And you use teeth and only teeth to determine that event. Ergo, the teeth speciated.
From your citationA Smooth Fossil Transition: Pelycodus.
The numbers at the bottom of the graph are computed values. Specifically, whenever a first lower molar tooth was found, its length and width were measured. The values plotted are the logarithm of the length times the width. The researcher reports reasonable evidence that this value correlates well with body size. He used this approach because there were a lot more teeth than anything else. (Teeth often fossilize.) By measuring just teeth, it was possible to have a lot more data points.
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As you can see from the ranges, a larger sample would have been nice.
The article goes on to say "Gingerich has since extended this work, but the conclusion has not changed. ". Okay let's see the new evidence. Teeth don't convince me.
Then later, they genus-ated.
The teeth in question are stated to be the most common remnant of the lineage in question. The gore trick is to assume no one knows anything unstated. In this case, there's nothing but teeth anywhere and the whole animals is made up from the tooth.
Can this be substantiated? Where does the burden of proof lie? What is the wilder claim, that Gingerich fabricated an animal from a tooth or that Gingerich has evidence for the divergence of two later genera from an earlier species? Can you show that the two later genera are based on teeth alone?
Gingerich (summarized in 1977) traced two distinct species of lemur-like primates, Pelycodus frugivorus and P. jarrovii, back in time, and found that they converged on the earlier Pelycodus abditus "in size, mesostyle development, and every other character available for study, and there can be little doubt that each was derived from that species." Further work (Gingerich, 1980) in the same rich Wyoming fossil sites found species-to-species transitions for every step in the following lineage: Pelycodus ralstoni (54 Ma) to P. mckennai to P. trigonodus to P. abditus, which then forked into three branches. One became a new genus, Copelemur feretutus, and further changed into C. consortutus. The second branch became P. frugivorus. The third led to P. jarrovi, which changed into another new genus, Notharctus robinsoni, which itself split into at least two branches, N. tenebrosus, and N. pugnax (which then changed to N. robustior, 48 Ma), and possibly a third, Smilodectes mcgrewi (which then changed to S. gracilis). Note that this sequence covers at least three and possibly four genera, with a timespan of 6 million years.The Transitional Fossils FAQ. This would seem to be an expansion of Gingerich's earlier claims.