Cerro Del Pueblo Formation Research Articles

Coahuilasaurus lipani, a New Kritosaurin Hadrosaurid from the Upper Campanian Cerro Del Pueblo Formation, Northern Mexico

The Late Cretaceous of Western North America (Laramidia) supported a diverse dinosaur fauna, with duckbilled dinosaurs (Hadrosauridae) being among the most speciose and abundant members of this assemblage. Historically, collecting and preservational biases have meant that dinosaurs from Mexico and the American Southwest are poorly known compared to those of the northern Great Plains. However, evidence increasingly suggests that distinct species and clades inhabited southern Laramidia. Here, a new kritosaurin hadrosaurid, represented by the anterior part of a skull, is reported from the late Campanian of the Cerro del Pueblo Formation, ~72.5 Ma, in Coahuila, Mexico. The Cerro del Pueblo Formation kritosaur was originally considered to represent the same species as a saurolophine from the Olmos Formation of Sabinas, but the Sabinas hadrosaur is now considered a distinct taxon. More recently, the Cerro del Pueblo Formation kritosaur has been referred to Kritosaurus navajovius. We show it represents a new species related to Gryposaurus. The new species is distinguished by its large size, the shape of the premaxillary nasal process, the strongly downturned dentary, and massive denticles on the premaxilla’s palatal surface, supporting recognition of a new taxon, Coahuilasaurus lipani. The dinosaur assemblage of the Cerro del Pueblo Formation shows higher diversity than the contemporaneous fauna of the Horseshoe Canyon Formation in Alberta. Furthermore, Kritosaurini, Lambeosaurini, and Parasaurolophini all persist into the latest Campanian in southern Laramidia after disappearing from northern Laramidia. These patterns suggest declining herbivore diversity seen at high latitudes may be a local, rather than global phenomenon, perhaps driven by cooling at high latitudes in the Late Campanian and Maastrichtian.

Ichnological records associated with dermestid beetles in dinosaur bones from Lala's Place (Maastrichtian), Ramos Arizpe, Coahuila, Mexico, and their taphonomic implications

We analyzed the ichnological record of hadrosaur remains from the dinosaur quarry CLP-3, Lala's Place, Ramos Arizpe, Coahuila, where taphonomic research is ongoing. These fossils have been determined to stratigraphically belong to the Cerro del Pueblo Formation, deposited in a deltaic floodplain environment. The Lala's Place quarries have been determined to belong to the early Maastrichtian (69 ± 5 Ma) through U/Pb detrital zircon dating. Thirteen trace fossil morphotypes were identified in six bone elements, interpreted to belong to a single individual. These traces were identified to belong to the ichnospecies Cuniculichnus seilacheri, cf. Cubiculum cooperi, Cubiculum atsintli. A new ichnospecies, Cubiculum subcorticalis n. isp., characterized by a composite feeding-pupation trace with subcortical chambers, is also described. Based on these findings, temporal range of the previously described ichnospecies is expanded to the Maastrichtian stage in the Cerro del Pueblo Formation. Previous work has reported these ichnospecies and associated them with dermestid beetles; this work also associates these traces with dermestids through morphological analyses and using for the first time the novel Usefulness in Identification and Differentiation (UID) index, recently proposed for this taxon. These traces indicate that the carcass was exposed to a subaerial environment for at least 20–30 days, reaching a dry stage in which dermestid adults fed, reproduced, and oviposited. Larvae produced these traces by excavating chambers to avoid cannibalism by other larvae.

Stratigraphic Reassessment of the Mexican Chasmosaurine Coahuilaceratops magnacuerna as the First Diagnostic Dinosaur Remains from the Cerro Huerta Formation (Lower Maastrichtian) Supporting the Southern Origin of the Triceratopsini

Very few remains of ceratopsid dinosaurs have been recovered so far from the Difunta Group of Coahuila, Mexico. The enigmatic chasmosaurine Coahuilaceratops magnacuerna was previously described on the basis of two partial skulls purportedly derived from the Cerro del Pueblo Formation (~73–72.5 Ma?). On the basis of a new measured section and lithological identification of the host rock, we reassign Coahuilaceratops to the overlying Cerro Huerta Formation (~71.5–70.5 Ma?). Thus, we formally assign the first dinosaur taxon to the Cerro Huerta Formation. This reassignment is more consistent with the relatively derived phylogenetic position of Coahuilaceratops, with implications for the southern Laramidia hypothesis concerning the origin of the Triceratopsini.

Troodontid (Theropoda: Troodontidae) Neurocranium from the Cerro del Pueblo Formation (Late Campanian) of Coahuila, Mexico

The fossil record of Troodontidae from Mexico’s Late Cretaceous is scarce since the majority of theropod specimens have not been identified beyond their family. In Coahuila’s locality La Parrita, a neurocranium that contributes to our understanding of Late Campanian troodontids in the Cerro del Pueblo Formation has been found. It is the first non-dental material described in Mexico for the family.

First record of caenagnathid dinosaurs (Theropoda, Oviraptorosauria) from the Cerro del Pueblo Formation (Campanian, Upper Cretaceous), Coahuila, Mexico

Herein we report the first caenagnathid dinosaur (Theropoda, Oviraptorosauria) material from the Upper Cretaceous Cerro del Pueblo (CdP) Formation of Coahuila, Mexico, comprising three partial tibiae. Caenagnathids are an unusual group of oviraptorosaur theropod dinosaurs mostly known by way of their toothless, beak-like jaws. Fossils ascribed to Caenagnathidae are well-known from many Late Cretaceous localities in Asia and North America, with a high number of specimens found in the mid-latitudes of North America. The postcranial material described in this study represents the southernmost Laramidian locality in which caenagnathids have been found to date and adds to the scant number of caenagnathid fossils found in southern North America. Overall, these discoveries underscore the high diversity of the dinosaurian fauna found in the CdP Formation.

Taphonomic attributes of the holotype of the lambeosaurine dinosaur Latirhinus uitstlani from the late Campanian of Mexico: Implications for its phylogenetic systematics

Latirhinus uistlani represents one of the most emblematic dinosaurs from Mexico. This hadrosaurid, originally described as a member of the Saurolophinae by Prieto-Márquez and Serrano-Brañas in 2012, was re-evaluated as a lambeosaurine by Ramírez-Velasco et al. (2021). In addition, these authors stated that the description of the 2012 holotype was based on a chimeric skeleton and designated a new holotype (a different concept for the composition of essentially the same individual). The composition of their 2021 holotype was based on the size, association and similar mode of preservation of the bones within the quarry. Notably, no details were provided regarding such mode of preservation. However, the fact that the type locality of L. uitstlani is an attritional bonebed where other similar-sized individuals were also present calls into question the criteria used by Ramírez-Velasco et al. (2021) in the composition of their holotype. We address this shortcoming by describing the taphonomic signature of the skeletal elements in the L. uitstlani holotype of Ramírez-Velasco et al. (2021), as well as that of other bones discussed collected from this species’ type locality and other sites of the late Campanian Cerro del Pueblo Formation. Our observations show different taphonomic attributes among the bones of the 2021 holotype, indicating that it is likely a chimera of different specimens. Such taphonomic attributes support a holotype for L. uitstlani consisting of the original elements listed in Prieto-Márquez and Serrano-Brañas (2012), with exclusion of the IGM 12712 jugal and a right scapula. We concur in that IGM 12712 is actually a fragmentary jugal, which represents an unusually large hadrosaurid specimen. We also tested the referral of L. uitstlani to Lambeosaurinae via a cladistic parsimony analysis that confirmed that this specimen belongs to that major clade of hadrosaurids; however, its relationships with other lambeosaurines remain unresolved. Finally, we re-evaluated the diagnostic utility of the characters used by Ramírez-Velasco et al. (2021) for referring other specimens to different hadrosaurid clades, concluding that several of them can only be referred to Hadrosauridae indeterminate.

Review of the taxonomic affinities of Latirhinus uitstlani, an emblematic Mexican hadrosaurid

This work presents a detailed study of the bones from the holotype of Latirhinus uitstlani. A Mexican hadrosaurid species known informally as “Isauria”, discovered by Don Ramón López, from the Upper Cretaceous Cerro del Pueblo Formation of Coahuila. The results indicate that this Campanian species from the Ejido Presa San Antonio is a chimera or Frankenstein. Its holotype originally includes bones that were individually misinterpreted, belonging to individuals of different sizes, identifiable to saurolophines and lambeosaurines, even, one bone coming from a different locality. Therefore, after classifying the components of the holotype, we rediagnosed L. uitstlani from its pectoral appendicular bones and pelvic bones, confirming their validity as a species. It was also reclassified as a member of the Lambeosaurine subfamily rather than to Saurolophine, and with an estimated body length of 8.72 m. In addition, we identified a large saurolophine, represented by three specimens, and a small lambeosaurine from the same locality of L. uitstlani, along with a small saurolophine from the Cerro de los Dinosaurios area, originally including in the holotype.

Tlatolophus galorum, gen. et sp. nov., a parasaurolophini dinosaur from the upper Campanian of the Cerro del Pueblo Formation, Coahuila, northern Mexico

In 2013, a joint team of INAH and UNAM paleontologists launched a project to recover a semi-articulated tail of a putative hadrosaur, that was discovered in 2005, on the superficial upper Campanian deposits of the Cerro del Pueblo Formation, in General Cepeda Municipality, Coahuila, northern México. Currently, this specimen is the most complete lambeosaurine so far found in México. Herein, Tlatolophus galorum gen. et sp. nov. is erected based on features shown in the head of this specimen. The distinctive characters of this new species are the skull high, with a length/height ratio equals to 1.79; the premaxilla wide, in which maximum/minimum width ratio is about 2.4; the maxillary ascending ramus has a low dorsal apex; the pterygoid dorsal crest is high and convex; the supracranial crest is high, spatula-shaped and similar to an inverse-comma; the occipital condyle is inclined 56° ventrally; the supraoccipital crest is laminar, wide and located inside a deep nuchal fossa; the squamosal shelf is moderately long, as long as the foramen magnum diameter; the dorsal margins of the infratemporal fenestra and orbit are located at the same level; and the nasal is elongated, caudally expanded, and bilobed. The phylogenetic analysis performed here recovers Tlatolophus within the Tribe Parasaurolophini; in this result, the supracranial crest spatula-shaped of this new parasaurolophini represent a plesiomorphic condition within the tribe.

Paraxenisaurus normalensis, a large deinocheirid ornithomimosaur from the Cerro del Pueblo Formation (Upper Cretaceous), Coahuila, Mexico

New ornithomimosaur material discovered from the Upper Cretaceous Cerro del Pueblo Formation of Coahuila, Mexico is described herein. The material includes postcraneal elements from several individuals, which are assigned to a new genus and species, Paraxenisaurus normalensis. This new taxon is characterized by the presence of a strongly curved and laterally compressed manual ungual I with a distally placed flexor tubercle divided by a deep sulcus and a deeply concave proximal, elliptical-shaped articular surface; a metacarpal III that has an expanded proximal articular end, which is similar in width to metacarpal II; a combination of posterior caudal vertebrae, where the most anterior vertebrae possess low dorsoventral prezygapophyses with nearly vertical articulation surfaces, while the most posterior vertebrae have prezygapophyses that face ventromedially; a non-arctometatarsalian pes, where the proximal end of metatarsal III is expanded and has a proximal ovoid outline; the presence of an attachment site for pedal digit I in the posterior surface of the distal quarter of metatarsal II; an expanded medial condyle of metatarsal II; a transversely wide distal end of metatarsal III, which has a semi-ginglymoid articular surface; distinctively broad and ventrally curved pedal unguals that depending on the digit, the proximodorsal process changes its position adopting a lip-shaped appearance; a rounded, large foramen on the medial side of each pedal ungual and the presence of a deep ventral fossa that surrounds a strongly developed, ridge-like flexor tubercle. This combination of characteristics separate Paraxenisaurus normalensis from other ornithomimosaurs previously described in North America and in other parts of the world. Phylogenetic analysis shows that within Ornithomimosauria, Paraxenisaurus normalensis is recovered as a deinocheirid ornithomimosaur, along with Garudimimus brevipes and Deinocheirus mirificus. Therefore, the finding of Paraxenisaurus normalensis in the Cerro del Pueblo Formation of Coahuila, Mexico represents the first record of the Deinocheiridae family in the Campanian of North America.

The first crocodyloform remains from the La Parrita locality, Cerro del Pueblo Formation (Campanian), Coahuila, Mexico

espanolEl registro de tetrapodos terrestres en la Formacion Cerro del Pueblo (Cretacico tardio, Campaniano) en Coahuila, incluye tortugas, pterosaurios, dinosaurios y crocodyliformes. Este ultimo grupo esta representado por goniofolididos, eusuquios indeterminados y Brachychampsa montana. En este trabajo se reportan los primeros restos de crocodyliformes de la localidad La Parrita, Formacion Cerro del Pueblo, con base en un diente aislado, vertebras y osteodermos. La asociacion de crocodyliformes, tortugas, dinosaurios y oogonias de cariofitas, proporcionan evidencia de ambientes fluviales en una llanura deltaica de tipo tropical para la Formacion Cerro del Pueblo durante el Cretacico tardio. EnglishThe record of land tetrapods of the Cerro del Pueblo Formation (Late Cretaceous, Campanian), in Coahuila, includes turtles, pterosaurs, dinosaurs, and crocodyliforms. This last group is represented only by goniopholidids, indeterminate eusuchians, and Brachychampsa montana. In this work we report the first crocodyliform remains from La Parrita locality, Cerro del Pueblo Formation, based on one isolated tooth, vertebrae, and osteoderms. The association of crocodyliforms, turtles, dinosaurs, and charophyte oogonia provide evidence for stagnant to fluvial environments on a delta plain with tropical climate for the Cerro del Pueblo Formation during the Late Cretaceous.

Teredolites trace fossils in log-grounds from the Cerro del Pueblo Formation (Upper Cretaceous) of the state of Coahuila, Mexico

Teredolites longissimus, a teredinid boring ichnofossil, is described from log-grounds found in the Cerro del Pueblo Formation of Coahuila, Mexico (Upper Cretaceous). Teredinids, commonly known as shipworms, are marine bivalves that bore into woody substrates and are known from the Jurassic Period to present day. Trace fossils of T. longissimus are taphonomically informative because they provide evidence for the timing and position of wood prior to burial. Colonization and behavior of teredinid bivalves is also dependent on the shipworm density, age of the bivalves, and decomposition of the woody substrate. This study explores the life histories and taphonomic histories of teredinid bivalves and log-grounds in the Cerro del Pueblo and adds to the growing literature on ichnofossils in this deposit.

Hadrosaurs from Cañada Ancha (Cerro del Pueblo Formation; upper Campanian-?lower Maastrichtian), Coahuila, northeastern Mexico

At Cañada Ancha, about 15 km northwest of Saltillo, northeastern Mexico, deposits of the upper Campanian-?lower Maastrichtian Cerro del Pueblo Formation exhibit bone clusters of disarticulated hadrosaurids, tentatively assigned here based on maxillary features to Velafrons coahuilensis and a second yet undetermined taxon. We discuss the taphonomy of the material as transported and buried on a delta plain. Orientation and breakage of bones as well as absence of strong abrasion indicate short-distance and high-energy transport by a viscose ‘flash flood’ or debris flow.

Terrestrial vertebrate paleocommunities from the Cerro del Pueblo Formation (Late Cretaceous; Late Campanian) at Las Aguilas, Coahuila, Mexico

Terrestrial vertebrate paleocommunities from the Cerro del Pueblo Formation (Late Cretaceous; Late Campanian) at Las Aguilas, Coahuila, Mexico

Preliminary assessment of hadrosaur dental microwear from the Cerro del Pueblo Formation (Upper Cretaceous: Campanian) of Coahuila, northeastern Mexico

Here we report new hadrosaur remains recovered from the Cerro del Pueblo Formation (Upper Cretaceous: Campanian) at La Parrita locality, northeastern Mexico. Although the material is fragmentary, the identification of dental microwear in three out of the four teeth collected is notable. This sample allows for a preliminary assessment of hadrosaur dental microwear from this geographic region and time frame. The variables studied were the orientation and average count of scratches, average count of pits, and average microwear feature width in an area of 400 X 400 µm at 35X magnification. The results show a predominance of dorsodistally-ventromesially inclined scratches in all three teeth indicating that the mandible primarily moved in an orthopalinal direction during the power stroke. The pattern of scratch orientation we recorded is comparable to that reported for different hadrosaur species from Alberta, Canada, and Wyoming, U.S.A.; suggesting similar jaw mechanics in the hadrosaurs from Coahuila. In contrast, there are significant differences in the average number of pits and microwear feature width between the Alberta and the Coahuila hadrosaurs samples, with the latter presenting more pits and finer microwear features. Given the similar jaw mechanics between the Alberta and Coahuila hadrosaurs, suggested by our analysis, the difference in average number of pits and microwear feature width is probably due to differences in diet and/or the type and amount of grit ingested during feeding. The greater number of pits in the hadrosaurs from Coahuila might indicate that these individuals ingested a greater proportion of hard food items than the Alberta hadrosaurs.

First occurrence of Parksosauridae in Mexico from the Cerro del Pueblo Formation (Late Cretaceous; Late Campanian) at Las Águilas, Coahuila

espanolLa localidad de Las Aguilas cerca de Porvenir de Jalpa, Coahuila, Mexico, es extremadamente rica en restos de fosiles dinosaurios comprendiendo huesos y huellas de varios taxa Campanianos. Aqui presentamos el registro de un diente con una corona bulbosa y asimetrica ademas de un centrum de una vertebra anficelica. Ambos asignados por nosotros como Parksosauridae. El material representa el primer registro de esta enigmatica familia para Mexico. EnglishThe Las Aguilas locality near Porvenir de Jalpa, Coahuila, Mexico, is extremely rich in fossil remains comprising both bones and trackways of several late Campanian dinosaur taxa. Here we present a tooth with an asymmetrically bulged crown and an isolated shallow amphicoelous vertebral centrum. Both are assigned by us to Parksosauridae. The material represents the first occurrence of this enigmatic family in Mexico.

Gastrochaenolites Leymerie in dinosaur bones from the Upper Cretaceous of Coahuila, north-central Mexico: Taphonomic implications for isolated bone fragments

Isolated bone fragments are typically disregarded during the collection of vertebrate remains because of the apparent lack of useful taxonomic information, as compared to intact or articulated bones. The presence of isolated bone fragments is occasionally reported, but no particular taphonomic data are conveyed and valuable depositional information is overlooked. However, through the analysis of borings and other traces of encrusting organisms present on bone fragments, we may obtain valuable information about their post-mortem histories within a depositional environment. In this study, bivalve borings in isolated hadrosaur bone fragments are described from the Campanian Cerro del Pueblo Formation of Coahuila, north-central Mexico. Two ichnotraces indicate transport from terrestrial to shallow-marine environments: Gastrochaenolites turbinatus and Gastrochaenolites cluniformis. These borings represent the first description of Gastrochaenolites at ichnospecies level in dinosaur bones. Additional relics of encrusting organisms and the fill of sediment provide evidence for subsequent reworking and reburial of the bones. The taphonomic analysis results an important clue for understanding the preservation of the studied fragmented bones within brackish and marine sedimentary settings, and an aid for reconstructing the Late Cretaceous environmental evolution in north-central Mexico.

Insect damage in dinosaur bones from the Cerro del Pueblo Formation (Late Cretaceous, Campanian) Coahuila, Mexico

This study represents the first description and analysis of insect borings on hadrosaur bones (Dinosauria: Hadrosauridae) from the Late Campanian Cerro del Pueblo Formation (CdP) of the State of Coahuila, Mexico. Here we describe seven different trace patterns that include a new Cubiculum ichnospecies and possible termite damage. The insect bone borings include holes, notches, chambers, furrows, tunnels and rosettes. Transitional structures can also be observed in the hadrosaur bones. Comparisons of these trace morphologies with extant necrophagous insect groups suggest that the CdP borings were likely the result of dermestid beetle larvae and possible termite osteophagy on a dry hadrosaur corpse prior to burial.

Oldest record of Mathildellidae (Crustacea: Decapoda: Goneplacoidea) associated with Retroplumidae from the Upper Cretaceous of NE Mexico

A new genus and species of the Mathildellidae Prebranchioplax cretacica (Crustacea: Decapoda: Goneplacoidea) is reported from shallow marine sediments of the upper Campanian Parras Shale and Cerro del Pueblo Formation (Parras Basin), Coahuila, NE Mexico. Prebranchioplax cretacica was collected from siliceous concretions associated with more abundant specimens of the retroplumid Costacopluma mexicana Vega and Perrilliat, 1989. P. cretacica bears similarities to Eocene species of Branchioplax from Japan, USA (Alaska and Washington), England, Hungary and Tajikistan as well as with Eogeryonidae (Portunoidea) species from the Upper Cretaceous of Spain and Marocarcinidae (Styracocarcinus) from Morocco. However, clear differences in the carapace frontal shape places P. cretacica in the Mathildellidae. This record represents the oldest known Mathildellidae, and along with the Retroplumidae, appear to have originated during the Late Cretaceous in ancient seas of Mexico, with a wide distribution during Paleogene times becoming restricted today to deep waters of the Indo-Pacific region and Atlantic Ocean. Comments on preservation and morphology of Costacopluma mexicana are also included. Crab specimens preserved in siliceous concretions from one locality (Entronque) show peculiar desiccation marks, and a possible model of taphonomy.

Taphonomic history of a ‘duck-bill’ dinosaur (Dinosauria: Ornithopoda) from the Cerro del Pueblo Formation (Upper Cretaceous, Campanian) Coahuila, Mexico: Preservational and paleoecological implications

The Cerro del Pueblo Formation in the state of Coahuila, Mexico is becoming recognized worldwide due to its abundant and diverse fossil material. While most previous paleontological work from this rock unit has been directed towards taxonomic investigation, this study is directed towards the taphonomy of a “duck-billed” dinosaur (Ornithischia: Hadrosauridae). The hadrosaur skeleton is represented by several skull bones, vertebrae and ribs, a scapula, pubis, and various appendicular elements. The following taphonomic parameters were considered: (1) bone frequency; (2) hydraulic equivalence; (3) degree of bone articulation; (4) abrasion; (5) weathering; (6) breakage; (7) tooth marks; and (8) trampling activities. The low degree of weathering and abrasion suggests that the specimen experienced a short time of subaerial exposure and underwent a short transportation distance before deposition. Burial occurred within a perimarine lagoonal environment. Furthermore, the lack of hydraulic equivalence with the rock matrix, a high degree of disarticulation and a chaotic distribution of the bones in the fossiliferous bed, suggest that it was transported as a “bloated carcass”. The finding of distinct types of tooth marks evidence some sort of predator/scavenging activities on the specimen. Finally, an almost vertical orientation of various bones and the presence of spiral fractures may indicate that these elements were trampled by other animals.

Permineralized infructescence from the Cerro del Pueblo Formation, Upper Cretaceous, Coahuila, Mexico

Permineralized infructescences are described from the Cerro del Pueblo Formation, Coahuila, Mexico. Morphological and anatomical observations of 584 infructescences support the identification and reconstruction of an infructescence, with fruit developed as nutlets. The fruit are each surrounded by bracts, and have a persistent style and stigma. They comprise a woody exocarp composed of macrosclereids, and mesocarp and endocarp with layers of brachysclereids. The seeds are fusiform with a thin seed coat. Seeds contain a distal hollow chamber, probably involved in dispersal, and an embryo with two cotyledons with probable helobial endosperm. The fruit and seed characters of the fossil do not correspond with an extant genus or family, thus, a new genus and species is proposed, Patocarpus coahuilensis gen. et sp. nov. Cevallos-Ferriz and Vázquez-Rueda, and is interpreted to be an extinct member of Proteales.