Table 2. Stratigraphic distribution of major ichthyosaurian taxa. Black, unequivocal occurrence from the ammonite/ [>
conodont zone; Grey, occurrence from a range, without specific knowledge of the exact, ammonite/conodont zoiie;
narrow white, hiatus; wide white, range of genera. The boundary between stages are timed on the basis of the 1999
Geologic Time Scale by the Geological Society of America (http:/ /geosociety.org/science/ timescale/ timesd.pdf). Ammonite/
conodont zones within each stage were arbitrarily given equal lengths. Therefore, the time axis is roughly
proportional to the actual time. For the Lower Triassic, the units typically used in ichthyopterygian literature are no
longer in use by the Geological Society of America, and instead a subdivision into the Induan and the Olenekian is used.
This arrangement is followed here, and the more traditional units are indicated by the following abbreviations: Gries,
Griesbachian; Din, Dinerian; Smi, Smithian; Spa, Olenekian.
CONODONT ZONE AMMONITE ZONE
Utatsusaurus
Isf/ordosaurus
Cbaohiisaurus ....ffefejwnensis 1
longirostris
Paruinatator
Cymbospondylus
buchsen
Snastasaurusf?)
comallanus
nordenskloeldll | ......I leptorhynchus 1 m m ...... i
Mlkadocephatus
Wîmàniùs........
Pessosaunjs
Otaôi/rosirts 1
odontopalalus 1
poputaris 1
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CaMomosaunts ...P?!PP}.
calilomicus
Hudsoneipidia
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Temnodontosaurus platyodon
eurycephalus I
.„«rtflwos.............. J
Excalibosaunjs
longirostris
™ ...... BHU.....
Stenopterygius megacephaius
........
quadriscissus
hàùftiânùs........... '
Chacaicosaurus
Moiiesàûrûs........
Ophthalmosaurus ."a**»::::::::::
Nannopterygius
Bmchypterygius
entheklodon
leptospondylus
Undorosaurus.......
Piatypterygius
bonapartei
gorodischensis
piaiyôaciÿ/us
campylodon
Time (ma) ^ ^ 2 4 8