Pterosaur Eggs

Speculation about how pterosaurs reproduced has been enhanced over the years by lack of evidence. Many scientists believed that pterosaurs must have laid eggs, but were they hard shelled as in birds, or leathery as in reptiles. To some, the thought of how a long bony wing would work in an egg was a problem to imagine. Bats give birth to live young without the need for eggs, so perhaps pterosaurs could also give birth to, live young.

Speculation became analysis when, in 2004, a pterosaur egg fossil was found in China.


Avodectes pseudembryon (Wang and Zhou 2004), IVPP-v13758, was discovered in the Jehol Biota, being about 121 million years old. It was a complete embryo in a shell. The wings were coiled as they developed (sketch above) and the preservation indicates clearly that the bones were well ossified before hatching. This would enable the newly hatched pterosaurs to use the wings very quickly after emerging from the egg.

Observations of the porosity of the egg shell suggested possible burial during development and the form of the shell was soft and leathery like a reptilian egg, having a shell that was non-laminar and 0.25mm thick. The embryo wingspan was estimated to be 27cm. The bone proportions are unlike any known pterosaur, but show similarities with Anhanguera and Istiodactylus specimens. This should not be taken as an indication of species, since the bone development and proportions may have been subject to changes during juvenile life.

A second egg, JZMP-03-03-2, was somewhat similar, but the skeletal bones were not articulated in the same clear way, so interpretation is a little more complex.
In the same year, a pterosaur egg, MHIN-UNSL-GEO-v246, was discovered in the Lagarcito Formation in Argentina. This formation is well known for the Pterodaustro fossils and this egg was clearly a Pterodaustro egg. The embryo was intact and articulated.
The egg was also from the Lower Cretaceous deposits about 100 million years ago, and the proportions of the embryo closely matched those of known juvenile specimens. Measurements of the shell indicated a very thin (30μm) leathery shell which was long and oval in shape measuring 22mm by 66mm. The estimated embryo wingspan was 27cm. This egg has many differences from the Chinese finds, but it does support the idea that all pterosaurs probably laid eggs.
The questions that are difficult to resolve are;

1. How many eggs did pterosaurs lay?
2. Did pterosaurs care for their young?
3. Where did pterosaurs nest and what nesting structures did they create?

I suspect that the answers to these types of questions will be different for each type of pterosaur. These creatures would have been subject to the same variations and constraints in their habitats as modern animals are subject to today.

Wang, X., and Zhou, Z., 2004, Pterosaur embryo from the Early Cretaceous: Nature, vol.429, p.621.

Chiappe, L. M., Codorniu, L., Grellet-Tinner, G., and Rivarola, D., 2004, Argentinian unhatched pterosaur fossil: Nature, vol.432, p. 571-572. (2 Dec 2004) 

Pterosaur Database Topics - eggs
 

A very Peculiar Pterosaur

Pterodaustro is represented by a number of specimens from Argentina. There is a complete skeleton, a partial juvenile and an egg, just to mention a few. This unusual pterosaur is quite well represented in the fossil record, certainly enough is known to make a convincing reconstruction.
Most unusually, this was a filter feeder with a fine sieve of unusually adapted teeth that would have been ideal for filter feeding on small aquatic living organisms. This was the Flamingo of the ancient world!
The diagram of the skull shows the peculiar nature of this animals jaw. This pterosaur has more teeth than any other pterosaur. It is likely that it has more teeth than any other Dinosauromorph. It is also the first pterosaur where gizzard stones have been observed to be present.

The holotype, which was originally described by Bonaparte, is PLV 2571 and is a right humerus in the Institute Miguel Lillo, Universitat Nacional Tucuman, Argentina. Most of the specimens come from South America which is probably where the species evolved within a specific shallow water habitat, where zooplankton and phytoplankton were abundant.

In 2004 un-hatched egg containing a juvenile Pterodaustro, from the Lagarcito Formation in Central Argentina was described. The lacustrine deposits in which it was found are called the Loma del Pterodaustro and they are dated to about 100 million years ago. The specimen MHIN-UNSL-GEO-V 246 has been studied using electron micrographs of the egg shell suggesting a leathery shell. Ghosting of proteins can be interpreted within the shell structure which has yealded a significant amount of information about this pterosaurs eggs.

Bonaparte J F, 1970 Pterodaustro guinazui gen.et sp.nov.. Pterosaurio de la formacion Lagarcito, Provincia de San Luis, Argentina, Acta Geologica Lilloana, 10(10):207-226

Bonaparte J F, 1971 Descripcion del craneo y mandibulas de Pterodaustro guinazi (Pterodactyloidea - Pterodaustriidae), de la Formacion Lagarcito, San Luis, Argentina, Publ. Mus. Mun. Cienc. Nat. Mar del Plata, Pp. 63-272

Bonaparte J F & Sanches T M, 1975 Restos de um Pterosaurio,Puntanipterus globosus de foracion la Cruz, provincia de San Luis, Argentina, Actas Primeiro Cong. A

L. M. ChiappeA. Chinsamy, 1996, Pterodaustro's true teeth, Nature 379, 211 - 212 (18 January 1996)rgentino Paleont. Biostretigr., 2:105-113

Frey E., Martill D. M., Chong-Diaz G. and Bell M., 1997, New pterosaurs from the Lower Cretaceous of Chile. J. Vert. Paleont. 17 (3)

Codorniú L, Chiappe L.M. Early juvenile pterosaurs (Pterodactyloidea: Pterodaustro guinazui) from the Lower Cretaceous of central Argentina. Can. J. Earth Sci. 2004;41:9–18

Chiappe L.M., Codorniú L., Grellet-Tinner G. and Rivarola D., 2004, Palaeobiology: Argentinian unhatched pterosaur fossil, Nature. 432, pp. 571-572 (2 Dec 2004)

A Chinsamy, L Codorniú, and L Chiappe, 2008, Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guiñazui, The Royal Society, Biol Lett. 2008 June 23; 4(3): 282–285