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Journal of Paleontology 92(2):254–271


individuals, but immature individuals are present in both size-classes. The presence of immatures in the medium and large size-classes indicates that those size-classes cannot be age- classes, and because those immature specimens seem not to be significantly smaller than mature adults, they are considered to be subadults. The medium and large size-classes are dimorphic in rostral crest size, and, based on comparison to the dimorphic size-classes of Pteranodon, they are tentatively interpreted as sexes, small females with small and low crests, and large males with large and tall crests. The pelvis of AMNH 22555, a specimen in the medium


size-class that has deep pubes and ischia that would have resulted in a relatively large pelvic canal like that seen in female Pteranodon, provides further support for the interpretation of sexual dimorphism. The Brasileodactylus and Araripesaurus specimens in the small size-class seem to be immature and differ from specimens assigned to Anhanguera only in the lack of rostral crests and symphyseal keels, and because they are smaller than mature adults in the medium and large size-classes they are considered to be large juveniles. Presumably if the specimens had grown to maturity they would have developed rostral crests and mandibular keels and their skulls would have resembled those of presumed females assigned to Anhanguera or presumed males assigned to Tropeognathus, Colobor- hynchus, and Maaradactylus. According to the above interpretation, the anhanguerid


sample consists of large males with large and tall rostral crests and symphyseal keels, small females with small rostral crests, and immature large juveniles lacking crests. Females are ~60% more abundant than males, males are ~30% larger than females, and large immature juveniles make up ~16% of the sample. The sample is similar to that of Pteranodon from the Smoky Hill Chalk Member in exhibiting sexual dimorphism, although the sex ratio and size dimorphism are not as marked as in Pteranodon. If those differences are real and do not result from collection and publication biases, they might reflect the fact that the Romualdo Member anhanguerids are ~20 my older than Pteranodon. Based on that interpretation, the Romualdo Member would represent a littoral multi-age feeding habitat of large juveniles through adults, and hatchlings and small juveniles were absent because they occupied other habitats.


Patterns and implications of ontogenetic niches.—The best evidence for ontogenetic niches in pterosaurs comes from the samples of pterosaurs in which one or more ontogenetic stages are absent or markedly rarer than expected: (1) Pteranodon and Nyctosaurus in which juveniles are absent or virtually so, (2) Rhamphorhynchus in which mature presumably breeding adults are much rarer than expected given the abundance of yearlings, and (3) Aurorazhdarcho in which yearlings and older juveniles are much rarer than expected given the abundance of hatchlings and young-of-the-year. One reviewer suggested that there are many possible explanations other than particular ontogenetic stages of those taxa being somewhere other than the Western Interior Seaway or the Solnhofen lagoons, but they offered no specific explanations, and none that I can devise seems as plausible. In addition, the fact that samples of other pterosaurs are consistent with the interpretations of ontogenetic niches and do not provide evidence of parental care and/or


delayed onset of flight until half grown supports the view that pterosaurs exhibited ontogenetic niches. There seems to be variation in the patterns of ontogenetic


probably had a significant impact on pterosaur diversity. The pattern of ontogenetic niches and food resources partitioned by size in Pteranodon, Nyctosaurus, and Anhanguera would have resulted in greater overall abundance of the species than if they had been limited to continental or coastal environments, but also resulted in a less-diverse pterosaur fauna than if each different ontogenetic niche occupied by Pteranodon, Nyctosaurus, and Anhanguera was occupied by a distinct species. In addition, pterosaur faunas would have been biased toward large species because hatchlings and juveniles of large species such as Pteranodon and Anhanguera would have competed with any small species that lived in the continental or coastal environ- ments. Therefore, the presence of ontogenetic niches would have meant that pterosaur diversity was like that of crocodilians, with relatively few large species and each having broad ecological roles in which they preyed on a wide variety of foods of different sizes while growing to ~10 times their size at hatching, filling what might have been many different niches. Thus, pterosaurs were not like speciose passerines with many similar small species filling many narrow ecological roles. Andres et al. (2010, 2014) suggested that there was a


niches in different pterosaurs. Ctenochasma and Azhdarcho have the simplest patterns. Ctenochasma’s pattern of abundance is consistent with hatchlings through adults occupying the same habitat and feeding on the same items throughout their life with no change of niche other than that hatchlings presumably fed on individuals of prey species, whereas juveniles and adults sieved to catch multiples. Azhdarcho’s pattern of abundance suggests that juveniles through adults occupied the same riverine habitat, probably feeding on differently sized prey, although hatchlings may have spent some time elsewhere. Other pterosaurs exhibit more complex patterns of ontogenetic niches. Pterodaustro’s pattern of abundance is similar to that of Ctenochasma except that large juveniles through adults probably fed on open lake waters, whereas hatchlings and small juveniles were elsewhere, probably in protected nearshore habitats. Rhamphorhynchus and Pterodactylus hatchlings and small juveniles remained in or around the Solnhofen lagoons that were presumably close to the nesting grounds, and large juveniles through adults presumably were elsewhere except when nesting. Large juveniles through adults of Anhanguera and subadults and adults of Pteranodon and Nyctosaurus were at sea and hatchlings and small juveniles were elsewhere. Note that one reviewer suggested that the recently described Hamipterus (Wang et al., 2014) and Caiuajara (Manzig et al., 2014), both of which are represented by samples with broad size ranges including juveniles through adults, should have been included in the survey of pterosaurs. However, the ontogenetic compositions of the samples have not been documented sufficiently for them to be considered here. The occurrence of ontogenetic niches in most pterosaurs


dichotomy between terrestrial (e.g., Sericipterus and Kryptodrakon) and aquatic pterosaurs. Whereas it is reasonable to accept that a particular species of pterosaur lived in the depositional environment in which its fossils are found, there is often no reason to think that the species was limited to that environment. Ctenochasmatoids with jaws specialized as fish traps and sieves were probably limited to


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