[N] 2012 Dinosaur embryobones discovered in Paimogo, Lourinhã
Among the more than one dozen dinosaur egg- and eggshell-bearing localities in the Upper Jurassic Lourinhã Formation of Portugal (upper Kimmeridgian–Tithonian), the nest from Paimogo was the first to be found and remains the largest and most significant. Located within the Amoreira-Porto Novo Member (uppermost Kimmeridgian), this nest has yielded about 300 embryonic bones and bone fragments identified as belonging to a theropod dinosaur.
The Paimogo nest comprised about 100 eggs (or eggshell concentrations that represented individual eggs), but much of the nest had been eroded, indicating that an even greater number of eggs would have been present originally. There is no clear nest structure, but eggs are more highly concentrated in the center, along with the majority of embryonic bones (suggesting a more advanced ontogenetic stage). All the eggs were crushed, but despite this compression, some eggs are complete and retain embryonic bones inside.
The embryonic anatomy is has been favorable compared to the holotype of Lourinhanosaurus antunesi Mateus 1998 from the same stratum and region. However, most Lourinhanosaurus autapomorphies are in the pelvis and vertebral laminae, rarely preserved in the embryos, making their positive identification more difficult. A single autapomorphy is present in both subadult and embryo: a medial condyle of the tibia that is half the transverse width of the fibular condyle. Other contemporary theropods differ from the embryos in specific details: the embryonic maxilla lacks an antorbital fenestra (present in Allosaurus), the ilium lacks a vertical ridge (present in Aviatyrannis), and the tibial cnemial crest is short (unlike Ceratosaurus). One other nest with embryo from Lourinhã area, in Porto das Barcas has been provisionally ascribed to Torvosaurus. This embryos specimen are much larger in size, and the eggshell structure is entirely different. If such ascription of Porto das Barcas embryos is correct, then Paimogo embryos cannot be Torvosaurus.
In general, the embryos are morphological miniatures of the adults, fully equipped for predation of small prey, and thus may have been precocial (i.e. relatively mature and mobile from the moment of birth or hatching). The teeth have large denticles on the distal carina only and bear some resemblance to those of more derived theropods, suggesting a role for pedomorphosis in theropod evolution.
Mateus, O., Carrano, M.T., Taquet P. (2012). Osteology of the embryonic theropods from the Late Jurassic of Paimogo, Portugal. Journal of Vertebrate Paleontology, Program and Abstracts, 2012, p.137. ISSN 1937-2809. 137.