Cretaceous dinosaurs in New Mexico

New Mexico has a relatively sparse Jurassic record of fossil vertebrates, much less than is known from either the Triassic or the Cretaceous strata in the state. The oldest Jurassic vertebrates from New Mexico are the osteichthyans Hulettia americana, Todiltia schoewei and Caturus dartoni from the Middle Jurassic (Callovian) Luciano Mesa Member of the Todilto Formation. The overlying Callovian-Oxfordian? Summerville Formation has yielded fragmentary sauropod dinosaur bones and teeth assigned to Camarasaurus, and theropod footprints identified as Megalosauripus and cf. Therangospodus. Most of New Mexico’s Jurassic vertebrate fossils are from the Upper Jurassic (Kimmeridgian-Tithonian?) Brushy Basin Member of the Morrison Formation and include the turtle Glyptops, the theropod dinosaurs Allosaurus and Saurophaganax, the ornithischian Stegosaurus and (mostly) sauropod dinosaurs identified as Apatosaurus, Brachiosaurus and Diplodocus (= “Seismosaurus”). The sparse record of Jurassic vertebrate fossils in New Mexico is partly due to the extensive eolian and evaporitic facies in parts of the Jurassic section, but mostly to a relative lack of effort to explore the Jurassic strata in New Mexico for vertebrate fossils. 97

Dinosaurs of New Mexico, New Mexico Museum of Natural History and Science Bulletin no, 2000

Cope (1885) published the first scientific report of dinosaur fossils from New Mexico. In the 115 years that followed, discoveries in Triassic, Jurassic and Cretaceous rocks have placed New Mexico in the forefront of dinosaur-collecting grounds (Fig. 1). Analysis of New Mexico's dinosaur fossils has been far reaching, touching upon every aspect of dinosaur paleontology, including biogeography, biostratigraphy, functional morphology, paleoecology, phylogeny, taphonomy and taxonomy. Indeed, this volume brings together ...

2010

New Mexico has a sparse but growing record of Jurassic dinosaurs. The oldest records are theropod footprints and a sauropod vertebra from the Middle-Upper Jurassic Summerville Formation. The footprints are part of a widespread large theropod-pterosaur ichnofacies in the Summerville and equivalent strata in the southern Western Interior. The sauropod is one of the oldest North American sauropods. The oldest theropod eggshell is from the Upper Jurassic Morrison Formation in New Mexico. Most New Mexican Jurassic dinosaurs are from the Upper Jurassic Morrison Formation and include Apatosaurus, Diplodocus carnegiei, Diplodocus (=Seismosaurus) hallorum, Camarasaurus, Allosaurus, and Stegosaurus. These dinosaurs are part of a homogenous Morrison dinosaur chronofauna found throughout the Western Interior and characteristic of the Comobluffian land-vertebrate faunachron.

For many years the diversity of dinosaurs of Mexico during the Late Cretaceous has been poorly understood. This is due to the limited taxonomical determinations and the abundant undescribed material. This paper presents a new review of the up-to-date osteological record of Late Cretaceous dinosaurs from Mexico, based on published papers, unpublished data and direct observation of the material housed in Mexican paleontological collections and in the field. Some diagnostic dinosaur bones were taxonomically reassigned and others reported in the literature were located in collections. We document new localities with dinosaur remains in Fronteras Sonora, Manuel Benavides and Jiménez Chihuahua, General Cepeda and Saltillo Coahuila. Additionally we report new material relating to tyrannosaurids, ornithomimids, ankylosaurs, ceratopsids and hadrosaurids which extends their geographic and temporal distribution in Mexico. This investigation has revealed a dinosaur faunal assemblage consistent with others studies of North American Late Cretaceous faunas, abundant large bodied dinosaurs and poorly represented small dinosaurs. The lack of oviraptorosaurs, lepoceratopsids and thescelosaurids suggests the need to develop new method in the search for smalldinosaurs in order to gain a more complete picture of dinosaur communities in Mexico and North America during the Late Cretaceous.

2010

We assign two incomplete dinosaur tracks from the Dakota Sandstone in Socorro County, west-central New Mexico to the ichnogenus Caririchnium sp., widely believed to represent the tracks of an iguanodontid ornithopod dinosaur. This is the first record of Cretaceous dinosaur tracks from west of the Rio Grande rift in New Mexico. Previous work suggests that the Dakota Sandstone in west-central New Mexico is of middle Cenomanian age, which makes these tracks younger than those of the so-called "dinosaur freeway" in the Dakota Group of northeastern New Mexico and eastern Colorado.

Studying the evolution and biogeographic distribution of dinosaurs during the latest Cretaceous is critical for better understanding the end-Cretaceous extinction event that killed off all non-avian dinosaurs. Western North America contains among the best records of Late Cretaceous terrestrial vertebrates in the world, but is biased against small-bodied dinosaurs. Isolated teeth are the primary evidence for understanding the diversity and evolution of small-bodied theropod dinosaurs during the Late Cretaceous, but few such specimens have been well documented from outside of the northern Rockies, making it difficult to assess Late Cretaceous dinosaur diversity and biogeographic patterns. We describe small theropod teeth from the San Juan Basin of northwestern New Mexico. These specimens were collected from strata spanning Santonian -Maastrichtian. We grouped isolated theropod teeth into several morphotypes, which we assigned to higherlevel theropod clades based on possession of phylogenetic synapomorphies. We then used principal components analysis and discriminant function analyses to gauge whether the San Juan Basin teeth overlap with, or are quantitatively distinct from, similar tooth morphotypes from other geographic areas. The San Juan Basin contains a diverse record of small theropods. Late Campanian assemblages differ from approximately co-eval assemblages of the northern Rockies in being less diverse with only rare representatives of troodontids and a Dromaeosaurus-like taxon. We also provide evidence that erect and recurved morphs of a Richardoestesia-like taxon represent a single heterodont species. A late Maastrichtian assemblage is dominated by a distinct troodontid. The differences between northern and southern faunas based on isolated theropod teeth provide evidence for provinciality in the late Campanian and the late Maastrichtian of North America. However, there is no indication that major components of small-bodied theropod diversity were lost during the Maastrichtian in New Mexico. The same pattern seen in northern faunas, which may provide evidence for an abrupt dinosaur extinction.

In 2003 vertebrate tracks attributed to pterosaur, crocodiles, turtles, hadrosaurs and sauropods have been reported from a locality close to Sabinas (Coahuila) in the Sierra Madre Oriental (Maastrichtian). Three trackways of medium-sized theropods could be observed. Evenly spaced parallel scratches forming a trackway might have been left by a swimming pterosaur. Furthermore a clear tetradactyl imprint, with claw marks only can be temptatively assigned to a pterosaur. So far, we have observed tracks of theropods only and probable prints of pterosaurs. The purported turtle tracks are small paired and tripled very faint scratches that have been produced by a xiphosuran arthropod. These are the first limulid tracks from Mexico. Another locality, Santa Helena, close to the village of Melchior Musquiz (Campanian) yields several surfaces with dinosaur fooprints. The best preserved trackway is attributed to a large theropod.

In 2003 vertebrate tracks attributed to pterosaur, crocodiles, turtles, hadrosaurs and sauropods have been reported from a locality close to Sabinas (Coahuila) in the Sierra Madre Oriental (Maastrichtian). Three trackways of medium-sized theropods could be observed. Evenly spaced parallel scratches forming a trackway might have been left by a swimming pterosaur. Furthermore a clear tetradactyl imprint, with claw marks only can be temptatively assigned to a pterosaur. So far, we have observed tracks of theropods only and probable prints of pterosaurs. The purported turtle tracks are small paired and tripled very faint scratches that have been produced by a xiphosuran arthropod. These are the first limulid tracks from Mexico. Another locality, Santa Helena, close to the village of Melchior Musquiz (Campanian) yields several surfaces with dinosaur fooprints. The best preserved trackway is attributed to a large theropod. kaupia | Darmstädter Beiträge zur Naturgeschichte | Heft 14 | 41-45 | Darmstadt, 18. Juli 2005 | 41

Science, 2007

It has generally been thought that the first dinosaurs quickly replaced more archaic Late Triassic faunas, either by outcompeting them or when the more archaic faunas suddenly became extinct. Fossils from the Hayden Quarry, in the Upper Triassic Chinle Formation of New Mexico, and an analysis of other regional Upper Triassic assemblages instead imply that the transition was gradual. Some