tas8831
Well-Known Member
Did I write 'creation'? Sorry - I meant evolution.
It seems that, along with fossil evidence showing the transition from small, multi-toed critters to the modern horses, we now have evidence - not only of horse evolution, but of one principle of evolution; the retention of developmental programming from ancestral species - that horses start to develop multiple digits on their autopodia (feet) which then regress, leaving only the one big middle digit.
So, a brief overview of manus and pes (hand and foot) development in the embryo.
The limb buds first appear as pairs of condensations of cells, the upper limb buds first (on the sides of the presumptive thorax), lower (on the sides of the presumptive pelvis area), later.
The buds expand until they look a bit like pencil erasers, then the ends of them start to flatten our a bit and expand sort of fan-like, forming the hand/foot plate (or in horses, I suppose, the hoof plates). Within these plates, condensations of mesenchyme form into digital rays, laying the groundwork for the future, in us, digits (fingers and toes). These rays eventually become cartilage, and later, bone. The digital rays can be seen in microscope cross-sections (aka transverse) as clusters of darker-staining cells.
"Evidence of five digits in embryonic horses and developmental stabilization of tetrapod digit number"
https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2019.2756
Now why would a designer have horse embryos start to develop 5 digits, only to have 4 of them regress.....
It seems that, along with fossil evidence showing the transition from small, multi-toed critters to the modern horses, we now have evidence - not only of horse evolution, but of one principle of evolution; the retention of developmental programming from ancestral species - that horses start to develop multiple digits on their autopodia (feet) which then regress, leaving only the one big middle digit.
So, a brief overview of manus and pes (hand and foot) development in the embryo.
The limb buds first appear as pairs of condensations of cells, the upper limb buds first (on the sides of the presumptive thorax), lower (on the sides of the presumptive pelvis area), later.
The buds expand until they look a bit like pencil erasers, then the ends of them start to flatten our a bit and expand sort of fan-like, forming the hand/foot plate (or in horses, I suppose, the hoof plates). Within these plates, condensations of mesenchyme form into digital rays, laying the groundwork for the future, in us, digits (fingers and toes). These rays eventually become cartilage, and later, bone. The digital rays can be seen in microscope cross-sections (aka transverse) as clusters of darker-staining cells.
"Evidence of five digits in embryonic horses and developmental stabilization of tetrapod digit number"
https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2019.2756
"We found that embryonic horse limbs develop five digit condensations that persist into later developmental stages through fusion of cell populations within days after initiation. Thus, even the highly modified monodactyl Equus FL maintain an ontogenetic reflection of their pentadactyl ancestors and follow a sequence of development similar to the iconic evolutionary transitions in the horse lineage."
Now why would a designer have horse embryos start to develop 5 digits, only to have 4 of them regress.....