Pterodaustro guinazui (Bonaparte 1969, 1970) MHIN-UNSL-GEO-V 246 (MIC V246), Albian, Late Cretaceous, ~105 mya, ~5cm tall, ~5 cm skull length, was derived from a sister to Ctenochasma gracile and was the last and most derived in the ctenochasmatid lineage. This is the embryo of the adult Pterodaustro.

A growth series is known in Pterodaustro. We know of Pterodaustro embryo (Chiappe et al. 2004, see below), hatchlings (Codorniú and Chiappe 2004), juveniles, sexually mature specimens and larger, older adults Chinsamy, Codorniú and Chiappe 2008. These contradict earlier traditions (Wellnhofer 1970, Bennett 1993a, b, 1995, 1996a, 2001a,b, 2006, 2007, Wang and Zhou 2004) that pterosaurs matured allometrically, like birds, crocs and mammals. Rather they matured isometrically like Huehuecuetzpalli (Reynoso 1998). Other examples of pterosaur embryos include the IVPP specimen and the JZMP specimen. Note that the Pterodaustro embryo has adult proportions in the skull and elsewhere. The jaws were more curved, the teeth were shorter, the sternal complex was larger, the tail was much shorter, the humerus was larger, the pelvis and prepubis were smaller, toe five was longer and the wing was slightly shorter. These characters would otherwise be considered traits to distinguish a species.

See more ctenochasmatids here. The dorygnathid tree is here. The pterosaur family tree is here.

The second embryo (MIC-V778, Grellet-Tinner et al. 2014, right) compared to the MIC-V246 original from Chiappe et al. 2004 (left). The 2014 embryo is slightly larger with more robust wing finger phalanges. Evidently it was closer to hatching and more ready to fly.

Pterodaustro is known from a complete growth series, from embryo to large adult. Note the long rostrum and small eyes in the embryo and hatchlings.

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Bennett SC 1993b. Year classes of pterosaurs from the Solnhofen limestone of southern Germany. Journal of Vertebrate Paleontology. 13, 26A.

Bennett SC 1995. A statistical study of Rhamphorhynchus from the Solnhofen limestone of Germany: year classes of a single large species. Journal of Paleontology 69, 569–580.

Bennett SC 1996a. Year-classes of pterosaurs from the Solnhofen limestones of Germany: taxonomic and systematic implications. Journal of Vertebrate Paleontology 16:432–444.

Bennett, SC 1996b. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoological Journal of the Linnean Society 118:261–309.

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Bennett SC 2006. Juvenile specimens of the pterosaur Germanodactylus cristatus, with a review of the genus. Journal of Vertebrate Paleontology 26:872–878.

Bennett SC 2007. A review of the pterosaur Ctenochasma: taxonomy and ontogeny. Neues Jahrbuch fur Geologie und Paläontologie, Abhandlungen 245:23–31.

Bonaparte J F 1970. Pterodaustro guinazui gen. et sp. nov. Pterosaurio de la Formacion Lagarcito, Provincia de San Luis, Argentina y su significado en la geologia regional (Pterodactylidae)", Acta Geologica Lilloana, 10: 209-225.

Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.

Chiappe LM, Codorniú L, Grellet-Tinner G and Rivarola D. 2004. Argentinian unhatched pterosaur fossil. Nature, 432: 571.

Codorniú L and Chiappe LM 2004. Early juvenile pterosaurs (Pterodactyloidea: Pterodaustro guinazui) from the Lower Cretaceous of central Argentina. Canadian Journal of Earth Science 41, 9–18. (doi:10.1139/e03-080)

Deeming C and Unwin DM 2007. Eggshell structure and its implications for pterosaur reproductive biology and physiology. Flugsaurier, the Wellnhofer pterosaur meeting, Munich, 12.

Grellet-Tinner G, Wroe S, Thompson SB and Ji Q 2007. A note on pterosaur nesting behavior. Historical Biology 19:273–277.

Grellet-Tinner G, Thompson c MB, Fiorelli LE, Argañaraz E, Codorniú L, Hechenleitner EM 2014. The first pterosaur 3-D egg: Implications for Pterodaustro guinazui nesting strategies, an Albian filter feeder pterosaur from central Argentina. Geoscience Frontiers 5 (2014) 759e765

Ji Q, Ji S-A, Cheng Y-N, You HL, Lü J-C, Liu Y-Q and Yuan CX 2004. Pterosaur egg with leathery shell. Nature 432:572.

Reynoso V-H 1998. Huehuecuetzpalli mixtecus gen. et sp. nov: a basal squamate (Reptilia) from the Early Cretaceous of Tepexi de Rodríguez, Central México. Philosophical Transactions of the Royal Society, London B 353:477-500.

Wang X-L and Zhou Z 2004. Palaeontology: pterosaur embryo from the Early Cretaceous. Nature 429: 623.

Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.

wiki/Pterodaustro