Ontogenetic status

The articular surfaces of the radius, ulna, pteroid, McIV, and WP1 are pitted and rough, indicating incomplete ossification, and similar pitting is visible on the carpal elements as well. The diaphyses of the radius, ulna, pteroid, McIV, and WP1 exhibit immature grain with many vascular canals opening onto the external surface of the bone. The proximal and distal rows of carpals are not fused into proximal and distal syncarpals, and the extensor tendon process is not fused to WP1. Thus, the specimen exhibits immature states of all three size-independent criteria that Bennett (Reference Bennett1993) used to identify immature specimens of Pteranodon and does not exhibit any evidence of osteological maturity, so it is immature.

Thin section

Cortical bone was sampled from the posterior side of the neck of McIV, just proximal to the distal condyles where it was thought that the bone would be thickest and provide the best chance of finding a line of arrested growth (LAG), if present. The resulting thin section (Fig. 3.1) is 540 µm thick, and exhibits well-vascularized plexiform bone (sensu Francillon-Vieillot et al., Reference Francillon-Vieillot, de Buffrénil, Castanet, Géraudie, Meunier, Sire, Zylberberg and Ricqlès1990) with vascular canals opening onto the external surface. The internal surface is uneven and appears to be resorptive. No LAG is evident, but a second section ground much thinner exhibits multiple discontinuous narrow circumferential bands of blue against a background of magenta when examined under polarized light with a first-order retardation (=λ) plate (Fig. 3.2). The spacing of the bands (~80 µm) suggests some sort of regular variation in fiber orientation. The pattern of bone and vascularization is similar to that previously found in the immature bone of a subadult Pteranodon (Bennett, Reference Bennett1993, fig. 2C), although the bone is thinner and the spacing between vascular canals is somewhat less than in the subadult.

Figure 3

Pteranodon sp. indet. (FHSM 17956). (1) Thin section of cortical bone from the distal end of metacarpal IV photographed under visible light; (2) thinner section photographed under polarized light and first order retardation (=lambda) plate showing narrow discontinuous circumferential bands of blue (light gray) against a background of magenta (medium gray); dark band at top is chalk residue on external surface of bone. Abbreviations: cb, circumferential band; ch, chalk; and vc, vascular canal. Scale bar is 300 μm.

Solnhofen Limestone

The Solnhofen Limestone consists of well-bedded lithographic limestones deposited in shallow hypersaline lagoons connected with open-marine environments (Barthel et al., Reference Barthel, Swinburne and Conway Morris1990). Anoxic bottom waters provided conditions favorable to the preservation of vertebrate skeletons, and Unwin (Reference Unwin2006) 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 (Reference Wellnhofer1970, Reference Wellnhofer1975) and restudied by Bennett (Reference Bennett1995, Reference Bennett1996, Reference Bennett2006, Reference Bennett2007a, Reference Bennett2007b, Reference Bennett2013a, Reference Bennett2013c, Reference Bennett2014b). Bennett (Reference Bennett1995) determined the ontogenetic ages of Rhamphorhynchus muensteri specimens, and noted that the sample of 109 specimens monographed by Wellnhofer (Reference Wellnhofer1975) 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 mature adult specimen with a wingspan of 1.8 m (Wellnhofer, Reference Wellnhofer1975; Bennett, Reference Bennett1995).

Bennett (Reference Bennett1996) noted year-classes in samples of the pterodactyloids monographed by Wellnhofer (Reference Wellnhofer1970). The sample of Pterodactylus antiquus consists of 28 specimens based on Wellnhofer’s data, Bennett’s (Reference Bennett1996) study, and Jouve’s (Reference Jouve2004, see also Bennett, Reference Bennett2013a) synonymization of P. kochi (Wagner, Reference Wagner1837) with P. antiquus after the addition of the Vienna specimen (NHMW 1975/1756/0000, Wellnhofer, Reference Wellnhofer1987) and the exclusion of JME-SOS 4593 that Bennett (Reference Bennett2006) referred to Germanodactylus cristatus (Wiman, Reference Wiman1925). Note that Vidovic and Martill (Reference Vidovic and Martill2014) erected the genus Aerodactylus for the species Pterodactylus scolopaciceps (Meyer, Reference Meyer1860), which Wellnhofer (Reference Wellnhofer1970) considered a junior synonym of P. kochi. They referred several Pterodactylus specimens to Aerodactylus, which they considered to differ from Pterodactylus in possessing a unique combination of features, but did not cite any features that did not fall within the range of variation of the hypodigm of P. antiquus. Five scatter plots of length measures were presented to support their interpretation, but: (1) all reflect only minor differences in skull depth, (2) slopes of regression lines of their Morphotype 1 (=Aerodactylus) in two plots (Vidovic and Martill, Reference Vidovic and Martill2014, figs. 9, 10) differed markedly from those of other Solnhofen pterodactyloids such that the morphotype probably is an unnatural assemblage, and (3) no evidence was presented to suggest that the differences do not merely reflect preservational (e.g., orientation, compression) or individual variation. In the end, despite arguing that the specimens differed, they did not present evidence or arguments that the differences are taxonomically significant, and therefore Aerodactylus scolopaciceps is considered a junior synonym of Pterodactylus antiquus.

The sample of P. antiquus consists of two distinct year-classes plus a few larger individuals that might represent more year-classes (Fig. 7.2). The first year-class consists of six hatchlings and young-of-the-year with wingspans of 17–23 cm, the second year-class consists of 20 yearlings with wingspans of 33–54 cm, and there are two larger more mature specimens with wingspans of 64 and 71 cm, respectively. Note that the largest known specimen of P. antiquus is a large isolated skull of an adult with a wingspan of 1.06 m (Bennett, Reference Bennett2013a) from the Hienheim Beds that are stratigraphically equivalent to the Mörnsheimer Limestone.

The sample of Ctenochasma elegans (Wagner, Reference Wagner1861) consists of 19 specimens based on the 15 listed in Bennett’s (Reference Bennett2007a) revision plus the four specimens that Wellnhofer (Reference Wellnhofer1970) had referred to Pterodactylus micronyx Meyer, Reference Meyer1856 (his Ex. 29 at Neuberg, Ex. 33 at Brno, Ex. 34 [TM 13104], and Ex. 37 [SM 405/NHMW 2012/0118/0001]), which Bennett (Reference Bennett2013a) referred to Ctenochasma on the basis of skeletal proportions. The sample consists of two distinct year-classes plus a few larger individuals that might represent more year-classes (Fig. 7.3). All specimens of >125 mm skull length and >83 cm wingspan consist of isolated skulls. The first year-class consists of 12 hatchlings and young-of-the-year with wingspans of 23–36 cm, the second year-class consists of four yearlings with wingspans of 75–97 cm, there are two larger more mature specimens with wingspans of ~1.3 m, and one large fully mature adult specimen with a wingspan of 1.9 m.

The sample of Aurorazhdarcho micronyx (Meyer, Reference Meyer1856) consists of 12 specimens after the holotype of A. primordius Frey et al., Reference Frey, Meyer and Tischlinger2011 was synonymized with Pterodactylus micronyx and the four specimens mentioned above that were referred to Ctenochasma elegans (Bennett, Reference Bennett2013a) are excluded, but only ten specimens after the two specimens that have different skeletal proportions and may represent a distinct taxon (Bennett, Reference Bennett2013a) are excluded. All of them, except the holotype of Aurorazhdarcho primordius, form what is interpreted as a single year-class of hatchlings and young-of-the-year with wingspans of 23–46 cm (Fig. 7.4). The single large specimen had a wingspan of 1.06 m.

The sample of Germanodactylus cristatus (Wiman, 1925) is too small to reveal the presence or absence of year-classes, but consists of two hatchlings with wingspans of 21 and 22 cm, one subadult, and one adult with a wingspan of 96 cm. Bennett (Reference Bennett2006) noted that the two hatchlings came from a single quarry, Workerszell near Eichstätt, that seems not to have produced any other pterosaur specimens, which suggests that that part of the basin was near the Germanodactylus nesting grounds and provided conditions preferred by the hatchlings, and that juveniles occupied other habitats.

Comparison of the ontogenetic compositions of the samples of Solnhofen pterosaurs reveals three different patterns of abundance. Rhamphorhynchus and Pterodactylus share a pattern with two year-classes, the second more than twice as abundant as the first, and subadults and adults rare to absent. It is surprising that yearlings are more abundant than hatchlings. The abundance of hatchlings suggests that the nesting grounds were close to the Solnhofen lagoons, and the abundance of juveniles indicates that they remained near the lagoons feeding and growing for up to two years. If one assumes that hatchlings and yearlings had equivalent mortality and preservation rates, this could have resulted if hatchlings were present near the lagoons for only part of the depositional season whereas yearlings were present for the entire season. Alternatively, yearlings might have had a higher mortality rate than hatchlings because they were transitioning to a different food source. If the histological transition that occurred in the larger individuals in the medium year-class correlates with the onset of sexual maturity, then Rhamphorhynchus probably would have first bred at two years old. Although specimens of ~1.8 m wingspan are expected to be rare, the relative rarity of specimens between the upper limit of the medium year-class and the largest specimens, which would represent two or more additional year-classes, suggests that sexually mature breeding individuals spent most of their time elsewhere. Comparable histological information is not available for Pterodactylus, but it is possible that Pterodactylus was similar to Rhamphorhynchus in age at first breeding and preferred habitat of adults.

Ctenochasma exhibits a second pattern with a single year-class of hatchlings and young-of-the-year and low numbers of older juveniles through adults. This suggests that Ctenochasma individuals remained near the lagoons feeding on small aquatic prey throughout their life, and is consistent with a high hatchling mortality followed by reduced mortality of juveniles through adults well adapted to their environment.

Aurorazhdarcho exhibits a third pattern with a single year-class of hatchlings and young-of-the-year and a few large adults, whereas yearlings and larger juveniles are absent. This suggests that the nesting grounds were close to the Solnhofen lagoons and that hatchlings spent only their first year near the lagoons, whereas older juveniles and adults left the lagoons and fed elsewhere, perhaps returning to the area only to lay their eggs. This might have been because the dentition of Aurorazhdarcho was suited to feeding on considerably larger prey than Ctenochasma, such that the preferred foods of older juveniles and adults were not available in the Solnhofen lagoons.

Bissekty Formation

The Bissekty Formation consists of ~67 m of medium- to coarse-grained sands with occasional cross-bedding and abundant fossils reflecting a fluvial environment with a very diverse vertebrate fauna, including the pterosaur Azhdarcho lancicollis Nesov, Reference Nesov1984 (Archibald et al., Reference Archibald, Sues, Averianov, King, Ward, Tsaruk, Danilov, Rezvyi, Veretennikov and Khodjaev1998; Averianov, Reference Averianov2010). The sample of Azhdarcho consists of one hatchling, five small juveniles, four large juveniles, two immature subadults, and one mature adult based on a count of proximal humeral fragments (A. Averianov, personal communication, 2015). That pattern of abundance is consistent with progressively decreasing mortality of small juveniles through adults occupying the same riverine habitat. If not attributable to a preservational bias, the relative rarity of hatchlings may suggest that the depositional area of the Bissekty Formation was some distance from the nesting grounds and protected habitats where hatchlings presumably spent their first months.

Lagarcito Formation

The “Loma del Pterodaustro” Lagerstätte within the Lagarcito Formation consists of ~8 m of laminated claystones and massive siltstones with a few sandstone beds deposited in the middle of a large, shallow perennial freshwater lake that supported abundant algae and invertebrates, a somewhat restricted fish fauna, and the pterosaur Pterodaustro guinazi Bonaparte, Reference Bonaparte1970 (Chiappe et al., Reference Chiappe, Rivarola, Cione, Frenegal-Martinez, Sozzi, Buatois, Gallego, Laza, Romero, Lopez-Arbarello, Buscalioni, Marsicano, Adamonis, Ortega, McGehee and Di Iorio1998; Prámparo et al., Reference Prámparo, Ballent, Gallego and Milana2005, Arcucci et al., Reference Arcucci, Prámparo, Codorniú, Giordano, Castillo-Elías, Puebla, Mego, Gómez and Bustos-Escalona2015). The vast majority of Pterodaustro specimens came from ~1 m of laminated claystones and the sample consists of one egg with embryo, an incomplete eggshell, two hatchlings little bigger than the embryo, no small juveniles, two catalogued and many other large juveniles, two immature subadults, and many mature adults (L. Codorniú, personal communication, 2015). The data in Table 2 are based on the arbitrary assumption that ‘many’ equates to 10. The pattern of abundance suggests that large juveniles through adults occupied the same lacustrine habitat, whereas the rarity of small juveniles suggests that they occupied other habitats.

Pterodaustro has been interpreted as feeding while standing in shallow waters, dipping its curving jaws into the water to sieve out small organisms (Wellnhofer, Reference Wellnhofer1991a; Chiappe et al., Reference Chiappe, Rivarola, Cione, Frenegal-Martinez, Sozzi, Buatois, Gallego, Laza, Romero, Lopez-Arbarello, Buscalioni, Marsicano, Adamonis, Ortega, McGehee and Di Iorio1998); however, it does not exhibit any wading adaptations such as elongate limbs. Whereas sieving on the wing is precluded because of the excessive drag the mandible would have produced, it is possible that Pterodaustro fed while floating, duck-like and sieving surface waters where prey might congregate to feed on phytoplankton. If that were the case, they could have fed on a much greater proportion of the lake’s surface area and the lake could have supported much larger populations of Pterodaustro than if they were restricted to shallow waters. In addition, if small juveniles remained in shallow protected waters near shore and large juveniles and adults ventured onto deeper waters, which would explain the absence of small juveniles in the sample.

One reviewer suggested that the large feet of ctenochasmatoids could be interpreted as a wading adaptation, and questioned whether Pterodaustro could have floated in a posture that would have permitted it to sieve given that computational analyses of floating postures have suggested that pterosaurs were nose heavy (Hone and Henderson, Reference Hone and Henderson2013). Those analyses and similar computational analyses of pterosaur body masses (Henderson, Reference Henderson2010), like the apocryphal mathematical proof that bumblebees (Bombus spp.) cannot fly, are based on questionable assumptions, in this case assumptions as to the volume and density of pterosaur body parts. In particular, the floating posture analyses ignored the probability that there were extraskeletal pneumatic spaces within the wings, such as the retrophalangeal wedge in Rhamphorhynchus (Bennett, Reference Bennett2016), which would have significantly increased buoyancy anteriorly and presumably resulted in a stable floating posture. As for feet, if Pterodaustro sieved while floating, then their enlargement could be interpreted as for paddling rather than wading.

The presence of eggs indicates that the area of deposition of the “Loma del Pterodaustro” was close to the nesting grounds of Pterodaustro. Grellet-Tinner et al. (Reference Grellet-Tinner, Thompson, Fiorelli, Argañaraz, Codorniú and Hechenleitner2014) compared Pterodaustro to grebes and flamingoes and suggested that it deposited and brooded its eggs in floating nests; however, there is no evidence of active incubation of eggs in pterosaurs (Unwin and Deeming, Reference Unwin and Deeming2008). The presence of the eggs in sediments deposited in the middle of the lake could be explained by flooding events washing eggs deposited on land into the lake. The presence of eggs and hatchlings in the middle of the lake might seem at variance with the absence of small juveniles in the same sediments, but floods that could have washed eggs into the lake probably would have overwhelmed non- and poorly flying hatchlings as well, but could have been escaped by better-flying small juveniles.

Romualdo Member of the Santana Formation

The Romualdo Member of the Santana Formation consists of shales to sandstones deposited in a large lake or inland sea (Maisey, Reference Maisey1991), and its vertebrate fossils preserved in abundant calcareous concretions represent a diverse fauna of fishes, turtles, crocodilians, and pterosaurs. The concretions seem to have formed in thin horizons (Saraiva et al., Reference Saraiva, Hessel, Guerra and Fara2007), such that the temporal range of the fauna is restricted.

Anhanguerids dominate the Romualdo Member pterosaur fauna, and are oversplit taxonomically because authors have considered minor morphological differences to be taxonomically significant such that many species are represented by single specimens. Authors have often not presented evidence or argumentation to suggest that the differences do not merely reflect ontogenetic or individual variation (but see Pinheiro and Rodrigues, Reference Pinheiro and Rodrigues2017), and I find most characters used to differentiate species of Anhanguera of doubtful significance. In my opinion, there are at least two distinct species of anhanguerid in that the holotypes of Tropeognathus mesembrinus Wellnhofer, Reference Wellnhofer1987 and T. robustus Wellnhofer, Reference Wellnhofer1987 exhibit multiple differences, but I concur with Rodrigues and Kellner (Reference Rodrigues and Kellner2013) in viewing T. robustus as referable to Anhanguera and I find no evidence to view any Anhanguera specimens represented by skull materials as not conspecific.

I assembled a broad sample of 31 anhanguerid specimens, including 21 referred to the most abundant anhanguerid genus, Anhanguera, or synonymous genera described and/or illustrated by Buisonjé (Reference Buisonjé1980), Campos and Kellner (Reference Campos and Kellner1985), Wellnhofer (Reference Wellnhofer1985, Reference Wellnhofer1991b), Kellner and Tomida (Reference Kellner and Tomida2000), and Veldmeijer (Reference Veldmeijer2002), four specimens assigned to Tropeognathus or Coloborhynchus (Wellnhofer, Reference Wellnhofer1987; Veldmeijer, Reference Veldmeijer2003a; Kellner et al., Reference Kellner, Campos, Sayão, Saraiva, Rodrigues, Oliveira, Cruz, Costa, Silva and Ferreira2013), the holotype of Maaradactylus kellneri (Bantim et al., Reference Bantim, Saraiva, Oliveira and Sayão2014), four specimens assigned to Brasileodactylus (Kellner, Reference Kellner1984; Veldmeijer, Reference Veldmeijer2003b; Veldmeijer et al., Reference Veldmeijer, Signore and Meijer2005, Reference Veldmeijer, Meijer and Signore2009), and the holotype of Araripesaurus castilhoi (Price, Reference Price1971). All specimens were evaluated for size and evidence of ontogenetic age using Bennett’s (Reference Bennett1993) size-independent criteria. Sixteen Anhanguera specimens are of a size corresponding to skull lengths of ~50 cm, whereas five specimens are of a size corresponding to skull lengths of ~62 cm. Four Anhanguera specimens exhibit evidence of immaturity, whereas the other 17 seem to be mature adults. All Anhanguera skulls exhibit low rostral crests, which is considered a diagnostic character of Anhanguera. The five specimens assigned to Tropeognathus, Coloborhynchus, and Maaradactylus are mature adults, larger and more robust than is typical of Anhanguera, but most only slightly larger than the largest specimens of Anhanguera, and all have large and tall rostral crests and/or deep symphyseal keels on their mandibles. The four specimens of Brasileodactylus resemble Anhanguera specimens, but lack rostral crests and symphyseal keels, and some are somewhat smaller than Anhanguera specimens. Two Brasileodactylus specimens are isolated incomplete jaws and their ontogenetic age cannot be assessed, but AMNH 24444 (skull length = 43 cm, Veldmeijer, Reference Veldmeijer2003b; thus ~15% smaller than the more abundant smaller specimens of Anhanguera with skull lengths of ~50 cm) and BSP 1991 I 27 (slightly larger than the smallest specimens of Anhanguera) exhibit size-independent indicators of skeletal immaturity. Lastly, the holotype of Araripesaurus castilhoi is an even smaller specimen, ~33% smaller than the more abundant smaller specimens of Anhanguera, consisting of a partial right wing that exhibits unfused carpal elements indicating immaturity, but is otherwise indistinguishable from Anhanguera specimens.

The anhanguerid sample exhibits three size-classes. The large size-class consists of 10 specimens, the Tropeognathus, Coloborhynchus, and Maaradactylus specimens and the five largest Anhanguera specimens, which have skull lengths of ~65 cm or more and, with the exception of NSM-PV 19892, all have large and tall rostral crests and/or deep symphyseal keels on their mandibles. NSM-PV 19892 was referred to Anhanguera because its rostral crest was small and low, but that probably is a result of its immaturity. Presumably, if the specimen had grown to maturity, the crest would have been larger and taller and the skull would have resembled that of specimens assigned to Tropeognathus. The medium size-class consists of the 16 smaller Anhanguera specimens with skull lengths of ~50 cm and low rostral crests. The smaller specimens assigned to Brasileodactylus and the even smaller the holotype of Araripesaurus castilhoi form a third, small size-class. All specimens in the small size-class that can be evaluated for ontogenetic age exhibit evidence of immaturity, whereas the medium and large size-classes consist primarily of mature 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, Coloborhynchus, 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 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., Reference Wang, Kellner, Jiang, Wang, Ma, Paidoula, Cheng, Rodrigues, Meng, Zhang, Ning and Zhonghe2014) and Caiuajara (Manzig et al., Reference Manzig, Kellner, Weinschütz, Fragoso, Vega, Guimarães, Godoy, Liccardo, Ricetti and Moura2014), 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 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 environments. 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. (Reference Andres, Clark and Xing2010, Reference Andres, Clark and Xing2014) suggested that there was a 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 feeding in aquatic environments, and the same may have been true of Rhamphorhynchus with jaws and teeth suited to spearing fishes. But many other pterosaurs had skulls, dentitions, and other features that would not have prevented them from succeeding in terrestrial environments, particularly as juveniles with usually somewhat more generalized morphologies (e.g., Dimorphodon, Scaphognathus, Anhanguera, Pteranodon). Therefore, it is not unreasonable to think that some pterosaurs may have exhibited ontogenetic niches such that they lived in terrestrial and aquatic environments at different times in their lives. There is nothing in the morphology of Sericipterus and Kryptodrakon (Andres et al., Reference Andres, Clark and Xing2010, Reference Andres, Clark and Xing2014) to distinguish them from pterosaurs found in aquatic environments; indeed, the dentition of Sericipterus has long slender teeth like those of its relatives Scaphognathus and Rhamphorhynchus found in aquatic environments. Thus, there is insufficient evidence to conclude that there was a dichotomy between terrestrial and aquatic pterosaurs.