The forelimb structure seen in both bat wings and human arms is very similar to that of an extinct land animal called eusthenopteron. this fact suggests that

  The fact that both the humans and the bats have very similar forelimb structure, the humans in the arms, the bats in their wings, which in turn is very similar to those of an ancient sarcopterygian called eusthenopteron, suggest that both species probably share a common distant ancestor.

  The eusthenopteron was an ancient species first thought to be living on land, though the latest research shows that it was only living in water, however, this animal is a distant ancestor of both species. This animal can be seen as ancestor to the humans and the bats because it is part of group that created the first animals on land, which in turn gave rise to the mammals later on, and both humans and bats are mammals, thus there's a connection and common ancestor of the both.

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.

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