When did our hominid ancestors first start using tools? This is a fascinating question of human paleontology, and it is also difficult to answer definitively. There are two basic reasons for this difficulty. The first is generic to all paleontology – our knowledge of when something emerged is dependent upon the oldest specimen. But the oldest specimen is likely not the very first emergence, so dates are frequently being pushed back when yet older specimens are discovered. Often scientists will say that something is “at least” a certain age old, knowing it could be older.

Tool uses specifically, however, has another challenge – we can only really know about tools that survive and are recognizable in the record. If early hominids were using wooden tools, for example, it would be very difficult to know this. If they were using unmodified stones this would also be difficult. We could potentially infer such use if the results were visible in the fossil record, such as marks on the bones of prey, but that can be difficult.

So when we talk about the earliest evidence for tool use in our ancestors we are talking about crafted stone tools. The oldest known stone tools date to 3.3 million years ago, at the Lomekwi 3 site in Kenya. At this time there were Australopithecines around but not yet any members of the genus Homo. H. habilis and H. rudolfensis date from 2.8-2.75 million years ago.

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One of the things I like about following paleontology news is that new evidence can just be discovered, and sometimes these new pieces to the puzzle can significantly change what we think about past life. One such controversy I have been following for a while is whether or not small specimens of Tyrannosaurus rex-like dinosaurs represent juvenile T-rexes or a separate smaller species of theropod dinosaur. A new analysis of a nearly complete Nanotyrannus specimen has definitively resolved the debate – Nanotyrannus was a separate genus.

There are several layers of context that make this story more interesting. First, why was it so difficult to determine if different specimens were the same genus or not? This is not just due to having incomplete specimens – even with complete specimens, this can sometimes be tricky. Will all unknown species paleontologists need to determine if morphological differences are just within-species variation, different growth stages, or even male-female differences. Are we looking at two different species or genera, or a male and female of the same species?

This can be particularly difficult with dinosaurs, because many dinosaur species grow very large over a long period of time. Further, they can undergo significant morphological change as they grow. Another similar controversy, for example, was between Triceratops and Taurasaurus, the latter being larger and with a slightly different frill. It was considered plausible that Taurasaurus specimens were just older Triceratops, and therefore bigger and with age-related changes to the frill. With further specimens and analysis it is now considered that Taurasaurus is its own genus within the family Ceratopsidae.

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