06/15/2020 - What kind of environment did Ardipithecus ramidus live in?

    Researcher Giday WoldeGabriel and his colleagues wrote a paper called The Geological, Isotopic, Botanical, Invertebrate, and Lower Vertebrate Surroundings of Ardipithecus ramidus in 2009 to explain how the evidence found in Ardipithecus' surroundings told a different story than some of the hypotheses posited by past anthropologists.

    I'd like to first introduce you to Ardipithecus ramidus, also known as "Ardi". Ardi was found in the Afar Rift region of North Eastern Ethiopia and is thought to have lived 4.4 million years ago (White et al. 2009). It was debated whether or not Ardi should be considered a hominin due to the fact that it had features of bipedality, but was still more primitive when comparing to Australopithecus. Ardi likely lived in woodlands, were more omnivorous than chimpanzees, and were more generalist eaters that fed in both the trees and on the ground. The discovery of Ardipithecus ramidus led anthropologists to question if the last common ancestor with chimpanzees (CLCA) was knucklewalking, quadrupedal arboreal climbers, or possibly even bipedal. 

https://www.researchgate.net/publication/235351215_Ardipithecus_ramidus_and_the_birth_of_humanity/figures?lo=1

    

    Ardi's skeletonized remains were found amongst "fossilized wood, seeds, and phytoliths", meaning Ardi was living in a forested area. Invertebrates, including insect larvae, broodballs and nests of dung beetles, diverse gastropods, and millipedes, were also found. Aquatic vertebrates were not common, but came occasionally during flooding and with predatory birds dropping them. With these fossils found, Giday WoldeGabriel et al. came to the conclusion that the savanna hypothesis was incorrect, and instead, early humans lived in much more forested habitats. 

    Stable isotopes in the area, such as carbon and oxygen isotopes, indicate Ardi walked with C4 plants in woodland habitats and woodland savanna floral habitats. This was measured by looking at the carbonate and oxygen values and comparing them to outputs of plants living today. It is thought that hackberry fruits from the Celtis trees were abundant in the area, but that could also be a preservational bias due to them easily being fossilized. There was evidence of Myrica, Hyphaene, Poaceae, and Cyperaceae found in Ardi's mandible, and some pollen grains from these species' were found in the surrounding areas. Overall, WoldeGabriel et al. state that Pliocene vegetation was abundant with palms, trees, and grasses. 

    The terrestrial gastropods that were found can be useful for showing vegetation patterns, rainfall, altitude, and temperature because their shell does not withstand transport via water well. The gastropods are often found today in groundwater forests. Catfish were of the most common lower vertebrates found in the assemblage, and are known for being able to survive in a wide range of temperatures and deoxygenated waters. Tortoises, turtles, crocodiles, lizards, snakes, and frogs were recovered.

    

    Charles Darwin's idea that bipedalism was evolved due to the expansion of the savannah has practically been debunked, as the skeleton of Ardipithecus, as well as the skeletons of other hominins in the area, were found amongst plants and animals found in forested environments.