Editing Canidae (section)

===Eocene epoch===
[[Carnivora]]ns evolved after the [[Cretaceous-Paleogene extinction event|extinction]] of the non-avian dinosaurs 66 million years ago. Around 50 million years ago, or earlier, in the [[Paleocene]], the Carnivora split into two main divisions: [[caniform]] (dog-like) and [[feliform]] (cat-like). By 40 Mya, the first identifiable member of the dog family had arisen. Named ''[[Prohesperocyon]] wilsoni'', its fossils have been found in southwest Texas. The chief features which identify it as a canid include the loss of the upper third molar (part of a trend toward a more shearing bite), and the structure of the middle ear which has an enlarged [[Tympanic part of the temporal bone|bulla]] (the hollow bony structure protecting the delicate parts of the ear). ''Prohesperocyon'' probably had slightly longer limbs than its predecessors, and also had parallel and closely touching toes which differ markedly from the splayed arrangements of the digits in [[bear]]s.<ref name=Wang-Tedford>{{cite magazine| last = Wang| first = Xiaoming| year = 2008| title = How Dogs Came to Run the World|magazine=Natural History Magazine| volume = July/August| url = http://www.naturalhistorymag.com/features/15771/how-dogs-came-to-run-the-world| access-date = 24 May 2014 }}</ref>

Canidae soon divided into three subfamilies, each of which diverged during the Eocene: [[Hesperocyoninae]] (about 39.74–15 Mya), [[Borophaginae]] (about 34–32 Mya), and [[Caninae]] (about 34–30 Mya; the only surviving subfamily). Members of each subfamily showed an [[Cope's rule|increase in body mass with time]] and some exhibited specialized [[hypercarnivorous]] diets that made them prone to extinction.<ref>{{cite journal | first1 = B.| last2 = Wang| last1 = Van Valkenburgh | first2 = X. | first3 = J. | title=Cope's Rule, Hypercarnivory, and Extinction in North American Canids| last3 = Damuth | s2cid = 12017658| journal=Science | volume=306| issue = #5693 | pages=101–104 | date=October 2004 | issn = 0036-8075| pmid = 15459388 | doi=10.1126/science.1102417|bibcode = 2004Sci...306..101V }}</ref>{{rp|Fig. 1}}