Adynomosaurus

Adynomosaurus Temporal range: Late Cretaceous (Early Late-Maastrichtian,
Restoration
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	†Ornithischia
Clade:	†Ornithopoda
Family:	†Hadrosauridae
Subfamily:	†Lambeosaurinae
Genus:	†Adynomosaurus Prieto-Márquez et al., 2019
Species:	†A. arcanus
Binomial name
†Adynomosaurus arcanus Prieto-Márquez et al., 2019

Adynomosaurus (meaning "weak shoulder lizard", in reference to the unexpanded shoulder blade) is a genus of lambeosaurine hadrosaurid dinosaur from the Late Cretaceous of what is now Catalonia, Spain.

Discovery and naming

In 2019, the type and only species Adynomosaurus arcanus, was named and described by Albert Prieto-Marquez, Víctor Fondevilla, Albert G. Selles, Jonathan R. Wagner and Angel Galobart in paleontological journal Cretaceous Research. The generic name is a composite of the Greek words ‘adýnamos’ (weak), ‘-mos’ (shoulder) and ‘sauros’ (lizard), and is a reference to the characteristically unexpanded morphology of the scapular blade of Adynomosaurus. The specific name arcanus means "secret" or "occult", alluding "to the elusive findings of taxonomically informative skeletal elements of this and other hadrosaurids in the South-Central Pyrenean Basin". It is based on MCD 7125 (Museu de la Conca Dellà, Isona, Lleida, Spain), a left scapula. This bone was one of a group of 34 bones recovered from the discovery site; the other bones have also been assigned to Adynomosaurus arcanus, and include vertebrae from the neck, sacrum, and tail, a sternal element, part of the pelvis, and parts of the forelimbs and hindlimbs. The discovery site, the Costa de les Solanes locality, is in rocks of the upper lower Maastrichtian Conques Formation.

Description

Scapulae of a standard lambeosaur; compared to this, the scapula of Adynomosaurus is underdeveloped, with reduced length and a small width on the bladed end (to the left)

In many respects, such as the vertebrae, humerus, femur, tibia, and metatarsals, the known anatomy of Adynomosaurus is indistinguishable from all other hadrosaurid dinosaurs. As a member of the hadrosaur family, it would've been a quadrupedal animal, while bearing the ability to walk upon its hindlegs bipedally. It would've had a long skull, ending in a beak, and a large array of complex teeth; as a lambeosaur, it would have possessed a cranial crest made of the nasal bones, filled with hollow internal passages. Despite its similarity to other hadrosaurs, some traits distinguish it from its relatives. Compared to other Spanish hadrosaurs, its dental anatomy stands out; the dentary of Koutalisaurus possesses tooth alveoli rotated slightly backwards, whereas in Arenysaurus and Blasisaurus they point upwards. Adynomosaurus possesses teeth intermediate to these conditions, rotated in the front half of the jaw but vertically oriented near the back. The tooth crowns are around three times taller than wide, also differing from the latter pair of genera, which have a more extreme ratio.

In regards to the anatomy of the postcranium, the supraacetabular crest of the ilium is V-shaped, and is extended very far back, all the way to the connection point with the ischium. Such an extreme extension of the crest is not presented in most lambeosaurines, but can be observed in Parasaurolophus cyrtocristatus as well as the Serrat del Corb hadrosaur. Also shared with these two taxa are features of the iliac process of the ischium; its dorsal and ventral (i.e. top and bottom) margins are nearly parallel and it is stout, with a broad articulate facet. The most distinctive part of its anatomy is its scapula, or shoulder bone, which bears the only traits unique to it among hadrosaurs. Specifically, the scapula is generally underdeveloped; its length, proportionally, seems to be the shortest of all hadrosaurs, though this is unable to be definitively confirmed due to incompleteness of the bone amongst known specimens. More definitively, the scapular blade (the flattened end) is only 75% the width of the proximal end (base) of the bone, unlike in all other lambeosaurines where it is as wide or wider. Likewise, the proximal constriction of the scapula - the middle portion connecting the proximal end to the blade - is very thin, hardly half as deep at the proximal end and around eighty percent the depth of the deepest section of the blade. The deltoid ridge of the bone is heavily reduced. These aspects of scapular anatomy are known to not be variable with age in other hadrosaurs, ruling out that as an expalantion of the condition in Adynomosaurus. The scapulae of Pararhabdodon and the Basturs Poble hadrosaur, from similar times and places, display more conventional anatomy, distinct from that of Adynomosaurus.

Classification

Adynomosaurus is member of the Hadrosauridae that including in clade Lambeosaurinae. It forms a polytomic relationships with Aralosaurus, Canardia, Jaxartosaurus, Tsintaosaurus, Pararhabdodon and other most basal know lambeosaurines.

Palaeoenvironment

Diagram of hadrosaur track depositional conditions, demonstrating the mudstone floodplains of meandering rivers (above) and braided rivers (below) hadrosaurs like Adynomosaurus lived in

Adynomosaurus is known from the Conques Formation of the Tremp Group, which in the Cretaceous was part of the Ibero-Armorican island, the largest of several Europe was at the time divided into at the time. The distinct Basturs Poble lambeosaur as well as the Serrat del Rostiar tsintaosaurin hadrosaur are known from equivalent geological units. It is well documented that a major change in the faunal composition of Late Cretaceous Europe occurred around the start of the Maastrichtian age, known as the "Maastrichtian Dinosaur Turnover". This saw the previously established dinosaurian herbivore fauna, composed of titanosaurs, rhabdodontids, and nodosaurids, go extinct in South-Western Europe and be replaced with different types of titanosaur as well lambeosaurine hadrosaurs, the latter of which go on to become overwhelmingly dominant across the region. Whether this was due directly to competition with lambeosaurs (which only arrive in Europe around the time of the turnover) or due to environmental changes that merely left a void for hadrosaurs is unknown. Despite the completeness of the change, there was a brief period of time wherein the pre- and post-turnover faunas coexist. The Conques Formation ecosystem is one such example, being one of only two known occurences of a rhabdodont, specifically Pareisactus, coexisting with hadrosaurs. Contrastingly, the enormous Abditosaurus, also from the formation, is considered characteristic of post-turnover titanosaur faunas.

The environment of the red mudstone unit (including the Conques Formation) of the Tremp Group has traditionally been considered fluvial floodplains. Sedimentary data associated with hadrosaur tracks preserved from the Tremp Group have been used to corroborate this. The ecosystem would've included abundant meandering rivers, with beds of either fine-grain or less often sand, as well as less common braided rivers, bedded with gravel. These rivers would've been interspersed across floodplains, possibly contiguous with estuarine conditions due to the proximity to marine environments (of the Tethys sea). The abundance of mudstone indicates flooding and fluctuating water levels in the ecosystem, which allowed the dinosaurs to leave tracks in the exposed wet mud which were then swiftly covered with water again to allow for preservation. In addition to the floodplains themselves, plant life would have colonized the abandoned rivers meanders and braid bars. Carbon and oxygen isotope values from dinosaur eggshells also provided evidence of a wet environment, and found a mean air temperature for the ecosystem of 21 °C (70 °F). A 2014 study proposed that the unit may have been more extensively marine-influenced than traditionally thought, something geologist Herbert Eisenscheer had previously proposed in a 1980s PhD thesis. In addition to sediment data, microfossils were investigated as an important source of evidence. Marine red algae and echinoderms among other marine microfossils were found to have been deposited into the river and mudplat environment by these tidal influences, likewise transported along water channels after death; in some modern environments tidal forces influences rivers and transports material as much as 80km inland. Sandy tidal flats may have been present, transitionally gradually into the mud sentiments beyond the reach of high tide, with the formation proposed to represent a tide-dominated delta and acting as a transitional ecosystem between fully freshwater and fully marine environments.

See also

• Timeline of hadrosaur research