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G Larry said: Some "bear" has a different proportion of body to leg and bammo, it's a dog. No further evidence, just an assertion that 'in North America this evolution continued'.

Okay.

Perhaps Alter Kaker can explain in more specific detail how Cynodictis is known to be ancestor to Cynodesmus. Assuming that Cynodesmus is truly a dog, how strong is the connection to Cynodictis? For that matter, are foxes just dogs or are they a unique species? What can be said of a common ancestor to both dogs and foxes?

I'm just guessing, but my guess is that more similar species, those which apparently more recently evolved and which are presumed to have common ancestors, would provide more fossil remains, since natural processes can destroy fossils over time but there is no way to re-create a fossil once destroyed. There would then be more evidence of an evolutionary link between dogs and foxes than between dogs and bears.

In the large scale, the fossil record gets sparser as you go back, yes. For instance, it's very hard to find Precambrian sediments that haven't been squished to where they're more metamorphic than sedimentary and thus don't have any fossils.

Here's the striking thing about what the fossil record shows about radiations like early carnivores, the great-granddaddy of them all probably being the Miacids. Pick any modern line: dog, cat, bear, weasels, civets, etc. Trace it back in time through the fossils. The farther back you go, the less a specimen looks like the modern form and the more it looks like its contemporaries on the other lines. That is, you can see the divergence in reverse.

For that matter, when you get back to those miacids, they don't look that different from their contemporaries, the ancestors of the hoofed mammals (ungulates).

This paper explains fossil record and taxonomy issues wonderfully: Taxonomy, Transitional Forms, and the Fossil Record.

Moving further up the taxonomic hierarchy, the condylarths and primitive carnivores (creodonts, miacids) are very similar to each other in morphology (Fig. 9, 10), and some taxa have had their assignments to these orders changed. The Miacids in turn are very similar to the earliest representatives of the Families Canidae (dogs) and Mustelidae (weasels), both of Superfamily Arctoidea, and the Family Viverridae (civets) of the Superfamily Aeluroidea. As Romer (1966) states in Vertebrate Paleontology (p. 232), "Were we living at the beginning of the Oligocene, we should probably consider all these small carnivores as members of a single family." This statement also illustrates the point that the erection of a higher taxon is done in retrospect, after sufficient divergence has occurred to give particular traits significance.

Figure 10. Comparison of skulls of the early ungulates (condylarths) and carnivores. (A) The condylarth Phenacodus possessed large canines as well as cheek teeth partially adapted for herbivory. (B) The carnivore-like condylarth Mesonyx. The early Eocene creodonts (C) Oxyaena and (D) Sinopa were primitive carnivores apparently unrelated to any modern forms. (E) The Eocene Vulpavus is a representative of the miacids which probably was ancestral to all living carnivore groups. (From Vertebrate Paleontology by Alfred Sherwood Romer published by The University of Chicago Press, copyright © 1945, 1966 by The University of Chicago. All rights reserved. This material may be used and shared with the fair-use provisions of US copyright law, and it may be archived and redistributed in electronic form, provided that this entire notice, including copyright information, is carried and provided that the University of Chicago Press is notified and no fee is charged for access. Archiving, redistribution, or republication of this text on other terms, in any medium, requires both the consent of the authors and the University of Chicago Press.)