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 Genus Species Material Notes Images 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. tepexiiNear-complete skeleton, minus the tail A basal scincomorph
Fish Mainly after González-Rodríguez (2016) and Applegate et al. (2006)
FishGenusSpeciesHigher taxonNotesImagesAmblysemius?cf. A. spCaturidaeOnly non-amiid amiiform from TlayúaAraripichthysA. weberiTeleosteiPossibly related to Late Cretaceous genera from North America?ArmigatusA. felixi, A. carrhenoaeEllimmichthyiformesFirst records of Armigatus from America, alongside the oldest species in the genus, the two species from Tlayúa also seem to clade closest to each otherAspidorhynchidae spp.InapplicableTeleosteiUndescribed species of Vinctifer and Belonostomus have been recordedAxelrodichthysA. cf. A. araripensisMawsoniidaeOnly known specimen was lost before descriptionBananogmius?cf. B. spTselfatiiformesOne of the few Mexican members of the clade other than TselfatiaCipactlichthysC. scutatusHalecomorphiBears large plate-like scutes along its midlineEllimmichthysE. spEllimmichthyiformesType genus of its orderElopomorpha spp.UnapplicableTeleosteiPossible species of Brannerion, Paraelops and Megalops are knownEpaelopsE. martineziElopiformesRelated to the Jurassic AnaethalionGonorynchiformes indet.UnapplicableOstariophysiOne specimen reported in the 1990s, but has not been studied sinceLycoptera?cf. L. spLycopteridaeOnly osteoglossiform fossil from Cretaceous MexicoMacrosemiocotzusM. americanusMacrosemiidaeSimilar to Macrosemius, but differs in a divided dorsal finMichinM. csernaiPachyrhizodontidaeLikely the most basal pachyrhizodontidNeoproscinetesN. spPycnodontidaeRelated to ProscinetesNotagogusN. novomundiMacrosemiidaeClosest to Notagogus helenaeNusaviichthysN. nerivelai, N. antigonaePachyrhizodontoideiFormerly misidentified as Notelops fossilsPachyamiaP. mexicanaVidalamiinaeAlso known from the Middle EastParaclupeaP. seilacheriEllimmichthyiformesFirst fossil of the genus outside of ChinaRanulfoichthysR. dorsonudusClupeomorphaSomewhat resembles Ellimmichthyiformes, but lacks their dorsal scutes, therefore it is likely a basal clupeomorphQuetzalichthysQ. perilliataeIonoscopiformes (Halecomorphi)Likely closest to OshuniaTahnaichthysT. magnuserrataPycnodontidaeBears two humps in front of its dorsal fin, a novel trait in pycnodontsTeoichthysT. kallistos, T. brevipinaOphiopsidae (Halecomorphi)Name of the type species (Teoichthys kallistos) translates to "God's most beautiful fish", in reference to the exquisite preservationTepexichthysT. aranguthyorumPycnodontidaeLikely fed on coral, as shown by gut contents and the large amount of wear on its teethTlalocbatosT. applegateiRhinopristiformesOnly chondrichthyan known from TlayúaTlayuamichinT. iztliSemionotiformesSpecific name translates to "obsidian", after the colour of the scalesUnamichthysU. espinosaiIchthyodectiformesDiscovered alongside two other currently undescribed ichthyodectiformsYabrudichthys?cf. Y. spAulopiformesLikely an enchodontid, mainly known from the Ein Yabrud site (hence its generic name)
Arthropods
ArthropodsGenusSpeciesHigher taxonNotesImagesArchaeoniscusA. aranguthyorumSphaeromatidea?Bears an unusual axial pouch unlike all extant isopods, may have been a fish ectoparasite or scavenger like modern cymothoidsAtocatleA. ranulfoiMesothelae?Indeterminate family due to poor preservation, likely within Mesothelae due to its distinct abdominal segments, but more recently its affinity as a spider is questionedDunlop, J. A., Penney, D. & Jekel, D. 2023. A summary list of fossil spiders and their relatives. In World Spider Catalog. Natural History Museum Bern, online at http://wsc.nmbe.ch , version 23.5IxtahuaI. benjaminiAnisoptera?Only known from a nymph, matches dragonfly nymphs in shapeProtaeglaP. minisculaAeglidaeEarliest aeglid fossil knownTepexicarcinusT. tlayuaensisTepexicarcinidae (basal Eubrachyura)Formerly assigned questionably to Homolidae due to an absence of clear carapace regions, but then separated into its own family as a basal eubrachyuranTipulidae indet.UnapplicableTipuloideaOnly known from a wing pair
Echinoderms
ArthropodsGenusSpeciesHigher taxonNotesImagesAstropectenA. spAstropectinidaeKnown from juvenile fossils preserving both dorsal and ventral sidesEchinasterE. spEchinasteridaeOnly known from a fossil in dorsal viewOphiactisO. applegateiOphiactidaeOne of the few articulated ophiuroids from the Early CretaceousOphidiasterO. spOphidiasteridaeOne of the few starfish from this formation which is not known from juvenile specimensPaleopentactaP. alencasteraeCucumariidaeLikely an infaunal suspsension feeder based on extant relativesParapsolusP. tlayuensisPsolidaeLikely a suspension-feeder attached to hard substrates based on extant psolidsPlutonasterP. spAstropectinidaeKnown from a juvenile specimenTamariaT. spOphidiasteridaeKnown from a juvenile
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.
Other invertebrates
Porifera Anthozoa Annelida
Plants
cf. Araucaria sp. cf. Frenolopsis Brachyphyllum sp. Podozamites sp. Zamites sp. Phaeophyceae
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