member of his audience, Miss Sue Hill, 

 introduced herself and showed him sev- 

 eral tiny jaw fragments that she had 

 found on her parents' ranch. Mr. Look 

 needed no more than a glance to see that 

 these fossils were unusual in that they 

 came from a geologic formation that had 

 previously yielded mostly large and me- 

 dium-sized mammals. In this formation, 

 the pantodonts Leptolambda, Titanoides, 

 Barylambda and Coryphodon, the uinta- 

 theres Probathyopsis and Bathyopsoides, or 

 the taeniodont Lampadophorous are the 

 large forms to be expected. Medium- 

 sized mammals such as carnivores, con- 

 dylarths, primates, insectivores, and un- 

 gulates are also known, as Mr. Look 

 knew. But only a few of the really small 

 mammals had ever turned up — forms 

 such as multituberculates, rodents, and 

 the smallest of insectivores and primates. 

 Mr. Look therefore immediately made 

 arrangements for Miss Hill to show him 

 the site of her discovery, near Rifle, 

 Colorado. Their trip to the area coin- 

 cided with a snowfall, and some snow 

 removal was necessary before Mr. Look 

 could dig out a somewhat larger sample 

 of specimens. This he sent off to me. 



On examining the specimens, I de- 

 termined to collect, at the earliest op- 

 portunity, whatever material remained. 

 During the second week in August, such 



an opportunity occurred; I joined Mr. 

 Look in Rifle and was taken to the Lynn 

 Hill ranch to meet Miss Hill and her 

 parents and to see the locality which, 

 by that time, had produced nearly 100 

 specimens. 



The DeBeque Formation extends over 

 several thousands of square miles of west- 

 ern Colorado in Rio Blanco, Garfield, 

 Mesa, and Delta counties. Rifle lies at 

 the eastern edge of this area where the 

 DeBeque Formation is lapped onto the 

 upturned Mesozoic sediments — the 

 Grand Hogback (Figure 2) — which, in 

 turn, flank the major upthrust structure 

 of the Park Range further to the east. 

 I discovered that tumbled blocks from a 

 massive sandstone channel situated fifty 

 to 75 feet higher in the section had pro- 

 tected the carnivore den site from rapid 

 erosion, and that most of the bone lens 

 was still intact under one of these truck- 

 sized, tumbled blocks of rock (Figure 1). 

 Once I made certain that there was no 

 articulation or clear association among 

 the jumbled mass of bone, it was a sim- 

 ple matter to dig out the entire lens with 

 pick and shovel and to sieve a concen- 

 trate of bone and pebbles for shipment 

 back to the Museum. 



Even a brief, preliminary study of 

 these materials confirms the significance 

 of the find made by Miss Hill and Mr. 



Look. It has provided us with an un- 

 usual sampling (Figure 3) of a fauna of 

 Early Tertiary time — a most interesting 

 period in the evolutionary history of the 

 placental mammals. 



During this period most of the domi- 

 nant mammals belonged to groups that 

 had evolved from generalized stocks some 

 ten million years earlier, and which had 

 become extinct by the end of another 

 ten to fifteen million years. Less con- 

 spicuous than the dominant mammals 

 were small, generalized mammals. These 



Figure 2 : The Early Tertiary DeBeque Formation in which the carnivore den 



was found in the foreground. Mesozoic sediments comprising 



the Grand Hogback are in the background. 



Figure 3 : Typical vertebrate bones 

 from the den. 



were just beginning the second great pla- 

 cental adaptive radiation that led to 

 most of the modern orders. The small, 

 unobtrusive insectivores, primates, and 

 condylarths of this discovery — species 

 that were only tantalizingly suggested 

 by a few specimens in the prior collec- 

 tions of the 1930's and 1940's — are rep- 

 resentatives of early critical stages in the 

 evolution of their respective lines. As 

 such, the fossils from the carnivore den 

 are certain to fill many gaps in our 

 knowledge. 



Throughout the collecting, the Lynn 

 Hill family was most cooperative and 

 helpful. We thank them for their gener- 

 osity in providing us with this important 

 collection, and welcome them as new 

 friends of the Museum. 



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