There is no doubt that bats and ostriches have captured the fascination of many people over the years with each of their unique evolutionary paths. How can a mammal be capable of flying, while a bird can’t? Bats, with their elongated fingers, adapted to form wings soar across the night sky, while ostriches, the largest living bird, have given up the ability to fly and adapted to a terrestrial lifestyle, becoming one the fastest runners on land.
These adaptations continue to bewilder us, but each is vital for them to thrive in their respective niches.
The evolutionary history of bats can be traced back over 50 million years and most likely to a small insectivorous mammal that inhabited forested environments. Although palaeontologists still haven’t confirmed which mammal bats may have evolved from, they likely developed the ability to fly to escape predation and/or to pursue an abundant supply of flying insects. Unlike birds and pterosaurs (an extinct clade of flying reptiles), in which the wing is supported by the bones of the arm and one finger, a bat’s wing membrane (patagium) is supported by the arm and by four elongated fingers. Hence the Greek name Chiroptera meaning ‘hand-wing’ which bats are commonly referred to.
A Dwarf Epauletted Fruit Bat (Micropteropus pussilus) shows off its elongated fingers and flexible wing membrane that resists tension while the stiff wings of birds in comparison deliver bending and torsional stress to the shoulders.
This unique adaptation allows bats to navigate through complex environments, even in complete darkness. How do they manoeuvre through the night skies? Just like other nocturnal mammals, bats’ eyes are made up of more photoreceptor cells called rods, which maximise their ability to see in the dark (this is as opposed to cones that maximise colour vision). However, nocturnal vision alone wasn’t enough. Bats are synonymous with echolocation whereby they send out ultrasonic sound waves to locate and prey upon insects with incredible precision. This prime example of convergent evolution opened up new ecological niches for bats to explore, leading to their eventual success as one of the most diverse and abundant groups of mammals on earth.
Wahlberg’s Epauletted Fruit Bat (epomophorus Wahlbergi). Bats’ diverse diets, including insects, fruits, nectar, and small vertebrates, showcase their exceptional adaptations to various ecological niches.
Ostriches, on the other hand, belong to the avian family and their ancestors can be traced back to around 40 million years ago. Initially, these birds were capable of flight, but their evolutionary journey took a different turn. In contrast to bats which took to the night skies to avoid competition over food on the ground, ostriches, emus, and other related flightless birds mainly obtained their food from the ground. As a result, there was no need for flight to search for their food, and over time, they became bulky and their wings became too weak due to a lack of use across generations. While ostriches still possess feathers, the individual barbules are not interlocked in the same way as a flying bird’s feathers, resulting in the feathers offering no wind resistance for them to get off the ground.
This ostrich shows off its powerful legs as it chases off a herd of buffalo approaching her clutch of eggs.
Along their evolutionary path, ostriches have instead developed long, powerful legs granting them the distinction of being not only the fastest running bird at 70km/h (45mph) but also the largest living bird (males at a maximum height of 2.75m/9ft and 130kg/290lbs). Ostriches are also known for their two massive toes, in comparison to most birds which have four toes. The inner toe also has one large nail that appropriately resembles a hoof and aids in traction allowing them to reach their impressive speeds. These combined evolutionary adaptations along with their herbivorous lifestyle have assisted them to have a considerable advantage in their native arid and semi-arid habitats.
While many evolutionary paths may pique our interest, the mammal that flies and the bird that runs certainly stand out and present fascinating examples of divergent evolution, where unique adaptations have shaped their distinctive identities. Yet another marvel of the natural world to appreciate! Let me know in the comments if any other evolutionary paths have you bewildered.
Kelsey Clark
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