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Updated: May 3, 2025
Flower's modest and admirable paper on the Ungulata, or hoofed animals, and their geological history. We refer to it here, not so much for the conclusions it reaches or suggests, as to commend the clearness and the impartiality of the handling, and the sobriety and moderation of the deductions.
The Ungulata or hoofed quadrupeds are now divided into the even-toed or odd-toed divisions; but the Macrauchenia of South America connects to a certain extent these two grand divisions. No one will deny that the Hipparion is intermediate between the existing horse and certain other ungulate forms.
At the same time the differentiation of artiodactyle and perissodactyle forms existed as long ago as in the period of the Eocene ungulata, and that in a marked degree, as has been before observed. Again, no armadillo now living presents nearly so remarkable a speciality of structure as was possessed by the extinct glyptodon.
Where, then, must we look for its five-toed ancestor? If we follow down other lines of recent and tertiary Ungulata, the same question presents itself. The Pigs are traceable back through the Miocene epoch to the Upper Eocene, where they appear in the two well-marked forms of Hyopopotamus and Choeropotamus; but Hyopotamus appears to have had only two toes.
"I have now told you of the members of the cattle and Sheep family, what they look like and where they live and how. There is still one more member of the order Ungulata and this one is in a way related to another member of Farmer Brown's barnyard. I will leave you to guess which one. What is it, Peter?"
Nevertheless, although the different lines of modification of the Carnivora and those of the Ungulata, respectively, approach one another, and, although each group is represented by less differentiated forms in the older tertiary rocks than at the present day, the oldest tertiary rocks do not bring us near the primitive form of either.
"Who remembers the name of the order to which all members of the Deer family belong?" asked Old Mother Nature. "I remember what it means, but not the name," spoke up Happy Jack Squirrel. "It means hoofed." "It is Un Un-Ungu " began Peter Rabbit and then stopped. For the life of him he couldn't think of the rest. "Ungulata," Old Mother Nature finished for him. "And Happy Jack has the meaning right.
Where, then, must we look for its five-toed ancestor? If we follow down other lines of recent and tertiary Ungulata, the same question presents itself. The Pigs are traceable back through the Miocene epoch to the Upper Eocene, where they appear in the two well-marked forms of Hyopotamus and Chaeropotamus; but Hyopotamus appears to have had only two toes.
The same moral is inculcated by the study of every other order of Tertiary monodelphous Mammalia. Each of these orders is represented in the Miocene epoch: the Eocene formation, as I have already said, contains Cheiroptera, Insectivora, Rodentia, Ungulata, Carnivora, and Cetacea.
And when we consider how large a portion of the Tertiary period elapsed before Anchitherium was converted into Equus, it is difficult to escape the conclusion that a large proportion of time anterior to the Tertiary period must have been expended in converting the common stock of the Ungulata into Perissodactyles and Artiodactyles.
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