Albert Prieto-Márquez

NEW INFORMATION ON THE CRANIUM OF BRACHYLOPHOSAURUS CANADENSIS (DINOSAURIA, HADROSAURIDAE), WITH A REVISION OF ITS PHYLOGENETIC POSITION

Abstract The cranium of the hadrosaurid dinosaur Brachylophosaurus canadensis is redescribed on the basis of abundant and complete material from the Lower Campanian Judith River Formation of Malta, northeastern Montana. The diagnosis of this taxon is emended, and the species Brachylophosaurus goodwini is now considered to be a junior synonym of Brachylophosaurus canadensis. Autapomorphies of Brachylophosaurus are: nasal greatly developed into paddle-like solid crest extending caudodorsally, overhanging dorsal region of skull; nasal possessing anteroposteriorly oriented groove terminating in elongated foramen located medial to prefrontal; prefrontal projecting posteriorly and resting dorsomedially over anterior process of postorbital and, more posteriorly, extending ventromedially under nasal; only anterior sharp tip of lacrimal contacting maxilla; jugal with ventrally projecting semicircular flange; extremely elongated, rod-like anterodorsal process of maxilla projecting medial to narial cavity along most of anteroposterior length of external naris; anteroposteriorly short exoccipital-supraoccipital roof posterior and dorsal to foramen magnum. Most autapomorphies of the junior synonym species Brachylophosaurus goodwini originated from misplacement of a nasal fragment and individual variation of the jugal. The new osteological information supports Brachylophosaurus canadensis as the sister taxon to Maiasaura peeblesorum, and suggests that the two taxa form a robust and basal clade within the Hadrosaurinae. Two new characters are discussed as phylogenetically informative for hadrosaurids: the mediolateral and anteroposterior predentary proportions and the length of the prequadratic process of the squamosal.

Mountain Building Triggered Late Cretaceous North American Megaherbivore Dinosaur Radiation

Prior studies of Mesozoic biodiversity document a diversity peak for dinosaur species in the Campanian stage of the Late Cretaceous, yet have failed to provide explicit causal mechanisms. We provide evidence that a marked increase in North American dinosaur biodiversity can be attributed to dynamic orogenic episodes within the Western Interior Basin (WIB). Detailed fossil occurrences document an association between the shift from Sevier-style, latitudinally arrayed basins to smaller Laramide-style, longitudinally arrayed basins and a well substantiated decreased geographic range/increased taxonomic diversity of megaherbivorous dinosaur species. Dispersal-vicariance analysis demonstrates that the nearly identical biogeographic histories of the megaherbivorous dinosaur clades Ceratopsidae and Hadrosauridae are attributable to rapid diversification events within restricted basins and that isolation events are contemporaneous with known tectonic activity in the region. SymmeTREE analysis indicates that megaherbivorous dinosaur clades exhibited significant variation in diversification rates throughout the Late Cretaceous. Phylogenetic divergence estimates of fossil clades offer a new lower boundary on Laramide surficial deformation that precedes estimates based on sedimentological data alone.

A Re-Evaluation of Secernosaurus koerneri and Kritosaurus australis (Dinosauria, Hadrosauridae) from the Late Cretaceous of Argentina

ABSTRACT Hadrosaurids form the most diverse and derived clade of ornithopod dinosaurs. Although well represented in Asia and North America, its presence in South America is known only from rare and fragmentary remains that are poorly documented and mostly unstudied. As a result, the impact of these animals on the phylogenetics and biogeography of hadrosaurids as a whole is poorly known. Here, we provide a revised and complete osteology of the type specimens and hypodigms for the only two taxa known from South America, Secernosaurus koerneri and Kritosaurus australis. Likewise, we infer the phylogenetic position and historical biogeography of South American hadrosaurids using a nearly complete taxonomic sampling of hadrosaurid species. Parsimony methods were used to infer phylogenetic relationships, whereas Fitch parsimony and Dispersal-Vicariance analyses were implemented to reconstruct ancestral areas. Kritosaurus australis is regarded as a junior synonym of Secernosaurus koerneri, based on a combination of iliac and pubic characters unique to these two taxa. Inclusion of 5. koerneri within the genus Kritosaurus is not supported by the phylogenetic analysis. S. koerneri is inferred to be a member of the Kritosaurus-Gryposaurus clade within Saurolophinae, as the sister taxon to the Argentinean unnamed hadrosaurid from Salitral Moreno. Another unnamed hadrosaurid from Big Bend National Park, Texas, is positioned as the closest outgroup to the South American clade. The results of this biogeographical analysis supports the hypothesis that the Secernosaurus clade originated in South America during the late Campanian after a dispersal event (probably followed by vicariance) from southern North America before the end of that geologic stage.

Diversity, Relationships, and Biogeography of the Lambeosaurine Dinosaurs from the European Archipelago, with Description of the New Aralosaurin Canardia garonnensis

We provide a thorough re-evaluation of the taxonomic diversity, phylogenetic relationships, and historical biogeography of the lambeosaurine hadrosaurids from the European Archipelago. Previously published occurrences of European Lambeosaurinae are reviewed and new specimens collected from upper Maastrichtian strata of the south-central Pyrenees are described. No support is found for the recognition of European saurolophines in the available hadrosaurid materials recovered so far from this area. A new genus and species of basal lambeosaurine, Canardia garonnensis, is described on the basis of cranial and appendicular elements collected from upper Maastrichtian strata of southern France. C. garonnensis differs from all other hadrosaurids, except Aralosaurus tuberiferus, in having maxilla with prominent subrectangular rostrodorsal flange; it differs from A. tuberiferus in a few maxillary and prefrontal characters. Together with A. tuberiferus, C. garonnensis integrates the newly recognized tribe Aralosaurini. Inference of lambeosaurine interrelationships via maximum parsimony analysis indicates that the other three known European lambeosaurines are representatives of two additional subclades (tribes) of these hadrosaurids: Tsintaosaurini (Pararhabdodon isonensis) and Lambeosaurini (the Arenysaurus ardevoli-Blasisaurus canudoi clade). The tribes Aralosaurini, Tsintaosaurini, Lambeosaurini, and Parasaurolophini are formally defined and diagnosed for the first time. Three event-based quantitative methods of ancestral range reconstruction were implemented to infer the historical biogeography of European lambeosaurines: Dispersal-Vicariance Analysis, Bayesian Binary MCMC, and Dispersal-Extinction-Cladogenesis. The results of these analyses, coupled with the absence of pre-Maastrichtian lambeosaurines in the Mesozoic vertebrate fossil record of Europe, favor the hypothesis that aralosaurins and tsintaosaurins were Asian immigrants that reached the Ibero-Armorican island via dispersal events sometime during the Maastrichtian. Less conclusive is the biogeographical history of European lambeosaurins; several scenarios, occurring sometime during the Maastrichtian, are possible, from vicariance leading to the splitting of Asian or North American from European ranges to a dispersal event from North America to the European Archipelago.

The lambeosaurine dinosaur Magnapaulia laticaudus from the late cretaceous of Baja California, Northwestern Mexico.

The taxonomy, osteology, phylogenetic position, and historical biogeography of the lambeosaurine hadrosaurid Magnapaulia laticaudus (new combination) are revised. The diagnosis of this species is amended on the basis on two autapomorphies (i.e., longest haemal arches of proximal caudal vertebrae being at least four times longer than the height of their respective centra; base of prezygapophyses in caudal vertebrae merging to form a bowl-shaped surface) and a unique combination of characters (i.e., downturned cranioventral process of the maxilla; tear-shaped external naris with length/width ratio between 1.85 and 2.85; neural spines of dorsal, sacral, and proximal caudal vertebrae being at least four times the height of their respective centra). A maximum parsimony analysis supports a sister taxon relationship between M. laticaudus and Velafrons coahuilensis. Both taxa constitute a clade of southern North American lambeosaurines, which forms a sister relationship with the diverse clade of helmet-crested lambeosaurines from northern North America that includes well-known genera like Corythosaurus, Lambeosaurus, and Hypacrosaurus. According to the results of a Dispersal-Vicariance analysis, southern North American lambeosaurines split from the northern forms via vicariance from a common ancestor that lived in both the northern and southern regions of the continent.

NEONTOLOGICAL EVALUATION OF PELVIC SKELETAL ATTRIBUTES PURPORTED TO REFLECT SEX IN EXTINCT NON-AVIAN ARCHOSAURS

Abstract Sex in non-avian archosaurs has been inferred using a variety of osteological attributes. However, little quantitative data have been presented showing that these phenotypes truly exist. In this study, testing for the presence of pelvic osteological correlates of sex in extant archosaurs was conducted, using skeletons of wild-caught A. mississippiensis as a neontological model. For outgroup comparison, the squamate Iguana iguana is included. A sample of 16 females and 19 males of A. mississippiensis, and 18 females and 10 males of I. iguana were examined. Measurements included pelvic canal area, dorsoventral depth, and mediolateral width of the pelvic canal, mediolateral width between the dorsal edge of each ilium, and ischium orientation. These data were analyzed using analyses of covariance, a t-test, and a recently developed geodesic distance shape analysis. Results indicate that there is sexual dimorphism in the proportions of the pelvic canal in A. mississippiensis, with females typically having deeper pelvic canals than males. This dimorphism might be synapomorphic for Archosauria. No dimorphism was found in I. iguana. The detection of dimorphism in A. mississipiensis required large sample sizes owing to substantial overlap between sexes. Thus, sexing isolated specimens using this metric is tenuous at best. Assuming similar variance in the relative pelvic depth versus width in other non-avian archosaurs, this criterion would also produce imprecise determinations of sex for these taxa.

The Braincase and Skull Roof of Gryposaurus notabilis (Dinosauria, Hadrosauridae), with a Taxonomic Revision of the Genus

ABSTRACT The facial and neurocranial anatomy of AMNH 5350, containing the most complete braincase available for Gryposaurus, is described in detail. The specimen, collected from Late Campanian outcrops of the Dinosaur Park Formation of southern Canada, is referred to G. notabilis because of the combination of a preorbital nasal protuberance positioned above the level of the frontals, narrow U-shaped posterior margin of the narial fenestra, dorsal margin of the infratemporal fenestra being wider than that of the orbit, and posterodorsal margin of the squamosal located dorsal to the skull roof. The flat nasal protuberance of AMNH 5350 differs from the arcuate lateral profile displayed in other specimens of G. notabilis, indicating that substantial intraspecific variation existed in this feature. The taxonomy of Gryposaurus is revised in light of the newly garnered anatomical data. Thus, G. incurvimanus is regarded as a junior synonym of G. notabilis, composed of subadult specimens of the latter. Characters thought to be diagnostic of G. incurvimanus are either present in G. notabilis (e.g., slightly excavated ventral surface of the nasal protuberance) or probably indicative of sub-adulthood (e.g., less developed and more anteriorly positioned nasal protuberance correlated with smaller skull size). A number of characters previously used to distinguish among Gryposaurus sepecies are shown to be intraspecifically variable (e.g., curvature of the lateroventral margin of the maxilla or ventral deflection of the dentary symphyseal process).

The ‘Unicorn’ Dinosaur That Wasn’t: A New Reconstruction of the Crest of Tsintaosaurus and the Early Evolution of the Lambeosaurine Crest and Rostrum

The lambeosaurine Tsintaosaurus spinorhinus has traditionally been reconstructed with an elevated, hollow, spike-like crest composed entirely of the nasal bones, although this has been disputed. Here, we provide a new reconstruction of the skull of this species based on reexamination and reinterpretation of the morphology and articular relationships of the type and Paratype skulls and a fragmentary crest. We confirm the presence of a supracranial crest composed of the elevated nasal bones, but also including the premaxillae. We hypothesize that the crest is a tall, lobate, hollow structure that projects dorsally and slightly caudally a distance greater than the height of the skull along the quadrate. In our reconstruction, the nasal passage passes through the crest, but enters the skull rostral to the tubular process of the nasals, not through it. Tsintaosaurus spinorhinus is rediagnosed on the basis of a suite of cranial autapomorphies including a circumnarial fossa subdivided into three accessory fossae, prefrontal with ascending rostral process and lateral flange, nasals fused sagittally to form elongate tubular process that rises dorsally from skull roof, each nasal being expanded rostrocaudally into a rhomboid distal process, and medial processes of premaxillae at the summit of the cranial crest inserted between rhomboid processes of nasals. Tsintaosaurus spinorhinus lacks characters that are present in more derived lambeosaurines (parasaurolophins and lambeosaurins), such as rotation of the caudal margin of the crest to an acute angle with the skull roof, lateral processes of the nasals that enclose part of the intracranial cavity and participate in the formation of the walls of the common median chamber, and a smooth narial fossa lacking ridges and accessory fossae. We hypothesize that ancestrally the rostrum of lambeosaurines may have been more similar to that in Saurolophinae, and became subsequently reduced in complexity during evolution of the group.

A Reapprisal of Barsboldia sicinskii (Dinosauria: Hadrosauridae) from the Late Cretaceous of Mongolia

Abstract The taxonomy and phylogenetic position of the hadrosaurid dinosaur Barsboldia sicinskii is revised. This species is rediagnosed based on the unique combination of iliac central plate with depth/length ratio less than 0.8 and sacral vertebrae with distally ‘clubbed’ neural spines at least four times higher than their centra. A maximum parsimony analysis of 47 hadrosauroid (39 hadrosaurid) species does not support the purported lambeosaurine affinities of B. sicinskii, but recovers this form as a basal saurolophine hadrosaurid based on unambiguous synapomorphies of the ilium. This result increases the diversity of saurolophine taxa in Asia, a continent with a hadrosaurid fossil record so far dominated by lambeosaurines. Finally, several vertebral and iliac characters previously regarded as diagnostic of Lambeosaurinae are discussed and shown to be uninformative from a taxonomic or phylogenetic standpoint.

A diminutive deinonychosaur (Dinosauria: Theropoda) from the Early Cretaceous of Öösh (Övörkhangai, Mongolia)

Prieto-Márquez, A., Minjin B. & Horner, J.R. iFirst article. A diminutive deinonychosaur (Dinosauria: Theropoda) from the Early Cretaceous of Öösh (Övörkhangai, Mongolia). Alcheringa, 1–19. ISSN 0311-5518. We describe a new specimen of small maniraptoran theropod from the Early Cretaceous Öösh locality, Övörkhangai province, central Mongolia. This exemplar ISMD-VP09 preserves a maxillary fragment, two teeth and partial appendicular elements. The strict consensus of a parsimony analysis of 68 coelurosaur taxa places this theropod within Deinonychosauria with an unresolved relationship with the other members of the clade. Support for this clade was based on two unambiguous synapomorphies: maxillary dentition with at least some teeth lacking denticles anteriorly, and ungual and penultimate pedal phalanx II highly modified for hyperextension, with ungual II being more strongly curved and substantially larger than that of digit III. The finding of a new small theropod specimen in the Öösh Formation adds to the deinonychosaur fossil record from the same beds, until now restricted to the dromaeosaurid Shanag ashile.