Darwinopterus

The large amount of variation among Darwinopterus specimens has been interpreted as sexual dimorphism. The first Darwinopterus specimen in which sex could be confidently identified was specimen ZMNH M8802 in the collections of the Zhejiang Museum of Natural History, nicknamed "Mrs T" (short for "Mrs Pterodactyl"), described by Lü Junchang and colleagues in January 2011. This specimen was preserved with the impression of an egg between its thighs in close association with its pelvis. This specimen had a broad pelvis and lacked any evidence of a crest. The egg was probably expelled from the body during decomposition, and its association with the Darwinopterus individual was used to support the hypothesis of sexual dimorphism.[2]

However, this hypothesis has been criticized. Pterosaur researcher Kevin Padian questioned some of the conclusions drawn by Lü et al., suggesting in a 2011 interview that, in other animals with elaborate display crests (such as ceratopsian dinosaurs), the size and shape of the crests change dramatically with age. He noted that the "Mrs T" specimen may simply have been a sub-adult which had not yet developed a crest (most animals are able to reproduce before they are fully grown).[2] In 2015, Wang e.a. reassigned the "Mrs T" specimen to Kunpengopterus.[8] Furthermore, a rigorous analysis of wukongopterid variation published in 2017 noted that crests among wukongopterids were subject to a large amount of individual variation, and that there was no consistent dimorphism in the pelvic anatomy of crested and uncrested wukongopterid specimens.[9]

The specimen preserved along with an egg (nicknamed "Mrs T"), described by Lü and colleagues in 2011, offers insight into the reproductive strategies of Darwinopterus and pterosaurs in general.[10] Like the eggs of later pterosaurs and modern reptiles,[11] the eggs of Darwinopterus had a parchment-like, soft shell.[2] In modern birds, the eggshell is hardened with calcium, completely shielding the embryo from the outside environment. Soft-shelled eggs are permeable, and allow significant amounts of water to be absorbed into the egg during development. Eggs of this type are more vulnerable to the elements and are typically buried in soil. The eggs of Darwinopterus would have weighed about 6 grams (0.21 oz) when they were laid, but due to moisture intake, they may have doubled in weight by the time of hatching.[2] The eggs were small compared to the size of the mother (the "Mrs T" specimen weighed between 110 grams [3.9 oz] and 220 grams [7.8 oz][2]), also more like modern reptiles than birds. David Unwin, a co-author of the paper, suggested that Darwinopterus probably laid many small eggs at a time and buried them, and that juveniles could fly upon hatching, requiring little to no parental care.[2] These results imply that reproduction in pterosaurs was more like that in modern reptiles and significantly differed from reproduction in birds.[10] However, in 2015, the counterplate of the specimen was reported, IVPP V18403, which showed a single additional egg present in the body, indicating that there were two active ovaries, producing a single egg at a time.[8]

Darwinopterus, like most wukongopterids, is a terrestrial pterosaur lacking speciations for piscivory; ergo, it was early on recognised to have been a terrestrial form. Originally, it was described as a raptorial hawking carnivore;[1] however, posterior analyses have found no speciations towards aerial predation. Instead, it appears to have been a saltatorial insectivore, hopping around both in the trees and on the ground, akin to some modern songbirds.[12] D. robustidens in particular might have preferred hard-shelled beetles.[7]