Learn Spanish (Latin America): El cráneo es diferente, puesto que es de una especie nueva. - The skull is different, given that it is from a new species.

Puesto que is a cause connector that means 'given that' or 'since.' It connects a result (the skull is different) to its cause (it is from a new species). You can definitely use porque ('because') here, but puesto que is slightly more formal. It is often used when explaining a logical conclusion or stating a fact that justifies the first part of the sentence.

Why does especie take the feminine article una if it doesn't end in 'a'?

While many feminine nouns end in 'a', especie is a word you just have to memorize as feminine (la especie). Also, note that even though it looks a bit like an English plural, una especie is strictly singular, meaning 'one species.' The plural form is exactly the same: las especies.

Why is the adjective placed after the noun here (especie nueva)?

Placing nueva after the noun is used for objective, literal descriptions. It tells us this is a factually new, undiscovered biological species. If it were placed before the noun (nueva especie), it might sound more subjective, like saying 'a new kind of thing' rather than a newly classified animal.

Why do we use es twice in this sentence instead of está?