In order to maintain constant oxygen supply to demanding flight muscles, and to counteract heat loss from an unfavourable body surface area to volume
ratio, the heart rate of very small birds can easily reach over 1000 beats per minute during flight...that's about 17 times per second.
The growing Dolphin fetus Shows evidence that it was once a land mammal similar to a dog.
There are 3 things:
1. Early on in the womb it grows two leg like limbs near the tail end which in time retract and dissapear.
2. Very late in the womb it grows whisker like hairs from the base of it's nose near the eye's which then fall out a few weeks after birth.
3. When it grows it's main fins/flippers they are translucent for a period of time and you can see finger like bones inside.
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