Syngonosaurus is an extinct genus of herbivorous iguanodont dinosaur, from the late Albian-age Lower Cretaceous Cambridge Greensand of Cambridgeshire, England. It has in the past been classified with either the armored dinosaurs or the ornithopods, but recent research indicates that Syngonosaurus is an iguanodontian ornithopod.
In 1869 Harry Govier Seeley informally erected "Acanthopholis macrocercus" for CAMSM B55570-55609, including a series of 19 vertebrae and numerous osteoderms. In 1879, he described the vertebrae as a new genus and species, Syngonosaurus macrocercus, voicing considerable doubts about the osteoderms being the same individual and taxon as the vertebrae.. Some authors considered Syngonosaurus to be an armored dinosaur, particularly as a synonym of Anoplosaurus (Nopsca 1902; Huene 1909, 1927; von Zittel 1911; Romer 1956, 1966; Kuhn 1964) and others attributed it to Iguanodontia (Lydekker 1889; Nopsca 1928; Stromer 1934; Tatarinov 1964; Bartholomai and Molnar 1981). In the description of the Australian taxonMuttaburrasaurus, Bartholomai and Molnar (1981) considered that Syngonosaurus and Eucercosaurus were synonymous. In their overview of ankylosaur material rom the Middle Cretaceous of the United Kingdom, Pereda-Suberbiola and Barrett (1999) showed that the material that Seeley (1869) called "Acanthopholis macrocercus" was a composite of more than one taxon , the Syngonosaurus vertebrae belonging to an ornithopod and the osteoderms to an ankylosaur. In 2020 a study was published showing that the type material of Syngonosaurus macrocercus was indeterminate bryond Iguanodontia.
- Seeley, H.G. (1869). Index to the Fossil Remains of Aves, Ornithosauria, and Reptilia from the Secondary Strata arranged in the Woodwardian Museum of the University of Cambridge. Deighton, Bell and Company. pp. xvii.
- Seeley, H.G., 1879, "On the Dinosauria of the Cambridge Greensand", Quarterly Journal of the Geological Society 35: 591-636
- A. Bartholomai & RE Molnar. 1981: " Muttaburrasaurus , a new iguanodontid (Ornithischia: Ornithopoda) dinosaur from the Lower Cretaceous of Queensland". Memoirs of the Queensland Museum , vol. 20, n. 2) , p. 319-349 .
- Superbiola, X.P.; Barrett, P.M. (1999). "A systematic review of ankylosaurian dinosaur remains from the Albian-Cenomanian of England". Special Papers in Palaeontology. 60: 177–208.
- Barrett, Paul M.; Bonsor, Joseph A. (2020). "A revision of the non-avian dinosaurs Eucercosaurus tanyspondylus and Syngonosaurus macrocercus from the Cambridge Greensand, UK". Cretaceous Research. 118: 104638. doi:10.1016/j.cretres.2020.104638.