Fig 1.
Left lateral view of the baculum of coyote (Canis latrans) with visible urethral groove on the ventral side, a dorsal ridge, and soft tissue attachment scars on the base. (Specimen 74824 from the Museum of Vertebrate Zoology, Berkeley, CA, USA).
Fig 2.
The partially preserved baculum of specimen F:AM 61088, exhibiting the complete distal end. A) Left lateral view showing the sigmoidal profile of the bone. B) Ventral view showing the beginning of the ventral groove about half way down the specimen, which then expands proximally. C) Dorsal view showing the lateral expansion where the ventral groove is present and the resulting dorsal crest. A,B and C are at the same scale; anterior at left. D) Slightly oblique view of the broken end. E) Oblique view of distal tip. F) Inferred cross-sections at two points along the specimen with caliper measurements indicated.
Fig 3.
Bacula from specimens F:AM 49097 (upper image in each panel) and F:AM 50213 (lower image in each panel). In each panel the specimens are roughly aligned based on the proximal ends of dorsal crest—it appears that F:AM 49097 is only missing a small portion of its proximal end, while F:AM 50213 is missing a larger portion of its distal end. A) Left lateral view, showing the ventral curvature in F:AM 49097 and soft tissue attachment marks on the proximal end of F:AM 50213. B) Right lateral view. The right side of specimen F:AM 49097 is less abraded giving a better view of the dorsal crest, which is absent from the proximal and distal ends. C) Dorsal view shows the dorsal crest of both specimens, and the triangular distal end of F:AM 50213. D) Ventral view showing the urethral groove in both specimens, although it is filled with matrix in specimen F:AM 49097. The distal surface for this specimen also shows that the specimen broke distally to the distal end of the groove. E) Cross section of the baculum F:AM 50213 where there is a clean break in the specimen. F) Inferred cross sections with caliper measurements indicated.
Fig 4.
The baculum of specimen F:AM 61723. A) Dorsal view showing the lateral expansion on the middle part of the shaft where the ventral groove is present. B) Lateral view showing the ventral curvature and the tapering of the bone distally. C) Ventral view showing the urethral groove. Same scale applies to A,B and C. D) Closer view of the distal tip (1cm scale bar). E) Inferred cross-sections at four points along the bone with caliper measurements indicated.
Fig 5.
The baculum of specimen USNM PAL 215320. Dashed area indicates material added to the specimen so that it could be mounted as part of an exhibit. A) Dorsal view, which indicates the lack of a lateral expansion seen in other species where the urethral groove is present. The mount obscures details of the proximal end. B) Left lateral view showing the ventrally curved profile. C) Ventral view showing the presence of a shallow groove along most of the length of the shaft but that disappears at both the distal and proximal ends. D) View of the distal end. There was insufficient information to infer cross-section shapes. Images courtesy of the Smithsonian Institution.
Fig 6.
The baculum of specimen UNSM 128864. A) Ventral view showing a deep urethral groove. B) Right lateral view, with the ventral side facing up on the picture, showing the baculum’s ventral curvature. C) Distal end in left lateral view. There was insufficient information to infer cross-section shapes.
Fig 7.
Lateral view silhouettes of bacula of borophagines and selected species within the suborder Caniformia.
The specimens represented were chosen to illustrate a substantial range of morphological variation of the canid bacula as well as a few representative morphologies observed in other families. [For further examples of morphological variation of bacula refer to 24, 26, 31]. Drawings for the Borophaginae are based on photographs in this paper. Silhouettes from extant species are based on specimens observed at the Museum of Vertebrate Zoology, Berkeley, California. Drawings from extinct species are based on published images for Amphicyon ingens [14], Daphoenus vetus and Hesperocyon gregarius [32]. The underlying phylogeny is for illustrative purposes and it is based on: Slater [21] for the relationship between the Borophaginae, Caninae and Hesperocyoninae; Slater and Friscia [33] for the position of Ursidae (grizzly bear), Mustelidae (marine otter and american mink), and Procyonidae (coati); Paterson et al. [34] for position of the Pinnipedia; and Tomiya and Tseng [35] for the position of the extinct Amphicyonidae (Amphicyon and Daphoenus). Time scale in million years ago, with ranges of extinct species projected to last fossil occurrences of the taxon.