Rallus adolfocaesaris, Alcover, Josep Antoni, Pieper, Harald, Pereira, Fernando & Rando, Juan Carlos, 2015

Alcover, Josep Antoni, Pieper, Harald, Pereira, Fernando & Rando, Juan Carlos, 2015, Five new extinct species of rails (Aves: Gruiformes: Rallidae) from the Macaronesian Islands (North Atlantic Ocean), Zootaxa 4057 (2), pp. 151-190 : 180

Rallus adolfocaesaris

Rallus adolfocaesaris n. sp. forms with the rails from Pico, Graciosa, Terceira and Santa Maria, a Macaronesian group of species that share the display of legs less robust and wings less reduced than R. lowei n. sp. The humerus of R. adolfocaesaris n. sp. is slightly more gracile than in R. aquaticus , but considerably wider than in R. lowei n. sp.. Its size (c. 33 mm in length) is similar to that of the Pico rail, and much larger than the São Miguel rail (20%) and São Jorge (31%) rails. The smaller humerus in relation to R. aquaticus suggests a shortening of the primary remiges, although this reduction was probably not so extreme as in R. lowei n. sp.

The hindlimb bones are gracile compared to R. lowei n. sp., and short in relation to R. aquaticus . R. adolfocaesaris n. sp. has a femur close in length to those of R. lowei n. sp., and slightly longer than in the rails of São Miguel, Terceira and Pico, but shorter than in R. aquaticus (7%) and longer than in R. minutus n. sp. (28%, see Figure 15 ). Its tibiotarsus is slightly shorter than in R. lowei n. sp., R. carvaoensis n. sp. and R. montivagorum n. sp., shorter than in R. aquaticus (19%) and longer than in R. minutus n. sp. (11%, Table 1 & Figure 16 ). The ANOVA performed on the tibiotarsus distal width (trait 25) identified significant morphological differences (F4,84=8.872; p <0.001) between R. adolfocaesaris n. sp. and R. carvaoensis n. sp. (p = 0.007) and R. minutus n. sp. (p = 0.002) but not with R. montivagorum n. sp. (p = 0.262) and R. aquaticus (p = 0.504). R. adolfocaesaris n. sp. has a similar tarsometatarsus length (U = - 0.342; p = 0.833) but a smaller tarsometatarsus distal (U = -2.449; p = 0.012) and proximal width (U = - 2.646; p = 0.006) than R. lowei n. sp. The tarsometatarsus is shorter (20%) than in R. aquaticus (U = - 2.838; p <0.001), and longer (25%, U = -2.236; p = 0.0.36) than in R. minutus n. sp. No differences were detected in tarsometarsus proximal (U = - 1.492; p = 0.171) and distal widths (U = -1.167; p = 0.262) between R. adolfocaesaris n. sp. and R. minutus n. sp. Seemingly, the ANOVA did not detect any relevant difference in tarsometatarsus length, and proximal and distal widths between R. adolfocaesaris n. sp. and the rails of São Miguel and Pico.

The ratio of humerus-to-femur length ratio (0.85) suggests that R. adolfocaesaris n. sp. was a flightless bird. According to this figure, and since the hindlimb bones are thinner than in R. lowei n. sp., the loss of the flying capacity should have been less extreme in R. adolfocaesaris than in the Madeiran rail. The short stout tarsometatarsus (relative to the femur) suggests that R. adolfocaesaris n. sp. could be a slow-pace runner.

Figures

FIGURE 15. Femora of Rallus spp. A, Rallus lowei n. sp., MMF 43420, L femur (specular image), (paratype). B, Rallus adolfocaesaris n. sp., MMF 43453, R femur, (paratype). C, Rallus carvaoensis n. sp., DZUL 3183, R femur. D, Rallus montivagorum, MCMa 1880.014, R femur. E, Rallus minutus n. sp. MCMa 1954.014, R femur. F, Rallus aquaticus, IMEDEA 12474, L femur (specular image). 1, cranial view. 2, caudal view. Scale bar: 2 cm.

FIGURE 16. Tibiotarsi of Rallus spp. A, Rallus lowei n. sp., MMF 43426 / 43427, R tibiotarsus (paratype) (specular image). B, Rallus adolfocaesaris n. sp., MMF 43447, L tibiotarsus, (paratype). C, Rallus carvaoensis n. sp., IMEDEA 104068, L tibiotarsus. D, Rallus montivagorum n. sp., IMEDEA 104097, R tibiotarsus (specular image). E, Rallus minutus n. sp. MCMa 1951.014, R tibiotarsus (specular image). F, Rallus aquaticus, IMEDEA 12474, R tibiotarsus (specular image). 1, cranial view. 2, caudal view. Scale bar: 2 cm.