# Tlayúa Formation

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 penneplain, 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

| Genus | Species | Material | Notes |
| Huehuecuetzpalli | H. mixtecus | Near-complete specimens of an adult and a juvenile | A primitive lizard |
| Pamizinsaurus | P. tlayuaensis | A single, crushed skull of a juvenile | An osteoderm-covered sphenodontian |
| Ankylosphenodon | A. pachyostosus | Front half of a partial skeleton | An aquatic sphenodontian |
| Tepexisaurus | T. tepexii | Near-complete skeleton, minus the tail | A basal scincomorph |

### Fish

Mainly after González-Rodríguez (2016) and Applegate et al. (2006)
* Araripichthys webri
* Armigatus carrenoae
* Armigatus felixi
* Axelrodichthys cf. araripensis
* Cipactlichthys scutatus
* Epaelops martinezi
* Macrosemiocotzus americanus
* Michin csernai
* Notagogus novomundi
* Nusaviichthys nerivelai
* Pachyamia mexicana
* Paraclupea seilacheri
* Quetzalichthys perrilliatae
* Ranulfoichthys dorsonudum
* Tahnaichthys magnuserrata
* Teoichthys brevipina
* Teoichthys kallistos
* Tepexichthys aranguthyrom
* Tlalocbatos applegatei
* Tlayuamichin itztli
* Unamichthys espinosai
* Ellimmichthys sp.
* cf. Amblysemius
* cf. Bananogmius
* Belonostomus sp.
* cf. Brannerion
* Lepidotes sp.
* cf. Lycoptera
* cf. Megalops
* Neoproscinetes sp.
* Notelops sp.
* cf. Paraelops
* cf. Rhacolepis
* Vinctifer sp.
* cf. Yabrudichthys
* Gonorhynchiform indet.

### Arthropods

* Archaeoniscus aranguthyorum
* Atocatle ranulfoi
* Ixtahua benjamini
* Protaegla miniscula
* Tepexicarcinus tlayuaensis
* Sphaeromatidae sp.
* Ostracoda?

### Mollusks

* Inoceramus sp.
* Pectinidae indet.
* Osteridae indet.
* Gastropoda indet.
* Neohibolites minimus obtusus
* Neohibolites minimus pinguis
* Neohibolites minimus claviformis
* Neohibolites praeultimus
* Mesohibolites semicanaliculatus
* Martoniceras sp.
* Hysteroceras sp.
* Anisoceras sp.

### Echinoderms

* Ophiactis applegatei
* Paleopentacta alencasterae
* Parapsolus tlayuensis
* Astropecten sp.
* Echinaster sp.
* Ophidiaster sp.
* Plutonaster sp.
* Tamaria sp.
* Crinoidea indet.

### Other invertebrates

* Porifera
* Anthozoa
* Annelida

### Plants

* cf. Araucaria sp.
* cf. Frenolopsis
* Brachyphyllum sp.
* Podozamites sp.
* Zamites sp.
* Phaeophyceae