Rallus lowei Alcover, Pieper, Pereira & Rando, 2015, n. sp.

Rallus lowei

R. lowei n. sp. is a highly distinctive species. It belongs to a group that combines robust leg bones (especially the tarsometatarsus) with small wings. It is the largest and heaviest member of this group, which also includes R. carvaoensis n. sp. and R. minutus n. sp. Two almost complete humeri of R. lowei n. sp., were available for study.

One of them is from an adult and measures ca. 29.7 mm, which represents about a 24% reduction compared with the average humerus length of R. aquaticus (Figure 11). This estimated humerus length falls between the average humerus lengths of the larger R. montivagorum n. sp. and R. adolfocaesaris and the smaller R. carvaoensis n. sp. and R. minutus n. sp. The ulna of R. lowei is shorter than in R. aquaticus (27% shorter), and than R. montivagorum n. sp. from Pico (14%), but longer than in R. minutus n. sp. (39%).

Its femur is slightly longer than in the Rallus species of Porto Santo, São Miguel and Pico, notably longer (28%) than in R. minutus n. sp. but shorter (8%) than that of R. aquaticus. Its tibiotarsus is longer (16%) than in R. minutus n. sp., slightly longer than in R. adolfocaesaris n. sp., close in size to those of the Pico, but shorter than in R. aquaticus (16%) (Table 1 & Figure 16). R. lowei n. sp. has a tarsometarsus similar in length to R. montivagorum n. sp. (p = 0.734), longer (12%) than in R. carvaoensis n. sp. (p = 0.003) and in R. minutus n. sp. (29%, p <0.001), but shorter (18%) than in R. aquaticus (p<0.001). The tarsometatarsus of the new species has the largest tarsometatarsus distal width (p<0.001 in all the cases) and proximal width reported within the species group (U = - 3.745; p <0.000, U = -3.337; p <0.001, U = - 3; p = 0.001, and U = - 4.124; p <0.000 respectively). In addition, the tarsometatarsus length is similar to R. adolfocaesaris n. sp. (U = - 0.342; p = 0.833), but has larger distal (U = - 2.449; p = 0.012) and proximal widths (U = - 2.646; p = 0.006) (Figure 17).

The quotient between the antitrochanterian width and the total length of the synsacrum is larger (20%) in R. lowei n. sp. than in R. aquaticus. This ratio is larger than in R. montivagorum n. sp., but slightly smaller than in R. minutus n. sp.

The stout configuration of all the hindlimb bones gives them a peculiar shape (see Figure 17 A), which combined with the very wide synsacrum, suggests the new species was a very robust bird (Figure 23). The species was flightless, as confirmed by the reduced wing bones compared to the hindlimb bones with ahumerus-to-femur length ratio (0.78) (Livezey 2003). The short stout tarsometatarsus relative to the femur suggests that R. lowei n. sp. might have been a slow-pace runner.