258


Journal of Paleontology 92(2):254–271


diameters of 18–20mm (FMNH P27476, YPM VP 2454, KUVP 85401, YPM VP 2755, LACM 51136 “B”, YPM VP 2444, 2490, and 2710, arranged in order of increasing diameter), although it should be noted that abrasion of the poorly ossified condyles may have reduced their diameters somewhat. The smallest of the eight specimens is 10% smaller than AMNH 4908, so presumably would have had an estimated wingspan in life of 3.0 m. Thus, FHSM 17956 is much smaller than the smallest previously known specimens; only ~53% the size of AMNH 4908 and ~59% the size of FMNH P27476. There is no information as to the sex of FHSM 17956, but if it was female it would have been ~53% the size of the smallest previously known female, whereas if it was male it would have been only ~37% the size of the smallest previously known male. FHSM 17956 exhibits immature states of the size


independent criteria Bennett (1993) used to assess maturity of specimens, i.e., incomplete ossification of epiphyses, immature grain on limb bone shafts, and no fusion of bones, and so is immature. Though much smaller than the smallest previously known specimens, it is otherwise indistinguishable from the immature subadults present throughout the sample of Pteranodon; thus no more immature morphologically than the most immature previously known specimens. However, because it is much smaller than the subadults, it is considered to be a juvenile. As such, it was presumably significantly younger than all previously known specimens. Although FHSM 17956 is much smaller than previously


known specimens, its morphology provides no evidence to suggest that it was incapable of flying out into the Western Interior Seaway where it was found (~200 km from the nearest shore). It is unlikely that it died elsewhere and floated out to sea before sinking to the bottom and becoming preserved; large


Figure 4. Scatter plots of limb element measurements of Pteranodon and Nyctosaurus from the Smoky Hill Chalk Member, Niobrara Formation. (1) Metacarpal (Mc) IV length plotted against wing phalanx (WP) 1 length. (2) Greatest diameter of dorsal condyle of distal wing metacarpal (McIV-d) against McIV length. Pteranodon data from Bennett (2001, fig. 119D, I) indicated by dotted squares, Nyctosaurus data from Bennett (2003, and unpublished data) indicated by plus signs, and FHSM 17956 indicated by the large dot. FHSM 17956 was not included in the samples from which the regression equations were calculated.


Table 1. Length measurements (in mm except as noted) of limb elements and the greatest diameter of the dorsal distal condyle of the wing metacarpal of small specimens of Pteranodon from the Smoky Hill Chalk Member. Wingspans in life estimated by the method of Bennett (2001).


FHSM 17956


Humerus Ulna


Wing phalanx 1 Wing phalanx 2 Wing phalanx 3 Wing phalanx 4 Femur Tibia


McIV dorsal condyle


Estimated span (m)


Metacarpal IV (McIV)


117* 160


74*


12.0 194


148* 1.76


154* 120* 63* 72*


FMNH P27476


— — —


18 —


— — — — —


3.0**


AMNH 4908


134 198 294


20


234* 129* 139 215 3.33


348 328


YPM VP 2345


140* 207* 308


19.9


380* 306


139* 218* 3.34


*length of incomplete or missing limb bone calculated with linear regression equations (Bennett, 2001) **wingspan estimated based on comparison to AMNH 4908


220* 108


dinosaurs (e.g., Claosaurus, Niobrarasaurus) occasionally floated to sea, but the Smoky Hill Chalk Member preserves no evidence that small terrestrial vertebrates (e.g., lizards, imma- ture crocodilians) did so. One reviewer argued that there is no evidence that FHSM 17956 flew to its resting place, an isolated


wing ripped off a carcass onshore could conceivably have floated to sea. That is true, but following that line of reasoning there is no evidence that any of the >1000 specimens of Pteranodon flew out to sea and no evidence that any pterosaur actually could fly. Despite that, all pterosaur workers find it most parsimonious to interpret pterosaurs as having flown. It is also most parsimonious to interpret FHSM 17956, smaller than but otherwise indistinguishable from the ~150 immature subadults in the sample of Pteranodon, as having flown out to sea, though it may not have done so intentionally and might have been blown by a storm. The thin section (Fig. 3) demonstrates that the bone his-


tology is similar to that of immature subadult Pteranodon (Bennett, 1993, fig. 2C), so is consistent with the interpretation of the specimen as immature. No LAG was found in the thin section, just as none was found in the thin section of the subadult, although LAGs do occur in Pteranodon bones (L.E. Wilson, personal communcation, 2016). Chinsamy et al. (2008, 2009) documented rapid growth without LAGs in Pterodaustro for the first 2–3 years until ~50% of full size was attained. Four LAGs were found in a tibia ~91% of full size, with the


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