Ankylopollexia

, Iguanodon, and Camptosaurus'') compared to other ornithopods Ankylopollexians varied greatly in size over the course of their evolution.. Jurassic genus Camptosaurus was small, no more than in length and half a tonne in weight. The largest known ankylopollexian, dating to the late Campanian age (around 70 million years ago), belonged to the hadrosaurid family, and is named Shantungosaurus. It was around to in length and weighed, for the largest individuals, up to . '' Primitive ankylopollexians tended to be smaller as compared to the larger, more derived hadrosaurs. There are, however, exceptions to this trend. A single track from a large ornithopod, likely a relative of Camptosaurus, was reported from the Lourinhã Formation, dating to the Jurassic in Portugal. The corresponding animal had an estimated hip height of around , much larger than the contemporary relative Draconyx. The primitive styracosternan Iguanacolossus was named for its distinct robustness and large size, likely around in length. Regarding hadrosaurs, one of the more basal members of Hadrosauroidea, the Chinese genus Bolong, is estimated to have been around . Another exception of this trend is Tethyshadros, a more derived genus of Hadrosauroidea. Estimated to have weighed , Tethyshadros have been found only on certain islands in Italy. Its diminutive size is explained by insular dwarfism. In addition a 44 cm scapula belonging to an ankylopollexian has been found in the Lourinhã Formation the length of the scapula indicates an animal similar in size to Camptosaurus. ==Classification==

'', showing the distinctive thumb of the group About 157 million years ago, Ankylopollexia and Dryosauridae are believed to have split into separate evolutionary branches. Originally named and described in 1986 by Paul Sereno, Ankylopollexia would receive a phylogenetic definition in a later paper by Sereno in 2005. The cladogram below follows the phylogenetic analysis of Bertozzo et al. (2017). ==Palaeobiology==

Brain The neurobiology of ankylopollexians has been studied as far back as 1871, when a well preserved cranium (specimen NHMUK R2501 The referral of this skull was reinforced in a later study, published in 1897. It was here inquired that the brain of the dinosaur may have been more closely associated to the cavity than that of modern reptiles, and so an endocast was created and studied. This was not the first endocast of an ankylopolloxian brain, for in 1893, the skull of a Claosaurus annectens (today referred to the genus Edmontosaurus) was used by Othniel Charles Marsh to create a cast of the brain cavity. Some basics remarks were made, including the small size of the organ, but interpreting minute features of the organ was noted to be difficult. The 1897 paper noted the similarity of the two endocasts. Ostrom supported the view that the brains of hadrosaurs and other dinosaurs would've likely only filled a portion of the cranial cavity, therefore hindering the ability to learn from endocasts, but noted they were still useful. He noted, similar to Marsh, noted the small predicted size of the organ, but also that it was significantly developed. A number of similarities to the brains of modern reptiles were noted. In a first for any terrestrial fossil vertebrate, Brasier et al. (2017) reported mineralized soft tissues from the brain of an iguanodontian dinosaur, from the Valanginian age (around 133 million years ago) Upper Tunbridge Wells Formation at Bexhill, Sussex. Fragmentary ornithopod remains were associated with the fossil, and though assigning the specimen to any one taxon with certainty wasn't possible, Barilium or Hypselospinus were put forward as likely candidates. The specimen compared well to endocasts of similar taxa, such as one from a Mantellisaurus on display at the Oxford University Museum of Natural History. Detailed observations were made with the use of a scanning electron microscope. Only some parts of the brain were preserved; the cerebellar and cerebral expansions were best preserved, whereas the olfactory lobes and medulla oblongata were missing or nearly so. The neural tissues seemed to be very tightly packed, indicating an EC closer to five (with hadrosaurs having even higher ECs), nearly matching that of the most intelligent non-avian theropods. Though it was noted this was in-line with their complex behaviour, as had been noted by Hopson, it was cautioned the dense packing may have been an artifact of preservation, and the original lower estimates were considered more accurate. Some of the complex behaviours ascribed can be seen to some extent in modern crocodilians, who fall near the original numbers. The advent of CT scanning for use in palaeontology has allowed for more widespread application of this without the need for specimen destruction. Modern research using these methods has focused largely on hadrosaurs. In a 2009 study by palaeontologist David C. Evans and colleagues, the brains of various lambeosaurine hadrosaur genera were scanned and compared to each other, related taxa, and previous predictions. Contra the early works, Evans' studies indicate that only some regions of the hadrosaur brain were loosely correlated to the brain wall. As with previous studies, EQ values were investigated; even the lowest end of the determined EQ range was still higher than that of modern reptiles and most non-maniraptoran dinosaurs, though fell well short of maniraptorans themselves. The size of the cerebral hemispheres was, for the first time, remarked upon, being far larger than in other ornithischians and all large saurischian dinosaurs; maniraptorans Conchoraptor and Archaeopteryx had very similar proportions. This lends further support to the idea of complex behaviours and relatively high intelligence, for non-avian dinosaurs, in hadrosaurids. Lambeosaurine Amurosaurus was the subject of a 2013 paper once again looking into a cranial endocast. A once again high EQ range was found, higher than that of living reptiles, sauropods and other ornithischians, but different EQ estimates for theropods were cited, placing the hadrosaur numbers significantly below the majority of theropods. Additionally, the relative cerebral volume was only 30% in Amurosaurus, significantly lower than in Hypacrosaurus, closer to that of theropods like Tyrannosaurus, though still distinctly larger than previously estimated numbers for more primitive iguanodonts. This demonstrated a previously unrecognized level of variation in neuro-anatomy within Hadrosauridae. ==Palaeobiogeography==

'' Ankylopollexians would in the Cretaceous become one of the most successful groups on the planet, being both widespread and numerous in nature. Around this time, ankylopollexians spread to Asia and Europe. An early example is the Chinese genus Bayannurosaurus, from the Berriasian. The oldest genus, found in Wyoming, is Camptosaurus dispar, which dates to around the Callovian-Oxfordian, about 156-157 million years ago. ==References==