be considered to have a sister group relationship to the Late Jurassic African taxon Dicraeosaurus, instead of to Amargasaurus from the Lower Cretaceous of South America. Rauhut et al. (2005, 671) conclude this is indicative of a rapid evolutionary radiation and dispersal of the Dicraeosauridae following the separation of the continents of the Southern and Northern Hemispheres during the latest Middle Jurassic. The following cladogram by Tschopp and colleagues (2015) shows the presumed relationships between members of the Dicraeosauridae: Paleoecology Rauhut and colleagues in 2005 noted that the tendency towards shorter-necks seen in dicraeosaurids, and most evident in Brachytrachelopan, runs counter to the lengthening of the neck seen in most sauropod lineages (brachiosaurids, titanosaurs, diplodocids, etc.) and indicates that this group of sauropods was "progressively adapting for low browsing and might have been specialized on specific food sources, as has been suggested for Amargasaurus and Dicraeosaurus." Moreover, the morphology of the cervical neural arches in Brachytrachelopan would have significantly restricted dorsal flexion of the neck and most likely indicates that this sauropod was specialized to a diet of plants "growing at heights of between about 1 and 2 m." Rauhut and colleagues also suggested that diet may have been a limiting factor in body size among dicraeosaurids, and that this may have placed them in the same ecological niche as "large low-browsing iguanodontian ornithopods." Such large iguanodontians are absent from the Late Jurassic Gondwanan sediments that have produced all known fossils of dicraeosaurids, while they are abundant in similar ecosystems of the same age in North America, where dicraeosaurids are absent. This may indicate that large iguanodontians and dicraeosaurids (especially Brachytrachelopan) were ecological analogs, resulting from parallel evolution in two distantly related dinosaurian lineages. References External links National Geographic Dicraeosaurids Kimmeridgian life Oxfordian life Tithonian life Late Jurassic extinctions Late Jurassic dinosaurs of South America Fossils of Argentina Jurassic Argentina Cañadón Asfalto Basin Fossil taxa described in 2005