Horse fingers

Here’s a paper that recovers overlooked data.
So it parallels what is done here.

Horses have only one finger and one toe,
right?

Now horses have portions of all five toes… extending to the hooves
(Solounias et al. 2017). And everybody overlooked that, until now (Figs. 1, 2).

Figure 1. Horse fingers 2 and 4 extend to the hoof, separated from the metacarpals 2 and 4 by unossified tissue. Image from Solounias et al. 2017.

Figure 1. Horse fingers extend to the hoof, separated from metacarpals by unossified tissue. Image from Solounias et al. 2017.

From the abstract:
“We revisit digit reduction in the horse and propose that all five digits are partially present in the modern adult forelimb.”

Figure 2. The modern horse, Equus, and extinct horse, Mesohippus manus. Colors over bones added here.

Figure 2. The modern horse, Equus, and extinct horse, Mesohippus manus. Colors over diagrams are from the original diagrams. Colors over proximal metacarpals added here. Image from Solounias et al. 2017.

Vestiges count.
Even when fused, bones are still there.

References
Solounias, et al. (6 co-authors) 2017. The evolution and anatomy of the horse manus with an emphasis on digit reduction. Royal Society Open Science 5:17182. http://dx.doi.org/10.1098/rsos.171782

 

1 thought on “Horse fingers

  1. It’s always been the case that metatarsals II and IV were known to be fused to III in Equus, the paper’s novel idea is that rugose ridges on II and IV are fused remnants of I and V. Also that the posterior side spurs on the ungual are remnants of digits I and V. But no bony portion of digits II and IV remain even in their interpretation, only portions of the ‘frog’, which is part of the keratinous hoof. So your figure is wrong in coloring and labeling m2.3 and m4.5 in the ungual.

    In any case, it’s cool if the ridges are fused metacarpals and the ungual spurs are homologous to digits I and V, but we’re discussing birds here, not horses. Theropods sometimes fuse metatarsal V to IV in the same way (e.g. Avimimus, Vorona), but that’s a thin element along the posterior recognized in 3D specimens, not the big wedge you show in Eogranivora based on a groove in a cross section. If your hypothesis of tiny side digits in theropod hands and feet was correct, we’d have reports in at least some of the thousands of specimens from a myriad of preservational environments. It’s not that professionals aren’t looking for or expecting tiny phalanges. The holotype of Shuvuuia has a 5 mm phalanx from manual digit II or III, and we have tiny phalanges III-2 from many Mesozoic ornithothoracines like the one your DGS missed in Eogranivora. But your proposed phalanges are cracks, or textures physically inside of bones, etc..

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