Anatomy and relationships of Lamb...
ARTICLE ANATOMY AND RELATIONSHIPS OF LAMBEOSAURUS MAGNICRISTATUS, A CRESTED HADROSAURID DINOSAUR (ORNITHISCHIA) FROM THE DINOSAUR PARK FORMATION, ALBERTA DAVID C. EVANS*,1 and ROBERT R. REISZ2 1University of Toronto at Mississauga, 3359 Mississauga Road, Mississauga, Ontario L5L 1C6, Canada, email@example.com 2University of Toronto at Mississauga, 3359 Mississauga Road, Mississauga, Ontario L5L 1C6, Canada, firstname.lastname@example.org ABSTRACT���The first detailed description of the lambeosaurine Lambeosaurus magnicristatus (Ornithischia: Hadro- sauridae) confirms that it is a distinct taxon characterized by its comparatively enormous cranial crest, formed predomi- nantly by the caudodorsal process of the premaxilla, and an acute crest-snout angle. The holotype of L. magnicristatus occurs stratigraphically higher than all other Dinosaur Park Formation lambeosaurines at the Dinosaur Provincial Park locality. The only referred specimen was collected over 170 kilometers southeast of the type locality. Correlation of its host stratum with the well-known Dinosaur Park section reveals that L. magnicristatus has no biostratigraphic overlap with L. lambei and suggests that it replaces L. lambei on a regional scale in southern Alberta at the end of ���Dinosaur Park time.��� Species-level phylogenetic analysis of Lambeosaurinae corroborates the monophyly of Lambeosaurus. The genus is characterized by five apomorphies, including a procumbent crest, complete enclosure of the ophthalmic canal of the laterosphenoid, the presence of a flange on the caudodorsal process of the premaxilla that overlaps the nasal in the rostral region of the crest, caudal extension of the premaxilla such that it forms the caudal margin of the crest, and a unique joint between the rostral nasal and the caudodorsal process of the premaxilla. Lambeosaurine phylogeny indicates that the development of a hypertrophied cranial crest evolved independently at least three times within the clade, suggesting that the crest enlargement is a recurring evolutionary trend within Lambeosaurinae. INTRODUCTION Lambeosaurinae is a monophyletic clade of ornithopod dino- saurs characterized by hypertrophied nasal passages and associ- ated cranial crests (Horner et al., 2004). Lambeosaurines were common in many Late Cretaceous ecosystems of Western North America and Asia and are well represented in the fossil record, particularly that of western Canada (Lull and Wright, 1942). Large sample size, taxonomic diversity, and increasing control of their chronostratigraphic and paleoecological contexts make the group an excellent clade with which to investigate modes and mechanisms of Late Cretaceous dinosaur evolution and histori- cal biogeography. The phylogenetic framework required to address many evolu- tionary questions is lacking because the interrelationships of lambeosaurines are currently unresolved. Phylogenetic analyses published to date are incomplete to the species-level and conflict with regards to the placement of several key North American taxa (e.g., Godefroit et al., 2004a Suzuki et al., 2004). For ex- ample, Lambeosaurus, the namesake of the clade, is notably poorly understood in light of the abundance of available mate- rial. Recent analyses have placed Lambeosaurus as sister-taxon to Corythosaurus casuarius (Suzuki et al., 2004), sister taxon to an unresolved Corythosaurus-Hypacrosaurus-Olorotitan clade (Godefroit et al., 2003 Godefroit et al., 2004a Godefroit et al., 2004b), in an unresolved polytomy with Corythosaurus and Hypacrosaurus (Godefroit et al., 2001 Horner et al., 2004 Prieto-Marquez et al., 2006), and even as a possible ���meta- species��� in a Lambeosaurus-Hypacrosaurus anagenetic lineage (Horner et al., 1992). All unequivocal Lambeosaurus material has been collected from the Dinosaur Park Formation (DPF) of southern Alberta (Horner et al., 2004 Ryan and Evans, 2005). Two species are generally recognized following the important biometric study of Dodson (1975), although several alternate taxonomic schemes have been proposed to accommodate Lambeosaurus cranial variation (Hopson, 1975 Carpenter, 1999). Lambeosaurus lam- bei (sensu Dodson, 1975) is known from several complete but briefly described postcranial skeletons, and over 15 skulls that represent several cranial ontogenetic stages (Parks, 1931, 1935 Sternberg, 1935 Dodson, 1975 Evans et al., 2005). Only two skeletons are typically assigned to L. magnicristatus, which is differentiated from L. lambei by the much larger size of its cra- nial crest (Sternberg, 1935 Dodson, 1975 Horner et al., 2004 Ryan and Evans, 2005). L. magnicristatus has only been tersely described on the basis of the poorly preserved holotype skull and ilium (Sternberg, 1935), and it is the only lambeosaurine hadro- saurid from the Cretaceous of Alberta to remain without de- scription of its postcranial skeleton. The holotype of Lambeosaurus magnicristatus (CMN 8705) originally consisted of a largely complete, articulated skeleton collected from within the boundaries of what is now Dinosaur Provincial Park, Alberta (Figs. 1, 2). Subsequent to description of the skull and ilium (Sternberg, 1935), the unprepared post- cranial skeleton suffered extensive water damage while in stor- age and major portions of most limb and girdle bones were de- stroyed and discarded. The remainder of the holotype remains unprepared. Fortunately, a second skeleton (TMP 66.04.01) col- lected from the Manyberries area of southeastern Alberta in- cludes an excellent skull and an undistorted articulated post- cranium (Figs. 1, 3, 4). Although the postcervical vertebrae and *Corresponding author Royal Ontario Museum, Department of Natu- ral History (Paleobiology), 100 Queen���s Park, Toronto, Ontario, Canada, M5S 2C6. Journal of Vertebrate Paleontology 27(2):373���393, June 2007 �� 2007 by the Society of Vertebrate Paleontology 373
most bones from the left side are not preserved, the right side consists of complete limb bones now lost, damaged or incom- plete in the holotype. The skull preserves considerable detail and provides new information on braincase and lower jaw anatomy. In this paper, the skull and skeleton of Lambeosaurus magnicris- tatus are described on the basis of all available material. Taxo- nomic issues including hypotheses of sexual dimorphism are evaluated in light of new anatomical and biostratigraphic data, and L. magnicristatus is systematically revised in the context of the most inclusive phylogenetic analysis of the clade. Institutional Abbreviations���AMNH, American Museum of Natural History, New York CMN, Canadian Museum of Na- ture, Ottawa MOR, Museum of the Rockies, Bozeman ROM, Royal Ontario Museum, Toronto TMP, Royal Tyrrell Museum of Paleontology, Drumheller YPM, Yale Peabody Museum, New Haven. SYSTEMATIC PALEONTOLOGY DINOSAURIA Owen, 1942 ORNITHISCHIA Seeley, 1888 HADROSAURIDAE Cope, 1869 LAMBEOSAURINAE Parks, 1923 LAMBEOSAURUS Parks, 1923 Type Species���Lambeosaurus lambei (Parks, 1923) Amended Diagnosis���Lambeosaurine hadrosaurid that has the following autapomorphies: crest procumbent with a crest- snout angle less than 110 degrees caudal margin of crest formed predominantly by the premaxilla (with the nasal contributing to the lateroventral region of a solid caudal process) rostral nasal- caudodorsal process of premaxilla (pm1) joint in which the nasal fits along ventral edge of the premaxilla premaxilla caudodorsal process with accessory ventral flange that overlaps the nasal in the rostral region of the crest (convergently evolved in Hypacro- saurus altispinus) complete enclosure of the ophthalmic canal of the laterosphenoid. Differs from Corythosaurus and Hypacro- saurus in three features of the crest: 1) the caudodorsal and caudolateral processes of the premaxilla are expanded rostrally and the apex of the crest occurs rostral to the orbit, 2) the nasal forms a relatively small contribution to the external crest surface, 3) caudodorsal process of the premaxilla extends to the caudal- most limit of the crest. LAMBEOSAURUS MAGNICRISTATUS (Sternberg, 1935) Lambeosaurus magnicristatum Sternberg 1935:364, Plate VII (original description). Lambeosaurus magnicristatus Sternberg: Wilfarth, 1938:34, fig. 16 (amended spelling). Holotype���CMN 8705 (Figs. 2, 5), originally a nearly com- plete articulated skeleton that consisted of a poorly preserved skull and most of the postcranium with the exception of the left hand and distal part of antebrachium, the right forelimb, ribs from the right side, and distal caudals. Undescribed portions of the skeleton that were severely damaged and discarded include most of the pre-sacral vertebrae and ribs, the distal ends of the left scapula and both femora, proximal segments of the left hu- merus, right tibia and right fibula, caudal dorsals, sacrum, left ilium, and pubes. Unprepared blocks containing the left antebra- chium and mid-caudal vertebrae with associated chevrons are missing. Only the skull and the right ilium are prepared. Locality and Horizon���RTMP Quarry No. 108 (Currie and Russell, 2005), Sternberg Map Quarry No. 46 (Sternberg, 1950), Dinosaur Provincial Park, Alberta, Canada (see Fig. 1) UTM 12U 460546E 5621615N (NAD 83). The quarry (707 m asl) is high stratigraphically within Dinosaur Park Formation, 47 m above the Oldman-Dinosaur Park formational contact. Referred Specimen���TMP 66.04.01 (Figs. 3, 4, 6���8), a well- preserved articulated skeleton that includes a complete skull ex- cept for a small caudodorsal portion of the crest. The post- cranium lacks all postcervical vertebrae, ribs from the left side, dorsal rib heads from the right side, all appendicular bones from FIGURE 1. Map of southern Alberta and stratigraphic position of Lam- beosaurus magnicristatus localities. Type locality (CMN 8705), Dinosaur Provincial Park, and the site of TMP 66.04.01, near Manyberries, Alberta, indicated by black stars on the map. Generalized stratigraphic sections (below) at each of the localities and another near Onefour, Alberta are aligned at the base of the Bearpaw Formation, and increments on left are in meters above Oldman Formation. The base of the Lethbridge coal zone is a chronostratigraphic datum across southern Alberta, whereas the Oldman- Dinosaur Park formational contact is a lithostratigraphic boundary, not a chronostraticgraphic datum across the same region. Dinosaur Provin- cial Park and Onefour sections from Eberth and Hamblin (1993) the Manyberries section is from D. Eberth (unpublished data, 2006). JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 27, NO. 2, 2007 374
the left side with the exception of the incomplete metacarpus, distal tibia and incomplete metatarsus. Many bones from the manus and pes are missing. Skin impressions from numerous areas of the right side of the body are also preserved. Locality and Horizon���Fourteen kilometers southeast of the town of Manyberries, Alberta (see Fig. 1) UTM 12U 532049E 5466577N (WGS 84), 973 m asl the likely location of the quarry was relocated in the summer of 2006 by DCE. Legal Land De- FIGURE 3. Skull of Lambeosaurus magnicristatus, TMP 66.04.01, in lateral view. Abbreviations: as for Figure 3, with: an, angular ar, articular cp, cultriform process ec, ectopterygoid p, parietal pl, palatine pra, prearticular. Roman numerals indicate foramen for corresponding cranial nerves. Scale bar equals 10 cm. FIGURE 2. Lambeosaurus magnicristatus, holotype skull, CMN 8705, in lateral view. Abbreviations: d, dentary ex, exoccipital-opisthotic j, jugal l, lacrimal m, maxilla n, nasal pd, predentary pm1, caudodorsal process of premaxilla pm2, caudolateral process of premaxilla po, postorbital prf, prefrontal q, quadrate qj, quadratojugal sa, surangular sq, squamosal. Shaded areas in outline represent regions obscured by plaster. Scale bar equals 10 cm. EVANS AND REISZ���LAMBEOSAURUS MAGNICRISTATUS 375