Figure - available from: PLOS One
This content is subject to copyright.
Desmocyon thomsoni 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.
Source publication
The baculum of mammals offers the opportunity to study the reproductive biology of extinct species given that it is a fossilizable part of the male genitalia and that its size and shape correlate with several aspects of the reproductive biology of extant mammals. Fossil bacula, however, are rare. Currently, bacula have been described from only two...
Citations
... The morphological diversity of the mammalian baculum is subject to direct selection as a result of their role in copulation (Rakotondramanana & Goodman, 2017;Stockley, 2012), and the total length of the baculum of adult individuals is considered a diagnostic criterion for species characterization (Douangboubpha et al., 2010;Latorre, 2023;Soisook et al., 2015;Srinivasulu et al., 2020;Thomas, 1915;Vercillo & Ragni, 2011). The length of the baculum of a Lyroderma collected in Thailand was about 1 mm (Soisook Table 5 Average p-distance within Megadermatidae based on COI sequences. ...
Lyroderma lyra is one of the six currently recognised species of the family Megadermatidae. Previous studies have suggested subspecific division within L. lyra, wherein the nominate sub-species is predominantly distributed in South Asia, and the other subspecies, L. lyra sinense is occurring in southern China and Southeast Asia. Based on the congruent results of comparative morphology of skulls and bacula, as well as phylogenetic tree reconstructions-the first ones including both subspecies and incorporating the most extensive geographic sampling of "sinense" to date-using COI and cytb sequences, we have elevated the Southeast Asian subspecies to a distinct species status, Lyroderma sinense.
... Boldface value indicates the distance between Lyroderma sinense and Lyroderma lyra. (Douangboubpha et al., 2010;Latorre, 2023;Soisook et al., 2015;Srinivasulu et al., 2020;Thomas, 1915;Vercillo & Ragni, 2011). The length of the baculum of a Lyroderma collected in Thailand was about 1 mm (Soisook et al., 2015), whereas the bacular length of an Indian specimen was about 0.5 mm (Srinivasulu et al., 2020), which is similar to our results. ...
Lyroderma lyra is one of the six currently recognised species of the family Megadermatidae. Previous studies have suggested subspecific division within L. lyra, wherein the nominate sub-species is predominantly distributed in South Asia, and the other subspecies, L. lyra sinense is occurring in southern China and Southeast Asia. Based on the congruent results of comparative morphology of skulls and bacula, as well as phylogenetic tree reconstructions-the first ones including both subspecies and incorporating the most extensive geographic sampling of "sinense" to date-using COI and cytb sequences, we have elevated the Southeast Asian subspecies to a distinct species status, Lyroderma sinense.
While the mammalian baculum shows enormous morphological variability, the baculum of canids is highly conserved, with most variation restricted to size. Here, we explore the allometric relationship between baculum length and body size in extant and extinct canids. Examination of 26 species in the extant subfamily Caninae using standard linear regression revealed isometry. Phylogenetic regression also revealed an allometric slope indistinguishable from isometry. This pattern differs from the substantially negative slopes seen in other mammalian clades. The strength of the canid allometric relationship (r2) is also greater than in other clades, suggesting functional constraints on their baculum size. The constraints may be related to the copulatory tie that is characteristic of canids, and/or their monogamous mating system. Complete bacula are known from just four extinct species. The two complete bacula from the extinct subfamily Borophaginae (Aelurodon ferox and Aelurodon stirtoni) fall on the same allometric relationship as the living canids. However, the baculum of the extinct dire wolf (Aenocyon dirus, from the extant subfamily Caninae) and from the extinct subfamily Herperocyoninae, Hesperocyon gregarius, are significantly longer than expected based on their body sizes, suggesting that they may have had a different reproductive biology from that of extant canines.
