The transitional foot of Homo floresiensis (‘the Hobbit’)

Earlier
the large reptile tree nested the bipedal Miocene gibbon, Oreopithecus (Figs 1,2), as the proximal outgroup to the genus Homo (Figs 1, 2). Click here for earlier posts on this topic.

Bipedality is a hallmark of the gibbon-human lineage
with the bipedal ape, Australopithecus (foot parts known in 2020 shown in Fig 4), an example of convergence. The gibbon, Hylobates, is an overlooked extant biped that also walks and runs bipedally (Fig 5).

Figure 1. The right pes of Oreopithecus, Homo floresiensis and Homo sapiens documenting the transition of a flexible, arboreal gibbon-like foot to an inflexible terrestrial human foot with the ‘Hobbit’ as a transitional taxon. Feet are otherwise largely unknown in Homo erectus. Note the decreasing ability of the hallux to adduct, the decreasing flexibility of the pes as shown by incomplete PILs (parallel interphalangeal lines) and the increasing width of the tarsals and heel (calcaneum). Revised April 28, 2022 with more ape pedes.

Here
(Fig 1) three right feet (= pedes) show the evolutionary transition of the foot from an arboreal gibbon-like Oreopithecus to a terrestrial human with increasing joint stiffness, decreasing abduction of the hallux and increasing heel width.

Figure 2. Other than the longer thighs and shorter shins, Homo floresiensis was the size and shape of Oreopithecus, a gibbon-like ancestor of humans.

In the middle of Oreopithecus and Homo sapiens
is the ‘Hobbit’, Homo floresiensis (Brown et al. 2004, 50,000 years ago, Fig 1). Here it serves as a transitional taxon with transitional traits.

Figure 3. The ‘Hobbit’, Homo floresiensis. Note the length of the feet is more or less normal relative to the height, but large relative to the shin (= tibia + fibula) and relatively wide with a short tarsus, as in Oreopithecus. The torso length is unknown.

This diagram
(Fig 1) sheds light on the role of Homo floresiensis in human evolution. Long considered an offshoot miniature of Homo erectus. Here the ‘Hobbit’ played a transitional role from previously overlooked gibbon-like ancestors (Figs 1, 2) to humans. As noted yesterday, when gibbons run, they adduct the hallux pullng it parallel to the other four toes, as in the human foot.

Figure 4. Competing traditional view of human foot evolution, what we had in 2020. Not much for Australopithecus afarensis (Lucy) evidently.

Figure 5. Taxa in the gibbon-human lineage.

Figure 6. Closeup of bipedal gibbon in figure 5 showing the hallux (big toe) extending anteriorly, as in humans. Here the hallux extends further than pedal digit 2. Compare to tracks in figure 7.

Figure 7. Miocene footprints from Crete (Gierlinski et al 2017). These are considered human-like due to the adducted hallux, but a bipedal walking Oreopithecus, a contemporary of this trackmaker (Fig 1) could have made similar tracks.

Gierlinski GD et al 2017 reported on a trackmaker from the late Miocene of Crete,
“The lateral digit impressions become progressively smaller so that the digital region as a whole is strongly asymmetrical. A large, rounded ball impression is associated with the hallux. Morphometric analysis shows the footprints to have outlines that are distinct from modern non-hominin primates and resemble those of hominins. The interpretation of these footprints is potentially controversial. The print morphology suggests that the trackmaker was a basal member of the clade Hominini, but as Crete is some distance outside the known geographical range of pre-Pleistocene hominins we must also entertain the possibility that they represent a hitherto unknown late Miocene primate that convergently evolved human-like foot anatomy.”

Figure 8. A left and right pair from the late Miocene trackmaker from Crete (Gierlinski et al 2017). They look human like because they were likely made by bipedal human ancestors in the gibbon-human lineage. Oreopithecus (Fig 1) was an Italian contemporary for this trackmaker from Crete.

Figure 9. Pleistocene Indonesia showing the homeland for Java Man (Homo erectus) at left and the Hobbit (Homo floresiensis) at bottom.

This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here. No genomic tests, please. Primatologists evidently haven’t included gibbon feet in their studies. Taxon exclusion remains the number one problem in paleontology. This is easily remedied.

References
Brown P et al 2004. A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia. Nature 431(7012): 1055–1061.
Gierlinski GD et al (8 co-authors) 2017. Possible hominin footprints from the late Miocene (c. 5.7 Ma) of Crete? Proceedings of the Geologists’ Associatiion 128(5–6):697–710.
Peters D 2000. Description and interpretation of interphalangeal lines in tetrapods
Ichnos, 7:11-41.
Peters D 2010. In defense of parallel interphalangeal lines. Historical Biology iFirst article, 2010, 1–6 DOI: 10.1080/08912961003663500
http://dx.doi.org/10.1080/10420940.2011.573605

wiki/Homo_floresiensis

Here’s a 2020 video interview with co-author Per Ahlberg from Gierlinski et al 2017
on the late Miocene trackway frorm Crete. Ahlberg makes the mistake of thinking walking gibbons abducted the hallux, as they do in climbing. Figures 5 and 6 show the opposite is true.