Quotes from:
Howard, H. 1946. A Review of the Pleistocene Birds of Fossil Lake, Oregon. Contributions to Paleontology, Carnegie Institution of Washington, Publication 551:141-195.
Here are just a few instances where Howard makes it clear that she considered paloregonus (the extinct swan species from Fossil Lake) to be similar to, but different from, Mute Swan (olor).
(Reproduced with permission from the Carnegie Institution.)
In describing paloregonus (p. 160):
"…. the bird apparently had the proportionately short tarsi and long toes characteristics of S. olor. In length of the skeletal elements, paloregonus exceeds S. olor throughout …."
In describing the furcula ("wishbone") that Shufeldt assigned to Anser condoni (p. 162):
"The blunt contour of the tip of the blade, with slight dorsal excrescence, has an almost exact counterpart in a furcula of S. olor now available (L. A. Co. Mus. no. Bi69), and in the symphyseal area closely resembles another specimen of the same species (L. A. Co. Mus. no. Bi1096). Both modern furculae, however, are smaller than the fossil. Each of the elements of the fossil swan has been found to run slightly larger than in S. olor, so that the size of the furcula is in keeping with that of the other bones assigned to S. paloregonus."
In describing the humerus bone of paloregonus (p. 163):
"The humeri now assigned to S. paloregonus are large, exceeding S. olor and C. columbianus in size ……"
In describing the carpometacarpus bone of paloregonus (p. 164):
"In size, these specimens exceed C. columbianus and S. olor and fall within the range of C. buccinator."
and
"Fossil similar to S. olor, though depression more proximal in extent than in living form and pisiform process itself broader and less pointed; …. "
and
"Distance from pisiform process to tip of internal edge of trochlea relatively less than in Cygnus or S. olor, and similar to S. melancoriphus."