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Journal of Paleontology 92(2):254–271


shale deposited in the Western Interior Seaway as the seaway regressed, narrowed, and received more terrigenous sediment (Gill et al., 1972). Like the Smoky Hill Chalk Member, on which it often lies conformably, it supported a diverse and abundant pelagic biota that was simply the continuation of the Smoky Hill Chalk Member’s fauna (Carpenter, 1990, 2008). The sample of Pteranodon from the Sharon Springs Member is much smaller than that from the Smoky Hill Chalk Member, but like that of the Smoky Hill Chalk Member it consists primarily of mature adults with a small percentage of immature subadults of virtually adult size (Bennett, 2001). Thus the Sharon Springs Member also represents a pelagic feeding habitat in the middle of the Western Interior Seaway where adult and subadult Pteranodon fed on relatively large fishes. The absence of hatchlings and juveniles in the Western


Interior Seaway poses three questions. At what age did Pteranodon subadults go to sea? What were Pteranodon hatchlings and juveniles doing before they went to sea? Where were Pteranodon hatchlings and juveniles?


Figure 5. Pteranodon sp. indet. Thin section of cortical bone of limb bone shaft of a mature adult after Bennett (1993, fig. 2C). Arrows point to closely spaced circumferential bands interpreted as lines of arrested growth of a very slow growing fully mature adult individual. Scale bar is 500 μm.


vertebrae just behind the posterior margin of the symphyseal shelf of the mandible (Fig. 6.1), and another female specimen consisting of an articulated cranium and mandible was pre- served in left lateral view with a small mass of fish remains in a similar position immediately behind the posteroventral end of the symphysis (G. Rockers, personal communication, 2015). In both specimens, the masses were presumably ejected from the gut perimortem. Brown (1943, p. 106) commented on AMNH 5098 and stated that the mass included “the joint of a crusta- cean,” but my examinations failed to find any such evidence. Most of the vertebrae are 3.5–4.0mm long, but the largest vertebra is 8.8mm long. It is not clear what fish species the vertebrae pertain to, but they are consistent with those of Enchodus, which is common in the Smoky Hill Chalk Member. The smaller vertebrae are comparable to those of an Enchodus ~23–27cm long, whereas the largest vertebra is comparable to those of an Enchodus ~53cm long, a fish that was quite large relative to the head and body of Pteranodon (Fig. 6.2). Thus, the Smoky Hill Chalk Member represents a pelagic feeding habitat in the middle of the Western Interior Seaway where adult and subadult Pteranodon spent much of their time feeding on rela- tively large fishes, and FHSM 17956 is a one-in-a-thousand occurrence of a small juvenile that apparently strayed from its normal habitat and flew out to sea. The Sharon Springs Member in western Kansas, South Dakota, and Wyoming consists of ~15m of gray claystone and


At what age did Pteranodon subadults go to sea?—Relatively little is known about pterosaur growth rates. Bennett (1995; Fig. 7.1) studied the sample of Rhamphorhynchus muensteri Goldfuss, 1831 from the Solnhofen Limestone monographed by Wellnhofer (1975) and found it to consist of two distinct size- classes plus a few larger individuals that might represent more size-classes. Specimens in the small size-class were most immature, specimens in the medium size-class were older but still immature, and only the largest specimens could be considered fully mature adults. I argued that the size-classes represent year-classes resulting from seasonal sampling of a population of individuals growing at a more or less uniform rate, and that the growth rate was comparable to that of extant Alligator.If Rhamphorhynchus maintained a constant growth rate, it would have taken ~3 years for hatchlings to grow to the size of the largest specimen (~1.8m wingspan); however, it is likely that the growth rate declined with increasing size and age and it took somewhat longer. Similarly, Bennett (1996, 2013a; Fig. 7.2) studied the sample of Pterodactylus antiquus (Sömmerring, 1812) from the Solnhofen Limestone mono- graphed by Wellnhofer (1970) and found it to consist of two distinct year-classes plus a few larger individuals that might represent more year-classes, which again suggested it would have taken at least three years to reach adult size (~1.1m wingspan). The patterns of growth of Rhamphorhynchus and Pterodactylus compare well to that of Pterodaustro (Chinsamy et al., 2008, 2009), which grew rapidly for 2–3 years until half grown and then grew progressively more slowly for another ~4 years until reaching full size (~2.5–3m wingspan, Witton, 2013; L. Codorniú, personal communication, 2015), except that Pterodaustro took longer to reach its greater full size. There is no evidence that juvenile Pterodaustro grew faster than juvenile Rhamphorhynchus in order to reach the larger size of adults, so Pterodaustro presumably prolonged the period of rapid growth. Prondvai et al. (2012) examined the bone histology of


selected elements of five specimens of Rhamphorhynchus. Two specimens in the first year-class exhibited fibrolamellar bone with occasional laminar endosteal bone, and on that basis they were interpreted as early juveniles. Two specimens in the


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