Saurolophus Excavation
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''Saurolophus'' (; meaning "lizard crest") is a
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of large
hadrosaurid Hadrosaurids (), also hadrosaurs or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod fami ...
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
from the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...
period of
Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
and
North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
, that lived in what is now the Horseshoe Canyon and Nemegt formations about 70 million to 66 million years ago. It is one of the few genera of
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
s known from multiple
continent A continent is any of several large geographical regions. Continents are generally identified by convention (norm), convention rather than any strict criteria. A continent could be a single large landmass, a part of a very large landmass, as ...
s. The
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
, ''S. osborni'', was described by
Barnum Brown Barnum Brown (February 12, 1873 – February 5, 1963), commonly referred to as Mr. Bones, was an American paleontologist. He discovered the first documented remains of ''Tyrannosaurus'' during a career that made him one of the most famous fossil ...
in 1912 from
Canadian Canadians () are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of their being ''C ...
fossils. A second valid species, ''S. angustirostris'', is represented by numerous specimens from
Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...
, and was described by
Anatoly Konstantinovich Rozhdestvensky Anatoly Konstantinovich Rozhdestvensky (, 1920–1983) was a Soviet paleontologist responsible for naming many dinosaurs, including '' Aralosaurus'' and '' Probactrosaurus''. References Soviet paleontologists 1920 births 1983 deaths Russi ...
. ''Saurolophus'' is distinguished by a spike-like crest which projects up and back from the skull. It was a
herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...
dinosaur which could move about either
biped Bipedalism is a form of terrestrial locomotion where an animal moves by means of its two rear (or lower) limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' ' ...
ally or
quadruped Quadrupedalism is a form of locomotion in which animals have four legs that are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four legs is said to be a quadruped (fr ...
ally.


Discovery and history

Barnum Brown recovered the first described remains of ''Saurolophus'' in 1911, including a nearly complete skeleton ( AMNH 5220). Now on display in the American Museum of Natural History, this skeleton was the first nearly complete dinosaur skeleton from Canada. It was found in rocks of early Maastrichtian age, in the
Upper Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cret ...
Horseshoe Canyon Formation The Horseshoe Canyon Formation is a stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta. It takes its name from Horseshoe Canyon, an area of badlands near Drumheller. The Horseshoe Canyon Formation is part of th ...
(then known as the Edmonton Formation) near Tolman Ferry on the
Red Deer River The Red Deer River is a river in Alberta and a small portion of Saskatchewan, Canada. It is a major tributary of the South Saskatchewan River and is part of the larger Saskatchewan / Nelson River, Nelson system that empties into Hudson Bay. T ...
in Alberta. Brown wasted little time in describing his material, giving it its own subfamily. ''Saurolophus'' was an important early reference for other hadrosaurs, as seen in the names of ''Prosaurolophus'' ("before ''Saurolophus''") and ''
Parasaurolophus ''Parasaurolophus'' (; meaning "beside crested lizard" in reference to ''Saurolophus'') is a genus of hadrosaurid "duck-billed" dinosaur that lived in what is now western North America and possibly Asia during the Late Cretaceous period, a ...
'' ("near ''Saurolophus''"). However, little additional material has been recovered and described. Instead, more abundant remains from Asia have provided more data. Initial remains were not promising; a partial fragmentary
ischium The ischium (; : is ...
from
Heilongjiang Heilongjiang is a province in northeast China. It is the northernmost and easternmost province of the country and contains China's northernmost point (in Mohe City along the Amur) and easternmost point (at the confluence of the Amur and Us ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
, that Riabinin named ''S. kryschtofovici''. Much better remains were soon recovered, though, but from
Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...
's early Maastrichtian-age
Nemegt Formation The Nemegt Formation (also known as Nemegtskaya Svita) is a geological formation in the Gobi Desert of Mongolia, dating to the Late Cretaceous. The formation consists of river channel sediments and contains fossils of fish, turtles, crocodilians ...
. The 1946–1949
Russian Russian(s) may refer to: *Russians (), an ethnic group of the East Slavic peoples, primarily living in Russia and neighboring countries *A citizen of Russia *Russian language, the most widely spoken of the Slavic languages *''The Russians'', a b ...
-
Mongolian Mongolian may refer to: * Something of, from, or related to Mongolia, a country in Asia * Mongolian people, or Mongols * Bogd Khanate of Mongolia, the government of Mongolia, 1911–1919 and 1921–1924 * Mongolian language * Mongolian alphabet * ...
paleontological expeditions recovered the large skeleton that became ''S. angustirostris'' as described by Anatoly Rozhdestvensky. Other skeletons from a variety of growth stages have also been discovered, and ''S. angustirostris'' is now the most abundant Asian hadrosaurid.


Species

Two species are regarded as valid today: the
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
''S. osborni'', and ''S. angustirostris''. ''S. osborni'' (Brown, 1912) is known from a skull and skeleton, two other complete skulls, and skull fragments. ''S. angustirostris'' (Rozhdestvensky, 1952) is known from at least 15 specimens. It differs from ''S. osborni'' by some details of the skull, as well as in the pattern of scales found in skin impressions. The Mongolian species had a longer skull (by 20%) and the front of the snout (the
premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...
ry bones) were more upwardly directed. ''S. angustirostris'' also had a distinctive row of rectangular scales along the midline of the back and tail, known as 'midline feature-scales'; these are not currently preserved in ''S. osborni''. In ''S. angustirostris'', the scales on the tail flank were arranged in vertical patterns, which may have corresponded to striped coloration in life. This area was covered in radial scale patterns in ''S. osborni'', possibly indicating a more mottled or spotted coloration. ''S. kryschtofovici'' (Riabinin, 1930) is not considered valid; either it is regarded as a dubious name, or as a synonym of ''S. angustirostris'' (although the name antedates ''S. angustirostris''). Until a 2011 reevaluation of the species by Phil R. Bell, ''S. angustirostris'' was not well-described. No
autapomorphies In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to ...
, unique derived traits, had been established distinguishing it from ''S. osborni''. Bell found in a publication earlier in the year that the two previous studies of ''S. angustirostris'', by Rozhdestvensky in 1952, and Maryanska and Osmolska in 1981, do not provide a comprehensive enough description to compare the species with ''S. osborni''. In 1939–40, two partial skeletons were found in the late Maastrichtian age
Moreno Formation The Moreno Formation is a Mesozoic geologic Formation (geology), formation located in San Joaquin Valley (California).Dinosaur remains diagnostic to the genus level are among the fossils that have been recovered from the formation.Weishampel, et ...
of
California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
. These specimens were referred to cf. ''Saurolophus'' sp. In 2010, one of the skulls was instead assigned to ''
Edmontosaurus ''Edmontosaurus'' ( ) (meaning "lizard from Edmonton"), with the second species often colloquially and historically known as ''Anatosaurus'' or ''Anatotitan'' (meaning "duck lizard" and "giant duck"), is a genus of hadrosaurid (duck-billed) din ...
''. A 2013 study placed the two specimens in a new species, ''S. morrisi''. In 2014, the species was reassigned to a new genus, ''
Augustynolophus ''Augustynolophus'' is an extinct genus of herbivorous saurolophine hadrosaur dinosaur which was discovered in the Moreno Formation in California, dating to the late Maastrichtian age, making it one of the last dinosaurs known from the fossil rec ...
''. Fossils of a possible third species of ''Saurolophus'' were unearthed in the Almond Formation in
Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...
by
Barnum Brown Barnum Brown (February 12, 1873 – February 5, 1963), commonly referred to as Mr. Bones, was an American paleontologist. He discovered the first documented remains of ''Tyrannosaurus'' during a career that made him one of the most famous fossil ...
back in 1937. A close relative of ''Saurolophus'' and ''Augustynolophus,'' and/or a possible species of the former was unearthed in the Javelina Formation in
Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...
back in 2016.


Description

''Saurolophus'' is known from material including nearly complete skeletons, giving researchers a clear picture of its bony anatomy. ''S. osborni'', the rarer
Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...
n species, was around long, with its skull long. It has been estimated to have weighed around . The larger
Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...
n species ''S. angustirostris'' was around long and weighed up to . The largest known skull of ''S.angustirostris'' measures in length. Aside from size, the two species are virtually identical, with differentiation hindered by lack of study.


Skull

The most distinctive feature of ''Saurolophus'' is its cranial crest, which is present in young individuals, but is smaller. It is long and spike-like and projects upward and backward at about a 45° angle, starting from over the eyes. This crest is often described as solid, but appears to be solid only at the point, with internal chambers that may have had a
respiratory The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies gr ...
and/or heat-regulation function. The unique crest of ''Saurolophus'' is made up almost completely by the nasal bones, and in ''S. angustirostris'' it is solid. In adult specimens the crests are a rounded triangular shape in cross section. The crest protrudes past the edge of the skull backwards. Thin processes from the frontals and prefrontals extend along the underside of the crest, probably to strengthen it. At the end of the crest is a swelling of the nasal, which is often termed differently. The holotype of ''S. angustirostris'' is a skull and postcrania, so the cranium of the species is well-described. Bell ''et al.'' re-evaluated the entire species in a 2011 publication with ''
Acta Palaeontologica Polonica ''Acta Palaeontologica Polonica'' is a quarterly peer-reviewed open access scientific journal of paleontology and paleobiology. It was established by Roman Kozłowski in 1956. It is published by the Institute of Paleobiology of the Polish Academ ...
''. Their description found the skull to be generalized among hadrosaurines, and are much larger than any skulls of ''S. osborni''. The most unusual feature for a hadrosaurine is the long, protruding, solid crest that extends upwards diagonally from the back of the skull roof. Unlike
lambeosaurines Lambeosauridae /ˌlæmbiəˈsɔːraɪniː/ (meaning 'lambe's lizards') is an extinct group of crested hadrosauroid dinosaurs. Description Size Uncertainty surrounds the size of lambeosaurs from the European continent. Hadrosaurs found there, a ...
, the crests are made up completely of the
nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Eac ...
. The premaxilla bones make up almost 50% of the entire skull length, and both sides are filled with small holes. Only in adult individuals has the front of the premaxillary contact been fused. Longer than the premaxilla, the nasal bones are the longest in the skull. They make up the entire length of the crest, and are never preserved as fused.


Classification

Barnum Brown, who described the first specimens, put it in its own
subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...
in "Trachodontidae" (=Hadrosauridae), the Saurolophinae. At the time, this also included ''
Corythosaurus ''Corythosaurus'' (; ) is a genus of hadrosaurid "duck-billed" dinosaur from the Late Cretaceous Period (geology), period, about 77–75.7 million years ago, in what is now Laramidia, western North America. Its name is derived from the Anci ...
'' and ''
Hypacrosaurus ''Hypacrosaurus'' (meaning "near the highest lizard"
reek υπο-, ''hypo-'' = less + ακρος, ''akros'', high Reek may refer to: Places * Reek, Netherlands, a village in the Dutch province of North Brabant * Croagh Patrick, a mountain in the west of Ireland nicknamed "The Reek" People * Nikolai Reek (1890–1942), Estonian military commander * Salme Ree ...
because it was almost but not quite as large as ''Tyrannosaurus'') is an extinct genus of hadrosaurid, duckbill dinosaur simila ...
'', the only well-known examples of what would become the
Lambeosaurinae Lambeosauridae /ˌlæmbiəˈsɔːraɪniː/ (meaning 'lambe's lizards') is an extinct group of crested hadrosauroid dinosaurs. Description Size Uncertainty surrounds the size of lambeosaurs from the European continent. Hadrosaurs found there, ...
. Brown thought that ''Saurolophus'' had an expanded tip to the
ischium The ischium (; : is ...
bone in the hip, as dinosaurs now recognized as lambeosaurines had, but this appears to have been based on a mistakenly associated lambeosaurine ischium. Additionally, he misinterpreted the crests of ''Saurolophus'' and lambeosaurines as being made of the same bones. Most publications before 2010 classified ''Saurolophus'' as a member of Hadrosaurinae, often known colloquially as the "flat-headed hadrosaurs". In 2010, the subfamily Saurolophinae was brought back into use because ''
Hadrosaurus ''Hadrosaurus'' (; ) is a genus of hadrosaurid ornithopod dinosaurs that lived in North America during the Late Cretaceous Period in what is now the Woodbury Formation in New Jersey about 83.6 to 77.9 Ma. The holotype specimen was found in flu ...
'' appears to have branched off prior to the "hadrosaurine"–lambeosaurine split. As a result, Hadrosaurinae by definition cannot include the traditional "hadrosaurines". Saurolophinae is the oldest available name for the former "hadrosaurine"
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
. ''Saurolophus'', as the name suggests, is a saurolophine, as it has a saurolophine
pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...
and a (largely) solid crest. The following cladogram of hadrosaurid relationships was published in 2013 by Alberto Prieto-Márquez ''et al.'' in ''Acta Palaeontologica Polonica'':


Paleobiology


Feeding

As a
hadrosaurid Hadrosaurids (), also hadrosaurs or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod fami ...
, ''Saurolophus'' would have been a
bipedal Bipedalism is a form of terrestrial locomotion where an animal moves by means of its two rear (or lower) limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' ...
/
quadruped Quadrupedalism is a form of locomotion in which animals have four legs that are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four legs is said to be a quadruped (fr ...
al
herbivore A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...
, eating a variety of
plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...
s. Its skull permitted a grinding motion analogous to
chewing Chewing or mastication is the process by which food is crushed and ground by the teeth. It is the first step in the process of digestion, allowing a greater surface area for digestive enzymes to break down the foods. During the mastication proc ...
, and its
teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...
were continually replacing and packed into
dental batteries Dinosaur teeth have been studied since 1822 when Mary Ann Mantell (1795-1869) and her husband Gideon Algernon Mantell, Dr Gideon Algernon Mantell (1790-1852) discovered an ''Iguanodon'' tooth in Sussex in England. Unlike Mammal tooth, mammal teeth ...
that contained hundreds of teeth, only a relative handful of which were in use at any time. Plant material would have been cropped by its broad beak, and held in the jaws by a
cheek The cheeks () constitute the area of the face below the eyes and between the nose and the left or right ear. ''Buccal'' means relating to the cheek. In humans, the region is innervated by the buccal nerve. The area between the inside of th ...
-like organ. Its feeding range would have extended from the ground to about above.


Crest function

The distinctive spike-like crest of ''Saurolophus'' has been interpreted in multiple ways, and could have had multiple functions. Brown compared it to the crest of a
chameleon Chameleons or chamaeleons (Family (biology), family Chamaeleonidae) are a distinctive and highly specialized clade of Old World lizards with 200 species described as of June 2015. The members of this Family (biology), family are best known for ...
, and suggested it could provide an area for muscle attachment and a connection point for a nonbody back frill like that seen in the
basilisk lizard ''Basiliscus'' is a genus of large corytophanid lizards, commonly known as basilisks, which are endemic to southern Mexico, Central America, and northern South America. The genus contains four species, which are commonly known as the Jesus Chr ...
.
Peter Dodson Peter Dodson (born August 20, 1946) is an American paleontologist who has published many papers and written and collaborated on books about dinosaurs. An authority on Ceratopsians, he has also authored several papers and textbooks on hadrosaurs a ...
interpreted similar features in other duckbills as having use in sexual identification. Maryańska and Osmólska, noting the hollow base, suggested that the crest increased the surface area of the respiratory cavity, and helped in thermoregulation.
James Hopson James Allen Hopson (born 1935) is an American paleontologist and professor (now retired) at the University of Chicago. His work has focused on the evolution of the synapsids (a group of amniotes that includes the mammals), and has been focused on ...
supported a function as a visual signal, and further mentioned the possibility that the inflatable skin flaps over the nostrils could have acted as resonators and additional visual signals. This idea has been picked up by authors of popular dinosaur works, such as David B. Norman, who discussed hadrosaurid display at length and included a life restoration of such an adaptation in action.


Ontogeny

In 2015 Leonard Dewaele and colleagues described a small and partial nest containing several juveniles of ''S. angustirostris''. The specimen (MPC-D 100/764) was recovered from the notorious Dragon's Tomb assambleage of the Nemegt Formation. The team noted that among remains, three or even four juveniles can be recognized, and two fragmentary eggshells were found in association. Juveniles within this block were identified as
perinate A perinate refers to a member of a viviparous species from approximately one month before birth to one month after it. The term is derived from the Latin root ''perinatus'', meaning "around birth." In medical and biological contexts, it specificall ...
s, as they had skull lengths less than five percent of the length of the skulls of the adults, indicating they were in the earliest developmental stage at the time of their deaths. Based on these juveniles, Dewaele and team indicated that during the ontogeny of ''S. angustirostris'' the distinct crest found in adults was poorly developed in infancy, the snout grew proportionally longer, the orbit became more oval-shaped, the doming of the frontal became less prominent, and the coronoid process became higher.


Social behavior

Bell and team in 2018 described the famous Dragon's Tomb assambleage of the Altan Uul II locality, Nemegt Formation, which contains a large-sized
bonebed A bone bed is any geological stratum or deposit that contains bones of whatever kind. Inevitably, such deposits are sedimentary in nature. Not a formal term, it tends to be used more to describe especially dense collections such as Lagerstätte. ...
of ''S. angustirostris''. This bonebed is largely monodominant (one dominant species), with at least three size-classes (juveniles, subadults, and adults) of ''S. angustirostris''. Examinations made to Dragon's Tomb suggest that at least 21 ''Saurolophus'' individuals can be currently found. The team indicated that this bonebed has a minimum size of about 2000 m2, which suggest that over 100 ''Saurolophus'' carcasses may have contributed to the event. However, they discussed that even though evidence clearly reflects a catastrophic mass-mortality of a social group of ''S. angustirostris'' and provide the first evidence of
gregariousness Sociality is the degree to which individuals in an animal population tend to associate in social groups (gregariousness) and form cooperative societies. Sociality is a survival response to evolutionary pressures. For example, when a mother wasp ...
in this taxon, the exact conditions and cause surrounding the group death can not be determined. Bell and team also noted that while Dragon's Tomb provides direct evidence for
social behaviour Social behavior is behavior among two or more organisms within the same species, it encompasses any behavior in which one member affects another. Social behavior can be seen as similar to an exchange of goods, with the expectation that when you ...
in ''S. angustirostris'', there is yet no evidence for it in ''S. osborni''. Nevertheless, gregariousness is apparently widespread in hadrosaurines.


Paleopathology

David W.E. Hone and Mahito Watabe in 2011 reported the left humerus of a nearly complete ''S. angustirostris'' skeleton (MPC-D 100/764) from the Bügiin Tsav locality of the Nemegt Formation, which was heavily damaged from bite marks attributed to the
sympatric In biology, two closely related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter each other. An initially interbreeding population that splits into two or more distinct spe ...
''
Tarbosaurus ''Tarbosaurus'' ( ; meaning "alarming lizard") is a genus of large tyrannosaurid dinosaur that lived in Asia during the Late Cretaceous epoch, about 70 million years ago (Maastrichtian age). It contains the single type species: ''Tarbosaurus ...
''. As suggested by the lack of damage to the rest of the skeleton (such as large wounds in skeletal remains indicative of
predation Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...
), this tyrannosaurid was likely
scavenging Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding be ...
an already dead ''S. angustirostris''. It is unlikely that a large-bodied predator such as ''Tarbosaurus'' would have left sparse feeding traces on a single humerus having an entire carcass to feed on. The humerus shows three distinctive feeding methods, interpreted as punctures, drag marks, and bite−and−drag marks. Hone and Watabe noted that bite marks were mostly located at the deltopectoral crest, suggesting that this ''Tarbosaurus'' was actively selecting which biting style employ to scavenge the bone.


Daily activity

Comparisons between the scleral rings of ''Saurolophus'' and modern birds and reptiles suggest that it may have been
cathemeral Cathemerality, sometimes called metaturnality, is an organismal activity pattern of irregular intervals during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood ...
, active throughout the day at short intervals.


Paleoenvironment


Horseshoe Canyon Formation

''S. osborni'' is known only from the upper part (unit 4) of the
Horseshoe Canyon Formation The Horseshoe Canyon Formation is a stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta. It takes its name from Horseshoe Canyon, an area of badlands near Drumheller. The Horseshoe Canyon Formation is part of th ...
. The formation is interpreted as having a significant marine influence, due to an encroaching
Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, or the Western Interior Sea) was a large inland sea (geology), inland sea that existed roughly over the present-day Great Plains of ...
, the
shallow sea Shallow water marine environment refers to the neritic marine environment between the shore and the shelf break. This environment is characterized by oceanic, geological and biological conditions, as described below, and water in this environment ...
that covered the midsection of North America through much of the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
. ''S. osborni'' may have preferred to stay inland. It lived alongside other dinosaur species including the ornithopods ''Hypacrosaurus altispinus'' and '' Parksosaurus warreni'',
ankylosaurid Ankylosauridae () is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. The oldest known ankylosaurids date to around 122 million years ago and went extinct 66 million years ago during the Cretaceous–Pal ...
''
Anodontosaurus lambei ''Anodontosaurus'' is an extinct genus of ankylosaurid dinosaurs within the subfamily Ankylosaurinae. It is known from the entire span of the Late Cretaceous Horseshoe Canyon Formation (mid Late Campanian to "middle" Maastrichtian stage, about 7 ...
'', pachycephalosaurid '' Sphaerotholus edmontonense'', ornithomimids '' Dromiceiomimus brevitertius'' and an unnamed species of ''
Struthiomimus ''Struthiomimus'', meaning "ostrich-mimic" (from the Greek στρούθειος/''stroutheios'', or "of the ostrich", and μῖμος/''mimos'', meaning "mimic" or "imitator"), is a genus of ornithomimid dinosaurs from the late Cretaceous of Nor ...
'', small
theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...
s including '' Atrociraptor marshalli'' and '' Albertonykus borealis'', and the
tyrannosaurid Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to fifteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera ...
''
Albertosaurus sarcophagus ''Albertosaurus'' (; meaning "Alberta lizard") is a genus of large tyrannosaurid theropod dinosaur that lived in northwestern North America during the early to middle Maastrichtian age of the Late Cretaceous period, about 71 million yea ...
''. The dinosaurs from this formation form part of the Edmontonian land vertebrate age. A 2001 study suggested that ''Saurolophus osborni'' was part of a distinct inland fauna characterized by an association between '' Anchiceratops ornatus'' and it, while the contemporary coastal fauna was characterized by the association of ''Pachyrhinosaurus canadensis'' and ''
Edmontosaurus regalis ''Edmontosaurus regalis'' is a species of comb-crested hadrosaurid dinosaur. Fossils of ''E. regalis'' have been found in rocks of western North America that date from the late Campanian age of the Cretaceous Geologic time scale#Terminology, Peri ...
''.Lehman, T. M., 2001, Late Cretaceous dinosaur provinciality: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, pp. 310-328. However, the association between ''S. osborni'' and ''Anchiceratops'' was later noted to be in error, ''Anchiceratops'' only occurs lower in the Horseshoe Canyon Formation, before the major transgression of the Western Interior Seaway represented by the Drumheller Marine Tongue.Sullivan, R.M. and Lucas, S. G. (2006). "The Kirtlandian land-vertebrate "age"–faunal composition, temporal position and biostratigraphic correlation in the nonmarine Upper Cretaceous of western North America." Pp. 7-29 in Lucas, S. G. and Sullivan, R.M. (eds.), ''Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35''.


Nemegt Formation

''S. angustirostris'' was one of the largest herbivores of the
Nemegt Formation The Nemegt Formation (also known as Nemegtskaya Svita) is a geological formation in the Gobi Desert of Mongolia, dating to the Late Cretaceous. The formation consists of river channel sediments and contains fossils of fish, turtles, crocodilians ...
, which lacked large
ceratopsians Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Asia and Europe, during the Cretaceous Period, although ancestral forms lived earlier, in the Late Jura ...
, but had
sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...
s and a more diverse theropod fauna. Unlike other Mongolian formations like the well-known
Djadochta Formation The Djadochta formation (sometimes transcribed and also known as Djadokhta, Djadokata, or Dzhadokhtskaya) is a highly fossiliferous geological formation in Central Asia, Gobi Desert, dating from the Late Cretaceous period, about 75 million ...
that includes ''
Velociraptor ''Velociraptor'' (; ) is a genus of small dromaeosaurid dinosaurs that lived in Asia during the Late Cretaceous epoch, about 75 million to 71 million years ago. Two species are currently recognized, although others have been assigned in th ...
'' and ''
Protoceratops ''Protoceratops'' (; ) is a genus of small protoceratopsid dinosaurs that lived in Asia during the Late Cretaceous, around 75 to 71 million years ago. The genus ''Protoceratops'' includes two species: ''P. andrewsi'' and the larger ''P. hellenik ...
'', the Nemegt is interpreted as being a well-watered region, like the
Dinosaur Park Formation The Dinosaur Park Formation is the uppermost member of the Belly River Group (also known as the Judith River Group), a major geologic unit in southern Alberta. It was deposited during the Campanian stage of the Late Cretaceous, between about 7 ...
in Alberta. When examined, the rock
facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with distinctive characteristics. The characteristics can be any observable attribute of rocks (such as their overall appearance, composition, or con ...
of the Nemegt formation suggest the presence of stream and river channels, mudflats, and shallow lakes. Sediments also indicate that a rich habitat existed, offering diverse food in abundant amounts that could sustain Cretaceous dinosaurs.Novacek, M. (1996). Dinosaurs of the Flaming Cliffs. Bantam Doubleday Dell Publishing Group Inc. New York, New York. It coexisted with the rare hadrosaurid '' Barsboldia'', flat-headed pachycephalosaurian '' Homalocephale'' and domed ''
Prenocephale ''Prenocephale'' (meaning "sloping head") is a genus of small pachycephalosaurid dinosaur from the Late Cretaceous Nemegt Formation of Mongolia. It was similar in many ways to its close relative, ''Homalocephale''. Discovery The holotype specime ...
'', the large ankylosaurid ''
Saichania ''Saichania'' (Mongolian meaning "beautiful one") is a genus of herbivorous ankylosaurid dinosaur from the Late Cretaceous period of Mongolia. The first fossils of ''Saichania'' were found in the early 1970s in Mongolia. In 1977 the type speci ...
'', rare
titanosaurs Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of Sauropoda, sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with tax ...
sauropods ''
Nemegtosaurus ''Nemegtosaurus'' (meaning 'Reptile from the Nemegt') was a sauropod dinosaur from the Late Cretaceous Period of what is now Mongolia. Measuring an estimated long and weighing , it was named after the Nemegt Basin in the Gobi Desert, where the ...
'' and ''
Opisthocoelicaudia ''Opisthocoelicaudia'' is a genus of sauropod dinosaur of the Late Cretaceous Period discovered in the Gobi Desert of Mongolia. The type species is ''Opisthocoelicaudia skarzynskii''. A well-preserved skeleton lacking only the head and neck wa ...
'', the
alvarezsaurid Alvarezsauridae is a family of small, long-legged dinosaurs. Although originally thought to represent the earliest known flightless birds, they are now thought to be an early diverging branch of maniraptoran theropods. Alvarezsaurids were highly ...
'' Mononykus'', three types of troodontids including ''
Zanabazar Öndör Gegeen Zanabazar (born Eshidorji) was the first '' Jebtsundamba Khutuktu'' and the first ''Bogd Gegeen'' or supreme spiritual authority, of the Gelugpa (Yellow Hat) lineage of Tibetan Mahayana Buddhism in Mongolia. The son of a Mongol ...
'', several
oviraptorosauria Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period (geology), Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like s ...
ns including ''
Rinchenia ''Rinchenia'' (named after Byambyn Rinchen) is a genus of oviraptorid dinosaur that lived in Asia during the Late Cretaceous epoch in what is now Mongolia, Nemegt Formation, around 70 million years ago. The type species, type and only known spec ...
'' and ''
Nemegtomaia ''Nemegtomaia'' is a genus of oviraptorid dinosaur from what is now Mongolia that lived in the Late Cretaceous Period (geology), Period, about 70million years ago. The first specimen was found in 1996, and became the basis of the new genus and s ...
'', the
ornithomimosaurs Ornithomimosauria ("bird-mimic lizards") are theropod dinosaurs which bore a superficial resemblance to the modern-day ostrich. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period (geology), Period of Laurasia (now Asia ...
'' Anserimimus'' and ''
Gallimimus ''Gallimimus'' ( ) is a genus of theropod dinosaur that lived in what is now Mongolia during the Late Cretaceous period, about seventy million years ago (mya). Several fossils in various stages of growth were discovered by Polish-Mongolian expe ...
'', and the giant theropods ''
Deinocheirus ''Deinocheirus'' ( ) is a genus of large ornithomimosaur that lived during the Late Cretaceous around 70 million years ago. In 1965, a pair of large arms, shoulder girdles, and a few other bones of a new dinosaur were first discovered in the ...
'' and ''
Therizinosaurus ''Therizinosaurus'' (; meaning 'scythe lizard') is a genus of very large therizinosaurid dinosaurs that lived in Asia during the Late Cretaceous period in what is now the Nemegt Formation around 70 million years ago. It contains a single speci ...
'', including the
tyrannosaurid Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to fifteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera ...
''
Tarbosaurus ''Tarbosaurus'' ( ; meaning "alarming lizard") is a genus of large tyrannosaurid dinosaur that lived in Asia during the Late Cretaceous epoch, about 70 million years ago (Maastrichtian age). It contains the single type species: ''Tarbosaurus ...
''. ''S. angustirostris'' was common, and would have been an important large herbivore in the Nemegt Formation. By comparison, ''S. osborni'' was rare in the Horseshoe Canyon Formation, and faced competition from other duckbills (genus ''
Hypacrosaurus ''Hypacrosaurus'' (meaning "near the highest lizard"
reek υπο-, ''hypo-'' = less + ακρος, ''akros'', high Reek may refer to: Places * Reek, Netherlands, a village in the Dutch province of North Brabant * Croagh Patrick, a mountain in the west of Ireland nicknamed "The Reek" People * Nikolai Reek (1890–1942), Estonian military commander * Salme Ree ...
because it was almost but not quite as large as ''Tyrannosaurus'') is an extinct genus of hadrosaurid, duckbill dinosaur simila ...
'').


See also

*
Timeline of hadrosaur research This timeline of hadrosaur research is a chronological listing of events in the History of paleontology, history of paleontology focused on the hadrosauroids, a group of herbivorous ornithopod dinosaurs popularly known as the duck-billed dinosa ...


References


External links


''Saurolophus'', from the Natural History Museum
{{Taxonbar, from=Q131096 Saurolophinae Dinosaur genera Maastrichtian dinosaurs Horseshoe Canyon Formation Nemegt Formation Taxa named by Barnum Brown Fossil taxa described in 1912 Dinosaurs of Canada Dinosaurs of Mongolia