Waptia e le sue uova

Un'altra meraviglia da Burgess Shale. In una Waptia fieldensis del Cambriano medio di Burgess shale sono state rinvenute delle uova in gestazione sotto il carapace di questo artropode di 505 milioni di anni fa. Del grande numero di esemplari collezionati nel ROM (979), ben 5 presentano la presenza di queste uova, ed il numero massimo di uova al momento determinato è di 24 unità.

Precedentemente Kunmingella douvillei del Chengjiang biota (più antica di Waptia di circa 7 milioni di anni) aveva ugualmente mostrato la presenza di uova, ma localizzate in una posizione differente, posteriore e sugli endopodi, in posizione ventrale.

Immagine tratta dal sito: http://www.geologypage.com/2015/12/burgess-shale-fossil-site-gives-up-oldest-evidence-of-brood-care.html#ixzz4UuHlL1E6

Abstract: Brood care, including the carrying of eggs or juveniles, is a form of parental care, which, like other parental traits [ 1 ], enhances offspring fitness with variable costs and benefits to the parents [ 2 ]. Attempts to understand why and how parental care evolved independently in numerous animal groups often emphasize the role of environmental pressures such as predation, ephemeral resources, and, more generally, the harshness of environment. The fossil record can, in principle, provide minimum age constraints on the evolution of life-history traits, including brood care and key information on the reproductive strategies of extinct organisms. New, exceptionally preserved specimens of the weakly sclerotized arthropod Waptia fieldensis from the middle Cambrian (ca. 508 million years ago) Burgess Shale, Canada, provide the oldest example of in situ eggs with preserved embryos in the fossil record. The relatively small clutch size, up to 24 eggs, and the relatively large diameter of individual eggs, some over 2 mm, contrast with the high number of small eggs—found without preserved embryos—in the bivalved bradoriid arthropod Kunmingella douvillei from the Chengjiang biota (ca. 515 million years ago). The presence of these two different parental strategies suggests a rapid evolution of a variety of modern-type life-history traits, including extended investment in offspring survivorship, soon after the Cambrian emergence of animals. Together with previously described brooded eggs in ostracods from the Upper Ordovician (ca. 450 million years ago), these new findings suggest that the presence of a bivalved carapace played a key role in the early evolution of parental care in arthropods.

Pubblicazione: http://dx.doi.org/10.1016/j.cub.2015.11.006