Suchoolithus


Suchoolithus is an oogenus of crocodylomorph eggs from the late Jurassic of Portugal. They are notable for their small size, and for being among the oldest known crocodylomorph eggs.

Description

Suchoolithus is known from a single, well-preserved egg clutch of 13 eggs. The eggs have a blunt, ellipsoid shape, and are quite small. All but two of the eggs are arranged horizontally in the clutch. The eggshell is only 163 μm thick, and is sculpted with tiny, irregular bumps on its outer surface. Like other crocodylian eggs, its shell is composed of thousands of tiny calcium carbonate crystal units; in S. portucalensis, these eggshell units are trapezoidal, tightly packed, and wider than they are tall. Russo et al. 2017 did not observe any pores openings on the eggshell's surface, though a possible pore canal was observed in one section of the shell.

History

Fossil crocodylian eggs are generally rare, though they have been discovered worldwide. In 2008, the Portuguese paleontologist Octávio Mateus discovered a fossilized egg clutch at the Lourinhã Formation of Portugal that would later become holotype of Suchoolithus. These eggs were first described in 2014 by Russo, Mateus, Balbino, and Marzola, who at the time tentatively referred them to Krokolithes, but noted their similarities to the Krokolithid Bauruoolithus. In 2016, João Russo, working with Octávio Mateus as his supervisor and Balbino as co-supervisor, completed his Master's Thesis at Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa, in which he named the oogenus and oospecies Suchoolithus portucalensis. The next year, Russo, Mateus, Marzola, and Balbino published the description of Suchoolithus in PLOS One.

Paleobiology and paleoecology

Suchoolithus is known exclusively from the upper Tithonian of the Late Jurassic Lourinhã Formation of Portugal, making it the oldest known crocodylomorph egg. This formation, representing the deposits of river deltas and alluvial fans, has similar fauna and flora to the contemporaneous Morrison Formation in the United States and the Tendaguru Formation in Tanzania. Several types of crocodylomorphs are known from the late Jurassic of Portugal, but given the small size of the eggs, it is most likely that Suchoolithus were laid by one of the smaller species, such as Bernissartia, cf. Alligatorium, Lisboasaurus, Lusitanisuchus, or Theriosuchus.