IOW, the question is not "ill formed" as some claim, there just is not an answer for it, I understand. So why would the person not just say there is no answer to the question as opposed to claiming it to be "ill formed" etc.? Is that nothing more than a deflection, a diversion?
The question is somewhat poorly formed. Historic animals are known via the fossil record, and confirmed through genetics. But, as someone said before me, the fossil record doesnt preserve every single species that has ever lived. Otherwise we would be buried in bones. There are only 13 or so full T rex skeletons for example, yet these animals were likely prevalent, and including various species, would number in tens if not hundreds of thousands.
With bovines, or cattle, we have human records of aurochs.
The
aurochs (
/ˈɔːrɒks/ or
/ˈaʊrɒks/; pl.
aurochs, or rarely
aurochsen,
aurochses), also
urus,
ure (
Bos primigenius), is an
extinctspecies of large wild
cattle that inhabited Europe, Asia, and North Africa. It is the ancestor of domestic cattle. The species survived in Europe until the last recorded aurochs died in the
Jaktorów Forest, Poland, in 1627.
Regarding horses, speciation of horses occurred before mankind had written language. There are bones of ancient horses. Were these fossils the direct ancestor to horses or a cousin? Or were they the direct ancestor to the direct ancestor? These are questions that cannot be specifically answered.
Hagerman horse - Wikipedia
Dinohippus - Wikipedia
Whenever you see on the news "missing link" or "we evolved from X species". Really the bones are giving us an idea of how we evolved, but they arent so specific as say, that ancestry website that gives you a detailed family tree. A fossil may be a second cousin, a third cousin. It could be a cousin that went extinct.
So the fossils give a general idea of how life evolved, its just not so precise as to distinguish very specific species.
And this important to understand. Some people do not understand this, and it leads to misconceptions. For example, the tracks that predate tiktaalik by i think what...9 million years or so. People might say, well if tiktaalik is our ancestor and was the first to walk on land, why are there tracks 9 million years before it? Without understanding that tiktaalik was more than likely not a specific ancestor of our own, but rather a closely related organism to our ancestor. And tiktaalik is still an ideal transitonal form, on the basis that it displays transitional morphology in the mid to late devonian, but it shouldnt be assumed that tiktaalik is
the transitional form, and that other early tetrapods could not be found immediately before or after it in the mid to late devonian.