| Amurosaurus | |
|---|---|
 | |
| Replica skeleton, Brussels | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ornithopoda |
| Family: | †Hadrosauridae |
| Clade: | †Euhadrosauria |
| Subfamily: | †Lambeosaurinae |
| Genus: | †Amurosaurus Bolotsky &Kurzanov, 1991 |
| Species: | †A. riabinini |
| Binomial name | |
| †Amurosaurus riabinini Bolotsky & Kurzanov, 1991 | |
| Synonyms | |
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Amurosaurus (/əˌmʊərəˈsɔːrəs/; "Amur lizard") is agenus oflambeosaurinehadrosauriddinosaur found in LateCretaceous (70 to 66 million years ago) deposits of what is now eastern Asia.[1]
RussianpaleontologistsYuri Bolotsky andSergei Kurzanov first described and named this dinosaur in 1991. The generic name is derived from theAmur River and theGreek wordsauros ("lizard"). The Amur (calledHeilongjiang or "Black Dragon River" inChinese) forms the border of Russia andChina, and is near where this dinosaur's remains were found. There is one knownspecies (A. riabinini), named in honor of the late Russian paleontologistAnatoly Riabinin, who conducted the first Russian expeditions to recover dinosaur remains in the Amur region in 1916 and 1917.[2][3]
All fossils ofAmurosaurus have been recovered from a single bonebed locality, discovered in 1984 within the city limits ofBlagoveschensk in theAmur Oblast offar eastern Russia. This bonebed is found in theUdurchukan Formation, the oldestgeologic formation in theTsagayan Group of far eastern Russia and northeastern China. This formation is thought to belong to theMaastrichtian stage of the LateCretaceous Period, and was deposited about 68 million years ago, or just prior to theLancian faunal stage of North America. The sediments were laid down in thefloodplain of ariver, which transported the fossils, but only a short distance, judging by the randomly assorted, disarticulated, but well-preserved bones within the bonebed, including fragile skull elements. Only a small section of the bonebed has been uncovered, but 90% of the remains found so far belong to lambeosaurines likeAmurosaurus, mostly juveniles, with the rest belonging to other taxa, such as thehadrosaurineKerberosaurus.Theropod teeth are also abundant, and there are many toothmarks on the bones, made bypredators orscavengers.[4] This bonebed containing many specimens was unearthed in 2008.[5]
Theholotype, or original specimen, consists of only amaxilla (upper jaw bone), and adentary (lower jaw bone), both from the left side of the same individual. However, most of the other bones of theskull and skeleton have also been preserved in the bonebed, albeit of many different individuals. This other material was described more recently, makingAmurosaurus the most abundant and completely known Russian dinosaur.[3]
A pathologicalulna of a specimen referred to the species, preserved with a hypertrophied and swollen distal region and with the distal articular surface engulfed within a large overgrowth of newly formed bone, was described by Bertozzo et al. (2023), who interpreted the bone as still healing prior to the animal's death, with the misalignment of the fracture and the resulting malunion of the two fragments of the bone probably causing the animal to limp and walk on three limbs.[6]
Sahaliyania (from "black" inManchu, a reference to theAmur/Heilongjiang River), is a junior synonym ofAmurosaurus. Its remains were found in abonebed in theMaastrichtian-ageYuliangze Formation, alongside rarer remains of thehadrosaurine hadrosaurid (flat-headed duckbill)Wulagasaurus.Sahaliyania was named byPascal Godefroit and colleagues in 2008. Thetype and only species isS. elunchunorum, named in honor of theElunchun people.[7]
Sahaliyania wasbased onGMH W453, a partial skull. Godefroit and colleagues assigned numerous other fossils from the bonebed to their new genus, representing much of the skull,pectoral girdle,upper arm, andpelvis. It can bedistinguished from other hadrosaurids by a variety of anatomical details. Godefroit and colleagues performed aphylogenetic analysis that placesSahaliyania as a lambeosaurine of uncertain relationships.[7] A 2022 article reassessedSahaliyania and considered it ajunior synonym ofAmurosaurus.[8]
Amurosaurus is characterized by manyautapomorphies, or unique features, of the skull, as well as thesigmoidal shape of theulna (the lower arm bone) when viewed from the front or side. Most other known lambeosaurines have hollow crests on the top of their skulls, and although the bones that would make up such a crest are unknown for this dinosaur, the bones on the roof of the skull are modified to support one, so it can be assumed thatAmurosaurus was crested as well. It has been estimated at 8 metres (26 ft) in length and about 3 metric tons (3.0 long tons; 3.3 short tons) in weight.[9] As a hadrosaurid,Amurosaurus would have beenherbivorous.[10]
The followingcladogram on the left shows the results of aphylogenetic analysis of lambeosaur relationships from a 2013 study by Albert Prieto-Márquez and colleagues, showingAmurosaurus as a derived member of thetribeLambeosaurini.[11] The cladogram on the right depicts the results from a 2014 study by Yuri Bolotsky and colleagues; this study incorporated novel skull material ofAmurosaurus which they found to indicate a more primitive spot among lambeosaurs.[12]
The 2020 osteological description of the material previously constituting the distinct genusSahaliyania found the latter genus to be a synonym ofAmurosaurus, allowing its newly restudied material to contribute to more robust tests of the classification ofAmurosaurus. With this new data,Amurosaurus was found to be a derived member ofLambeosaurinae closely related toLambeosaurus, something that had been recovered in some previous studies. The cladogram from this study is reproduced below:[13]
