Analyzing thepenis bones of five specimens of the extinct bear Indarctos arctoidesfound in the Cerro de los Batallones (Madrid), scientists from the Museum of Natural Sciences-CSIC and the Institut Català de Paleontologia Miquel Crusafont have concluded thatthis species maintained long copulations and that the females probably mated with several males in the fertile period. The conclusions have been published in the journalPLOS ONE.
Thestaff or penile boneis the bone structure present in the penis of some groups of mammals, including insectivores, rodents, carnivores and primates (except humans). In the specific case of carnivores, it is quite developed in caniforms (dogs, badgers or bears) while in feliforms (such as cats and hyenas) it is reduced or even absent. Its morphology and size is different in each group, and in many cases, its function is to act as a physical support to maintain the erection and facilitate copulation.
The staff is a fossil remnant thatappears very rarely in excavationss, since it is an elongated and delicate bone and is only present in half of the living population (males). On this occasion, Juan Abella and his team analyzed five belonging to extinct bears about 9 million years ago. The bones described belong to 4 adult individuals and a subadult, and the average bone length of the adult individuals is about 24 cm., Much longer than those of current bears of similar size, such as the brown bear. They arethe first staves of fossil bones to be found(not counting those of the Pleistocene cave bear, a much more recent species) and were excavated in several campaigns, during the years 2008, 2010 and 2012.
Researchers have compared the size and shape of these staffs with that of some current mammalian species to infer some aspects of the sexual and social behavior of Indarctos arctoides. And they have come to the conclusion that this specieskept long copulationsand that the staff acted as a physical support during intercourse, so that she could maintain penetration and have longer ejaculations. It is also possible that they had a reproductive system where several males copulated with the same female.
Long copulas occur in specieswhere sexual encounters are infrequent to ensure successful fertilization. This occurs with species that have a low density of individuals or when populations are highly fragmented and geographically separated. In the case of Indarctos arctoides, their distribution would be very restricted to the lush riparian forests and they would not be able to live in open areas, where they would enter into competition with the large saber-toothed tigers and with the amphithoids, extinct carnivores with both external characteristics. canids like bears. The fact that the staff of Indarctos arctoides is considerably larger than that of other bear species of similar size leads researchers to suppose that it is a sexually selected characteristic, that is,females preferred to mate with males with larger staves. This characteristic would be transmitted to the offspring so that the average size of the staff of this species would increase throughout evolution.
