congresos y reuniones científicas
The cotylar fossa is not a common synapomorphy to link Afrotherian Mammals and South American Native Ungulates
LORENTE, M., GELFO, J.N., BOND, M., LÓPEZ, G.M., KRAMARZ, A. AND M. REGUERO
Congreso; IV Congreso de Paleontología de Vertebrados; 2011
Universidad Nacional de San Juan
THE COTYLAR FOSSA IS NOT A COMMON SYNAPOMORPHY TO LINK AFROTHERIAN MAMMALS AND SOUTH AMERICANNATIVE UNGULATESM. LORENTE1-2, J.N. GELFO1-2-3, M. BOND1-2-3, G.M. LÓPEZ1-3, A. KRAMARZ 2-4 and M. REGUERO1-21División Paleontología de Vertebrados, Museo de La Plata. Paseo del Bosque s/n B1900FWA, La Plata, Buenos Aires, Argentina2Consejo Nacional de Investigaciones Técnicas y Científicas (CONICET)3Cátedra Paleontología de Vertebrados, Facultad de Ciencias Naturales y Museo de La Plata, UNLP. firstname.lastname@example.orgMACN, Av. A. Gallardo 470, 1405 CABAThe cotylar fossa was defined as an anterior extension of the medial malleolar facet of the astragalus that deepens into a cup and receives thecondylar articular surface developed on the tibial medial malleolus (MacPhee, 1994). This character was considered as a reliable afrotheriansynapomorphy (Tabuce et al., 2007), and later as a synapomorphy shared by most Afrotheria, Notoungulata, Astrapotheria and Xenungulata(Agnolin and Chimento, 2011). Here we analyze tarsal remains of representatives from all South American native ungulate groups, and comparethem with extant afrotherians. The state of cotylar fossa of the malleolar facet is extremely variable among Notoungulata. Is absent inbasal taxa as Pleurostylodon (Isotemnidae), and in Homalodotherium (Homalodotheriidae). In Miocochilius, Protypotherium and Interatherium(Interatheriidae) the medial malleolar facet is vertical. In contrast, in Nesodon (Toxodontidae) the neck of the astragalus is extremely reducedand the head is almost in contact with the trochlea, the malleolar facet is well developed and extends over the head forming a depressioncomparable to a cotylar fossa. In Astrapotheria and Pyrotheria the astragalar morphology is modified since the more graviportal lifestyle. InParastrapotherium and Liarthrus (Astrapotheriidae) there is a structure comparable to a cotylar fossa, but is absent in the astragali assignedto the basal astrapotheriid Trigonostylops (Trigonostylopidae). In Pyrotherium (Pyrotheriidae) there is a long and thin medial facet without acotylar fossa. In Xenungulata, Carodnia (Carodniidae) has a prominent posteromedial protuberance of the astragalus, a broad and flat head,somewhat medially oriented, which together forms a medial groove in the talus, but is improbable that this could be homologous to a cotylarfossa. In Macrauchenia (Litopterna, Macraucheniidae) the malleolous of the tibia is not extended over the medial side of the astragalus and nocotylar fossa is present. However in South American ?condylarths?, considered as not related to afrotherian mammals (Agnolin and Chimento,2011), the astragali presumably assigned to Lamegoia, Paulacoutoia and Didolodus (Didolodontidae) have a well developed cotylar fossa.Summarizing, the cotylar fossa is absent in most native ungulates groups or in their stem taxa. The cotylar fossa could not be considered asa character to link native ungulates with afrotherians. In fact, this character was convergently developed in non-afrotherians, as in primates,macropodid marsupials, laurasic ?condylarths? as Meniscotherium and some dinocerates as Probathyopsis.Agnolin, F.L. and Chimento, N.R. 2011. Afrotherian affinities for endemic South American ?ungulates? Mammalian Biology 76: 101-108.McPhee, R.D.E. 1994. Morphology, adaptations, and relationships of Plesiorycteropus, and a diagnosis of a new order of eutherian mammals. Bulletin AmericanMuseum of Natural History 220: 1-214.Tafforeau, P. and Jaeger, J.J. 2007. Early tertiary mammals from North Africa reinforce the molecular Afrotheria clade. Proceedings Royal Society of London274: 1159-1166.