The Skeletons of Recent and Fossil Gymnogyps 
Harvey I. Fisher 1 
A study of the skulls of the cathartid 
vultures (Fisher, 1944: 272-296) revealed 
certain fundamental differences in the con¬ 
formation and proportions of skulls of 
Recent Gymnogyps californianus and fossil 
Gymnogyps from the tar pits of the Rancho 
La Brea Pleistocene.' Even though some of 
these differences were slight morphologi¬ 
cally, their presence in areas of minimal vari¬ 
ation such as the occipital ring of bones, the 
basitemporal area, and the posterior palatal 
region indicated that the Recent and fossil 
condors were not identical. Further, the 
magnitude of other differences and the 
absence of overlap in the ranges of certain 
significant measurements demonstrated that 
two species probably were involved. 
Before that study was made, it was be¬ 
lieved that the fossils from the Pleistocene 
of Rancho La Brea belonged to californianus, 
as did all Recent birds of this genus. There 
remained, however, the species am plus, 
from the Pleistocene deposits of Samwel 
Cave in northern California. Further study 
of am plus showed it to be conspecific with 
the Rancho La Brea specimens because the 
characters by which it had first been dif¬ 
ferentiated were shown to be identical in 
specimens from the two deposits. As a 
result, the name californianus was restricted 
to the living form of Gymnogyps, and 
am plus applied to all the Pleistocene speci¬ 
mens known from western North America. 
It has been suggested that the two stocks 
of condors represent subspecies of the same 
species, i.e., chronological subspecies. There 
may be a chronocline with the mean size of 
1 Department of Zoology and Entomology, 
University of Hawaii. Manuscript received 
February 13, 1947. 
the individuals of the population decreasing 
from Pleistocene to Recent times. If this be 
true for this species, as has been found for 
other warm-blooded species, the fact might 
illustrate Bergmann’s rule in a temporal 
rather than a geographic way. Although this 
present analysis of the skeleton tends to bear 
out the belief that two subspecies are in¬ 
volved, it is still necessary to consider the 
major specific differences in the skulls, and 
to remember that the skeletal elements 
studied in this investigation are in general 
more plastic and more subject to the influ¬ 
ence of external environmental conditions 
than are the bones of the skull. Thus, one 
would expect to find in these elements a 
greater similarity between the two series of 
specimens. 
At present the only criteria by which 
these two species can be segregated are skull 
characters. Except in the oil deposits of 
southern California, fossil deposits seldom 
contain complete skulls of birds. Hence, it 
seemed desirable to obtain some means of 
separating the two species on the basis of 
other bony elements. For that reason, pri¬ 
marily, this study was undertaken. Second¬ 
arily, it seemed pertinent to test the often- 
repeated assumption that "Pleistocene forms 
are more variable than Recent forms.” It 
has been noted previously that paleontolog¬ 
ical series of a species often do show consid¬ 
erable variability. This variability may be 
explained in two ways: (1) the fossil species 
actually is more variable; (2) the series is 
inadequate and heterogeneous because of age 
and sex factors that cannot be determined 
and because the series often comes from 
various localities and from deposits of dif¬ 
ferent ages. 
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