Comments onthe Taxonomy and Geographic Distributionof Some North American Rabbits

BY

E. RAYMOND HALL and KEITH R. KELSON

University of Kansas PublicationsMuseum of Natural HistoryVolume 5, No. 5, pp. 49-58October 1, 1951

University of KansasLAWRENCE1951

UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

Editors: E. Raymond Hall, Chairman, A. Byron Leonard, Edward H. Taylor, Robert W. Wilson

Volume 5, No. 5, pp. 49-58October 1, 1951

UNIVERSITY OF KANSASLawrence, Kansas

PRINTED BYFERD VOILAND, JR. , STATE PRINTERTOPEKA, KANSAS1951[Illustration]23-7436

Comments on the Taxonomy and Geographic Distribution of Some NorthAmerican Rabbits

BY

E. RAYMOND HALL AND KEITH R. KELSON

In preparing maps showing the geographic distribution of North Americanlagomorphs, some conflicting statements in the literature have led us toexamine the pertinent specimens of the Florida cottontail and theAudubon cottontail with results as given below. The study here reportedupon was aided by a contract between the Office of Naval Research, Department of the Navy, and the University of Kansas (NR 161-791). Unless otherwise indicated, catalogue numbers are of the United StatesNational Museum and most of the specimens are in the Biological Surveyscollection of the Fish and Wildlife Service. Grateful acknowledgment ismade to persons in charge of the collections for permission to use thecollections under their charge. 

Sylvilagus floridanus similis Nelson

 1907. _Sylvilagus floridanus similis_ Nelson, Proc. Biol. Soc. Washington, 20:82, July 22. 

Some confusion has existed concerning the subspecific identity of theFlorida cottontail in Nebraska because of the way in which Nelsonrecorded specimens in his "The Rabbits of North America" (N. Amer. Fauna, 29:fig. 11, and pp. 169-174, August 31, 1909). He (_op. Cit. _:174) listed the following specimens under the western subspecies, _S. F. Similis_: Two topotypes (Nos. 87784 and 18738/25532) and ofcourse the type; the specimen (No. 116288) from the Snake River [= SnakeCreek of maps], 11 mi. NW Kennedy; two from Neligh (126074 and 151438);and one (probably 18680/25410) from Kennedy. But, he listed (_op. Cit. _:172) under _S. F. Mearnsi_, the eastern subspecies, a specimen(10721) from Brownlee, and two from Kennedy. One of the two from Kennedyprobably was the one that is recorded in the files of the U. S. Fish andWildlife Service as "identified by Cary. Spec. In Univ. Nebraska". Theother, or third, specimen from Kennedy, we judge, did not exist at allbut was recorded by Nelson because a card in the reference file, underKennedy, Nebraska, in addition to No. 18680/25410, carried a secondentry, a number 3471X. The latter is the X-catalogue number of specimenNo. 116288 from the Snake River! The X-catalogue is used in place of afield catalogue for specimens sent to the mammal collection of theUnited States Fish and Wildlife Service, by persons who do not keepregular field numbers of their own. It seems that Nelson prepared (orhad prepared) his lists of specimens, at least in part, from cardsrather than from the labels on the specimens themselves. Some furtherconfusion as to names that Nelson intended to apply to cottontails inNebraska resulted from the fact that his map (_op. Cit. _:fig. 11)indicated that the localities mentioned above for _S. F. Mearnsi_ werewithin the geographic range of _S. F. Similis_. 

Our comparison of each of the Nebraskan specimens with specimens of _S. F. Mearnsi_ in comparable pelage from Iowa and with the type andtopotypes of _S. F. Similis_ reveals that each of the specimens of whichcatalogue numbers are given above is clearly referable to _Sylvilagusfloridanus similis_. 

Because some mammalogists have suspected that intergradation between_Sylvilagus floridanus similis_ and _Sylvilagus nuttallii grangeri_occurs along the eastern base of the Rocky Mountains, we have examinedspecimens which may throw light on this matter. 

From _S. F. Similis_ (holotype and three topotypes), _S. N. Grangeri_(eight practical topotypes from Redfern, South Dakota) differ asfollows: Throat patch darker; hind foot shorter; ear (dry) from notchlonger; rostrum narrower; posterior extension of supraorbital processenclosing a longer and wider space between it and the braincase;superior border of premaxilla straight in profile instead of convexdorsally; tympanic bullae more inflated; external auditory meatus larger(diameter of the meatus more, instead of less, than crown length ofupper molars); posterior border of palate without, instead of with, spine. 

Specimens of the two species from places as near each other as extremesoutheastern Montana (_S. F. Similis_ from Boxelder Creek, Capitol andthe Little Missouri River) and Devils Tower, Wyoming (_S. N. Grangeri_), seem not to differ in the length of the hind foot and the ear and in thecolor of the spot on the chest. Also, the presence or absence of thespine on the posterior margin of the palate is subject to individualvariation in these specimens but the other cranial differences, mentioned above, still are apparent. These same cranial differences arereadily apparent between specimens of the two species taken only fivemiles apart in eastern Wyoming (for the precise localities, see thefollowing paragraph). It is concluded, therefore, that _S. F. Similis_and _S. N. Grangeri_ do not inter-grade along the eastern base of theRocky Mountains. 

Data on specimens from Laramie County in eastern Wyoming show that _S. F. Similis_ is a heavier animal than _S. N. Grangeri_ and also that_similis_ molts earlier. For example, an adult female (K. U. No. 15936)taken on July 13, 1945, three miles east of Horse Creek P. O. , 6400 ft. , weighed 1374 grams and is in fresh pelage, whereas an adult female of_S. N. Grangeri_ (K. U. No. 15935), taken on July 17, 1945, two mileswest of Horse Creek P. O. , 6600 ft. , weighed only 1149 grams, and stillhas some of the worn winter pelage on the upper parts. 

Sylvilagus floridanus holzneri (Mearns)

 1896. _Lepus sylvaticus holzneri_ Mearns, Proc. U. S. Nat. Mus. , 18:554, June 24. 

 1904. _Sylvilagus floridanus holzneri_, Lyon, Smithsonian Miscl. Coll. , 45:336, June 15. 

Examination of cottontail rabbits from Arizona in the Biological SurveysCollection and the United States National Museum indicates that_Sylvilagus audubonii_ can be distinguished from _Sylvilagus nuttallii_and _Sylvilagus floridanus_ by the larger (more inflated) tympanicbullae. Topotypes of _Sylvilagus nuttallii pinetis_ and other specimensfrom Alpine, Mt. Thomas, Springerville, the Prieto Plateau at 9000 feeton the south end of the Blue Range, and the Tunitcha Mountains arecharacterized by a posteriorly pointed supraoccipital shield and a long, wide space between the braincase and the posterior extension of thesupraorbital process. The cottontails with equally small tympanic bullaefrom more western and more southern localities are referable to_Sylvilagus floridanus holzneri_ on the basis of a posteriorly truncateor emarginate supraoccipital shield and a narrower and shorter space(usually a "foramen") between the braincase and the posterior extensionof the supraorbital process. In _S. F. Holzneri_ the posterior end ofthe posterior process fuses with the braincase whereas the posterior endof this process in Arizonan specimens of _S. N. Pinetis_ merely liesagainst the braincase or projects free of it. In specimens from Arizonathe difference in shape of the posterior border of the supraoccipitalshield and the difference in size of the space between the braincase andthe posterior extension of the supraorbital process are the onlydifferences of taxonomic worth found by us. Many other features of theskull, of color of pelage, and of size of external parts all fell withinthe range of individual variation of a series of specimens from onelocality. 

Specimens from the following localities in Arizona are referable to_Sylvilagus floridanus holzneri_ (Mearns). 

 Hualpai Mts. , Nos. 117461, 117462, 117488, 117490, 117495, 227735, and 227832; Ft. Whipple, No. 214157; Prescott, No. 34667/46752; Mayer, No. 247495; Reynolds Creek Ranger Station, Sierra Ancha Mts. , Gila Co. , No. 247734; Fish Creek, Tonto National Forest, 2000 ft. , No. 212833; north base Mt. Turnbull, 4500 ft. , No. 214339; Ash Creek, 6100 ft. , Graham Mts. , No. 204363; Pinery Canyon, 7500 ft. , Chiricahua Mts. , No. 247953; Thomas Caņon, 2 mi. E Baboquivari Mts. , No. 244420; Pine Springs, 15 mi. South of Colorado Caņon, No. 2425 Amer. Mus. Nat. Hist. On December 4, 1950, we removed the skull of No. 2425 to more certainly ascertain the identity of the individual. 

The specimens listed above include those that Nelson (N. Amer. Fauna, 29:211, August 31, 1909) listed from the Hualpai Mountains, PineSprings, and Prescott under the name _Sylvilagus nuttallii pinetis_. Nelson (_op. Cit. _:Pl. X, fig. 2) figured one of these skulls from theHualpai Mountains as _S. N. Pinetis_ and the cranial measurements (_op. Cit. _:201) that he records for _S. Nuttallii pinetis_ likewise are ofthese same specimens of _Sylvilagus floridanus holzneri_. Nelson'sdescription (_op. Cit. _:207-210) seems to have been affected by theerroneous (as we see the matter) inclusion of these specimens of _S. F. Holzneri_ in the materials identified by him as _Sylvilagus nuttalliipinetis_. 

The specimens so far mentioned from Arizona can be identified with ease. The identification becomes difficult, however, when the holotype of _S. F. Holzneri_, from the Huachuca Mountains, is examined. The difficultyresults from the holotype having a barely detectable emargination in theposterior border of the supraoccipital shield. In this respect theholotype is intermediate between _S. F. Holzneri_ (as known by specimensfrom more western localities in Arizona) and _S. N. Pinetis_ from theWhite Mountains to the northward. As noted above, _S. F. Holzneri_ has adeep notch and _S. N. Pinetis_ has none. This intermediacy of theholotype supports the possibility, mentioned by Nelson (_op. Cit. _:200), that intergradation occurs between _S. F. Holzneri_ and _S. N. Pinetis_. Additional evidence, however, is against this possibility; the notch inthe supraoccipital is deeper in specimens (No. 66136, from ChiricahuaMts. , and No. 204364, from Ash Creek in Graham Mts. ) from mountainsgeographically intermediate between the Huachuca Mountains and the WhiteMountains. Also, the holotype of _S. F. Holzneri_ differs from _S. N. Pinetis_ and agrees with other specimens of _S. F. Holzneri_ fromfarther southwest in Arizona in the robustness of the posteriorextensions of the supraorbital processes and in the considerable degreeof fusion of the tips of these processes with the squamosals. Additionally, the rostrum of the holotype is wide and deep as in otherspecimens of _S. Floridanus_ from more eastern localities and is unlikethe narrow and shallow rostrum of _S. N. Pinetis_. 

If intergradation occurs in Arizona between the species _Sylvilagusfloridanus_ and _Sylvilagus nuttallii_, as Nelson (_op. Cit. _:200)intimated it might, the intergrades probably will be found along theTonto Rim or in the territory between the Blue Range and the GrahamMountains. 

Sylvilagus floridanus cognatus Nelson

 1907. _Sylvilagus cognatus_ Nelson, Proc. Biol. Soc. Washington, 20:82, July 22. 

We have examined the specimens recorded by Nelson (N. Amer. Fauna, 29:193, August 31, 1909) and conclude that Nelson (_op. Cit. _)accurately described them. We differ from Nelson on one point ofinterpretation; we prefer to use the trinomial, instead of the binomial, for _cognatus_ because the kind and amount of difference between it andsubspecies of _Sylvilagus floridanus_ (_S. F. Holzneri_ and possibly _S. F. Llanensis_) is on the order of magnitude that distinguishessubspecies, and not full species, of _Sylvilagus_. 

The specimen (W. D. Hollister, original No. 208) from the DatilMountains, lent to us by the Colorado Museum of Natural History, doeshave, as Nelson (_op. Cit. _) pointed out, larger tympanic bullae and aslenderer rostrum than do other specimens of _S. F. Cognatus_. Nevertheless, No. 208, agrees with _cognatus_ and differs from_Sylvilagus nuttallii pinetis_ in the greater vertical depth of thezygoma, the greater transverse width of the first pair of upperincisors, the broader posterior extensions of the supraorbitalprocesses, the fusion (instead of freedom from, or mere touching to, thebraincase) of the tips of these extensions, the less upturnedsupraorbital processes, and the more nearly truncate posterior margin ofthe supraorbital shield. Therefore, the specimen is referable to_Sylvilagus floridanus cognatus_. The slender rostrum and large tympanicbullae of No. 208 are either individual variations or features peculiarto the population of _Sylvilagus floridanus_ in the Datil Mountains. 

Sylvilagus floridanus robustus Bailey

 1905. _Lepus pinetis robustus_ V. Bailey, N. Amer. Fauna, 25:159, October 24. 

Nelson (N. Amer. Fauna, 29:194-195, August 31, 1909) described specimensfrom the Big Bend area of Texas. This was the only area from whichNelson had specimens. Our examination of these same specimens indicatesthat his description of them was accurate. Davis and Robertson (Jour. Mamm. , 25:271, September 8, 1944) recorded a specimen, under the name_Sylvilagus robustus_, from "The Bowl, Guadalupe Mountains, CulbersonCounty, Texas. " Our examination of the skull of this specimen([female] adult, No. 658, Mus. Zool. , Louisiana StateUniversity) indicates that it is, among named kinds of rabbits, bestreferred to _robustus_. The specimen is morphologically as well asgeographically intermediate between _S. F. Cognatus_ and _S. Robustus_. This morphological intermediacy is illustrated by certain of thefollowing cranial measurements of three adult females: No. 108695(_robustus_), Chisos Mts. ; No. 658 from the Guadalupe Mts. ; and No. 128651, NE slope Capitan Mts. Basilar length, 59. 2, 54. 2, 54. 4; lengthof nasals, 33. 9, 31. 1, 32. 2; breadth of rostrum above premolars, 19. 3, 17. 5, 17. 0; depth of rostrum in front of premolars, 15. 8, 14. 8, 14. 0;interorbital breadth, 20. 4, 19. 1, 19. 7; parietal breadth, 27. 2, 27. 1, 26. 5; diameter of bulla, 13. 3, 12. 2, 10. 7. Considering the intermediatenature of specimen No. 648, and the kind and amount of differencebetween _Sylvilagus floridanus cognatus_ and _S. Robustus_, it seemsappropriate to us to use the name-combination _Sylvilagus floridanusrobustus_. 

Actual intergradation, in the sense of interbreeding between individualsof a continuously distributed population of animals, probably does notoccur regularly between _S. F. Cognatus_ and _S. F. Robustus_ norbetween several populations within either one of these subspecies; insouth-central Arizona and western Texas the animals are said to occuronly in the higher parts of the mountains. Consequently a givenpopulation is separated from another by low-lying territory inhospitableto the species _Sylvilagus floridanus_. This low-lying territory isinhabited by another species, _Sylvilagus audubonii_. More intensivecollecting in the region concerned may, however, show a continuousdistribution of the species _Sylvilagus floridanus_ in several areaswhere it seems now to have an interrupted distribution. 

Sylvilagus audubonii neomexicanus Nelson

 1907. _Sylvilagus audubonii neomexicanus_ Nelson, Proc. Biol. Soc. Washington, 20:83, July 22. 

Nelson (N. Amer. Fauna, 29:230, August 31, 1909) listed under_Sylvilagus audubonii cedrophilus_ Nelson an adult female, skin withskull (U. S. Nat. Mus. , Biol. Surv. Coll. , No. 108698) from fifteen milessouth of Alpine, Texas. Nelson (_loc. Cit. _) remarked that the"bleached" color of the back and the great lateral breadth of thetympanic bullae of No. 108698 were peculiarities not possessed by anyother specimen examined. Geographically, the locality of capture is farsouth of other known occurrences of _S. A. Cedrophilus_ andapproximately on the boundary separating the range of _S. A. Minor_ fromthat of _S. A. Neomexicanus_. The large size, which may have inducedNelson to refer the specimen to _S. A. Cedrophilus_, is not surprisingconsidering that the individual is a female and fully adult. Acombination of new and old fur on the upper parts presents a patternthat might be duplicated in other specimens of _S. A. Neomexicanus_. Thelateral inflation of the tympanic bullae can be interpreted asintergradation with the geographically adjacent _S. A. Minor_ to thesouth; _S. A. Minor_ has large bullae. There are no features otherwisewhich suggest that the specimen is anything other than _Sylvilagusaudubonii neomexicanus_ and we refer it to that subspecies. 

Sylvilagus audubonii minor Mearns

 1896. _Lepus arizonae minor_ Mearns, Proc. U. S. Nat. Mus. , 18:557, June 24. 

 1907. _S[ylvilagus]. A[uduboni]. Minor_, Nelson, Proc. Biol. Soc. Washington, 20:83, July 22. 

Nelson (N. Amer. Fauna, 29:230, August 31, 1909) listed, withoutcomment, under _Sylvilagus audubonii cedrophilus_ Nelson, a skin withskull inside (Amer. Mus. Nat. Hist. , 5419, [female] adult or sub-adult)from San Diego, Chihuahua, Mexico. We locate San Diego approximately 230miles south and 60 miles east of El Paso, Texas. Thus, the specimen isfrom near the center of the geographic range of _Sylvilagus auduboniiminor_. With the permission of Mr. G. G. Goodwin of the American Museumof Natural History we removed the skull. It differs in no essentialfeatures from those of other specimens of _S. A. Minor_. For example, ofspecimens in the United States National Museum, Biological SurveysCollection, a female (No. 132002) from Guzman in Chihuahua, and a male(No. 51020) from Santa Rosalia in the same state, are almostindistinguishable from the San Diegan specimen. The specimen is withoutexternal measurements but the length of the hind foot and length of earfrom the notch in the dry state (80 and 57, respectively) agree with thecorresponding measurements of _S. A. Minor_. Color of the skin furnishesno diagnostic character as between _S. A. Minor_ and _S. A. Cedrophilus_. We identify the specimen from San Diego as _Sylvilagusaudubonii minor_. 

_Transmitted January 30, 1951. _

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