The pre-australopith fossils are especially significant because they challenge some of the long-standing explanations of our evolutionary history. Describe two reasons the pre-australopiths force us to rethink the savanna hypothesis in particular. (Hint: Think about the anatomical traits of the pre-australopiths and the environmental and temporal context in which they lived.)

Two important reasons are listed here:

- Pre-australopithecines show evidence of bipedalism but they lived in forested areas  

- Ardipithecus ramidus is a human ancestor that lived in a wooded environment approximately 4.2 to 4.5 million years ago

The savanna hypothesis states that early hominid traits were selected in response to increased aridity conditions and the emergence of savanna landscapes (i.e., open grasslands), as forests receded. This hypothesis enables us to understand better the evolution of bipedalism.

Pre-Australopithecines represent the oldest hominids that date from at least ​7 to 4.4 million years ago (mya), depending on the species. Pre-australopithecines show evidence of bipedalism (and/or dentition similar to the later hominins who exhibit bipedalism), but it has been shown that they lived in forested areas. Therefore, this observation contradicts the savanna hypothesis which states that bipedalism evolved as an adaptation to the savanna.

Ardipithecus ramidus is a human ancestor dating to between 4.5 and 4.2 mya. The Ardipithecus ramidus fossils were discovered in Ethiopia alongside faunal remains, thereby indicating they lived in a wooded environment. In consequence, Ardipithecus ramidus fossils contradict the open savanna explanation for the origin of bipedalism.

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explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.

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