The Tlayúa Formation is an

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

Konservat-Lagerstätte near Tepexi de Rodríguez,

Puebla Puebla, officially the Free and Sovereign State of Puebla, is one of the 31 states that, along with Mexico City, comprise the Federal Entities of Mexico. It is divided into 217 municipalities and its capital is Puebla City. Part of east-centr ...

, Central Mexico. It consists of three members (Lower, Middle and Upper), spanning the lower

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

of the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

to the lower

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

of the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

. 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 A Fossil-Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that preserves an exceptionally high amount of palaeontological information. ''Konzentrat-Lagerstätten'' preserv ...

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

, Central Mexico, near Tepexi de Rodríguez, and consists of a series of

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

quarries A quarry is a type of open-pit mine in which dimension stone, rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some jurisdictions to manage their safet ...

that has seen commercial use for decades.

Stratigraphy

The Tlayúa Formation consists of two

stratigraphic units A stratigraphic unit is a volume of Rock (geology), rock of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable petrography, petrographic, lithology, lithologic or paleontology, ...

(Tlayúa and Barranca Abuelo) and three

members Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...

. The Lower Member is lower

in age. It consists of bioturbated limestones, and is characterised by the presence of the non-

rudist Rudists are a group of extinct box-, tube- or ring-shaped marine heterodont bivalves belonging to the order Hippuritida that arose during the Late Jurassic and became so diverse during the Cretaceous that they were major reef-building organis ...

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

'' 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

strata, though it has since been determined to be Upper Albian. The Middle Member consists of fine-grained

lithographic Lithography () is a planographic method of printing originally based on the immiscibility of oil and water. The printing is from a stone (lithographic limestone) or a metal plate with a smooth surface. It was invented in 1796 by the German ...

limestones, interspersed with hematitic layers that preserve its vertebrate fauna. The Upper Member is

in age, and consists of a sequence of dolomites. It is characterised by the presence of the miliolid

foraminiferan Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of Rhizarian protists characterized by streaming granular ectoplasm for catching food and other uses; and commonl ...

'' 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 Crocodilia () is an Order (biology), order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorp ...

and

turtle Turtles are reptiles of the order (biology), order Testudines, characterized by a special turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Crypt ...

fossils. The Lower Member of the Tlayúa Formation represents a

carbonate A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...

environment which apparently had stressed biodiversity. The depositional environment of the Middle Member was likely

arid Aridity is the condition of geographical regions which make up approximately 43% of total global available land area, characterized by low annual precipitation, increased temperatures, and limited water availability.Perez-Aguilar, L. Y., Plata ...

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 Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

and

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

s. For this reason, it is considered a Konservat-Lagerstätte. About 70% of the

macrofossil Macrofossils, also known as megafossils, are the preserved remnants of organic beings and their activities that are large enough to be visible without a microscope. The term ''macrofossil'' stands in opposition to the term microfossil. Microfoss ...

s are

osteichthyan Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

fish. Other vertebrates include chelonians,

pterosaur Pterosaurs are an extinct clade of flying reptiles in the order Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 million to 66 million years ago). Pterosaurs are the earli ...

lepidosaurs The Lepidosauria (, from Greek meaning ''scaled lizards'') is a Order (biology), superorder or Class (biology), subclass of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata also includes Lizard, lizards and Snake, snakes. Sq ...

, and

crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large, semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term "crocodile" is sometimes used more loosely to include ...

Cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...

foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

gymnosperm The gymnosperms ( ; ) are a group of woody, perennial Seed plant, seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, conifers, cycads, Ginkgo, and gnetoph ...

sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...

cnidarians Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...

annelid The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to vario ...

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

bivalves Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...

arachnid Arachnids are arthropods in the Class (biology), class Arachnida () of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, opiliones, harvestmen, Solifugae, camel spiders, Amblypygi, wh ...

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

isopods Isopoda is an Order (biology), order of crustaceans. Members of this group are called isopods and include both Aquatic animal, aquatic species and Terrestrial animal, terrestrial species such as woodlice. All have rigid, segmented exoskeletons ...

, anomurans, brachyurans,

crinoid Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that remain attached to the sea floor by a stalk in their adult form are commonly called sea lilies, while the unstalked forms, called feather stars or comatulids, are ...

echinoid Sea urchins or urchins () are echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal zone to deep seas of . They typically have a globular body covered by a spiny p ...

s, 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

have been discovered from the formation. Though tentatively assigned to ''Pteranodon'' sp. and ''Nyctosaurus'' sp. in 2008, they likely represent either an early

azhdarchoid Azhdarchoidea (International Phonetic Alphabet, , meaning "azhdarchid-like forms") is a group of pterosaurs within the suborder Pterodactyloidea. Pterosaurs belonging to this group lived throughout the Early Cretaceous, Early and Late Cretaceous ...

or an indeterminate ornithocheiromorph.

Lepidosaurs

Fish

Mainly after González-Rodríguez (2016) and Applegate ''et al.'' (2006) * '' Araripichthys weberi'' * '' 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 aranguthyorum'' * '' 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 Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a Basal (phylogenetics) , basal clade and a sister taxon of the Eumetazoa , diploblasts. They are sessility (motility) , sessile ...

Anthozoa Anthozoa is one of the three subphyla of Cnidaria, along with Medusozoa and Endocnidozoa. It includes Sessility (motility), sessile marine invertebrates and invertebrates of brackish water, such as sea anemones, Scleractinia, stony corals, soft c ...

Annelida The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to variou ...

Plants

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

Phaeophyceae Brown algae (: alga) are a large group of multicellular algae comprising the class Phaeophyceae. They include many seaweeds located in colder waters of the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and polar regio ...