Three New Beavers from Utah.
by Stephen D. Durrant.
The subspecific identity of beavers from Utah seems never to have been carefully investigated. With the exception of the name _Castor canadensis repentinus_ applied to animals from Zion and Parunuweap canyons by Presnall (1938:14), all other writers from 1897 until the present time, have used for animals from Utah, the name combination _Castor canadensis frondator_ Mearns, the type of which is from Sonora, Mexico. Study of specimens of beavers from Utah, accumulated in the collections of the Museum of Zoology, University of Utah, proves these animals to be far more variable than formerly supposed, and discloses the existence of three hitherto unnamed kinds, which are named and described below.
We recognize the need for caution in proposing new names for American beavers, because the transplanting of these animals from one watershed to another may have permitted the animals of a given area to change genetically, say, through hybridization, and may also have altered the geographic distribution of the several kinds. The officials of the Utah State Fish and Game Commission have assured us that such transplants have not occurred in the areas where these three new kinds are found, and further that nowhere in the state have transplants been made from one major drainage system to another; such transplants as have been made were only within the same major drainage system.
The capitalized color terms used in this paper are after Ridgway, Color Standards and Color Nomenclature, Washington, D. C., 1912. All measurements are in millimeters. We are indebted to the officials of the United States National Museum for the loan of comparative materials.
~Castor canadensis pallidus~ new subspecies
_Type._--Female, adult, skin and skull, number 719, Museum of Zoology, University of Utah; Lynn Canyon, 7,500 ft., Boxelder County, Utah; September 7, 1932; collected by W. W. Newby.
_Range._--Known only from the Raft River Mountains.
_Diagnosis._--Size small; tail and hind foot short (see measurements).
Color (type): Pale, upper parts uniformly Ochraceous-Buff; underfur Snuff Brown; underparts uniformly Light Buff, grading to Light Ochraceous-Buff at base of tail; underfur Light Drab; front and hind feet Light Ochraceous-Buff. Skull: Rostrum short; nasals broad (breadth averaging 54 per cent of length), constricted posteriorly and barely projecting posteriorly beyond premaxillae; zygomatic arches robust, but not widely spreading (zygomatic breadth 77 per cent of basilar length); mastoid breadth 73 per cent of zygomatic breadth; anterolateral margin of orbit narrow (6.2); occipital condyles visible from dorsal view; condylobasal length greater than occipitonasal length; upper incisors narrow (Orange Chrome in color); coronoid processes high and wide; cheek teeth narrow.
_Measurements._--Measurements of the type are as follows: Total length, 1040; length of tail, 380; length of hind foot, 157; length of ear, 35; occipitonasal length, 129.1; basilar length, 116.6; mastoid breadth, 65.6; interorbital breadth, 23.6; length of nasals, 43.3; zygomatic breadth, 89.7; breadth of nasals, 23.4; alveolar length of upper molariform teeth, 30.4.
_Comparisons._--From topotypes and near topotypes of _Castor canadensis taylori_, _C. c. pallidus_ differs as follows: Size smaller; tail and hind foot shorter. Color: Markedly lighter throughout. Skull: Nasals shorter and wider (breadth of nasals averages 54 per cent of length of nasals, as opposed to 46 per cent); nasals barely projecting posteriorly beyond premaxillae; rostrum shorter; zygomatic breadth relative to basilar length less; mastoid breadth actually as well as relatively greater; interorbital breadth greater; occipitonasal length shorter rather than longer than condylobasal length; tympanic bullae smaller; coronoid process higher and wider; cheek teeth narrower.
From specimens of _Castor canadensis baileyi_, from 20 miles north northeast of Elko, Elko County, Nevada, _C. c. pallidus_ differs as follows: Body smaller; tail longer; hind foot shorter; ears shorter: Color: Markedly lighter throughout. Skull: Larger; nasals shorter and wider (breadth of nasals averages 54 per cent of length of nasals as opposed to 41 per cent); nasals barely projecting posteriorly beyond premaxillae; rostrum broader; zygomatic breadth relative to basilar length less; mastoid breadth actually as well as relatively greater; occipitonasal length less rather than greater than condylobasal length; tympanic bullae smaller; coronoid process higher and wider; cheek teeth narrower.
From one topotype and two specimens of _Castor canadensis repentinus_, from the Colorado River at Yuma, Yuma County, Arizona, _C. c. pallidus_ differs as follows: Tail and hind foot shorter. Color: Lighter throughout. Skull: Narrower; nasals shorter and wider (breadth of nasals averages 54 per cent of length of nasals as opposed to 47 per cent); nasals barely projecting posteriorly beyond premaxillae; rostrum shorter; zygomatic breadth relative to basilar length less; mastoid breadth actually as well relatively greater; tympanic bullae narrower and smaller; coronoid process higher and wider; cheek teeth narrower.
From one specimen of _Castor canadensis concisor_, from Trappers Lake, Garfield County, Colorado, and from the original description of that subspecies (Warren and Hall, 1939: 358), _C. c. pallidus_ differs as follows: Size smaller. Color: Markedly lighter throughout. Skull: Smaller, narrower; nasals shorter and wider (breadth of nasals averages 54 per cent of length of nasals as opposed to 48 per cent); rostrum shorter; zygomatic breadth relative to basilar length less; mastoid breadth relative to zygomatic breadth greater; tympanic bullae narrower and smaller; jugals narrower; distal end of meatal tube smaller; coronoid process shorter and wider; angular process shorter and rounded rather than nearly pointed; cheek teeth narrower.
From the type and near topotypes of _Castor canadensis rostralis_, _C.
c. pallidus_ differs as follows: Size smaller; tail and hind foot shorter. Color: Markedly lighter throughout. Skull: Smaller and narrower; rostrum shallower and narrower; posterior end of nasals more constricted and barely projecting posteriorly beyond premaxillae; zygomatic breadth relative to basilar length less; mastoid breadth actually as well as relatively greater; dorsal surface of lacrimal bone larger; tympanic bullae narrower; coronoid process higher and wider; angular process not projecting so far caudad; cheek teeth narrower.
From the type and near topotypes of _Castor canadensis duchesnei_, _C.
c. pallidus_ differs as follows: Size smaller; tail and hind foot shorter. Color: Lighter throughout. Skull: Shorter, narrower and less massive; nasals shorter and wider (breadth of nasals averages 54 per cent of length of nasals as opposed to 46 per cent); nasals barely projecting posteriorly beyond premaxillae; rostrum shorter and narrower; zygomatic breadth relative to basilar length less; mastoid breadth actually as well as relatively greater; tympanic bullae narrower and smaller; coronoid process higher and wider; angular process not projecting so far caudad; cheek teeth narrower.
_Remarks._--The Raft River Mountains of extreme northwestern Utah, where _C. c. pallidus_ occurs, are the only mountains of the state within the drainage of the Snake River. The Snake River proper lies 50 miles to the northward in Idaho and contains another kind of beaver, _C. c. taylori_ (Davis, 1939: 273). Although occurring within the same drainage as _C.
c. taylori_, _C. c. pallidus_ is as distinct from it as from any other named kind. The relationships of _C. c. pallidus_, as indicated by the short rostrum and short, wide nasals, are rather more with _C. c.
rostralis_ of the Wasatch Mountains, than with _C. c. taylori_.
The pale color of the animals belonging to _C. c. pallidus_ was noted at the time of capture, and is the same in the young specimen (625 mm.
total length) as in the type, an adult.
_Specimens examined._--Total, 2, distributed as follows: _Boxelder County_: Raft River, 5 mi. S Yost, Raft River Mountains, 6,000 ft., 1; Lynn Canyon, Raft River Mountains, 7,500 ft., 1.
~Castor canadensis rostralis~ new subspecies
_Type._--Male, young adult, skin and skull, number 5199, Museum of Zoology, University of Utah; Red Butte Canyon, Fort Douglas, 5,000 ft., Salt Lake County, Utah; October 13, 1947; collected by Harold S. Crane and Clifton M. Greenhalgh, original number 446 of Crane.
_Range._--Known from the western streams of the Wasatch Mountains; probably occurs in all streams draining westward into the basin of Pleistocene Lake Bonneville.
_Diagnosis._--Size large; tail and hind foot long (see measurements).
Color (type): Upper parts Snuff Brown, purest on head; underfur Brownish Black (2); base of tail Cinnamon Buff; hind feet Carob Brown; ears Blackish Brown (2); underparts Auburn, grading posteriorly to Cinnamon Buff; underfur Light Drab. Skull: Large, massive; nasals short and broad (breadth averaging 54 per cent of length) and moderately convex transversely; rostrum deep and broad; ventral surface of rostrum moderately concave dorsally; dorsal surface of lacrimal bone small; frontal region generally flat; zygomatic arches robust and widely spreading (zygomatic breadth averaging 82 per cent of basilar length).
_Measurements._--Measurements of the type and average and extreme cranial measurements of 6 unsexed adults from Charleston, are, respectively, as follows: Total length, 1,330; length of tail, 470; length of hind foot, 170; length of ear, 34; occipitonasal length, 128.2, 134.3 (142.1-129.5); basilar length, 112.4, 117.2 (128.2-113.2); mastoid breadth, 62.5, 64.3 (68.9-60.2); interorbital breadth, 27.9, 26.0 (26.9-26.0); zygomatic breadth, 91.3, 93.8 (105.8-90.8); length of nasals, 44.9, 43.9 (51.3-41.5); breadth of nasals, 24.5, 23.7 (25.7-22.0); alveolar length of upper molariform teeth, 28.3, 30.9 (32.5-28.7).
_Comparisons._--From topotypes and near topotypes of _Castor canadensis taylori_, _C. c. rostralis_ differs as follows: Color: Darker on upper parts owing to darker underfur, guard hairs actually lighter. Skull: Longer; nasals shorter and wider (breadth of nasals averages 54 per cent of length of nasals as opposed to 47 per cent); extension of nasals posterior to premaxillae less; rostrum shorter, broader and deeper; dorsal surface of lacrimal bone smaller; zygomatic breadth relative to basilar length greater; mastoid breadth relative to zygomatic breadth less; coronoid process shorter; coronoid and condyloid processes farther apart and space between them shallower.
From one topotype and two specimens from the Colorado River at Yuma, Yuma County, Arizona, of _Castor canadensis repentinus_, _C. c.
rostralis_ differs as follows: Size larger; tail longer. Color: Darker throughout. Skull: Longer; nasals shorter and wider (breadth of nasals relative to length of nasals averages 54 per cent as opposed to 47 per cent); extension of nasals posterior to premaxillae less; rostrum shorter, deeper and wider; zygomatic breadth relative to basilar length greater; mastoid breadth actually as well as relatively greater; dorsal surface of lacrimal bone smaller; coronoid and condylar processes farther apart and space between them shallower.
From specimens of _Castor canadensis baileyi_, from 20 miles north northeast of Elko, Elko County, Nevada, _C. c. rostralis_ differs as follows: Size larger; tail and hind foot longer. Color: Darker throughout. Skull: Larger in all measurements taken; nasals markedly wider (breadth of nasals relative to length of nasals averages 54 per cent as opposed to 41 per cent); extension of nasals posterior to premaxillae less; dorsal surface of lacrimal bone smaller; mastoid breadth relative to zygomatic breadth less.
From one specimen of _Castor canadensis concisor_, from Trappers Lake, Garfield County, Colorado, and from the original description of that subspecies (Warren and Hall, 1939: 358), _C. c. rostralis_ differs as follows: Color: Guard hairs lighter; underfur darker (blackish as opposed to brownish). Skull: Longer and narrower; nasals broader and shorter (breadth of nasals averages 54 per cent of length of nasals as opposed to 48 per cent); dorsal surface of lacrimal bone smaller; distal end of meatal tube smaller; distal end of angular process rounded rather than pointed; coronoid process shorter; coronoid and condylar processes farther apart and space between them shallower.
Among known kinds of _Castor canadensis_, _C. c. rostralis_ is most like _Castor canadensis duchesnei_, from which the former subspecies differs as follows: Tail and hind foot longer. Color: Darker throughout. Skull: Nasals shorter and wider (breadth of nasals averages 54 per cent of length of nasals as opposed to 46 per cent); nasals less arched transversely; rostrum shorter, deeper and broader; ventral surface of rostrum less concave dorsally; dorsal surface of lacrimal bone smaller.
For comparison with _Castor canadensis pallidus_, see account of that subspecies.
_Remarks._--Animals from Kamas, in the drainage of the Weber River, are intergrades between _C. c. rostralis_ and _C. c. duchesnei_, but their short, wide nasals and wide rostra make them referable to _C. c.
rostralis_.
The available specimens of _C. c. rostralis_ are all from streams which ultimately empty into Great Salt Lake, which is in the northern part of the basin of Pleistocene Lake Bonneville. Some streams drain into the Lake Bonneville Basin without emptying into Great Salt Lake proper.
Beavers from these streams, we suspect, when they become known, will be found to be related to _C. c. rostralis_.
_Specimens examined._--Total, 16 (2 skins and skulls, 14 skulls only), distributed as follows: Summit County: Kamas, 5,500 ft., 6. _Salt Lake County_: Red Butte Canyon, Fort Douglas, 5,000 ft., 1; Millcreek Canyon, 6 mi. above mouth, 7,000 ft., 1. _Wasatch County_: Charleston, Heber Valley, 5,500 ft., 8.
~Castor canadensis duchesnei~ new subspecies
_Type._--Male, young adult, skin and skull, number 4625, Museum of Zoology, University of Utah; Duchesne River, 10 miles northwest of Duchesne, 5,600 ft., Duchesne County, Utah; September 23, 1946; collected by Dave Thomas, original number 160 of K. R. Kelson.
_Range._--Drainage of the Duchesne and White rivers in Utah and Colorado.
_Diagnosis._--Size large; tail long (see measurements). Color (type): Upper parts Sayal Brown, purest on head, grading to Cinnamon Buff at base of tail; underfur Fuscous; hind feet Burnt Umber; ears Fuscous Black; underparts Tawny Olive; underfur Smoke Gray. Skull: Large, massive; nasals long, slender (breadth averaging 46 per cent of length) and markedly convex transversely; rostrum long and attenuate; zygomatic arches heavy and widely spreading (zygomatic breadth averaging 81.5 per cent of basilar length); ventral surface of rostrum markedly concave dorsally, especially immediately behind upper incisors; nasals extend posterior to premaxillae.
_Measurements._--Measurements of the type and average and extreme cranial measurements of 9 unsexed adults, from Currant Creek, are, respectively, as follows: Total length, 1,176; length of tail, 458; length of hind foot, 165; length of ear, 33; occipitonasal length, 123.6, 132.1 (138.5-122.3); basilar length, 98.6, 114.4 (125.8-99.2); mastoid breadth, 60.4, 65.1 (67.2-64.1); interorbital breadth, 23.0, 25.1 (26.1-23.7); zygomatic breadth, 88.3, 94.2 (99.7-89.5); length of nasals, 46.1, 48.4 (51.5-46.2); breadth of nasals, 20.5, 22.5 (24.5-18.8); alveolar length of upper molariform teeth, 28.9, 29.9 (32.2-26.5).
[Illustration: FIGS. 1-4 Dorsal views of skulls of _Castor canadensis_.
1/2]
FIG. 1. _Castor canadensis rostralis_, male, young adult, no. 5199 (holotype), Mus. Zool., Univ. Utah.
FIG. 2. _Castor canadensis pallidus_, female, adult, no. 719 (holotype), Mus. Zool., Univ. Utah.
FIG. 3. _Castor canadensis duchesnei_, male, young adult, no. 4625 (holotype), Mus. Zool., Univ. Utah.
FIG. 4. _Castor canadensis concisor_, male, adult, no. 2090, Mus. Nat. Hist., Univ. Kansas, from Trappers Lake, Garfield County, Colorado, obtained by L. L. Dyche, October 22, 1891.