making them the fastest runners on two legs.

Final Answer:
The correct answer is Ostrich.