doi: 10.1371/journal.pone.0141304.
eCollection 2015.
A New Brachylophosaurin Hadrosaur (Dinosauria: Ornithischia) with an Intermediate Nasal Crest from the Campanian Judith River Formation of Northcentral Montana
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- PMID: 26560175
- PMCID: PMC4641681
- DOI: 10.1371/journal.pone.0141304
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A New Brachylophosaurin Hadrosaur (Dinosauria: Ornithischia) with an Intermediate Nasal Crest from the Campanian Judith River Formation of Northcentral Montana
PLoS One.
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Abstract
Background: Brachylophosaurini is a clade of hadrosaurine dinosaurs currently known from the Campanian (Late Cretaceous) of North America. Its members include: Acristavus gagslarsoni, which lacks a nasal crest; Brachylophosaurus canadensis, which possesses a flat paddle-shaped nasal crest projecting posteriorly over the dorsal skull roof; and Maiasaura peeblesorum, which possesses a dorsally-projecting nasofrontal crest. Acristavus, from the lower Two Medicine Formation of Montana (~81-80 Ma), is hypothesized to be the ancestral member of the clade. Brachylophosaurus specimens are from the middle Oldman Formation of Alberta and equivalent beds in the Judith River Formation of Montana; the upper Oldman Formation is dated 77.8 Ma.
Methodology/principal findings: A new brachylophosaurin hadrosaur, Probrachylophosaurus bergei (gen. et sp. nov.) is described and phylogenetically analyzed based on the skull and postcranium of a large individual from the Judith River Formation of northcentral Montana (79.8-79.5 Ma); the horizon is equivalent to the lower Oldman Formation of Alberta. Cranial morphology of Probrachylophosaurus, most notably the nasal crest, is intermediate between Acristavus and Brachylophosaurus. In Brachylophosaurus, the nasal crest lengthens and flattens ontogenetically, covering the supratemporal fenestrae in large adults. The smaller nasal crest of Probrachylophosaurus is strongly triangular in cross section and only minimally overhangs the supratemporal fenestrae, similar to an ontogenetically earlier stage of Brachylophosaurus. Sutural fusion and tibial osteohistology reveal that the holotype of Probrachylophosaurus was relatively more mature than a similarly large Brachylophosaurus specimen; thus, Probrachylophosaurus is not simply an immature Brachylophosaurus.
Conclusions/significance: The small triangular posteriorly oriented nasal crest of Probrachylophosaurus is proposed to represent a transitional nasal morphology between that of a non-crested ancestor such as Acristavus and the large flat posteriorly oriented nasal crest of adult Brachylophosaurus. Because Probrachylophosaurus is stratigraphically and morphologically intermediate between these taxa, Probrachylophosaurus is hypothesized to be an intermediate member of the Acristavus-Brachylophosaurus evolutionary lineage.
Conflict of interest statement
Figures
Members of Brachylophosaurini indicated in blue: Acristavus gagslarsoni, Probrachylophosaurus bergei gen. et sp. nov., Brachylophosaurus canadensis, and Maiasaura peeblesorum. Radiometric dates are indicated in dark gray, and have been recalibrated to the Fish Canyon sanidine standard (28.305 +/- 0.036 Ma) of Renne et al. [10] from the originally published values [–15]; see text and Table 1 for further recalibration details.
Inset shows North America in dark grey with Montana and southern Alberta in light grey. Kennedy Coulee, locality of Probrachylophosaurus bergei gen. et sp. nov., marked with red star. Other Brachylophosaurini localities indicated with black dots: Malta, Brachylophosaurus canadensis; Onefour, B. canadensis; DPP (Dinosaur Provincial Park), B. canadensis; Choteau, Acristavus gagslarsoni and Maiasaura peeblesorum.
(A) Preserved skull elements of MOR 2919, left lateral view. Predentary not included due to its poor preservation and diagenetic compression. (B) Outline of skull reconstruction, left lateral view. The outline accounts for diagenetic distortion of the posterior braincase, but otherwise does not correct for distortion of skull elements. Outlined regions where left skull material was not preserved are based on right bones when available. Regions with neither left nor right material preserved are hypothesized reconstructions based on Brachylophosaurus canadensis skulls. (C) Braincase with left nasal crest, dorsal view. (D) Outline of braincase reconstruction with nasal crest, dorsal view. Reconstruction accounts for diagenetic lateral compression and distortion of posterior braincase. Abbreviations: d, dentary; ex, exoccipital; f, frontal; j, jugal; l, lacrimal; m, maxilla; n, nasal; p, parietal; pd, predentary; pf, prefrontal; pm, premaxilla; po, postorbital; q, quadrate; qj, quadratojugal; sa, surangular; sq, squamosal.
Datum (0 m) is the top of the Marker A coal of the Taber Coal Zone of the Foremost Formation. Radiometric dates were recalibrated from Goodwin and Deino [11] samples collected southwest of MOR JR-518 in Kennedy Coulee; their stratigraphic heights are indicated on the section. This section is atypical for Kennedy Coulee sections in that it has a relatively thin Herronton Sandstone Zone (HSZ) low in section, and more sandstones in the upper part of the section, whereas most of the coulee has a thick sandstone zone above the Marker A coal, and is dominated by mudstone in the upper regions. The region indicated with “?” below the HSZ may or may not be classified as a continuation of the Taber Coal Zone.
(A-D, F) Probrachylophosaurus bergei gen. et sp. nov., MOR 2919. Estimated reconstruction of anterodorsal process indicated with dashed line. (A) left maxilla, lateral view; (B) left maxilla, medial view; (C) right maxilla, lateral view; (D) right maxilla, medial view; (E) Brachylophosaurus canadensis right maxilla, lateral view MOR 1071-8-13-98-559; (F) teeth of MOR 2919 left maxilla demonstrating slight sinuosity of median carinae. Abbreviations: adp, anterodorsal process; mf, maxillary foramen.
(A, B), Probrachylophosaurus bergei gen. et sp. nov. adult, MOR 2919, left jugal; (A) lateral view; (B) medial view. (C, D) P. bergei subadult, MOR 1097, right jugal reconstructed with dashed line; (C) medial view; (D) lateral view. (E, F) Brachylophosaurus canadensis adult, MOR 1071-7-16-98-248-Q, right jugal reversed. Note that the postorbital process was broken at its base and should be inclined more posteriorly; (E) lateral view; (F) medial view. Abbreviations: cvf, caudoventral flange; lp, lacrimal process; pop, postorbital process; pp, palatine process; qjp, quadratojugal process; rp, rostral process.
(A, B, E) Probrachylophosaurus bergei gen. et sp. nov., MOR 2919, posterior right lacrimal; (A) lateral view; (B) medial view; (C, D, F) Brachylophosaurus canadensis, MOR 1071-7-10-98-171, left lacrimal reversed; (C) lateral view; (D) medial view; (E) posterior view MOR 2919, medial portion reconstructed with dashed line; (F) posterior view MOR 1071-7-10-98-171. Abbreviations: ld, lacrimal duct; lf, lacrimal foramen.
(A-D) Adult, MOR 2919, posterior left nasal, crest pointing right except for (D); (A) dorsal view; (B) ventral view showing rugose nasofrontal suture; (C) lateral view; (D) medial view. (E, F) Subadult, MOR 1097, posterior right nasal; (E) dorsal view; (F) ventral view showing linearly striated nasofrontal suture.
In Probrachylophosaurus bergei gen. et sp. nov. and slender Brachylophosaurus canadensis morphotypes, the nasal crest is narrow and triangular in cross section. In B. canadensis, the nasal crest flattens as it grows wider. (A) Probrachylophosaurus bergei subadult, MOR 1097; (B) P. bergei adult, MOR 2919; (C) Brachylophosaurus canadensis slender morphotype, MOR 1071-7-7-98-86; (D) B. canadensis intermediate morphotype, FMNH PR 862; (E) B. canadensis robust morphotype, MOR 794.
Anterior is to the left. Specimen is from the Judith River Formation near Malta, Montana, in a horizon equivalent to the Comrey Sandstone Zone of the middle Oldman Formation. Borders of the nasals are indicated by white arrows. The specimen is heavily fractured, and the nasals are slightly elevated above the frontals, but this is due to fracturing; when undeformed, the nasals would have lain flush over the frontals, with no open space in between. There is no projection forming an overhanging, posteriorly oriented nasal crest as would be seen in larger Brachylophosaurus canadensis specimens.
In the stratigraphically oldest specimen, the adult Probrachylophosaurus bergei gen. et sp. nov., (A) MOR 2919, from the Judith River Formation equivalent of Unit 1 of the lower Oldman Fm, the nasofrontal suture extends over less than half of the frontals. This suture extends over approximately half of the frontals in subadult Brachylophosaurus canadensis specimens (B) MOR 1071-7-13-99-87-I and (C) MOR 1071-C-3-3, from the Judith River Formation equivalent of the Comrey Sandstone of the middle Oldman Fm, and migrates posteriorly to completely cover the frontals in the adult (D) GPDM JRF.65, a condition also seen in adult B. canadensis from the upper Judith River Formation, (E) MOR 720. Border of nasofrontal suture in (A-C) indicated with arrows.
In subadult Brachylophosaurus, the nasofrontal suture covers 50–75% of the dorsal frontal surface; in adults, the nasofrontal suture covers the entire dorsal surface. In Brachylophosaurus specimens from the Comrey Sandstone Zone of the middle Oldman Formation and its Judith River Formation equivalent in Malta, Montana (solid black circles; CMN 8893, JRF.65, MOR 940, and MOR 1071 specimens C-3-3, 6-30-98-4, 7-13-99-87-I, and 7-7-98-86), the relative coverage of the nasofrontal suture increases with frontal length until the frontal is entirely covered by the nasofrontal suture. Larger adult Brachylophosaurus braincases from an unknown stratigraphic height in the Oldman Formation of Alberta (open squares; FMNH PR PR 862, TMP 1990.104.001) and the Upper Judith River Formation of central Montana (open triangle; MOR 720; stratigraphic height relative to Oldman Formation of Alberta unknown) also have the frontals entirely covered by the nasofrontal suture. Probrachylophosaurus gen. nov. from the Montana Judith River Formation equivalent of the lower Oldman Formation (black x; MOR 2919) differs from the Brachylophosaurus growth trajectory in having a subadult Brachylophosaurus degree of coverage in an adult sized skull.
MOR 2919 (A) right postorbital and orbital margin of frontal, lateral view; (B) left squamosal, lateral view. Abbreviations: asppo, articulation for the squamosal process of the postorbital; f, frontal; jp, jugal process; om, orbital margin; poqp, postquadratic process; prqp, prequadratic process; qc, quadrate cotylus; sp, squamosal process.
(A-D) Adult, MOR 2919, left quadrate; (A) lateral view; (B) medial view; (C) dorsal view of squamosal condyle; (D) ventral view of surangular condyle. (E-G) Adult, MOR 2919, right quadrate with broken pterygoid flange; (E) lateral view; (F) dorsal view of squamosal condyle; (G) medial view. (H-J) Subadult, MOR 1097, right quadrate; (H) dorsal view of squamosal condyle; (I) lateral view with missing portion reconstructed with dashed line; (J) ventral view of surangular condyle. Condyles are all oriented with the lateral side down. Abbreviations: dqf, dorsal quadratojugal flange; pdp, posterodorsal process; pf, pterygoid flange; vqf, ventral quadratojugal flange.
MOR 2919, right lateral view. Abbreviations: abs, alar process of basisphenoid; bo, basioccipital; exo, exoccipital; p, parietal; po, postorbital; ppbs, pterygoid process of basisphenoid; ps, parasphenoid (broken and deflected dorsally); sqs, squamosal suture on parietal, broken; V-XII, cranial nerve foramina.
MOR 2919 (A) predentary, ventral view; (B) right dentary, lateral view; (C) right dentary, medial view; (D) right surangular, lateral view; (E) right surangular, medial view; (F) left dentary, lateral view; (G) left dentary, medial view. The anterior portion of the right dentary was crushed mediolaterally, flattening the symphyseal region into a vertical orientation. The coronoid process of the left dentary was fractured, displacing the coronoid process anteromedially. Abbreviations: cp, coronoid process; path, pathology; pes, proximal edentulous slope.
Caudodorsal point absent in: Probrachylophosaurus gen. nov. adult, MOR 2919, (A) right coronoid process, anterior margin broken, (B) left coronoid process, dorsal margin broken and entire process fractured and misaligned; (C) Acristavus, MOR 1155, right coronoid process, posterior margin broken. Caudodorsal point develops ontogenetically and with individual variation in Brachylophosaurus: (D) subadult, MOR 1071-8-1-99-313, right coronoid process; (E) subadult, MOR 1071-7-10-98-179, left coronoid process, anterior margin broken; (F) adult, MOR 1071-8-98-X, left coronoid process. Caudodorsal point develops ontogenetically in Maiasaura: (G) juvenile, MOR 547-W-55-2P, left coronoid process; (H) adult, OTM F138, left coronoid process of cast. The original description of OTM F138 [36] includes a photograph of the left dentary with a complete caudodorsal point, but the cast at MOR does not include the caudodorsal point, suggesting that when the resin was poured into the mold, it did not completely fill this area. The missing caudodorsal point is indicated by a black outline traced from the left dentary photograph in Trexler [36].
MOR 2919 vertebrae are pictured in anterior view in their approximate order within their series. Serial position of vertebrae is not listed because the complete series of cervicals and dorsals were not preserved, and so their exact serial positions cannot be determined with confidence. However, the last cervical vertebra pictured, “C14”, is consistent with the morphology of cervical 14 in CMN 8893, the holotype of Brachylophosaurus canadensis [23]. Atlas fragments and other vertebral fragments not pictured.
MOR 2919 vertebrae, neural spines, and chevrons are pictured in left lateral view in their approximate order within their series. Due to the disarticulated and incomplete nature of this caudal vertebral series, exact serial positions cannot be determined with confidence. Gaps between pictured vertebrae indicate noticeably missing segments of multiple vertebrae; additional vertebrae may be missing between any two vertebrae pictured here. Additional caudal vertebral fragments not pictured.
MOR 2919, all elements in lateral view; (A) left ilium; (B) partial proximal left ischium; (C) right ilium with dashed line indicating missing area; (D) partial proximal right ischium; (E) left pubis; (F) right pubis.
MOR 2919 (A) left tibia, lateral view; (B) right tibia, lateral view; (C) left fibula, lateral view; (D) right fibula, lateral view; (E) left astragalus, anterior view; (F) right astragalus, anterior view; (G) right metatarsal II, medial view; (H) right metatarsal IV, medial view.
The strict consensus of two most parsimonious trees resulting from adding Probrachylophosaurus bergei gen. et sp. nov. to Prieto-Márquez’s [29] matrix with minor character recodings and exclusions as discussed in text was plotted using the age ranges for each taxon; branch lengths do not reflect the number of character state changes. Values on branches represent bootstrap support; branches without values had less than 50% support. Tree statistics: shortest tree length = 614, Consistency Index = 0.72, Retention Index = 0.68, Rescaled Consistency Index = 0.49. Age ranges of Brachylophosaurini are those recalibrated in Fig 1; age ranges of other taxa are approximate, and are based on unrecalibrated previously published dates [, , , , –48]. Note that the age scale changes before and after 80 Ma. Also note that the age of Bactrosaurus has been variably proposed to be any time from late Turonian to early Maastrichtian in age [–51].
The strict consensus of two most parsimonious trees resulting from adding Probrachylophosaurus bergei gen. et sp. nov. to Gates et al.’s [3] matrix was plotted using the age ranges for each taxon; branch lengths do not reflect the number of character state changes. Because species within the same genus had the same codings, only genera are listed in the phylogeny. Values on branches represent bootstrap support; branches without values had less than 50% support. Tree statistics: shortest tree length = 188, Consistency Index = 0.70, Retention Index = 0.65, Rescaled Consistency Index = 0.45. Age ranges are approximate, and are based on those in Gates et al. [3], aside from Brachylophosaurini, which have been recalibrated as in Fig 1. Note that the age scale changes before and after 80 Ma. Also note that the age of Bactrosaurus has been variably proposed to be any time from late Turonian to early Maastrichtian in age [–51].
Numbered green arrows identify lines of arrested growth (LAGs). The closely spaced outer LAGs are indicated with tick marks along a green line. Numbers around the circumference of the cross-section indicate the number of LAGs preserved in that radial segment of the tibia. Note that diagenetic crushing has displaced several segments radially inward. Thumbnail image in lower right corner colors the area between each pair of LAGs to highlight locations of radial displacement as well as to indicate bone deposition between later LAGs occurring primarily along the posteromedial region. A high-resolution version of this figure is available at http://www.morphobank.org/index.php/Projects/Media/id/377387/project_id/2157 .
This is a higher-resolution image of the posteromedial cortex pictured in Fig 24, as indicated by the black box on the upper right thumbnail image of the entire mid-diaphyseal cross-section. Numbered green arrows identify lines of arrested growth (LAGs), including the multiple lines of LAG zone 8 (see text). A high-resolution version of this figure is available at http://www.morphobank.org/index.php/Projects/Media/id/377388/project_id/2157 .
Age in years was determined by counting the number of lines of arrested growth within the tibial cortex. MOR 2919 left tibia is 119 cm long. Maiasaura data are taken from the largest tibia with complete histologic data (93 cm long) from Woodward et al. [53]. Inflection points in the growth of Probrachylophosaurus occur at 5 years and 10 years; these inflection points occur earlier in Maiasaura, at 2–3 years and 8 years. In Maiasaura, the first inflection point is interpreted as sexual maturity, and the second inflection point occurs at the initiation of the external fundamental system (EFS), representing skeletal maturity [53]. Although MOR 2919 has an apparent second inflection point, it does not possess an EFS, so it is not skeletally mature.
Margins of the remodeled region are indicated with dashed green lines. Numbered green arrows identify lines of arrested growth. Dark areas near edge of cortex are sections of bone that began to separate from the slide, requiring additional adhesive. Black box on the thumbnail image on lower right indicates location of Fig 27 within the entire tibial cross-section. A high-resolution version of this figure is available at http://www.morphobank.org/index.php/Projects/Media/id/377389/project_id/2157 .
The right femur (length 129.5 cm) of MOR 794 was histologically sampled using a core of the outer cortex of the anteromedial mid-diaphysis rather than a complete cross-section of the mid-diaphysis, so the complete LAG record was not sampled and the individual’s age in years is unknown. Green arrow indicates the outermost LAG. Cortical surface is on the right.
Probrachylophosaurus bergei gen. et sp. nov. is proposed as an intermediate member of the lineage leading from Acristavus gagslarsoni to Brachylophosaurus canadensis. Shaded blue areas indicate known elements of Probrachylophosaurus. Skull outlines of Acristavus and Brachylophosaurus are used courtesy of Terry A. Gates. The reconstruction of the MOR 1071 Brachylophosaurus skull is a composite of an articulated skull roof with a scaled-down copy of the MOR 794 skull outline. All skulls are scaled to the same 10 cm scale bar. The horizontal axis is not to scale; the MOR 1071 reconstruction is much closer to MOR 794 in size and hypothesized maturity than MOR 1097 is to MOR 2919. Radiometric ages have been recalibrated to the Fish Canyon sanidine standard (28.305 +/- 0.036 Ma) of Renne et al. [10] from the originally published values [, –13]; see text and Table 1 for further recalibration details. The age of the Acristavus holotype was precisely estimated by Gates et al. [3]. The age of the Comrey Sandstone Zone of the Oldman Formation is not tightly constrained, leading to uncertainty in the exact age of Brachylophosaurus.
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References
-
- Prieto-Márquez A (2005) New information on the cranium of Brachylophosaurus canadensis (Dinosauria, Hadrosauridae), with a revision of its phylogenetic position. Journal of Vertebrate Paleontology 25: 144–156.
-
- Varricchio DJ, Horner JR (1993) Hadrosaurid and lambeosaurid bonebeds from the Upper Cretaceous Two Medicine Formation of Montana: taphonomic and biologic implications. Canadian Journal of Earth Sciences 30: 997–1006.
-
- Gates TA, Horner JR, Hanna RR, Nelson RC (2011) New unadorned hadrosaurine hadrosaurid (Dinosauria, Ornithopoda) from the Campanian of North America. Journal of Vertebrate Paleontology 31: 798–811.
-
- Horner JR (1984) Three ecologically distinct vertebrate faunal communities from the Late Cretaceous Two Medicine Formation of Montana, with discussion of evolutionary pressures induced by interior seaway fluctuations In: McBane J. D. and Garrison P. B., editors. Montana Geological Society Field Conference and Symposium. Northwest Montana and Adjacent Canada; pp. 299–303.
-
- Horner JR, Makela R (1979) Nest of juveniles provides evidence of family structure among dinosaurs. Nature 282: 296–298.
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Fieldwork and research funding was generously provided to JRH by the Ameya Preserve, Damaris Wagoner, David Sands, and other generous donors to the Museum of the Rockies Student Fund and Horner Fund; and to EAFF by the Tampa Bay Fossil Club and the Montana State University Department of Cell Biology and Neuroscience. Travel funding was generously provided to EAFF by the Doris O. and Samuel P. Welles Research Fund (University of California Museum of Paleontology), the M.A. Fritz Travel Grant for the Advancement of Studies in Palaeontology (Royal Ontario Museum), the Jackson School of Geosciences Student Member Travel Grant (Society of Vertebrate Paleontology), and the College of Letters and Science Student Research Travel Grant (Montana State University). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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