Brachylophosaurus Research Articles

The quest for a generic bird target to detect the presence of bird in food products and considerations for paleoprotein analysis.

It can be important for consumers to know whether food products contain animal material and, if so, of which species. Food products with animal material as an ingredient often contain collagen type 1. LC-MS/MS (Liquid Chromatography-tandem Mass Spectrometry) was applied as technique to generically detect bird. Unlike for example fish, that have experienced longer divergence times, it is still possible to find generic LC-MS targets for avian type 1 collagen. After theoretical target selection using 83 collagen 1α2 bird sequences of 33 orders and construction of a common ancestor sequence of birds, experimental evidence was provided by analyzing extracts from 10 extant bird species. Two suitable options have been identified. The combination of VGPIGPAGNR and VGPIGAAGNR (pheasant only) covers all investigated birds and was not found in other species. The peptide EGPVGFpGADGR covers all investigated birds, but also occurs in several species of crocodiles and turtles. The presence of the generic peptide (combination) was confirmed in food products, proving the principle, and can therefore be used to detect the presence of bird. Furthermore, it is shown how the use of constructed ancestor sequences could benefit the field of paleoproteomics, in the interpretation of collagen MS/MS spectra of ancient species. Our theoretical analysis and assessment of reported Brachylophosaurus canadensis collagen 1α2 MS/MS data provided support for several previous peptide sequence assignments, but we also propose that our constructed ancestral bird sequence GPpGESGAVGPAGPIGSR may fit the MS/MS data better than the original assignment GLPGESGAVGPAGPpGSR.

Taphonomic and Diagenetic Pathways to Protein Preservation, Part II: The Case of Brachylophosaurus canadensis Specimen MOR 2598

Simple SummaryReports of the recovery of proteins and other molecules from fossils have become so common over the last two decades that some paleontologists now focus almost entirely on studying how biologic molecules can persist in fossils. In this study, we explored the fossilization history of a specimen of the hadrosaurid dinosaur Brachylophosaurus which was previously shown to preserve original cells, tissues, and structural proteins. Trace element analyses of the tibia of this specimen revealed that after its bones were buried in a brackish estuarine channel, they fossilized under wet conditions which shifted in redox state multiple times. The successful recovery of proteins from this specimen, despite this complex history of chemical alterations, shows that the processes which bind and stabilize biologic molecules shortly after death provide them remarkable physical and chemical resiliency. By uniting our results with those of similar studies on other dinosaur fossils known to also preserve original proteins, we also conclude that exposure to oxidizing conditions in the initial ~48 h postmortem likely promotes molecular stabilization reactions, and the retention of early-diagenetic trace element signatures may be a useful proxy for molecular recovery potential.Recent recoveries of peptide sequences from two Cretaceous dinosaur bones require paleontologists to rethink traditional notions about how fossilization occurs. As part of this shifting paradigm, several research groups have recently begun attempting to characterize biomolecular decay and stabilization pathways in diverse paleoenvironmental and diagenetic settings. To advance these efforts, we assessed the taphonomic and geochemical history of Brachylophosaurus canadensis specimen MOR 2598, the left femur of which was previously found to retain endogenous cells, tissues, and structural proteins. Combined stratigraphic and trace element data show that after brief fluvial transport, this articulated hind limb was buried in a sandy, likely-brackish, estuarine channel. During early diagenesis, percolating groundwaters stagnated within the bones, forming reducing internal microenvironments. Recent exposure and weathering also caused the surficial leaching of trace elements from the specimen. Despite these shifting redox regimes, proteins within the bones were able to survive through diagenesis, attesting to their remarkable resiliency over geologic time. Synthesizing our findings with other recent studies reveals that oxidizing conditions in the initial ~48 h postmortem likely promote molecular stabilization reactions and that the retention of early-diagenetic trace element signatures may be a useful proxy for molecular recovery potential.

Deep Time Paleoproteomics: Looking Forward

The goal of paleoproteomics is to characterize proteins from specimens that have been subjected to the degrading and obscuring effects of time, thus obtaining biological information about tissues or organisms both unobservable in the present and unobtainable through morphological study. Although the description of sequences from Tyrannosaurus rex and Brachylophosaurus canadensis suggested that proteins may persist over tens of millions of years, the majority of paleoproteomic analyses have focused on historical, archeological, or relatively young paleontological samples that rarely exceed 1 million years in age. However, recent advances in methodology and analyses of diverse tissues types (e.g., fossil eggshell, dental enamel) have begun closing the large window of time that remains unexplored in the fossil history of the Cenozoic. In this perspective, we discuss the history and current state of deep time paleoproteomics (DTPp), here defined as paleoproteomic study of samples ∼1 million years (1 Ma) or more in age. We then discuss the future of DTPp research, including what we see as critical ways the field can expand, advancements in technology that can be utilized, and the types of questions DTPp can address if such a future is realized.

A new brachylophosaurin (Dinosauria: Hadrosauridae) from the Upper Cretaceous Menefee Formation of New Mexico.

Brachylophosaurini is a clade of hadrosaurid dinosaurs from the Campanian of western North America. Although well-known from northern localities in Montana and Alberta, including abundant material of Brachylophosaurus canadensis and Maiasaura peeblesorum and the holotypes of Acristavus gagslarsoni and Probrachylophosaurus bergei, material from southern localities in Utah and Colorado is restricted to a partial skull referred to A. gagslarsoni and several indeterminate specimens. Here we describe Ornatops incantatus gen. et sp. nov., a new brachylophosaurin known from a partial skeleton from the Allison Member of the Menefee Formation in New Mexico. Ornatops is the first brachylophosaurin reported from New Mexico and the southernmost occurrence of the clade. Ornatops shares with Probrachylophosaurus and Brachylophosaurus a caudally expanded nasofrontal suture on the frontals, but also exhibits an autapomorphic nasofrontal suture morphology, with a horizontal rostral region and elevated caudal region with two prominent parasagittal bumps, which is different from other brachylophosaurin specimens, including juvenile and adult Brachylophosaurus. A phylogenetic analysis places Ornatops in a trichotomy with Probrachylophosaurus and Brachylophosaurus, with Maiasaura and Acristavus as successive outgroups.

A fossil protein chimera; difficulties in discriminating dinosaur peptide sequences from modern cross-contamination.

A decade ago, reports that organic-rich soft tissue survived from dinosaur fossils were apparently supported by proteomics-derived sequence information of exceptionally well-preserved bone. This initial claim to the sequencing of endogenous collagen peptides from an approximately 68 Myr Tyrannosaurus rex fossil was highly controversial, largely on the grounds of potential contamination from either bacterial biofilms or from laboratory practice. In a subsequent study, collagen peptide sequences from an approximately 78 Myr Brachylophosaurus canadensis fossil were reported that have remained largely unchallenged. However, the endogeneity of these sequences relies heavily on a single peptide sequence, apparently unique to both dinosaurs. Given the potential for cross-contamination from modern bone analysed by the same team, here we extract collagen from bone samples of three individuals of ostrich, Struthio camelus. The resulting LC–MS/MS data were found to match all of the proposed sequences for both the original Tyrannosaurus and Brachylophosaurus studies. Regardless of the true nature of the dinosaur peptides, our finding highlights the difficulty of differentiating such sequences with confidence. Our results not only imply that cross-contamination cannot be ruled out, but that appropriate measures to test for endogeneity should be further evaluated.

Collagen found in 195 million-year-old dinosaur bone, perhaps

Until now, the oldest proteins found were collagen fragments from an 80 million-year old Brachylophosaurus canadensis dinosaur femur. A new finding claims to have beaten that record by more than 100 million years. Robert R. Reisz, a paleontologist at the University of Toronto, and coworkers report that they have found collagen in tiny channels of a 195 million-year-old Lufengosaurus dinosaur rib fragment uncovered in Yunnan Province, China (Nat. Commun. 2017, DOI: 10.1038/ncomms14220). But some scientists aren’t convinced. These skeptics question whether the analysis of the fossil actually points to collagen. Usually when fossilized bones are analyzed, researchers dissolve the inorganic material and extract the organic material. Reisz and coworkers instead examined the organic material as it sat in the fossil. They looked for collagen in thin, longitudinal slices of bone using synchrotron-derived Fourier transform infrared microspectroscopy. By analyzing the sample without dissolving the bone, “we can act...

Expansion for the Brachylophosaurus canadensis Collagen I Sequence and Additional Evidence of the Preservation of Cretaceous Protein.

Sequence data from biomolecules such as DNA and proteins, which provide critical information for evolutionary studies, have been assumed to be forever outside the reach of dinosaur paleontology. Proteins, which are predicted to have greater longevity than DNA, have been recovered from two nonavian dinosaurs, but these results remain controversial. For proteomic data derived from extinct Mesozoic organisms to reach their greatest potential for investigating questions of phylogeny and paleobiology, it must be shown that peptide sequences can be reliably and reproducibly obtained from fossils and that fragmentary sequences for ancient proteins can be increasingly expanded. To test the hypothesis that peptides can be repeatedly detected and validated from fossil tissues many millions of years old, we applied updated extraction methodology, high-resolution mass spectrometry, and bioinformatics analyses on a Brachylophosaurus canadensis specimen (MOR 2598) from which collagen I peptides were recovered in 2009. We recovered eight peptide sequences of collagen I: two identical to peptides recovered in 2009 and six new peptides. Phylogenetic analyses place the recovered sequences within basal archosauria. When only the new sequences are considered, B. canadensis is grouped more closely to crocodylians, but when all sequences (current and those reported in 2009) are analyzed, B. canadensis is placed more closely to basal birds. The data robustly support the hypothesis of an endogenous origin for these peptides, confirm the idea that peptides can survive in specimens tens of millions of years old, and bolster the validity of the 2009 study. Furthermore, the new data expand the coverage of B. canadensis collagen I (a 33.6% increase in collagen I alpha 1 and 116.7% in alpha 2). Finally, this study demonstrates the importance of reexamining previously studied specimens with updated methods and instrumentation, as we obtained roughly the same amount of sequence data as the previous study with substantially less sample material. Data are available via ProteomeXchange with identifier PXD005087.

Trace fossils of possible parasites inside the gut contents of a hadrosaurid dinosaur, Upper Cretaceous Judith River Formation, Montana

AbstractTiny sinuous trace fossils have been found within probable gut contents of an exceptionally preserved specimen of a hadrosaurid dinosaur,Brachylophosaurus canadensis, from the Judith River Formation of Montana. Approximately 280 examples of the trace fossils were observed in 19 samples of gut region material. The tubular structures typically are about 0.3 mm across. Many have thin calcareous linings or layers, and some exhibit fine surficial striae. At least two dozen of these trace fossils share walls with adjacent tubular traces, and this association can extend for several millimeters. While the trace fossils share some characteristics with fine rhizoliths, these features are most consistent with tiny burrows, or possibly body impressions, of worms (vermiform organisms) of uncertain biologic affinity. Such trace fossils have not been reported previously, and herein described asParvitubulites striatusn. gen. n. sp. Either autochthonous (parasites) or allochthonous (scavengers) worms may have created the trace fossils, but taphonomic factors suggest that autochthonous burrowers are more likely. Several lines of evidence, such as constant diameters and matching directional changes, suggest that the paired trace fossils were made by two individuals moving at the same time, which implies sustained intraspecific contact.Parvitubulites striatusprovides a rare record of interactions between terrestrial, meiofaunal-sized, soft-bodied invertebrates and a dinosaur carcass. The evidence that the worms may have parasitized a living hadrosaur and subsequently left traces of intraspecific behavior between individual worms adds unique information to our understanding of Mesozoic trophic interactions.

A New Brachylophosaurin Hadrosaur (Dinosauria: Ornithischia) with an Intermediate Nasal Crest from the Campanian Judith River Formation of Northcentral Montana.

BackgroundBrachylophosaurini 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 FindingsA 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/SignificanceThe 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.

Kinetic Limitations of Intracranial Joints in Brachylophosaurus canadensis and Edmontosaurus regalis (Dinosauria: Hadrosauridae), and Their Implications for the Chewing Mechanics of Hadrosaurids

The highly specialized tooth morphology and arrangement of the dental battery of hadrosaurids has led to much speculation surrounding the chewing mechanics of this successful group of herbivorous dinosaurs. Pleurokinesis, a long established hypothesis explaining the ornithopod chewing mechanism, proposes a transverse power stroke in hadrosaurids that was accommodated by vertical adduction of the mandible, lateral rotation of the maxilla at the maxilla-premaxilla joint, lateral rotation of the jugal-maxilla complex at its contact with the lacrimal, and posterolateral rotation of the quadrate at its contact with the squamosal. A secondary series of movements were also thought to have occurred as a consequence of these primary movements. In this article, the intracranial joint morphology is described for both Brachylophosaurus canadensis and Edmontosaurus regalis and their permissive kinematics are established. Based on this evidence, the movements associated with pleurokinesis are not accommodated in these hadrosaurine dinosaurs. Rather, the movements that seem most likely to have produced the observed dental wear patterns are those associated with the mandible about the jaw joint. The structure of this joint appears well-suited to have accommodated some translation as well as rotation of the mandible about the quadrate condyle. Three-dimensional modeling of the alternate mandibular movements reveals that not all the combined labiolingual width of the lingual and buccal facets of the tooth row was involved in the power stroke. Rather, limits on the degree of mandibular long axis rotation suggest that only the lingual facet and the more medial portion of the buccal facet were utilized.

Influence of Microbial Biofilms on the Preservation of Primary Soft Tissue in Fossil and Extant Archosaurs

BackgroundMineralized and permineralized bone is the most common form of fossilization in the vertebrate record. Preservation of gross soft tissues is extremely rare, but recent studies have suggested that primary soft tissues and biomolecules are more commonly preserved within preserved bones than had been presumed. Some of these claims have been challenged, with presentation of evidence suggesting that some of the structures are microbial artifacts, not primary soft tissues. The identification of biomolecules in fossil vertebrate extracts from a specimen of Brachylophosaurus canadensis has shown the interpretation of preserved organic remains as microbial biofilm to be highly unlikely. These discussions also propose a variety of potential mechanisms that would permit the preservation of soft-tissues in vertebrate fossils over geologic time.Methodology/Principal FindingsThis study experimentally examines the role of microbial biofilms in soft-tissue preservation in vertebrate fossils by quantitatively establishing the growth and morphology of biofilms on extant archosaur bone. These results are microscopically and morphologically compared with soft-tissue extracts from vertebrate fossils from the Hell Creek Formation of southeastern Montana (Latest Maastrichtian) in order to investigate the potential role of microbial biofilms on the preservation of fossil bone and bound organic matter in a variety of taphonomic settings. Based on these analyses, we highlight a mechanism whereby this bound organic matter may be preserved.Conclusions/SignificanceResults of the study indicate that the crystallization of microbial biofilms on decomposing organic matter within vertebrate bone in early taphonomic stages may contribute to the preservation of primary soft tissues deeper in the bone structure.

The first complete description of the holotype of Brachylophosaurus canadensis Sternberg, 1953 (Dinosauria: Hadrosauridae) with comments on intraspecific variation

The holotype of Brachylophosaurus canadensis was collected by C.M. Sternberg in 1936 from the Oldman Formation (Upper Cretaceous) of Alberta, Canada, with a brief description focusing on the cranium following in 1953. A re-description of the holotype skeleton confirms its position as a hadrosaurine dinosaur exhibiting the following unique combination of characters: paddle-like solid nasal crest; posteriorly elongated prefrontal; only the anterior tip of the lacrimal contacting maxilla; extremely elongated anterior maxillary process; and a quadratojugal with a noncrescentic posterior margin variably forming a paraquadratic foramen with the quadrate. Comparison of the holotype with other specimens assigned to the taxon reveals numerous morphological differences. These variable features include the presence/absence of an accessory premaxillary foramen, the number of maxillary/dentary vertical tooth rows, the number of functional teeth per tooth row contributing to the dental occlusal surface, the bones forming the mandibular glenoid, the presence/absence of a nasal foramen, nasal crest morphology, the number of cervical vertebrae, and axis morphology. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 373–397.

Glishades ericksoni, a new hadrosauroid (Dinosauria: Ornithopoda) from the Late Cretaceous of North America

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).

Probable Gut Contents Within A Specimen Of Brachylophosaurus Canadensis (Dinosauria: Hadrosauridae) From the Upper Cretaceous Judith River Formation Of Montana

Abstract An exceptionally preserved subadult specimen (JRF 115H) of a hadrosaurid, Brachylophosaurus canadensis, from the Judith River Formation near Malta, Montana, contains abundant plant fragments concentrated within the body cavity. We examined the taphonomy of the carcass and analyzed the gut-region material to test whether the organic remains represent fossilized gut contents. The dinosaur was buried in a fluvial channel setting, and the excellent articulation, integument impressions, and lack of scavenging indicate rapid burial. The organic material occupies a volume of at least 5750 cm3, and comparable material is not found outside the carcass. The carcass contents include ∼63% clay, ∼16% undetermined matrix, ∼12% organic matter, and ∼9% larger inorganic clasts—mostly 50–100 μm quartz grains. Most of the organics appear to be mm-scale leaf fragments. The most parsimonious explanation for the presence and composition of the gut-region material is that much of the plant fossils represent reworked br...

AN OSSIFIED TENDON TRELLIS IN CHASMOSAURUS (ORNITHISCHIA: CERATOPSIDAE)

The ornithischia and its sister group, the Saurischia, comprise the Dinosauria. Ornithischians (Weishampel, 2004) are a diverse group of primarily quadrupedal herbivores that include such familiar dinosaurs as the armored stegosaurs and ankylosaurs (Thyreophora), as well as the duckbilled hadrosaurs, pachycephalosaurs, and ceratopsians (Cerapoda). The Ceratopsia (You and Dodson, 2004) includes a number of relatively small basal forms such as psittacosaurs and Neoceratopsia, which comprises protoceratopsids and the larger, more derived horned Ceratopsidae. Ossified tendons occur throughout the body of many birds (Vanden Berge and Storer, 1995), but reports in other Saurischia are rare (but see Sereno et al., 2004). However, they occur in nearly all ornithischian dinosaurs except stegosaurs (Sereno and Dong, 1992). The presence of ossified tendons above the sacrum is thought to be a diagnostic character of the Ornithischia (Weishampel, 2004). Many taxa also develop them in association with the caudal and/or thoracic vertebrae. Ossified tendons usually occur in bundles along the epaxial region of the vertebral column and the hypaxial region of the tail in basal ornithopods such as Hypsilophodon Galton, 1974. Similar tendon bundles are known in pachycephalosaurs (Sues and Galton, 1987) and ankylosaurs possess tendons associated with the tail “club” (Coombs, 1995). The ornithopod group Iguanodontoidea (Hadrosauridae and Iguanodontidae plus Protohadros Head, 1998 and Ouranosaurus Taquet, 1976) developed a rhomboidal trellis of ossified tendons (Fig. 1), often considered to be synapomorphic (e.g., Sereno, 1999), along the dorsal side of their vertebral columns (Dollo, 1886; Brown, 1916; Parks, 1920; Lull and Wright, 1942; Norman, 1980, 1986; Prieto-Marquez, 2001; Horner et al., 2004). Note that Hadrosauriformes is synonymous with Iguanodontoidea, but the latter is preferred (Norman, 2004) and used here. Figure 1 — Brachylophosaurus canadensis Sternberg, 1953, MOR 794. Posterior thoracic vertebrae showing the ossified tendon trellis …

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.

Histologic determination of ontogenetic patterns and processes in hadrosaurian ossified tendons

ABSTRACT Development and metaplasia of ossified tendons in two hadrosaurine dinosaurs (Maiasaura peeblesorum and Brachylophosaurus canadensis) are described by comparison with the known developmental processes of ossified tendons in turkeys (Meleagris gallopavo). Mineralized primary tendon tissue and replacement patterns suggest that ossified tendons in hadrosaurs grew initially in a manner similar to those in turkeys. That is, biomineralization begins with apatite deposition and is followed by resorption of mineralized primary tissue and subsequent bone formation. Earlier ontogenetic onset of tendon ossification and later offset among ossified tendons of hadrosaurs differentiates them from tendons of turkeys. In addition, an external fundamental system (EFS) in hadrosaurian tendons indicates that they grew radially beyond the original tendon boundary, a process unknown among avian tendons. Tendon histology indicates that hadrosaurian ossified tendons developed in step with the skeletal system and that ossification was not induced by biomechanical stresses.