The Tlayúa Formation is an Cretaceous Konservat-Lagerstätte near Tepexi de Rodríguez, Puebla, Central Mexico. It consists of three members (Lower, Middle and Upper), spanning the lower Albian of the Early Cretaceous to the lower Cenomanian of the Late Cretaceous. It consists of a series of limestone quarries that preserve lagoonal palaeoenvironments, such as a shelf lagoon, a shallow lagoon surrounded by a peneplain, and a tidal flat. It is notable for preserving high quantities of vertebrate and invertebrate fossils, and is thus considered a Lagerstätte.
Description The Tlayúa Formation was first described by Jerjes Pantoja-Alor in 1992. It is located in the Tlayúa ravine, which itself lies in the southern portion of Puebla, Central Mexico, near Tepexi de Rodríguez, and consists of a series of limestone quarries that has seen commercial use for decades.
Stratigraphy The Tlayúa Formation consists of two stratigraphic units (Tlayúa and Barranca Abuelo) and three members. The Lower Member is lower Albian in age. It consists of bioturbated limestones, and is characterised by the presence of the non-rudist bivalve Chondrodonta and the rudist bivalve Toucasia polygyra. The Middle Member, corresponding to the Tlayúa Quarry, is the most fossiliferous. Its age has been difficult to ascertain, as the foraminiferan Spiroloculina cretacea is known exclusively from lower Cenomanian strata, though it has since been determined to be Upper Albian. The Middle Member consists of fine-grained lithographic limestones, interspersed with hematitic layers that preserve its vertebrate fauna. The Upper Member is Cenomanian in age, and consists of a sequence of dolomites. It is characterised by the presence of the miliolid foraminiferan Dicyclina schlumbergi.
Depositional environments The depositional environment of the Tlayúa Formation was likely a shallow, coastal lagoon, with some freshwater influence, as indicated by the presence of crocodilian and turtle fossils. The Lower Member of the Tlayúa Formation represents a carbonate environment which apparently had stressed biodiversity. The depositional environment of the Middle Member was likely arid for much of the year, with the exception of seasonal rains and storms. The Upper Member likely represents a tidal flat. The Tlayúa Formation may have been part of an island, though a connection to the North American mainland cannot be discounted.
Paleobiota The formation contains a diverse array of vertebrate and invertebrate fossils. For this reason, it is considered a Konservat-Lagerstätte. About 70% of the macrofossils are osteichthyan fish. Other vertebrates include chelonians, pterosaurs, lepidosaurs, and crocodiles. Cyanobacteria, foraminifera, algae, gymnosperms, sponges, cnidarians, annelids, gastropods, ammonites, bivalves, arachnids, insects, isopods, anomurans, brachyurans, crinoids, echinoids, holothuroids, stelleroids, and ophiuroids, have also been recovered from the Tlayúa Formation.
Archelosaurs
The remains of several indeterminate archelosaur taxa have been recovered from the Tlayúa Formation. Indeterminate crocodilians and turtles have been identified. Partial, articulated wings of an unidentified pterosaur have been discovered from the formation. Though tentatively assigned to Pteranodon sp. and Nyctosaurus sp. in 2008, they likely represent either an early azhdarchoid or an indeterminate ornithocheiromorph.
Lepidosaurs
Fish Mainly after González-Rodríguez (2016) and Applegate et al. (2006)
Arthropods
Echinoderms
Mollusks
Other invertebrates
Plants
References
Further reading L. Martin-Medrano and P. Garcia-Barrera. 2006. Fossil Ophiuroids of Mexico. In F. J. Vega, T. G. Nybor, M. D. C. Perrillat, M. Montellano-Ballesteros, S. R. S. Cevallos-Ferriz, S. A. Quiroz-Barroso (eds.), Topics in Geobiology 24:115-131
