Tetraoninae, Vigors, 1825

James, Helen F., 2020, The Irvingtonian Avifauna of Cumberland Bone Cave, Maryland, Zootaxa 4772 (1), pp. 111-131 : 118

Tetraoninae sp.

Material and Descriptions. USNM PAL 641987, l coracoid: sternal half lacking the lateral process and with much of the dorsal surface of the bone damaged, collected in the 1990s. The bone agrees in morphological details with the four species under consideration but does not preserve enough morphological detail to allow for diagnosis at the species level. It is moderately larger than comparative skeletons of B. umbellus . The bone has been gnawed by a small mammal, likely a rodent.

USNM PAL 641975, l coracoid: shaft missing sternal end and part of processus acrocoracoideus, collected May 14, 1999. In galliforms, the ventral surface of the shaft typically has a blunt crest running from the acrocoracoid process nearly to the sternal end of the bone. The fossil differs from L. lagopus , L. mutus , and F. canadensis , and agrees with B. umbellus , in having this crest more prominent, so that the ventral surface attains a more acute angle. It differs from B. umbellus and F. canadensis , and agrees more with Lagopus , in having a wider facies articularis humeralis. This combination of attributes leaves the generic assignment of the bone uncertain.

USNM PAL 641976 , l scapula: cranial one-third only, collected on October 8, 1999. The bone is immature, with its shaft heavily striated and articular surfaces pitted. It is smaller than comparative adult Bonasa umbellus skeletons .

USNM PAL 641974, l humerus: shaft only, preserving the proximal tip of the brachial depression, collected in the 1990s. The bone appears adult. The size of the bone and the stout, curvy shaft agree well with B. umbellus and F. canadensis .

USNM PAL 11690, l humerus: distal half, referred to B. umbellus by Wetmore (1927). A well-preserved specimen that agrees in fine detail with B. umbellus but also closely resembles L. lagopus and F. canadensis . In the comparative series examined, B. umbellus tends to have a more distinct olecranon fossa than the other two species. The fossil tends to agree with B. umbellus in this regard, but the trait is variable and is insufficient grounds for positive attribution.

USNM PAL 641988, abraded ulnare collected in the 1990s. An uncatalogued radiale, stored with this one and with the same provenience data, could well be the same species.

USNM PAL 769091 , ulnare: complete, collected on May 14, 1999 .

USNM PAL 641978 , left carpometacarpus: proximal end only, collected by Trent Spielman probably on October 2, 1996 (illegible) .

USNM PAL 641977, l femur: shaft only, collected in 2009.Agrees with B. umbellus and F. canadensis in having the caudal intramuscular lines less wide-set than in Lagopus . The shaft circumference is greater than in comparative skeletons of B. umbellus and F. canadensis , but still much smaller than in Tympanuchus .

Remarks. I have referred only two of the ten bones of Tetraoninae in the assemblage to B. umbellus and have left the rest unidentified to genus, including the distal humerus referred to the species by Wetmore (1927). As Steadman (2005) observed, postcranial skeletal elements of B. umbellus and F. canadensis , other than the tarsometatarsus, generally cannot be distinguished. However, I note that the other eight bones provide no clear evidence to refute the supposition that B. umbellus is the only species of Tetraoninae present. Note too that although I referred the two tarsometatarsi to the living species, it is possible that they instead represent a chronospecies of B. umbellus or an extinct species of Bonasa .

Cumberland Bone Cave provides the sole Irvingtonian fossil record of B. umbellus and the oldest fossil record of the genus and species. The species has been reported from late Pleistocene and Holocene sites in North America, particularly in the southeast (e.g., Brodkorb 1959; Wetmore 1962; Steadman 2005). Bonasa umbellus is the only extant species of grouse that occurs in the mid-latitude Appalachians or in the mixed hardwood forest habitat that is characteristic of the region at present ( Rusch et al. 2000).