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Journal of Paleontology 92(2):254–271


What were Pteranodon hatchlings and juveniles doing before they went to sea?—Pteranodon hatchlings and juveniles presumably were flying and feeding independently like those of Rhamphorhynchus, Pterodactylus, and Pterodaustro. They would have resembled females in having pointed edentulous, roughly equilength jaws comparable to those of herons, storks, and many other extant birds, which would have been well suited to feeding on all manner of small animals. The more conservative interpretation is that Pteranodon hatchlings and juveniles fed on suitably sized aquatic prey (e.g., crustaceans, small fishes) in shallow waters and progressed to larger and larger prey as they grew. However, they also could have fed on suitably sized prey in terrestrial environments (e.g., arthropods, small tetrapods), much as extant storks do.


Where were Pteranodon hatchlings and juveniles?—At present, there is no evidence to suggest where Pteranodon hatchlings and juveniles were, but if they fed on suitably sized aquatic prey, then they could have lived around lakes, rivers, wetlands, and estuaries, or along beaches and coastlines, wherever small aquatic prey was available, whereas if they fed on suitably sized terrestrial prey, then they could have lived in varied terrestrial environments. Bennett (1994b) envisioned Pteranodon laying eggs and rearing young in crowded colonies on islands free of terrestrial predators, much as do many extant seabirds. How- ever, whereas pterosaurs do seem to have aggregated to lay their eggs in colonies (Bell and Padian, 1995; Wang et al., 2014), there is no evidence that they did so on islands and they probably laid their eggs near those environments that provided suitable niches for hatchlings so that hatchlings would not need to travel far to find food and relative safety. The sample of Nyctosaurus gracilis (Marsh, 1876) from the


Smoky Hill Chalk Member, though numerically smaller than that of Pteranodon, is similar to it in most respects. It consists of 30 specimens with wingspans of 1.6–3.3m (Bennett, 1994a, 2003, and unpublished data), 11 of which are immature, but do not differ significantly in size from mature individuals and are considered to be subadults, whereas the other 19 are considered to be adults. There is size variation in the sample, but bimodality reflecting sexual dimorphism has not been demonstrated. As with Pteranodon, the sample of Nyctosaurus consists of mature adults and immature subadults of similar size that were feeding in the middle of the Western Interior Seaway and there is no evidence of hatchlings or juveniles. Although the absence of hatchling and juvenile Nyctosaurus is less significant statisti- cally than the one in 1000 occurrence of a juvenile Pteranodon, the absence indicates that hatchlings and juveniles occupied different environment(s) and ecological niche(s) than adults such that Nyctosaurus exhibited ontogenetic niches. The pattern of ontogenetic niches exhibited by Pteranodon


and Nyctosaurus would have permitted hatchlings and juveniles to occupy environments that provided suitably sized prey and an optimal balance between prey availability and predation risk,


yet permitted large adults to access the abundant supply of large fishes in theWestern Interior Seaway that would not have been available if adults stayed around their breeding grounds and continental or coastal environments with hatchlings and juveniles. At sea, the marked size dimorphism of Pteranodon with modal males of 5.6m wingspan, ~50% larger than modal


females of 3.8mwingspan (Bennett, 1992), would have enabled males to feed on significantly larger fishes than females. This suggests that the available food resources of the Western Interior Seaway were partitioned between Pteranodon sexes by size, and Nyctosaurus with wingspans of 1.6–3.3m and more lightly built jaws than Pteranodon presumably fed on even smaller prey that represented a third partition of the Seaway’s food resources. Thus, Pteranodon sexes and Nyctosaurus seem to have occupied three different niches at sea so as to reduce competition.


Other pterosaurs


Having found evidence of ontogenetic niches in the size and age distributions of samples of Pteranodon and Nyctosaurus from the Smoky Hill Chalk Member and Sharon SpringsMember, the size and age distributions of samples of other pterosaurs from selected well-studied Konservat-Lagerstätten were surveyed for evidence of ontogenetic niches (Table 2). Whereas the complete absence of eggs, hatchlings, small juveniles, and large juveniles save FMNH 17956 provides evidence of ontogenetic niches in Pteranodon, in other pterosaurs the presence of eggs, hatchl- ings, and small juveniles or the absence of subadults and adults can provide evidence of ontogenetic niches. Eggs are unlikely to travel far, so their presence indicates proximity to nesting grounds. Similarly, hatchlings are unlikely to travel great dis- tances, so it is reasonable to assume that localities where hatchlings have been found are relatively close to nesting grounds. Subadults and adults probably could travel great dis- tances, so their absence or unexpected rarity will suggest that they were not normally present or abundant in the depositional environment.


Solnhofen Limestone.—The Solnhofen Limestone consists of well-bedded lithographic limestones deposited in shallow hypersaline lagoons connected with open-marine environments (Barthel et al., 1990). Anoxic bottom waters provided condi- tions favorable to the preservation of vertebrate skeletons, and Unwin (2006) reported >1000 pterosaur specimens have been found. Small fishes (e.g., Leptolepides) were a significant component in the fauna, and demonstrate that the lagoons and/or nearby waters would have provided abundant food for piscivorous pterosaurs. The pterosaurs of the Solnhofen Limestone of southern


Germany were monographed by Wellnhofer (1970, 1975) and restudied by Bennett (1995, 1996, 2006, 2007a, 2007b, 2013a, 2013c, 2014b). Bennett (1995) determined the ontogenetic ages of Rhamphorhynchus muensteri specimens, and noted that the sample of 109 specimens monographed by Wellnhofer (1975) consists of two distinct size-classes interpreted as year-classes resulting from seasonal sampling of a population of individuals growing at a more or less uniform rate over the course of several years, plus a few larger individuals that might represent additional year-classes (Fig. 7.1). The first year-class consists of 33 hatchlings and young-of-the-year with wingspans of 29–59 cm, the second year-class consists of 73 yearlings with wingspans of 86–132 cm, there are two larger more mature specimens with wingspans of ~1.5 m, and there is one large fully


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