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Glishades ericksoni, a new hadrosauroid (Dinosauria: Ornithopoda) from the Late Cretaceous of North America
Abstract
A new genus and species of hadrosauroid dinosaur, Glishades ericksoni, is described based on paired partial premaxillae collected from the Upper Cretaceous Two Medicine Formation of Montana, in the Western Interior of the United States of America. This taxon is diagnosed on the basis of a unique combination of characters: absence of everted oral margin, arcuate oral margin with wide and straight, obliquely oriented, and undeflected anterolateral corner, grooved transversal thickening on ventral surface of premaxilla posterior to denticulate oral margin, and foramina on anteromedial surface above oral edge and adjacent to proximal end of narial bar. Maximum parsimony analysis positioned G. ericksoni as a derived hadrosauroid. Exclusion of G. ericksoni from Hadrosauridae was unambiguously supported by the lack in AMNH 27414 of a dorsomedially reflected premaxillary oral margin. Furthermore, the maximum agreement subtree positioned G. ericksoni as the sister taxon to Bactrosaurus johnsoni. This position was unambiguously supported by posteroventral thickening on the ventral surface of the premaxilla (independently derived in saurolophid hadrosaurids and Ouranosaurus nigeriensis) and having foramina on each premaxilla on the anterior surface, adjacent to the parasagittal plane of the rostrum (reconstructed as independently derived in Brachylophosaurus canadensis, Maiasaura peeblesorum, and Edmontosaurus annectens).
... The holotype and only specimen of Glishades ericksoni (AMNH 27414) consists of a united pair of partial premaxillae, and is notable for its very small size (86 mm total width). The holotype was collected along the Milk River, 48 km (30 miles) west (though not necessarily due west) of Sweetgrass, Montana, Glacier County, in the Two Medicine Formation (Prieto-Márquez 2010a). This description is the approximate location of Landslide Butte, a series of exposures that generally correspond to the upper 60 m of the formation (Horner et al. 2001), likely dated between 74.5 and 74 million years old (Foreman et al. 2008;Rogers et al. 1993). ...
... Small foramina are present in the three hadrosaurid specimens along the rostral surface of the oral margin adjacent to the proximal end of the narial bar ( Fig. 1e-h), similar to that described in AMNH 27414 (Prieto-Márquez 2010a), as well as in Bactrosaurus (Prieto-Márquez 2011). The ventral aspect of the oral margin in all four specimens ( Fig. 1m-p) is similarly denticulate with a deep peripheral groove that results in the 'double-layer' morphology present in all hadrosaurids and some non-hadrosaurid hadrosauroids (Horner et al. 2004;Prieto-Márquez 2010a). The oral margin is not strongly reflected dorsally in any of the specimens. ...
... (1) the absence of a reflected margin of the premaxilla; (2) the presence of foramina on the rostral surface of the premaxilla; (3) a groove on the ventral surface of the premaxilla caudal to the oral margin, which results in a "double-layer" morphology; and (4) a straight and wide oral margin, which Although the small size of AMNH 27414 is suggestive of juvenile status, Prieto-Márquez (2010a, 2011 argued that these characters do not vary ontogenetically in hadrosauroids, and thus could be confidently coded in a phylogenetic analysis and used as evidence of the unique taxonomic identity of Glishades. However, as we show above, the vast majority of the characters used to diagnose G. ericksoni are present in a similar combination in immature specimens of Prosaurolophus, Gryposaurus, and Maiasaura. ...
Glishades ericksoni was named on the basis of partial paired premaxillae collected from the Late Campanian Two Medicine Formation of Montana, and was described as a non-hadrosaurid hadrosauroid. This interpretation of G. ericksoni has significant implications for hadrosauroid diversity and distribution because it represents the first occurrence of a non-hadrosaurid hadrosauroid in the Late Campanian of North America, and therefore implies either a prolonged period of sympatry between these forms and hadrosaurids or a biotic interchange with Asia. Given its small size, and therefore potential juvenile status, the taxonomic identity of G. ericksoni is re-evaluated here. Comparison with similarly-sized, taxonomically determinate, and coeval hadrosaurid specimens from the Two Medicine Formation (Prosaurolophus, Gryposaurus, and Maiasaura) suggest that the combination of characters used to distinguish G. ericksoni as a non-hadrosaurid hadrosauroid are more widely distributed or individually variable in hadrosaurids, or can be explained as the result of ontogenetic variation. In particular, the unique combination of characters used to diagnose G. ericksoni is also found in juvenile individuals of Prosaurolophus, Gryposaurus, and Maiasaura. Inclusion of juveniles of these taxa, scored on the basis of comparable anatomy, in the original phylogenetic analysis recovers the juvenile hadrosaurid specimens outside Hadrosauridae. Consequently, G. ericksoni cannot be confidently differentiated from a juvenile saurolophine, which are common in the upper and middle sections of the Two Medicine Formation, and is thus considered a nomen dubium. Given their absence in well-sampled Late Campanian and Maastrichtian deposits, non-hadrosaurid hadrosauroids appear to have been completely replaced by hadrosaurids in western North America by the Late Campanian.
... This association is very different from the coeval western North American Triceratops "fauna" of the "Lancian Land Vertebrate Age" (see Weishampel et al., 2004) in which ceratopsians are the dominant dinosaurs, and hadrosaurids are represented only by the hadrosaurine Edmontosaurus (Anatotitan is a junior synonym of Edmontosaurus; Campione and Evans, 2011). By the mid-Campanian, western North American hadrosauroids were represented only by hadrosaurids McDonald et al., 2010;Prieto-Márquez, 2010a, 2010bEvans et al., 2012;Campione et al., 2013). Lambeosaurines practically disappeared at the beginning of the Late Maastrichtian (Campione and Evans, 2011;Sullivan et al., 2011); Hypacrosaurus is reported from the 31n polarity zone of the Horseshoe Canyon Formation (Eberth and Currie, 2010;Eberth et al., 2013). ...
Latest Cretaceous hadrosauroids from the Upper Campanian–Maastrichtian of Ukraine, Bulgaria, Romania,
Italy, Slovenia, Germany, Belgium and the Netherlands, France, and Spain are reviewed. This record includes
the non-hadrosaurid Telmatosaurus transsylvanicus and Tethyshadros insularis, and the lambeosaurines Parahabdodon isonensis, Arenysaurus ardevoli, and Blasisaurus canudoi. Orthomerus is a nomen dubium and Koutalisaurus kohlerorum is probably a junior synonym of Parahabdodon isonensis. The European hadrosauroids lived in an archipelago of relatively small islands (European Archipelago) and
most have a diminutive size when compared to the largest (“adult”) hadrosauroids from the uppermost Cretaceous of western North America and Asia. The Romanian hadrosauroids (“Tisia-Dacia” Island) were insular “dwarfs,” as were other hadrosauroids living on other European islands. However, a few relatively large individuals are reported from the relatively large “Ibero-Armorican” Island (Spain and France) and histological studies are needed to test the extent to which hadrosauroid insular dwarfism was expressed in the archipelago. The latest Cretaceous hadrosauroid assemblages from Europe more closely resemble those of eastern Asia than those of western North America.
Ornithopod dinosaurs are relatively common in the Cretaceous of Australia, particularly in the state of Victoria, which has yielded five taxa to date: two from the upper Strzelecki Group (upper Barremian–lower Aptian), and three from the Eumeralla Formation (upper Aptian–upper Albian). Whereas four of these are based solely on cranial material, Diluvicursor pickeringi is represented by a partial postcranium and is the only ornithopod specimen heretofore reported from the Eric the Red West (ETRW) site. Herein, we describe nine ornithopod dentulous elements from the Eumeralla Formation: seven from ETRW, and two from nearby sites. The four ETRW maxillae are divided into three morphotypes that are morphologically compatible with Leaellynasaura amicagraphica, Atlascopcosaurus loadsi, and cf. Galleonosaurus dorisae, respectively. Although this implies that Diluvicursor might not represent a distinct taxon, this is circumstantial. The new Leaellynasaura maxillae are evidently adult exemplars, contrasting with the juvenile holotype, whereas the sole Atlascopcosaurus maxilla is more complete than all previously referred specimens; consequently, revised diagnoses of both taxa are presented. Finally, the presence in the Eumeralla Formation of cf. Galleonosaurus—otherwise known only from the upper Strzelecki Group—implies that this taxon persisted from the Barremian to the Albian, and potentially indicates remarkable environmental stability in southeast Australia during the late Early Cretaceous.
Prosaurolophus maximus Brown is a saurolophine hadrosaurid known from numerous complete, articulated skulls from the Dinosaur Park Formation (Campanian, Alberta, Canada) that range in size by approximately half a metre in total skull length. Therefore, it is an important taxon for understanding patterns of growth and variation in saurolophines. This study describes the cranial anatomy of P. maximus from the type locality of Dinosaur Provincial Park (Dinosaur Park Formation: Campanian) on the basis of ten articulated skulls, quantitatively examines its range of osteological variation, and provides the first hypothesized ontogenetic series for this taxon. A second species, Prosaurolophus blackfeetensis Horner, was named on the basis of geologically younger material from Montana (Two Medicine Formation: Campanian) that is diagnosed by putative morphological differences in the nasal crest. However, considerable nasal crest variation in the sample from the Dinosaur Park Formation does not permit quantitative differentiation of P. blackfeetensis from P. maximus. Furthermore, a species-level phylogenetic analysis of saurolophines that includes both P. maximus and P. blackfeetensis as originally defined recovers them as sister taxa that do not differ morphologically in the character matrix. Based on both the morphometric and phylogenetic data, this study supports the hypothesis that P. blackfeetensis is a junior synonym of P. maximus, thereby substantially increasing its temporal range to 1.6 million years, and a concomitant period of morphological stasis in this taxon. © 2013 The Linnean Society of London
Phylogenetic reconstructions are sensitive to the
influence of ontogeny on morphology. Here, we use foetal/
neonatal specimens of known species of living baleen whales
(Cetacea: Mysticeti) to show how juvenile morphology of
extant species affects phylogenetic placement of the species.
In one clade (sei whale, Balaenopteridae), the juvenile is
distant from the usual phylogenetic position of adults, but in
the other clade (pygmy right whale, Cetotheriidae), the juvenile
is close to the adult. Different heterochronic processes at
work in the studied species have different influences on juvenile
morphology and on phylogenetic placement. This study
helps to understand the relationship between evolutionary
processes and phylogenetic patterns in baleen whale evolution
and, more in general, between phylogeny and ontogeny; likewise,
this study provides a proxy how to interpret the phylogeny
when fossils that are immature individuals are included.
Juvenile individuals in the peramorphic acceleration clades
would produce misleading phylogenies, whereas juvenile individuals
in the paedomorphic neoteny clades should still
provide reliable phylogenetic signals.
Huehuecanauhtlus tiquichensis gen. et sp. nov. is the southernmost diagnostic basal hadrosauroid in the Americas. The holotype and referred material of this taxon came from Santonian strata in the Michoacán State, southwestern Mexico. Huehuecanauhtlus tiquichensis is diagnosed on the basis of a combination of dental, axial, and appendicular characters, including the following: at least two teeth exposed on the occlusal plane of the dentary and maxilla; seven sacral vertebrae; tall neural spines of caudal vertebrae; supraacetabular process long; and short and trapezoidal (in lateral view) postacetabular process. It differs from other hadrosauroids in having an ilium with extreme ventral deflection of the preacetabular process.
Maximum parsimony cladistic analysis placed H. tiquichensis as a closely related outgroup to adrosauridae. The occurrence of H. tiquichensis in the Santonian of North America may be explained as a dispersal event from Asia to North America that occurred no later than the Albian or, alternatively, as a vicariant event of a most recent common ancestor widespread in both landmasses.
The juvenile anatomy of various cranial and appendicular elements of the hadrosauroid dinosaur Bactrosaurus johnsoni is described in detail. Growth changes are documented from juvenile to adult stages for each skeletal element available. In the studied skull, ontogenetic trends consist of: development of features on the ventral surface of the frontal; reduction in the slope of the posteromedial process of the premaxilla; a posterior shift of the dorsal process of the maxilla; development of concavities on the medial surface of the prefrontal; increased robustness and development of the ventral flange of the jugal; decreased curvature of the long axis of the quadrate; increased ventral deflection of the dentary; and changes in the length/width proportions and depth of the anterior surface of the predentary. In the appendicular skeleton, the majority of ontogenetic variation from juvenile to adult occurs in the limb bones, including increased robustness of the deltopectoral crest of the humerus; relative shortening of the ulna; increased development of the fourth trochanter and mediolateral widening of the distal end of the femur; increased expansion of the cnemial crest of the tibia; and the increased prominence of articular protuberances and flanges of the metatarsals. A survey of the phylogenetically informative characters present in B. johnsoni indicates that several characters concerning the frontal, maxilla, jugal, quadrate, predentary, dentary, scapula, humerus and ilium are affected by ontogeny. Nevertheless, the majority of phylogenetic characters are not ontogenetically variable, suggesting that a substantial amount of the information provided by juvenile and subadult specimens for phylogenetic inference is reliable in basal hadrosauroids.
The precise phylogenetic relationships of many non-hadrosaurid members of Iguanodontia, i.e., basal iguanodonts, have been unclear. Therefore, to investigate the global phylogeny of basal iguanodonts a comprehensive data matrix was assembled, including nearly every valid taxon of basal iguanodont. The matrix was analyzed in the program TNT, and the maximum agreement subtree of the resulting most parsimonious trees was then calculated in PAUP. Ordering certain multistate characters and omitting taxa through safe taxonomic reduction did not markedly improve resolution. The results provide some new information on the phylogeny of basal iguanodonts, pertaining especially to obscure or recently described taxa, and support some recent taxonomic revisions, such as the splitting of traditional "Camptosaurus" and "Iguanodon". The maximum agreement subtree also shows a close relationship between the Asian Probactrosaurus gobiensis and the North American Eolambia, supporting the previous hypothesis of faunal interchange between Asia and North America in the early Late Cretaceous. Nevertheless, the phylogenetic relationships of many basal iguanodonts remain ambiguous due to the high number of taxa removed from the maximum agreement subtree and poor resolution of consensus trees.
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