Saurolophus

Although often labelled as a duck billed dinosaur,‭ *‬Saurolophus* is more technically defined as a hadrosaurid due to its placement within‭ ‬the Hadrosauroidea.‭ ‬Even more specifically,‭ *‬Saurolophus* is defined as the type genus of the Saurolophinae,‭ ‬the group of solid crested to crestless hadrosaurids that were previously known as hadrosaurines before the then type genus of *Hadrosaurus* was found to not actually be a member of this group.‭

      *Saurolophus* fossils were first discovered in Alberta,‭ ‬Canada along the Red Deer River.‭ ‬Used to establish the type species of *S.‭ ‬osborni* by Barnum Brown,‭ *‬S.‭ ‬osborni* may have shared its environment with other hadrosaurid genera such as *Edmontosaurus* and *Hypacrosaurus*.‭ ‬Compared to the known remains of these other two genera however,‭ *‬Saurolophus* does not seem to have been as common.‭ ‬Here in Alberta at this time,‭ *‬Saurolophus* and other dinosaurs like it may have been preyed upon by large tyrannosaurs such as *Albertosaurus*,‭ ‬though smaller theropods like *Troodon*,‭ ‬*Saurornitholestes* and *Richardoestesia* may have also been threats,‭ ‬particularly to smaller juvenile *Saurolophus*.‭ *‬S.‭ ‬osborni* would have likely come into contact with other kinds of dinosaurs such as horned ceratopsians like *Pachyrhinosaurus* and *Anchiceratops*,‭ ‬as well as armoured ankylosaurs like nodosaurs‭ ‬like *Euoplocephalus* and *Edmontonia* respectively.

      The species that has really increased out understanding of *Saurolophus* however is *S.‭ ‬angustirostris‭* (‬named by Rozhdestvensky,‭ ‬1952‭)‬,‭ ‬based upon fossils from the Nemegt Formation of Mongolia.‭ ‬There are subtle differences in the skulls of these species which in *S.‭ ‬angustirostris* is twenty per cent longer than *S.‭ ‬osborni*.‭ ‬Skin impressions for both these species are also known and again there appears to be a difference in the scalation.‭ ‬*S.‭ ‬angustirostris* had rows of square scales that ran along the back and tail,‭ ‬as well as having varying scales forming vertical stripes down the tail.‭ ‬By contrast *S.‭ ‬osborni* lacked the square scales along its back,‭ ‬instead being smooth,‭ ‬and the scales on the tail formed radial patterns instead of vertical stripes.‭ ‬The most obvious difference between these species however is that at twelve meters long *S.‭ ‬angustirostris* seems to have been much larger than *S.‭ ‬osborni* which is so far only known from fossils that point to a length of just under ten meters long.

      Aside from these differences,‭ *‬S.‭ ‬angustirostris* seems to have lived in a similar way to *S.‭ ‬osborni*,‭ ‬though the sign ificantly higher number of fossils attributed to this species suggest that *S.‭ ‬angustirostris* was one of the more common herbivores in its ecosystem.‭ ‬Like with *S.‭ ‬osborni*,‭ *‬S.‭ ‬angustirostris* likely came into contact with ankylosaurs though this time genera like Tarchia,‭ ‬but higher levels of other kinds of dinosaurs such as ornithomimosaurs like‭ *‬Gallimimus* and the mysterious *Deinocheirus*,‭ ‬oviraptorids like *Avimimus*,‭ ‬therizinosaurs like *Therizinosaurus* and probably most interestingly sauropods like *Nemegtosaurus* and *Opisthocoelicaudia*.‭ ‬Again principal predators of *S.‭ ‬angustirostris* would have included tyrannosaurs,‭ ‬though this time *Tarbosaurus* and *Alioramus*.‭ ‬Smaller predators such as *Zanabazar* and *Adasaurus* could have also been a threat.

      Another species called *S.‭ ‬kryschtofovici‭* (‬named by Riabinin,‭ ‬1930‭) ‬was based upon the description of an incomplete ischium‭ (‬part of the hip‭) ‬recovered from Heilongjiang Province of China.‭ ‬Due to the fragmentary nature of the fossil it is based upon,‭ *‬S.‭ ‬kryschtofovici* is widely considered a nomen dubium because it tis near impossible to attribute any further fossil discoveries to this species.‭ ‬Because‭ ‬the ischium in question was discovered in China,‭ ‬there has been light speculation that it might actually be a specimen of the better known *S.‭ ‬angustirostris* from nearby Mongolia.‭ ‬If a link could be established then under standard rules governing the naming of animals,‭ *‬S.‭ ‬angustirostris* would actually become a junior synonym to *S.‭ ‬kryschtofovici* since this species was named first.‭ ‬However this is unlikely to happen because of the aforementioned poor state of preservation for the *S.‭ ‬kryschtofovici* type specimen.

      A possible species,‭ ‬the description for which is still in press at the time of writing is *S.‭ ‬morrisi*.‭ ‬These remains were first discovered in the Moreno Formation of California,‭ ‬USA between‭ ‬1939‭ ‬and‭ ‬1940‭ ‬but not assigned to‭ *‬Saurolophus‭* (‬with at least one skull to *Edmontosaurus‭*) ‬until‭ ‬2010.‭ ‬Later study saw a more complete description of the remains as *S.‭ ‬morrisi* by Prieto-Márquez‭ & ‬Wagner in‭ ‬2012.‭ ‬One significant thing about this discovery is that these are the first dinosaur remains discovered in the Moreno Formation which is actually full of marine reptiles.‭ ‬Some of these include mosasaurs like *Plotosaurus* to plesiosaurs like *Aphrosaurus* and *Morenosaursus*,‭ ‬so it will be interesting to see how dinosaurs like *Saurolophus* existed in these ecosystems,‭ ‬especially when you consider that others such as *Lambeosaurus* are also thought to have had a particularly close association with marine ecosystems.‭

      The distinguishing feature of *Saurolophus* is the crest which forms a single blunt spike-like rearward projection that rises from the top of the skull.‭ ‬Interestingly for a saurolophine hadrosaurid,‭ ‬this crest is not completely solid,‭ ‬and is actually hollow where it joins the skull.‭ ‬Despite this *Saurolophus* is still classified with the other solid/non-crested hadrosaurids because of similarities in the hips between these genera,‭ ‬as well as a crest that while partly hollow,‭ ‬is still more solid than the hollow crested lambeosaurine hadrosaurids.

      Like with other hadrosaurids,‭ *‬Saurolophus* is thought to have been primarily quadrupedal in standard locomotion,‭ ‬but possibly bipedal when foraging or possibly even running from predators.‭ ‬By being able to switch between bipedal and quadrupedal postures,‭ ‬*Saurolophus* was capable of feeding upon plants of varying heights,‭ ‬from low down near the‭ ‬ground to moderately high beyond the range of other low browsers.‭ ‬The‭ ‘‬duck-bill‭’ ‬of *Saurolophus* would have been effective at snipping vegetation so that mouthfuls could easily be passed back to the rear grinding teeth.‭ ‬A theory that is steadily gaining more popularity is that hadrosaurs like *Saurolophus* where able to‭ ‘‬chew‭’ ‬because of special skull bones that came apart when the lower jaw was pressed against them.‭ ‬This would cause the upper and lower batteries of grinding teeth to slide against each other like two pieces of sandpaper to process vegetation before swallowing.

      The eyes of *Saurolophus* were supported internally by bony growths called scleral rings that helped keep the shape of the eye.‭ ‬These rings are also known in modern day reptiles and birds,‭ ‬and when the scleral rings of *Saurolophus* are compared with species that we can observe today we notice that they most closely match those of cathemeral reptiles and birds.‭ ‬This means that *Saurolophus* was likely active for short periods throughout the day,‭ ‬during both daylight and night-time hours.‭ ‬This also matches theories of about the daily activity patterns of other hadrosaurid genera where the scleral rings are also known and found to be cathemeral also.