Struthio camelus spatzi Stresemann, 1926: 139

Elzanowski, Andrzej & Louchart, Antoine, 2022, Metric variation in the postcranial skeleton of ostriches, Struthio (Aves: Palaeognathae), with new data on extinct subspecies, Zoological Journal of the Linnean Society 195 (1), pp. 88-105 : 95-97

Struthio camelus spatzi Stresemann, 1926: 139 .

Holotype: Egg, Museum für Naturkunde , Berlin, ZMB B.1180a (not examined).

Referred specimen: Adult male skeleton ZMB 36879 Stresemann, 1927: 135.

Remark: The skeleton ZMB 36879 comes from one of three birds, referred to by Stresemann (1927) as ‘cotypes’, kept at that time in Berlin Zoo.

Expanded diagnosis: Smaller than the living subspecies (with most dimensions 88–100%) except for the synsacrum (Supporting Information, Table S3), postacetabular pelvis (Supporting Information, Table S4), distal ends of the humerus (Supporting Information, Table S2 ), femur except for a smaller corpus diameter (Supporting Information, Table S5), and pedal phalanges III/1 and III/2 ( Fig. 2 ; Supporting Information, Tables S9 and S10). Tarsometatarsus length <440 mm (as in S. c. syriacus). The ratio of the length of tibiotarsus to tarsometatarsus is> 1.15, compared with 1.11–1.14 in extant ostriches. Phalanges III/1 and III/2 are as in extant ostriches, with the respective total lengths of ~ 90 mm (in the lower range of S. c. camelus ) and 60 mm (as in S. c. camelus ). The ratio of the length of tarsometatarsus to phalanx III/2 is 7.1, compared with 7.6–9.0 (8.0–9.0 for males) in extant ostriches. The pattern of egg pores of the intermediate type is as described by Schönwetter (1927), Sauer (1968, 1972) and Mikhailov & Zelenkov (2020).

SKELETAL VARIATION AND SEXUAL DIMORPHISM

Although the coefficients of variation of most measurements in the living ostriches do not exceed 6% (Supporting Information, Tables S2–S 13), some of them are distinctly higher as a result of variable ossification (intrinsic variation) or, in addition, some indeterminacy owing to the absence of exact measurement points when taking minimum width or depth measurements across continuous surfaces. A high intrinsic variability affects single details, such as the sternal interspinal width ( CV = 7.4), pelvic angular width ( CV = 10.1), the cranial ( CV = 8.5) and caudal ( CV = 12.1) interforaminal distances of the tarsometatarsus and the proximal width between the cotylar margins of phalanx III/1 ( CV = 7.1).

The indeterminacy and variability of measurement position might have contributed to the variation of the sternal postcostal width ( CV = 9.6), pelvic postacetabular width ( CV = 8.9), fibular corpus width ( CV = 8.8), tarsometatarsal corpus depth ( CV = 8.4) and many transverse measurements of phalanx III/2: corpus width ( CV = 9.1), apical width ( CV = 7.0), trochlear depth ( CV = 7.1) and foveal width ( CV = 7.1), with the foveal width also being highly variable in phalanx III/3 ( CV = 9.5). The most variable and thus the least usable measurement turned out to be the interischiadic width (ischiadic span) of the pelvis ( CV = 19.9), suggesting a strong intrinsic component of this variability in addition to the indeterminacy of the measurement point.

With a notable exception for the length of the tibiotarsus (Supporting Information, Table S6) and, especially, the tarsometatarsus (Supporting Information, Table S8), most measurement values (71 of 95medians), including the transverse measurements of the tibiotarsus and tarsometatarsus, tend to be higher in females. However, the differences proved to be statistically significant or near-significant in only 14 measurements ( Table 2 ). In ten of them, the ostrich females have consistently wider and/or deeper ends of limb bones, which suggests that the female skeleton (at least the appendicular skeleton) is more robust even if the males are taller owing to longer tarsometatarsi and tibiotarsi. Only three bones, namely the scapulocoracoid, humerus and pedal phalanx III/3, are significantly longer compared with males.

Figures

Figure 2. Simpson’s ratio diagram comparing the lengths of scapulocoracoid (SC), humerus (H), femur (F), tibiotarsus (TT), tarsometatarsus (TM), and the first (III/1), second (III/2), and third (III/3) pedal digit III phalanges of living and extinct ostriches (Struthio), with Struthio camelus australis NHMUK 1857.2.24.10 as a reference (the black straight line at level 0). See the Supporting Information for the adopted lengths of limb segments (Table S17) and their LOG (decimal logarithmic) values (Table S18).