In many types of dating you can follow the beds to adjacent places that have been dated. This is what they did, and what they mean by an adjacent basin. Of course ichnofossils including tracks are found in diverse types of sedimentary rocks, and hominins tracks are known from beach deposits such as the oldest known human fossils (tracks) from England. “Calcareous nannoplankton data from sediments exposed near Trachilos and belonging to the same sub-basin indicate deposition during calcareous nannofossil biozone CN9bB, between 6.023 and 6.727 Ma._______________________________________________________________________________From the Nature article “Calcareous nannoplankton data from sediments exposed near Trachilos and belonging to the same sub-basin indicate deposition during calcareous nannofossil biozone CN9bB, between 6.023 and 6.727 Ma.”

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The paleoenvironment at Trachilos is well understand. It was a lagoon beach bar, and not subaqueous when the prints were made. As I recall they were dated by forams above and below the tracks stratigraphically.

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Humans incisors have multiple functions. Two of which are grasping and scraping. Before we ate meat our incisors still scraped such as removing plant material from harder cores or surfaces, and scraping fruit from large seeds. Sheepshead fish use their teeth for scraping. ____________________________________________________________________________________________________A basic chisel like design for front teeth comes up often and is one of the dental morphological traits likely to be convergent. “Human like” “incisors” are not just seen in primates and fish, other mammals have them as well. Rodents have two on the top and two on the bottom, which grow through their lives. The first mammals had incisors and chisel like incisors are largely plesiomorphic for mammals.

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In the Western USA deserts ground sloths often held a desert (xeric) niche eating Joshua trees when other forage was not abundant. Joshua trees are very slow growing. The niche is not filled with the extinction of ground sloths. Tree eating herbivores have a strong tendency to grow larger over time (and thus thicker bones to support the weight), including in xeric environments. _________________________________________________________________________________________________Tree eating animal evolution can largely be seen in terms of linear evolution for larger body size. With extinction events followed by other often related populations entering the emptied niche and in turn growing larger over time. This is one of the rare cases since the Carboniferous when linear evolution is a good model. _________________________________________________________________________________________________In the last 2.1 million years and especially starting at about 600kya it is likely linear evolution is a good model for human evolution. Before 2.1mya linear evolution as in general is a poor model for human evolution and is one of the causes of a lot of incorrect thinking in paleoanthropology. Of course I am not the only messenger about linear evolution usually being a poor model, this is widely known in modern biology and more and more paleoanthropology (Fuentes etc.) are lecturing against the evils of linear evolution models and “missing links”.

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