Lineage (NCBI): root » Eukaryota » Opisthokonta » Metazoa » Eumetazoa » Bilateria » Coelomata » Deuterostomia » Chordata » Craniata <chordata> » Vertebrata <Metazoa> » Gnathostomata <vertebrate> » Euteleostomi » Sarcopterygii
Rhipidistia Look for this name in NCBI Wikipedia Animal Diversity Web
http://palaeo-electronica.org/content/fc-1 Benton et al. 2015
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The Xishacun Formation yields members of the micronatus- newportensis spore assemblage (Cai et al., 1994; Zhao and Zhu, 2010). The top of this zone lies near the end of the Lochkovian (Becker et al., 2012). The Lochkovian is dated as 419 Ma ± 3.2 Myr to 410.8 Ma ± 2.8 Myr, from which we derive our minimum age for the divergence of crown Sarcopterygii of 408 Ma.
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A soft maximum age for the lungfish-tetrapod divergence is given by the diverse late Silurian gnathostome assemblage of the Kuanti Formation, Yunnan, China. This deposit yields articulated remains of stem sarcopterygians, placoderms, and galeaspids (Zhang et al., 2010; Zhu et al., 2009, 2012, 2013), as well as undescribed acanthodians (Zhu et al., 2009). Crown sarcopterygians and crown rhipidistians are, however, completely lacking. We therefore propose the oldest possible age of this deposit as a maximum constraint for the divergence between lungfishes and tetrapods. The base of the Ludlow is dated as 427.4 Ma ± 0.5 Myr, from which we derive an estimate of 427.9 Ma.
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Youngolepis is universally regarded as a stem-group lungfish in maximum-parsimony (Cloutier and Ahlberg, 1996; Zhu et al., 1999; Zhu et al., 2001; Zhu and Yu, 2002; Friedman, 2007a; Zhu et al., 2009) and Bayesian (Friedman, 2007b; Zhu et al., 2009) analyses of sarcopterygian interrelationships based on morphological data. This makes the genus the oldest representative of crown Rhipidistia, the clade uniting lungfishes and tetrapods to the exclusion of coelacanths. Youngolepis is best known from Youngolepis praecursor, the type species from the middle to late Lochkovian Xitun Formation of Yunnan, China. The anatomy of Y. praecursor is known in great detail (e.g., Chang, 1982), and it is character information from this species that is used to infer the position of the genus within sarcopterygian phylogeny. Although the specimens of Youngolepis sp. from the Xishacun Formation are fragmentary and poorly preserved, Zhu and Fan (1995) provide clear evidence for this generic identification.
Zhu, M., Zhao, W., Jia, L., Lu, J., Qiao, T., and Qu, Q. 2009. The oldest articulated osteichthyan reveals mosaic gnathostome characters. Nature, 458:469-474.
Zhu, M. and Fan, J. 1995. Youngolepis from the Xishancun Formation (early Lochkovian) of Qujing, China. Geobios, Mémoire Spéciale, 19:293-299.
Cloutier, R. and Ahlberg, P.E. 1996. Morphology, characters, and the interrelationships of basal sarcopterygians, p. 445-479. In Stiassny, M.L.J., Parenti, L.R. and Johnson, G.D. (eds), Interrelationships of fishes. Academic Press, San Diego.
Friedman, M. 2007a. Styloichthys as the oldest coelacanth: implications for early osteichthyan interrelationships. Journal of Systematic Palaeontology, 5:289-343.
riedman, M. 2007b. The interrelationships of Devonian lungfishes (Sarcopterygii: Dipnoi) as inferred from neurocranial evidence and new data from the genus Soederberghia Lehman, 1959. Zoological Journal of the Linnean Society, 151:115-171.
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