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Horned dinosaurs (Ornithischia: Ceratopsidae) from the Upper Cretaceous (Campanian) Cerro del Pueblo Formation, Coahuila, Mexico

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... The most important discoveries of dinosaur fauna in the CdP Formation have been made relatively recently, resulting in multiple descriptions of new genera and species within the past two decades (e.g. Gates et al., 2007;Loewen et al., 2010;Prieto-Márquez and Serrano-Brañas, 2012;Serrano-Brañas et al., 2020;Ramírez-Velasco et al., 2021). Compared to some groups of herbivorous dinosaurs (hadrosaurs and ceratopsians), discoveries of theropod remains in the CdP are relatively rare. ...
... pers.), distinct groups of plants (Calvillo-Canadell and Cevallos-Ferriz, 2007;Estrada-Ruiz and Cevallos-Ferriz, 2007;Maccracken com. pers.), several dinosaur taxa (Murray et al., 1962;McBride et al., 1974;Rodríguez de la Rosa and Cevallos-Ferriz, 1998;Serrano-Brañas et al., 2006;Gates et al., 2007;Loewen et al., 2010;Aguillón-Martinez, 2010;Prieto-Márquez and Serrano-Brañas, 2012;Serrano-Brañas and Espinosa-Chávez, 2017;Serrano-Brañas et al., 2020), other types of vertebrates (Rodríguez de la Rosa and ; Location of the El Palmar [sites A (BENC 1 / 2 ) and B (BENC 1 / 1 ), marked with a blue star with a 1] and the USB (BENC 18 / 1 , marked with a blue star with a 2) collecting sites (c). Satelital map modified from https://satellites.pro/mapa de Mexico #25.653,906,-101.550751, 10. ...
... Notably, the dinosaur discoveries of greatest scientific importance have been made relatively recently, resulting in multiple descriptions of new genera and species. Among these discoveries are the hadrosaurs Velafrons coahuilensis (Gates et al., 2007), Latirhinus uitstlani (Prieto-Márquez andSerrano-Brañas, 2012;Serrano-Brañas and Prieto-Márquez, 2022) and Tlatolophus galorum (Ramírez-Velasco et al., 2021), the ceratopsian Coahuilaceratops magnacuerna (Loewen et al., 2010), and the deinocheirid ornithomimosaur Paraxenisaurus normalensis (Serrano-Brañas et al., 2020). Other dinosaur groups have also been reported so far from the CdP, such as ankylosaurids (Rivera-Sylva and Espinosa-Chávez, 2006), thescelosaurs (Parkosauridae, Rivera-Sylva et al., 2018), dromaeosaurids (Aguillón-Martinez, 2010, troodontids (Rodríguez de la Cevallos-Ferriz, 1998), ornithomimids (Aguillón-Martinez, 2010;Rivera-Sylva et al., 2019) and tyrannosaurids (Torres-Rodríguez et al., 2010;Rivera-Sylva et al., 2019). ...
Article
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.
... The most important discoveries of dinosaur fauna in the CdP Formation have been made relatively recently, resulting in multiple descriptions of new genera and species within the past two decades (e.g. Gates et al., 2007;Loewen et al., 2010;Prieto-Márquez and Serrano-Brañas, 2012;Serrano-Brañas et al., 2020;Ramírez-Velasco et al., 2021). Compared to some groups of herbivorous dinosaurs (hadrosaurs and ceratopsians), discoveries of theropod remains in the CdP are relatively rare. ...
... pers.), distinct groups of plants (Calvillo-Canadell and Cevallos-Ferriz, 2007;Estrada-Ruiz and Cevallos-Ferriz, 2007;Maccracken com. pers.), several dinosaur taxa (Murray et al., 1962;McBride et al., 1974;Rodríguez de la Rosa and Cevallos-Ferriz, 1998;Serrano-Brañas et al., 2006;Gates et al., 2007;Loewen et al., 2010;Aguillón-Martinez, 2010;Prieto-Márquez and Serrano-Brañas, 2012;Serrano-Brañas and Espinosa-Chávez, 2017;Serrano-Brañas et al., 2020), other types of vertebrates (Rodríguez de la Rosa and ; Location of the El Palmar [sites A (BENC 1 / 2 ) and B (BENC 1 / 1 ), marked with a blue star with a 1] and the USB (BENC 18 / 1 , marked with a blue star with a 2) collecting sites (c). Satelital map modified from https://satellites.pro/mapa de Mexico #25.653,906,-101.550751, 10. ...
... Notably, the dinosaur discoveries of greatest scientific importance have been made relatively recently, resulting in multiple descriptions of new genera and species. Among these discoveries are the hadrosaurs Velafrons coahuilensis (Gates et al., 2007), Latirhinus uitstlani (Prieto-Márquez andSerrano-Brañas, 2012;Serrano-Brañas and Prieto-Márquez, 2022) and Tlatolophus galorum (Ramírez-Velasco et al., 2021), the ceratopsian Coahuilaceratops magnacuerna (Loewen et al., 2010), and the deinocheirid ornithomimosaur Paraxenisaurus normalensis (Serrano-Brañas et al., 2020). Other dinosaur groups have also been reported so far from the CdP, such as ankylosaurids (Rivera-Sylva and Espinosa-Chávez, 2006), thescelosaurs (Parkosauridae, Rivera-Sylva et al., 2018), dromaeosaurids (Aguillón-Martinez, 2010, troodontids (Rodríguez de la Cevallos-Ferriz, 1998), ornithomimids (Aguillón-Martinez, 2010;Rivera-Sylva et al., 2019) and tyrannosaurids (Torres-Rodríguez et al., 2010;Rivera-Sylva et al., 2019). ...
... Their fossils are known primarily from upper Campanian and Maastrichtian deposits, reaching peak diversity in the late Campanian but remaining diverse and abundant in the Maastrichtian (e.g., Sampson et al., 2010Sampson et al., , 2013 when the giant triceratopsins dominated many paleoecosystems. Ceratopsids are known from Mexico to Alaska (e.g., Langston, 1959, 1975Lawson, 1976;Sampson, 1995;Holmes et al., 2001;Hunt and Lehman, 2008;Loewen et al., 2010;Sullivan and Lucas, 2010;Fiorillo and Tykoski, 2012;McDonald et al., 2016;Lehman et al., 2017;Lund et al., 2016;Rivera-Sylva et al., 2016, 2017, with one species known from Asia (Xu et al., 2010). However, many species have restricted geographic ranges. ...
... The late Campanian fauna of New Mexico is also quite diverse, particularly in the Fruitland and Kirtland formations of the San Juan This study adds to a growing body of work on the evolution of chasmosaurine ceratopsids in North America (e.g., Loewen et al., 2010;Sampson et al., 2010;Sullivan and Lucas, 2010;Longrich, 2011;Mallon et al., 2012Mallon et al., , 2014Mallon et al., , 2016Wick and Lehman, 2013;Ryan et al., 2014;Brown and Henderson, 2015;Lehman et al., 2017;Fowler and Freedman Fowler, 2020) showing high horned dinosaur diversity, and complex biogeography. ...
Article
The horned dinosaurs (Ceratopsidae) were a diverse family of herbivorous dinosaurs originating in the Late Cretaceous in western North America (Laramidia). As one of the most species-rich dinosaur groups, their diversity and distribution are important to understanding Cretaceous dinosaur evolution. Ceratopsids have previously been hypothesized to have high levels of endemism despite inhabiting a relatively small land mass with few barriers to dispersal. Here, we document a new chasmosaurine ceratopsid, Sierraceratops turneri gen. et sp. nov., from the Upper Cretaceous (latest Campanian–Maastrichtian) Hall Lake Formation of south-central New Mexico, consistent with the hypothesis that southern Laramidia supported an endemic dinosaur fauna. Sierraceratops is distinguished by its relatively short, robust, and mediolaterally compressed postorbital horns; a flattened medial ridge on the posterior end of the pterygoid; a jugal with pronounced anterior flanges; a long pyramid-shaped epijugal horncore; a D-shaped cross section of the median parietal bar; and a squamosal with a pointed tip and low episquamosal ossifications. Phylogenetic analysis recovers Sierraceratops as sister to Bravoceratops and Coahuilaceratops, part of a clade endemic to the southwestern United States and Mexico. Sierraceratops adds to the diversity and disparity of the Chasmosaurinae in the Late Cretaceous and provides additional evidence for Laramidian endemism. Together with Sierraceratops, the Hall Lake Formation dinosaur fauna suggests that the latest Cretaceous of southern Laramidia was characterized by endemic clades and distinct community structures.
... El espécimen PAL 01-2019 fue descubierto a 25 m al norte de la cantera donde se descubrió el ceratospido descrito por Porras-Múzquiz y Lehman (2011), 8 km al sureste de Palaú en el Rancho Valadez. Se ha recuperado un isquion en muy mal estado de preservación el cual es masivo y fuertemente curveado como en otros chasmosaurinos de gran tamaño como Pentaceratops y Coahuilaceratops (Lehman, 1990;Loewen et al., 2010) (Fig. 2, V). Por otro lado, el espécimen SAB 01-2019 fue descubierto en la localidad de Cañada Honda, a 12 km al sureste de Sabinas, el espécimen corresponde a dos centra anfiplatianos de vertebras dorsales, circulares, los cuales son cortos craniocaudalmente además de que se encuentran ligeramente constreñido por el medio; además de un fragmento de mandíbula con el esmalte marcado de dos dientes claramente ceratópsidos, donde se aprecia la forma de hoja, el lóbulo mesial como el distal y la cresta primaria (Fig. 2, K-U). ...
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This book Mexican Biodiversity and Ecology: New knowledge and technologies for current challenges is a compilation of scientific studies carried out by researchers from various institutions in the country. Its objective is to present current information on issues of biological diversity and ecology of relevant species in terms of conservation, as well as aspects of sustainable use of natural resources. Bio-logical diversity comprises the accumulation of living organisms considering all levels of their organization (genes, populations, species, communities, habitats, ecosystems and landscapes). Ecology, on the other hand, seeks to understand the relationships that exist between organisms and the biotic and abiotic elements in their environment. Both lines of research are closely related and form the basis for the appropriate use of available natural resources. In this context, the studies presented in this book deal with the diversity of bacterial genes, microbiotas, yeasts, snails, shrimps, insects, fish, dinosaurs, avifauna and vegetation. In the ecological aspect, varied information is offered covering climatic issues, fires, the effect of growth-promoting bacteria in plants, as well as relevant topics on fish, herpetofauna, birds, mammals, fungi, lichens and vegetation. Regarding the use of natural resources, the book contains information on the use of species for economic and human health purposes, biological control, biostimulants, bacterial biocontrol activity, meliponiculture and environmental education through botanical gardens. It is hoped that this work will provide the reader with a broad overview of the topics that are currently being studied in these lines of research and that seek to increase knowledge of living beings, promoting their conservation and sustainable use. conservation and sustainable use.
... The Cerro del Pueblo Formation is one of the most studied geological formations in Mexico with a very diverse faunal record, composed mainly of dinosaurs and other reptiles (Wolleben 1977;Rodriguez-de la Rosa and Cevallos-Ferriz 1998;Kirkland et al. 2000;Cifuentes-Ruiz et al. 2006;Rivera-Sylva and Espinosa-Chávez 2006;Loewen et al. 2010;Brinkman 2014;Rivera-Sylva et al. 2018, 2019bSerrano-Brañas et al. 2020), flora (Rodriguez-de la Rosa and Cevallos-Ferriz 1994;Estrada-Ruiz and Cevallos-Ferriz 2007;Estrada-Ruiz et al. 2009;Cevallos-Ferriz and Vázquez-Rueda 2016), and trace fossils (Rodriguez-de la Rosa and Cevallos-Ferriz 1998;Rodríguez-de la Rosa 2007;Rivera-Sylva et al. 2017;Serrano-Brañas et al. 2018a, b, 2019. Three hadrosaurid taxa are known so far from this formation: Kritosaurus navajovius Brown, 1910(Kirkland et al. 2006Prieto-Márquez 2014b), Latirhinus uitstlani Serrano Brañas, 2012 (Prieto-Márquez andSerrano Brañas 2012) and Velafrons coahuilensis Gates, Sampson, Delgado de Jesús, Zanno, Eberth, Hernandez-Rivera, Aguillón-Martínez, andKirkland, 2007 (Gates et al. 2007). ...
Article
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New hadrosaurid postcranial material is reported, collected near Presa San Antonio, Parras de la Fuente municipality, Coahuila, Mexico, in a sedimentary sequence belonging to the upper Campanian of the Cerro del Pueblo Formation, in the Parras Basin. The skeletal remains include partial elements from the pelvic girdle (left ilium, right pubis, ischium, and incomplete sacrum), a distal end of a left femur, almost complete right and left tibiae, right metatarsals II and IV, cervical and caudal vertebrae. Also, partially complete forelimb elements are present, which are still under preparation. The pubis shows characters of the Lambeosaurinae morphotypes, but the lack of cranial elements does not allow us to directly differentiate this specimen from the already described hadrosaurid taxa from the studied area, such as Velafrons coahuilensis, Latirhinus uitstlani, and Kritosaurus navajovius. This specimen, referred as Lambeosaurinae indet., adds to the fossil record of the hadrosaurids in southern Laramidia during the Campanian.
... During the Campanian age of the Late Cretaceous, centrosaurine ceratopsians were among the most common terrestrial herbivores in the western landmass of North America known as Laramidia with a geographic range extending from Alaska (Fiorillo and Gangloff 2003; 1 3 2010; Fiorillo and Tykoski 2012;Tykoski and Fiorillo 2013) through Alberta, Canada (Lambe 1904(Lambe , 1913Sternberg 1950;Ryan and Russell 2005;Ryan 2007; Ryan et al. 2007;Currie et al. 2008;Farke et al. 2011;Ryan et al. 2012a, b;Evans and Ryan 2015), Montana (Dodson 1986;Sampson 1995;McDonald and Horner 2010;Ryan et al. 2010;Chiba et al. 2018), Utah (Kirkland and DeBlieux 2010;Loewen et al. 2013a;Sampson et al. 2013) Arizona , New Mexico (Wolfe and Kirkland 1998;Wolfe 2000), to Mexico (Murray et al. 1960;Loewen et al. 2010;Rivera-Sylva and Carpenter 2014;Rivera-Sylva et al. 2016, 2017. ...
Article
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An associated incomplete skeleton of a ceratopsid dinosaur from the Campanian deposits of the Allison Member of the Menefee Formation in New Mexico, USA is described. Although it was originally described over two decades ago, newly prepared portions of the Menefee Formation skeleton and reinterpretations of previously known morphology, in addition to newly described specimens have provided new information on ceratopsids, and centrosaurines in particular. These new data allow for a thorough reassessment of the specimen and the erection of a new taxon: Menefeeceratops sealeyi gen. et sp. nov., potentially the oldest recognized member of Centrosaurinae. Menefeeceratops sealeyi is represented by diagnostic cranial and postcranial skeletal elements. The cranial elements include a portion of the left premaxilla, a nearly complete left postorbital horncore, a parietal fragment, the right and left squamosals, the left jugal, the predentary, and the left dentary. Postcranial material consists of two cervical vertebrae, eight dorsal vertebrae, a partial sacrum with six sacral vertebrae, 11 dorsal ribs, the distal left radius, proximal and distal portions of the left ulna, the left femur, and a left metatarsal II. The taxonomic validity of Menefeeceratops sealeyi is supported by a combination of several morphological characters. These include a lack of epiossifications on the lateroposterior edge of the parietal (shared with Machairoceratops), three epiossifications on the squamosal, and three smaller, secondary undulations as part of episquamosal locus S1. There are also two subequal embayments on the posterior free margin of the squamosal with the more dorsal embayment (between episquamosal loci 1 and 2) distinctly larger than the ventral (= lateroventral) one (between episquamosal loci 2 and 3), three ridges on the lateral (dorsolateral) surface of the squamosal, an elongate posterior portion of the squamosal, the presence of a shallow but distinct groove on the medial surface of the squamosal nearly paralleling the ventrolateral and ventroposterior edges, elongate postorbital (= supraorbital) horns that are anteriorly curved distally, and two elongate ridges on the lateral surface of the dentary that diverge anteriorly, creating a distinct anterior triangular fossa. Phylogenetic analysis of Menefeeceratops sealeyi places this new species as a basal centrosaurine, most closely related to Crittendenceratops krzyzanowskii, thus adding to the growing record of centrosaurines discovered in western North America. It thus provides new information about the diversity of morphologies throughout different species and the temporal and paleobiogeographic distribution of these animals throughout Laramidia during the Late Cretaceous. Its presence as one of the, if not the, oldest members of the Centrosaurinae also suggests centrosaurines originated in the southern portions of western North America and the southern Rocky Mountain region, and subsequently radiated north during the upper middle to late Campanian.
... El espécimen PAL 01-2019 fue descubierto a 25 m al norte de la cantera donde se descubrió el ceratospido descrito por Porras-Múzquiz y Lehman (2011), 8 km al sureste de Palaú en el Rancho Valadez. Se ha recuperado un isquion en muy mal estado de preservación el cual es masivo y fuertemente curveado como en otros chasmosaurinos de gran tamaño como Pentaceratops y Coahuilaceratops (Lehman, 1990;Loewen et al., 2010) (Fig. 2, V). Por otro lado, el espécimen SAB 01-2019 fue descubierto en la localidad de Cañada Honda, a 12 km al sureste de Sabinas, el espécimen corresponde a dos centra anfiplatianos de vertebras dorsales, circulares, los cuales son cortos craniocaudalmente además de que se encuentran ligeramente constreñido por el medio; además de un fragmento de mandíbula con el esmalte marcado de dos dientes claramente ceratópsidos, donde se aprecia la forma de hoja, el lóbulo mesial como el distal y la cresta primaria (Fig. 2, K-U). ...
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El cambio climático puede influenciar la frecuencia, severidad y extensión de los incendios forestales. Los incendios son perturbaciones comunes en el medio ambiente que pueden tener repercusiones ecológicas y económicas graves e impredecibles; no obstante, también es un conductor importante del funcionamiento del ecosistema, la dinámica de la biota y el ciclo de nutrientes. Es por lo anterior, que el presente trabajo tuvo como objetivo identificar el impacto en la actividad microbiana total del suelo después de un incendio ocurrido en el Cañón de San Lorenzo. Los resultados demostraron un incremento en el pH, CE y MOS en comparación a la zona testigo no incendiada, mas no fue significativo estadísticamente. Por otro lado, la respiración basal sí presentó diferencia significativa entre la zona incendiada y testigo durante todo el tiempo de incubación, presentando una disminución en la zona perturbada, lo que pudo deberse a factores como la transferencia del calor del fuego en el subsuelo que incrementa directamente la mortalidad de las comunidades microbianas, disminuyendo así la biomasa y metabolismo, así como a una menor humedad en el suelo, el cambio de las propiedades fisicoquímicas o la baja disponibilidad de nutrientes fácilmente degradables.
... El espécimen PAL 01-2019 fue descubierto a 25 m al norte de la cantera donde se descubrió el ceratospido descrito por Porras-Múzquiz y Lehman (2011), 8 km al sureste de Palaú en el Rancho Valadez. Se ha recuperado un isquion en muy mal estado de preservación el cual es masivo y fuertemente curveado como en otros chasmosaurinos de gran tamaño como Pentaceratops y Coahuilaceratops (Lehman, 1990;Loewen et al., 2010) (Fig. 2, V). Por otro lado, el espécimen SAB 01-2019 fue descubierto en la localidad de Cañada Honda, a 12 km al sureste de Sabinas, el espécimen corresponde a dos centra anfiplatianos de vertebras dorsales, circulares, los cuales son cortos craniocaudalmente además de que se encuentran ligeramente constreñido por el medio; además de un fragmento de mandíbula con el esmalte marcado de dos dientes claramente ceratópsidos, donde se aprecia la forma de hoja, el lóbulo mesial como el distal y la cresta primaria (Fig. 2, K-U). ...
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Se describe la abundancia y diversidad de bacterias fecales de un pool de muestras de caballo en libre pastoreo en la reserva de la Biosfera Mapimí. Se realizó secuenciación masiva V3-V4 del gen 16S rRNA con Illumina. Los resultados se analizaron con QIIME y la referencia taxonómica EzBioCloud. Se identificaron 10 phyla, 16 clases, 26 órdenes, 46 familias, 134 géneros y 136 especies. Los phyla Proteobacteria, Firmicutes y Actinobacteria fueron los más abundantes. El género de mayor abundancia fue Brevudimonas; se identificaron cinco géneros asociados a infecciones en caballos (Clostridium, Fusobacterium, Klebsiella, Nocardia y Rhodococcus).
... As the premaxillae of MOR 1122 are only partially preserved (Farke 2007), MOR 1122 7-22-00-1 represents the stratigraphically lowest occurring well-preserved ceratopsid premaxilla from the HCF. Premaxillae are taxonomically informative in chasmosaurine ceratopsids (e.g., Wu et al. 2007;Sampson et al. 2010;Loewen et al. 2010) including Triceratops. In Triceratops prorsus, the premaxilla contributes to a convex rostrum typically supporting an elongate nasal horn whereas in Triceratops horridus, the rostrum is more elongate with the caudally inclined nasal process of the premaxilla (NPP) typically supporting a smaller nasal horn (Forster 1996;Longrich and Field 2012; fig. ...
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A well-preserved large chasmosaurine ceratopsid premaxilla (MOR 1122 7-22-00-1) collected from the basal sandstone of the Cretaceous Hell Creek Formation (HCF) represents one of the stratigraphically lowest ceratopsid occurrences in the formation. The specimen was discovered in 2000, during the excavation of a large Torosaurus latus skull (MOR 1122) which was later hypothesized to represent an advanced growth stage of the more commonly recovered HCF ceratopsid Triceratops. MOR 1122 7-22-00-1 compares favorably with the incomplete premaxillae of the MOR 1122 skull and reveals details of premaxilla morphology from this stratigraphic zone. It preserves large, closely spaced ventromedial foramina, a narrow triangular process, and a thin septal flange at the base of the narial strut. The nasal process is narrow, caudally inclined and has a forked dorsal surface which appears to represent an intermediate between the morphology expressed in the slightly stratigraphically lower ceratopsid Eotriceratops xerinsularis from the Horseshoe Canyon Formation of Alberta and specimens recovered higher in the HCF. MOR 1122 7-22-00-1 expresses a deep recess extending medial to the strut of the triangular process, a feature shared with other HCF ceratopsid specimens but not Eotriceratops or other earlier occurring triceratopsin taxa. The morphology of MOR 1122 7-22-00-1 is consistent with noted stratigraphic trends in HCF ceratopsids and highlights the increased complexity of the narial region in uppermost Cretaceous triceratopsins.
Chapter
Two new specimens of the chasmosaurine ceratopsid Torosaurus latus from the Hell Creek Formation of Montana offer insight into the morphology, intraspecific variation, and phylogenetic relationships of the species. T. latus is recognizable by a broad parietal with a crescentic or cardiform caudal border, circular to mediolaterally elongated parietal fenestrae, and the occurrence of 10 or more parietal epoccipitals. The rest of the skull is virtually indistinguishable from that of Triceratops and other closely related chasmosaurines. Variation in T. latus specimens encompasses the size and shape of the frill, size and orientation of the horns, and morphology of the postfrontal fontanelle. The phylogenetic placement of T. latus within the Chasmosaurinae is equivocal; the genus is more derived than Anchiceratops, but the position of T. latus relative to Arrhinoceratops and the Triceratops-Diceratops clade is uncertain.
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Chasmosaurus irvinensis (sp. nov.) is distinguished from other species of this genus by the possession of a broad snout, absence of a brow horn (the position of which is occupied by a pit or rugosities suggestive of bone resorption), broadly rounded and open jugal notch, subrectangular squamosal, straight posterior parietal bar bearing 10 epoccipitals, eight of which are flattened, strongly curved anterodorsally, and nearly indistinguishably coossified to their neighbours, and small, transversely oriented parietal fenestrae restricted to the posterior portion of the frill. This species, restricted to the upper part of the Dinosaur Park Formation, is significantly younger than the other recognized Canadian Chasmosaurus species, C. belli and C. russelli. Phylogenetic analysis shows that C. irvinensis is most closely related to the other Canadian Chasmosaurus species and more distantly related to Chasmosaurus mariscalensis from Texas.
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Historically, the scarcity of non-adult Triceratops fossils collected from Upper Cretaceous sediments of North America limited our understanding and promoted controversy with regard to the morphology, and presence or absence of cranial epi-ossifications in this widely known horned dinosaur. The recent discovery of several exceptionally well preserved juvenile and subadult Triceratops skulls and numerous juvenile, subadult, and adult cranial elements, from the Hell Creek Formation of eastern Montana, confirms the ontogeny and morphology of epi-ossifications in this study. We propose to standardize the terminology for these four cranial epi-ossifications: epinasal, epijugal, epiparietal, and episquamosal. We describe the ontogeny and timing of the fusion of each of these epi-ossifications and the rostral from a cranial growth series. Although the timing is variable, the epinasal fuses first, followed by the rostal, the epijugals, the episquamosals, and lastly by the epiparietals. Co-ossification of the epinasal, rostral and epijugals unites several of the anterior (rostral-nasal-premaxillae) and lateral (jugal-quadratojugal) skull elements. In combination with forward directed postorbital horns and a massive fan-shaped frill, cranial epi-ossifications may have enhanced visual display and species communication in Triceratops.