Saurolophus

Saurolophus Temporal range: Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Mounted S. angustirostris skeleton at Nagoya City Science Museum
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	†Ornithischia
Clade:	†Ornithopoda
Family:	†Hadrosauridae
Subfamily:	†Saurolophinae
Tribe:	†Saurolophini
Genus:	†Saurolophus Brown, 1912
Type species
†Saurolophus osborni Brown, 1912
Other species
†S. angustirostris Rozhdestvensky, 1952

Saurolophus (

Barnum Brown recovered the first described remains of Saurolophus in 1911, including a nearly complete skeleton (

Two species are regarded as valid today: the type species 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.^[7] 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 premaxillary bones) were more upwardly directed.^[8] 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.^[9]

S. kryschtofovici (Riabinin, 1930) is not considered valid; either it is regarded as a dubious name,^[10][7] or as a synonym of S. angustirostris^[6] (although the name antedates S. angustirostris).^[11]

Until a 2011 reevaluation of the species by

In 1939–40, two partial skeletons were found in the late Maastrichtian age Moreno Formation of California. These specimens were referred to cf. Saurolophus sp. In 2010, one of the skulls was instead assigned to Edmontosaurus.^[12] A 2013 study placed the two specimens in a new species, S. morrisi.^[11] In 2014, the species was reassigned to a new genus, Augustynolophus.^[13]

Description

Saurolophus is known from material including nearly complete skeletons, giving researchers a clear picture of its bony anatomy. S. osborni, the rarer Albertan species, was around 8.2–8.5 m (27–28 ft) long, with its skull 1.0 m (3.3 ft) long.^[14][15] It has been estimated to have weighed around 3 tonnes (3.0 long tons; 3.3 short tons).^[15] S. angustirostris, the Mongolian species, was larger; it got as large as 13 m (43 ft) in length, and larger remains are reported. It has been estimated to have potentially weighed up to 11 tonnes (11 long tons; 12 short tons).^[15] The largest known skull of S.angustirostris measures 1.22 m (4.0 ft) in length.^[8] Aside from size, the two species are virtually identical, with differentiation hindered by lack of study.^[10]

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 and/or heat-regulation function.^[16] The unique crest of Saurolophus is made up almost completely by the nasal bones, and in S. angustirostris it is solid.^{[clarification needed]} 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.^[8]

Restoration of S. angustirostris

Restoration of S. osborni

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

Classification

Barnum Brown, who described the first specimens, put it in its own subfamily in "Trachodontidae" (=Hadrosauridae), the Saurolophinae. At the time, this also included Corythosaurus and Hypacrosaurus, the only well-known examples of what would become the Lambeosaurinae.^[3] Brown thought that Saurolophus had an expanded tip to the ischium 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.^[17]

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 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. Saurolophus, as the name suggests, is a saurolophine, as it has a saurolophine pelvis and a (largely) solid crest.^[18]

The following cladogram of hadrosaurid relationships was published in 2013 by Alberto Prieto-Márquez et al. in Acta Palaeontologica Polonica:^[19]

Saurolophinae

Brachylophosaurini Acristravus gagstarsoni Brachylophosaurus canadensis Maiasaura peeblesorum Shantungosaurus giganteus Edmontosaurus Edmontosaurus regalis Edmontosaurus annectens Saurolophini Kerberosaurus manakini Sabinas OTU Prosaurolophus maximus Saurolophus morrisi (now Augustynolophus) Saurolophus osborni Saurolophus angustirostris Kritosaurini Wulagasaurus dongi Kritosaurus navajovius Big Bend UTEP OTU Secernosaurus koerneri Willinakaqe salitralensis Gryposaurus Gryposaurus latidens Gryposaurus notabilis Gryposaurus monumentensis

Paleobiology

Feeding

As a

dental batteries 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-like organ. Its feeding range would have extended from the ground to about 4 m (13 ft) above.^[7]

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

basilisk lizard. Peter Dodson interpreted similar features in other duckbills as having use in sexual identification.^[20] Maryańska and Osmólska, noting the hollow base, suggested that the crest increased the surface area of the respiratory cavity, and helped in thermoregulation.^[16] James Hopson 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.^[21] 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.^[22]

Ontogeny

Highlited juvenile remains from block MPC-D 100/764, representing possibly four individuals

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 perinates, 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.^[23]

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

social behaviour in S. angustirostris, there is yet no evidence for it in S. osborni. Nevertheless, gregariousness is apparently widespread in hadrosaurines.^[24]

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

scavenging 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.^[25]

Daily activity

Comparisons between the

cathemeral, active throughout the day at short intervals.^[26]

Paleoenvironment

Horseshoe Canyon Formation

S. osborni is known only from the upper part (unit 4) of the

S. angustirostris was one of the largest herbivores of the

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).^{[citation needed]}

See also

• Timeline of hadrosaur research

References

External links

• Saurolophus, from the Natural History Museum

Data related to Saurolophus at Wikispecies

Wikimedia Commons has media related to Saurolophus.