Re: HP-LCA foot not chimp-like?


alandarwinvanarsdale
 

Assuming Ardipithecus is close to a “common ancestor” of Homo and Pan in foot osteology is almost as unlikely as assuming such a “common ancestor” was Pan like in foot osteology. There is no evidence such a “common ancestor” existed, and considerable genetic and fossil evidence both Pan and Homo are results of mosaic, not linear, evolution. That both are complex hybrids including HGT and inter-specific gene flow events even from other distantly related Old World monkeys. And an HGT event from baboons to Pan has been detected. A plethora of symplesiomorhpies of course, that does not seem to add anything in favor of or against their arguments. Of course all extant Hominid feet share many plesiomorphorphic trasits, this hardly needs to be stated, one can easily see this just by looking at fossil and extant Hominid feet.

 

Sent from Mail for Windows

 

From: Marc Verhaegen
Sent: Friday, March 11, 2022 3:53 PM
To: AAT@groups.io
Subject: [AAT] HP-LCA foot not chimp-like?

 

The foot of the human-chimpanzee last common ancestor was not African

ape-like:

a response to Prang (2019)

Morgan E Chaney ... CO Lovejoy 2021 JHE

 

keywords: Ardipithecus, Cuboid, Midfoot

 

1. Introduction

Huxley (1863) & Darwin (1871) speculated that African apes were humans’

closest living relatives,

so the notion that the HP-LCA was essentially a chimp has pervaded

inferences about its locomotor behavior.

Robust refutations of these notions are now available (Machnicki & Reno

2020, Reno 2014, Sayers cs 2012, White cs 2015),

but relying only on an examination of foot-bone lengths from

Ardipith.ramidus ARA-6/500, Prang (2019) argued that the HP-LCA foot was

likely similar to modern African apes, although it exhibits a plethora

of symplesiomorphies.

A.ramidus lacks advanced grasping-related adaptations evident in the

feet of extant great apes, e.g.

- decreased dorso-plantar heights of their metatarso-cuneiform joint

surfaces,

- proximo-distal (PD) shortening of their mid-foot tarsals (Lovejoy cs

2009a):

Prang (2019: 8) concluded: “modern humans evolved from an ancestor with

an African ape-like foot, ass.x terrestrial plantigrady & vertical

climbing.”

We contend here that data do not support this assertion over earlier

conclusions that the HP-LCA was a predom.above-branch clambering

quadruped (Lovejoy cs 2009c).

Prang’s (2019) analysis is insufficient for 3 reasons:

1) his results support only the simple conclusion that the HP-LCA

relative forefoot bone lengths were similar to extant African apes.

2) intrinsic foot proportions are at least partially reflective of body

mass. Because the body size of ARA-VP-6/500 & the HP-LCA was likely

similar to chimps, their proximity to the latter in Prang’s (2019)

phylomorpho-space plots is unsurprising & uninformative.

3) numerous primitive soft-tissue retentions in the human foot are

uniquely derived in Pan & Gorilla (Lovejoy cs 2009).

...

 

(the HP-LCA had a flat foot? --mv)

 

 

 

 

 

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