Lambeosaurinae

 

Uncertainty surrounds the size of lambeosaurs from the European continent. Hadrosaurs found there, alongside other dinosaurs, have traditionally been considered representatives of the phenomenon of insular dwarfism, as the continent was then made up of many smaller islands. Many fossil remains from the continent are smaller than those of hadrosaurs found elsewhere in the world, with only isolated remains indicating individuals of adult size by the standards of their relatives in North America and Asia. It remains possible, however, that at least some cases instead represent misidentification of juvenile remains.^[2][3] The presence of genuine dwarfed taxa has been validated in some cases;^[2][4] adults of the genus Minqaria, for example, are thought to be around 3.5 metres (11 ft) in length.^[5] Contrastingly, the genus Pararhabdodon has a projected adult size similar to those of hadrosaurs on other continents, and known remains of Adynomosaurus and hadrosaurs from the Basturs Poble bonebed are of this adult size themselves.^[6] Why hadrosaurs of such variable sizes co-exist, despite being subject to the same environmental pressures, remains unclear.^[4]

Lambeosaurines originated on the continent of Laurasia during the Late Cretaceous, being initially found throughout modern Europe and Asia. Around the Campanian stage, lambeosaurines of the tribe Corythosauria colonized the landmass of Laramidia (modern western North America) via Beringia and spread as far south as Mexico, radiating into a diverse array of a body plans, including famous taxa such as Parasaurolophus and Lambeosaurus. For unknown reasons, lambeosaurines largely disappeared from North America around the Campanian/Maastrichtian boundary (the last remaining confirmed American member being Hypacrosaurus), but continued their dominance in Laurasia up to the end of the Cretaceous, with some members such as Ajnabia and Minqaria even colonizing northern Africa from Europe. However, fragmentary remains, including a partial humerus, resembling those of lambeosaurines have been reported from the late Maastrichtian-aged New Egypt Formation of New Jersey, USA. If these are lambeosaurine remains, these specimens are unique both for representing the only potential record of lambeosaurines from the landmass of Appalachia (suggesting that lambeosaurines had managed to migrate eastwards to Appalachia during the Maastrichtian, following the partial closure of the Western Interior Seaway), and potentially representing one of the latest records of the group from North America.^[7]

 

Lambeosaurines have been traditionally split into the tribes or clades Parasaurolophini (Parasaurolophus, Charonosaurus, others (?).) and Lambeosaurini (Corythosaurus, Hypacrosaurus, Lambeosaurus, others.).^[8] Corythosaurini (synonym of Lambeosaurini, see below) and Parasaurolophini as terms entered the formal literature in Evans and Reisz's 2007 redescription of Lambeosaurus magnicristatus. Corythosaurini was defined as all taxa more closely related to Corythosaurus casuarius than to Parasaurolophus walkeri, and Parasaurolophini as all those taxa closer to P. walkeri than to C. casuarius. In this study, Charonosaurus and Parasaurolophus are parasaurolophins, and Corythosaurus, Hypacrosaurus, Lambeosaurus, Nipponosaurus, and Olorotitan are corythosaurins.^[9] However, later researchers pointed out that due to the rules of priority set forth by the ICZN, Any tribe containing Lambeosaurus is properly named Lambeosaurini, and that therefore the name "Corythosaurini" is a junior synonym, and the definition had Corythosaurus casuarius changed to Lambeosaurus lambei, and the same for Parasaurolophini.^[10] In more recent years Tsintaosaurini (Tsintaosaurus + Pararhabdodon) and Aralosaurini (Aralosaurus + Canardia) have also emerged.^[11]

The following cladogram was recovered in a 2022 phylogenetic analysis by Xing Hai, and colleagues.^[12]

A 2013 study describing the genus Canardia found it to form a grouping with Aralosaurus, therein named as Aralosaurini and defined as the most exclusive clade of hadrosaurs containing both Canardia and Aralosaurus.^[13] Though one 2022 study recovered the tribe as monophyletic,^[12] most modern analyses fail to recover a natural grouping between the two genera.^[14][15][16] Daniel Madzia and colleagues registered the name under Phylocode in a 2021 study and redefined it as "the largest clade containing Aralosaurus tuberiferus and Canardia garonnensis but not Lambeosaurus lambei, Parasaurolophus walkeri, and Tsintaosaurus spinorhinus".^[17]

Numerous members of the clade Lambeosaurinae are known from Europe, dating to the end of the Cretaceous period.^[13] These various named taxa have traditionally been found to group into numerous different lambeosaur lineages, including Aralosaurini, Tsintaosaurini, Lambeosaurini,^[13][15] and Parasaurolophini.^[18] However, a study by Nick Longrich and colleagues proposed European lambeosaurs to form a singular monophyletic group, therein named Arenysaurini, based upon a phylogenetic analysis incorporating data based on geographic origin. They phylogenetically defined the tribe as all hadrosaurids closer to Arenysaurus ardevoli than Tsintaosaurus spinorhinus, Parasaurolophus walkeri, or Lambeosaurus lambei. In addition to the various named genera, indeterminate remains from across the continent including the Basturs Poble bonebed were proposed to represent arenysaurs.^[15]

The existence of a tsintaosaur clade of lambeosaurines was first recognized by palaeontologists Albert Prieto-Márquez and Johnathan R. Wagner, who in 2009 published a paper recognizing a phylogenetic relationship between Tsintaosaurus and Pararhabdodon based both on shared anatomical traits and a phylogenetic analysis.^[19] A 2013 study by Prieto-Márquez corroborated the existence of this grouping, and coined the tribe Tsintaosaurini to refer to it. The type genus is Tsintaosaurus, and it was defined as the smallest clade containing Tsintaosaurus spinorhinus and Pararhabdodon isonensis.^[13] Several studies since have corroborated the existence of the clade,^[17][20][21] though some others have failed to recover it, instead finding the two genera in a polytomy of basal lambeosaurs.^[17][22][14] A 2021 paper by Daniel Madzia and other ornithischian researchers, focused on a revising ornithischian nomenclature and converting existing group names into Phylocode-compliant clades, re-formalized the coining of Tsintaosaurini and revised its definition to be the most inclusive group including T. spinorhinus and P. isonensis, but not Aralosaurus tuberiferus, Lambeosaurus lambei, or Parasaurolophus walkeri.^[17] Longrich and colleagues instead consider the two genera unrelated, with Pararhabdodon being part of Arenysaurini.^[15]

The term Corythosaurini was first used by Brett-Surman in 1989, who characterized the taxon via reference to the premaxilary expansion into a hollow helmet-like cranial crest, as well as higher neural spines.^[23] The clade was formally defined via phylogenetic analysis by Evans and Reisz in 2007,^[24] and this was confirmed by multiple other analyses.^[25] In 2011, Sullivan et al. observed that by the rules of priority set by the International Code of Zoological Nomenclature, the name of the tribe ought to be Lambeosaurini due to its containing the defining type genus (Lambeosaurus) of its superior taxon (Lambeosaurinae).^[26] It is defined as all lambeosaurines closer to Lambeosaurus lambei than to Parasaurolophus walkeri, Tsintaosaurus spinorhinus, or Aralosaurus tuberiferus.^[17]

• Timeline of hadrosaur research