A Jurassic mammal from South America

Abstract

The Jurassic period is an important stage in early mammalian evolution, as it saw the first diversification of this group, leading to the stem lineages of monotremes and modern therian mammals. However, the fossil record of Jurassic mammals is extremely poor, particularly in the southern continents. Jurassic mammals from Gondwanaland are so far only known from Tanzania and Madagascar, and from trackway evidence from Argentina. Here we report a Jurassic mammal represented by a dentary, which is the first, to our knowledge, from South America. The tiny fossil from the Middle to Late Jurassic of Patagonia is a representative of the recently termed Australosphenida, a group of mammals from Gondwanaland that evolved tribosphenic molars convergently to the Northern Hemisphere Tribosphenida, and probably gave rise to the monotremes. Together with other mammalian evidence from the Southern Hemisphere, the discovery of this new mammal indicates that the Australosphenida had diversified and were widespread in Gondwanaland well before the end of the Jurassic, and that mammalian faunas from the Southern Hemisphere already showed a marked distinction from their northern counterparts by the Middle to Late Jurassic.

A Middle Jurassic abelisaurid from Patagonia and the early diversification of theropod dinosaurs

“…In contrast, other theropod lineages, which arose at approximately the same time, such as 'elaphrosaurs' [31], ceratosaurids [7,9,36] and basal tetanurans [19], achieved a Pangean distribution during this time (see the electronic supplementary material). Interestingly, a similar biogeographic pattern has recently been inferred for other groups of Mesozoic vertebrates, such as basal eusauropods [37], heterodontosaurid ornithischians [38] and mammals [39,40], in which some clades were restricted to southern Gondwana during the Jurassic, whereas other clades had a global distribution. The congruent pattern of restricted distribution for multiple vertebrate clades during Pangean times may be related to a common biogeographic cause.…”

A new, nearly complete stem turtle from the Jurassic of South America with implications for turtle evolution

“…The tree consistency index, the tree retention index and other measures of clade support ( jackknifing, bootstrap and symmetric resampling) were calculated using TNT (see the electronic supplementary material). (c) Locality and horizon All specimens were recovered from the Queso Rallado locality (Rauhut et al 2002), 5.5 km from the west of Cerro Có ndor Village, Chubut Province, Argentina. Queso Rallado is located in outcrops of the Cañ adó n Asfalto Formation (Stipanicic et al 1968), which is considered to be Middle to Upper Jurassic ( Tasch & Volkheimer 1970;Nullo & Proserpio 1975).…”

The upper dentition and relationships of the enigmatic Australian Cretaceous mammal Kollikodon ritchiei

“…These include: from the Aptian Flat Rocks locality in Victoria, the ausktribosphenids Ausktribosphenos nyktos (Rich et al, 1997) and Bishops whitmorei (Rich et al, 2001a), the monotreme Teinolophos trusleri (Rich et al, 1999(Rich et al, , 2001b, and the multituberculate Corriebaatar marywaltersae (Rich et al, 2009); from the Albian Dinosaur Cove locality in Victoria, the partial humerus of (the possible monotreme) Kryoryctes cadburyi (Pridmore et al, 2005); and from Lightning Ridge in New South Wales a very large, mammal-like isolated tooth (Clemens et al, 2003). Most recent phylogenetic analyses have placed ausktribosphenids and monotremes within a larger Gondwanan radiation termed Australosphenida (Luo et al, 2001(Luo et al, , 2002(Luo et al, , 2007aMartin and Rauhut, 2005;Rougier et al, 2011;Wood and Rougier, 2005), together with the early Jurassic (Toarcian) (Cúneo et al, 2013) South American Asfaltomylos (Rauhut et al, 2002) and Henosferus (Rougier et al, 2007), and the middle Jurassic (Bathonian) Ambondro mahabo (Flynn et al, 1999) from Madagascar. Some authors, however, have questioned the inclusion of monotremes within Australosphenida (Pascual et al, 2002;Rich et al, 2002;Rowe et al, 2008;Woodburne, 2003).…”