Thursday, 15 April 2021

Evolution News - If This Is Not A Transitional Hominin, What Would Be?

KNM-ER 2598 partial occipital
a Inset image indicates the approximate anatomical location of the KNM-ER 2598 occipital.
b Posterior view and right lateral view are shown.
Revisiting a Renowned Skull From Early Human Homo Erectus | AMNH

When it was discovered about 50 years ago at East Turkana in northern Kenya, the skull fragment of what came to be known as Homo erectus, was believed to be the oldest specimen of a truly human species known, at 1.9 million years old.

However, some people doubted the age of this specimen, suggesting the remains could have been moved there from later strata by wind or water. Now a study led by American Museum of Natural History Assistant Curator Ashley Hammond has revisited the site and found more fragments of what are believed to be H. erectus associated with strata that confirm the original dating of the earlier skull fragment.

Not only did they not find anything to corroborate the suggestion of a later origin being translocated to the East Turkan site, but they also found other monimin remains, as described in the American Museum of Natural History news release: At the same time, fieldwork assisted by students and staff from the Koobi Fora Field School led to the discovery of two new hominin specimens within 50 meters of the reconstructed location. The specimens, a partial pelvis and a foot bone, potentially are H. erectus. They could be from the same individual, but there is no way to prove that after the fossils have been separated for so long. Still, they might be the earliest postcrania—“below the head”—specimens yet discovered for H. erectus.

[...]

One of two new hominin specimens, a partial pelvis, found at the East Turkana site in Kenya.

Credit: A. Hammond/© AMNH
The researchers also collected fossilized teeth from other kinds of vertebrates, mostly mammals, from the area. From the enamel, the team analyzed isotope data to paint a better picture of the environment in which the H. erectus individual lived. The work suggests that this early H. erectus was found in a paleoenvironment that included primarily grazers that prefer open environments to forest areas and was near a stable body of water.

[...]

The researchers also collected fossilized teeth from other kinds of vertebrates, mostly mammals, from the area. From the enamel, the team analyzed isotope data to paint a better picture of the environment in which the H. erectus individual lived. The work suggests that this early H. erectus was found in a paleoenvironment that included primarily grazers that prefer open environments to forest areas and was near a stable body of water.
Proximal 3rd metatarsal anatomy.
Proximal left the third metatarsal KNM-ER 77071 is inset to show lateral, proximal, and medial views. Comparative MT3s for Homo erectus (KNM-ER 803, D2021, D3479), Homo habilis (OH 8), Homo naledi (UW 101-145768), humans, and chimpanzees are shown below in lateral, proximal, medial, and dorsal views. MT4 facets indicated by solid arrows, and MT2 facets indicated by the dashed arrows. Like the other hominin fossils, KNM-ER 77071 has only a single dorsal MT2 facet on the medial side. Metatarsal models scaled to the same height of the base for visual comparison. UW 101-1457, D2021, and D3479 images are mirrored for consistency.
The team published their findings, open access, yesterday in the journal Nature Communications:

Abstract

The KNM-ER 2598 occipital is among the oldest fossils attributed to Homo erectus but questions have been raised about whether it may derive from a younger horizon. Here we report on efforts to relocate the KNM-ER 2598 locality and investigate its paleontological and geological context. Although located in a different East Turkana collection area (Area 13) than initially reported, the locality is stratigraphically positioned below the KBS Tuff and the outcrops show no evidence of deflation of a younger unit, supporting an age of >1.855 Ma. Newly recovered faunal material consists primarily of C4 grazers, further confirmed by enamel isotope data. A hominin proximal 3rd metatarsal and partial ilium were discovered <50 m from the reconstructed location where KNM-ER 2598 was originally found but these cannot be associated directly with the occipital. The postcrania are consistent with fossil Homo and may represent the earliest postcrania attributable to Homo erectus.

I’m really focused on trying to piece together the evolutionary history of the ape and hominin pelvis. The pelvis is really informative about the biology of an animal. It can tell you about what species you’re looking at. It can tell you about whether or not you’re looking at a male or a female. Sometimes you can even tell if an individual has given birth. And you can even get information about where an individual is from.

I still think it’s a really big question about what the starting point for the human lineage looked like. What kind of behaviors we were using, how we became bipedal and so forth.

Ashley S. Hammond, Lead author
Palaeoanthropologist
Assistant curator
Division of Anthropology
American Museum of Natural History,
New York, NY, USA
In their discussion, the team say:
The most straightforward interpretation of the geological data presented here is that the new hominin fossils, and presumably KNM-ER 2598, weathered out of the UB1 sandstone and lay exposed on the surface until they were discovered. We found no evidence of deflation at the KNM-ER 2598 cairn location and surrounding Cluster-1 area. The sandstones and sandstone fragments found in Cluster-1 have distinctive sedimentary features (i.e., trough and planar cross-bedding) aligning them with UB1 and, furthermore, are petrographically distinctive from the younger sandstones (KS) overlying the KBS Tuff. A mixture of surface sandstones was found about 200 m away from the KNM-ER 2598 cairn location, in locations where torrential runoff moves the KS sandstones into drainage areas overlying Burgi Member outcrops (e.g., “modern KBS debris” shown in Fig. 3). Although we cannot completely exclude the possibility that these hominin fossils are derived from younger sediments, the hypothesis that the fossils on the Cluster-1 surface could result from deflation of a younger sedimentary package that has subsequently eroded away is not supported by any of our observations.

So, the challenge for creationists who believe that there are no such thing as transitional species, is to explain why these H. erectus fossils should not be regarded as transitional between the extinct hominid apes such as Australopithecus and early hominins that were ancestral to modern H. sapiens. What would you expect a transitional species, midway between apes and modern humans, to look like and why doesn't H. erectus meet that expectation?

We can discuss how fossils were being formed nearly 2 million years before you believe the Universe was created later...


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