Bennett—Smallest Pteranodon
adults ventured onto deeper waters, which would explain the absence of small juveniles in the sample. One reviewer suggested that the large feet of ctenochasma-
toids 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, 2013). Those analyses and similar computational analyses of pterosaur body masses (Henderson, 2010), like the apocryphal mathe- matical 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, 2016), whichwould 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. (2014) 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, 2008). 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 sand- stones deposited in a large lake or inland sea (Maisey, 1991), and its vertebrate fossils preserved in abundant calcareous concretions represent a diverse fauna of fishes, turtles, croco- dilians, and pterosaurs. The concretions seem to have formed in thin horizons (Saraiva et al., 2007), 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 taxonomi- cally 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, 2017), and I find most characters used to differ- entiate 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, 1987 and T. robustus Wellnhofer, 1987 exhibit multiple differences, but I concur with Rodrigues and Kellner (2013) 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.
267 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 (1980), Campos and Kellner (1985), Wellnhofer (1985, 1991b), Kellner and Tomida (2000), and Veldmeijer (2002), four specimens assigned to Tropeognathus or Coloborhynchus (Wellnhofer, 1987; Veldmeijer, 2003a; Kellner et al., 2013), the holotype of Maaradactylus kellneri (Bantim et al., 2014), four specimens assigned to Brasileo- dactylus (Kellner, 1984; Veldmeijer, 2003b; Veldmeijer et al., 2005, 2009), and the holotype of Araripesaurus castilhoi (Price, 1971). All specimens were evaluated for size and evidence of ontogenetic age using Bennett’s (1993) size-independent criteria. Sixteen Anhanguera specimens are of a size corre- sponding 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, 2003b; 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 speci- men, ~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 ~65cm 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 ~50cm 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
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