caa a22 4500 388017465 CHVBK 20180307124915.0 cr unu---uuuuu 161130e199801 xx s 000 0 eng 10.1017/S0022336000024069 doi S0022336000024069 pii (NATIONALLICENCE)cambridge-10.1017/S0022336000024069 The forefin of Chensaurus chaoxianensis (Ichthyosauria) shows delayed mesopodial ossification [Elektronische Daten] [Ryosuke Motani, Hailu You] The hitherto poorly known forefin of Chensaurus chaoxianensis (Ichthyosauria) from the Lower Triassic (Spathian) is redescribed on the basis of the holotype and two new specimens. The humerus resembles that of Utatsusaurus hataii but is distinctive in having an emarginated anterior margin. The anteroproximal prominence of the radius is well developed, unlike that of other ichthyosaurs. All three specimens have five metacarpals and many phalanges, but only three carpals, which are identified as the ulnare, intermedium, and fourth distal carpal. These specimens show that delayed mesopodial ossification occurred in ichthyosaurs, at least in an early evolutionary stage. Because delayed mesopodial ossification is common among diapsids and is unknown in Jurassic ichthyosaurs, it was lost during the evolution of the Ichthyosauria. The osteogenic developmental axis appears to have continued into the fourth digit, as in other amniotes. The ossification pattern provides conclusive evidence to support the suggestion that the basal element of the fifth digit in Early Triassic ichthyosaurs is a metacarpal, rather than a carpal. Copyright © The Paleontological Society Motani Ryosuke Department of Zoology, University of Toronto, 25 Harbord Street, Toronto, Ontario, M5S 3G5 Canada aut You Hailu Department of Geology, University of Pennsylvania, Hayden Building, Philadelphia 19104 aut Journal of Paleontology Cambridge University Press 72/1(1998-01), 133-136 0022-3360 72:1<133 1998 72 JPA https://doi.org/10.1017/S0022336000024069 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1017/S0022336000024069 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Motani Ryosuke Department of Zoology, University of Toronto, 25 Harbord Street, Toronto, Ontario, M5S 3G5 Canada aut NATIONALLICENCE 700 1- You Hailu Department of Geology, University of Pennsylvania, Hayden Building, Philadelphia 19104 aut NATIONALLICENCE 773 0- Journal of Paleontology Cambridge University Press 72/1(1998-01), 133-136 0022-3360 72:1<133 1998 72 JPA CC0 http://creativecommons.org/publicdomain/zero/1.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-cambridge