Canardia

Life restoration with hypothetical crest-shape

It is not known if Canardia had a hollow bony crest on the skull like most lambeosaurines. Although no complete skull is known for the two groups of hadrosaurs to which it has been successively attached, both have very different cranial conformation. Aralosaurus, one of the most primitive lambeosaurine, didn't have a crest on the skull roof because the latter was not modified to accommodate such a structure. Instead, it had a hollow structure in front of the orbits. However, as only a fragment of this structure has been preserved, its size and shape are unfortunately unknown.[6] In contrast, the morphology of the skull roof in Arenysaurus clearly shows that it supported a cranial crest. But as no Arenysaurini crest has yet been discovered, their exact morphologies are still unknown.[7]

Appendicular bones of Canardia. Left Scapula in lateral view (A). Left sternal plate in ventrolateral view (B). Distal blade of left scapula in lateral view (C). Fragmentary right pubis in lateral view (D). Left humerus in medial (E), rostral (F), and lateral (G) views.[1]

Paleontologists agree on a probable Asian origin of European lambeosaurines. According to Prieto-Marquez and colleagues, Canardia and the Spanish genus Pararhabdodon had as closest relatives the Asian genera Aralosaurus and Tsintaosaurus, respectively. These are respectively 20 and 15 million years older than their presumed European relatives. Thus, Canardia and Pararhabdodon would both belong to rather archaic groups of lambeosaurines for their time and the Ibero-Armorican island would have constituted an ultimate refuge for these ancient groups of lambeosaurines.[1][8] Longrich and colleagues, who place Canardia and all other European lambeosaurines in the Arenysaurini clade, also suggest an Asian origin for paleogeographic reasons.[2] As no lambeosaurines were known in the rich localities of late Campanian and early Maastrichtian ages of the Ibero-Armorican Island, it was suggested that the ancestors of Canardia had to reach this island rather late, perhaps at the end of the early Maastrichtian or during the late Maastrichtian.[1] The discovery later in Spain of numerous lambeosaurines remains in the highest levels of the lower Maastrichtian argues for the first hypothesis.[9][10] This migration was probably carried out in several stages, firstly by temporary terrestrial links between the landmass of Western Asia and the eastern islands of the European archipelago, then between the different European islands up to the Ibero-Armorican Island.[8] From this island, the lambeosaurines would then have reached North Africa by oceanic dispersal, the hadrosaurs swimming, drifting, or rafting (in the case of early juvenile hadrosaurs) over great distances, the Ibero-Armorican island and the coasts of Morocco (where Ajnabia lived) being separated at the time by 500 km of open sea.[2]

The Marnes d’Auzas Formation is 100 m thick. It corresponds to sediments whose depositional environment evolved from the paralic domain (coastal lagoons, tidal marsh, tidal muddy channel) at the base of the formation, towards a more continental domain (alluvial plain, fluvial channels) in its upper part.[4] From a paleogeographic point of view, the sites of the Marnes d’Auzas Formation were located on the west coast of the Ibero-Armorican Island (which included much of France and Spain), facing the Atlantic Gulf.[8]

Few other vertebrates fossils have been found with the Canardia remains. The type locality of Tricouté 3, in the basal part of the Marnes d’Auzas Formation, has yielded only a crocodilian tooth,[4] whereas the marine Marly limestone of Gensac Formation (the lateral equivalent of the top of the Marnes d’Auzas) has not yet yielded other terrestrial vertebrates remains.[3] However, a more diverse fauna is known from the Cassagnau localities, in the middle part of the Marnes d’Auzas Formation.[11][4] The Cassagnau's fauna is also located near Marignac-Laspeyres and includes several fish (Lepisosteidae, Phyllodontidae, Sparidae),[11][4] Amphibians (Albanerpetontidae),[11][4] several turtles including a complete carapace of Iberoccitanemys convenarum,[11][4][12] various crocodylians including teeth of a Musturzabalsuchus-like form and a complete skull attributed to Thoracosaurus neocesariensis,[11][4][13] two squamates (an indeterminate lizard and a varanoid form[11][4] which is probably a freshwater mosasauroid[14]), a probable enantiornithe bird,[11][4] an indeterminate dromaeosaurid (known only by teeth),[11][4] an indeterminate theropod of larger size (only known by a tooth characterized by its anterior carina running on the lingual side of the teeth),[4] an indeterminate titanosaurian sauropod represented by teeth and a metacarpal[11][4] (the shape of the teeth suggests that they belong to an Atsinganosaurus-like form),[15] and an indeterminate lambeosaurine hadrosaur. The latter is exclusively represented by juvenile individuals and includes an articulated postcranial skeleton, teeth, and two left dentaries, one of them being associated with a predentary.[11][4][1] No maxilla is preserved in these specimens, so it is not possible to know if this hadrosaur belongs to Canardia or to another lambeosaurine. The Marnes d’Auzas Formation is also present in the department of Ariège, notably near the village of Mérigon. There, a coarse sandstone bed at the top of the formation, has yielded a tooth and a dentary fragment of an indeterminate hadrosaur, as well as a cervical vertebra of a giant Azhdarchid pterosaur of 9 meters wingspan.[16][4]