Diphydontosaurus avonis
By Ripley Cook
Etymology: Reptile with two types of teeth
First Described By: Whiteside, 1986
Classification: Biota, Archaea, Proteoarchaeota, Asgardarchaeota, Eukaryota, Neokaryota, Scotokaryota Opimoda, Podiata, Amorphea, Obazoa, Opisthokonta, Holozoa, Filozoa, Choanozoa, Animalia, Eumetazoa, Parahoxozoa, Bilateria, Nephrozoa, Deuterostomia, Chordata, Olfactores, Vertebrata, Craniata, Gnathostomata, Eugnathostomata, Osteichthyes, Sarcopterygii, Rhipidistia, Tetrapodomorpha, Eotetrapodiformes, Elpistostegalia, Stegocephalia, Tetrapoda, Reptiliomorpha, Amniota, Sauropsida, Eureptilia, Romeriida, Diapsida, Neodiapsida, Sauria, Lepidosauromorpha, Lepidosauria, Rhynchocephalia, Sphenodontia
Referred Species: D. avonis
Status: Extinct
Time and Place: 227 to 200 million years ago, from the Norian to Rhaetian of the Late TriassicÂ
Diphydontosaurus is known from Southern England and Wales, and possibly also from Northern Italy.
Physical Description: Diphydontosaurus is an early-derived relative of the tuatara, one of the oldest in fact. Like the tuatara, it resembles a lizard in appearance, probably even more so than living tuataras. It was also very small too. Like, really small. 10 centimetres long from head-to-tail with a skull less than 15 millimetres long, small. The skull itself has massive eyes and a pretty short snout, so it was probably a rather cute looking little reptile. The most distinctive features of Diphydontosaurus are its jaws and teeth. Living tuataras have their teeth fused to the jaw bones (acrodont), which wear down and canât be replaced. Diphyodontosaurus has these teeth at the back of its jaws, but the teeth in front were attached in sockets (pleurodont), like some lizards. These teeth were sharp and peg-like, perfect for puncturing the carapaces of insects, while the teeth at the back formed a shear for slicing through them. Diphydontosaurus also lacked the characteristic âbeakâ at the tip of the jaws found in later sphenodonts, and probably didnât chew its food the way modern tuataras can (yes, tuataras can chew). Diphydontosaurus would also have had a typmanum, a.k.a. an eardrum, visible at the back of its head, again like most lizards but unlike the living tuatara.
Diet: Diphydontosaurus was insectivorous, as evidenced by its small size and teeth, although like some living insular lizards it may have eaten plants to supplement its diet.
Behavior: Diphydontosaurus was likely an active predator or insects and other small arthropods. Its large eyes and well developed ear openings indicate that it likely relied heavily on these senses for hunting and catching prey. They may have especially congregated around the abundant fissures and sinkholes in their habitat, where moist soils and plants would have attracted plenty of insects and other arthropods, and so too the Diphydontosaurus. Being small would have been handy for clambering over steep rock faces after prey, out of reach of other, larger reptiles.
Ecosystem: Diphydontosaurus was part of a diverse collection of island ecosystem in the latest Triassic of Europe, populating low-lying islands of limestone pockmarked with deep fissures and caves eroded into the karst. The species found on each island differed, but there was some broad similarities. The largest land animals on these islands were the possibly dwarfed prosauropod dinosaurs Thecodontosaurus and Pantydraco, as well as small theropods. Pseudosuchian archosaurs were here too, including the small predator Terrestrisuchus and the enigmatic Aenigmaspina, both extremely long-legged, agile animals well suited for navigating the karst-riddled landscape. There was also a drepanosaur around, as well as the gliding reptiles Kuehneosaurus and Kuehneosuchus whose affinities remain mysterious. They could be lepidosaurs like sphenodonts, or, they may belong to the strange allokotosaurs on the archosaur side of the tree! The jury is still out on them. Some of the islands also hosted small mammaliaforms, including Morganucodon and Eozostrodon.
Stem-tuataras like Diphydontosaurus were remarkably diverse, and it coexisted with numerous other genera such as Gephyrosaurus, Clevosaurus, and Planocephalosaurus, each with multiple species, and there are still more new types of sphenodont to be described! Such a high density of different sphenodonts on these islands implies they were all specialised for different ways of life. Diphydontosaurus was one of the most abundant of all sphenodonts on the islands of Late Triassic Europe, no doubt thanks to its small size and insectivorous diet. However, this small size left it vulnerable, and it may have been preyed upon by its larger, more predatory cousins like Clevosaurus.
Other: Diphydontosaurus is one of the oldest known, and is the earliest diverging, sphenodont, the group of animals that includes living tuataras but excludes the even earlier-diverging rhyncocephalians, the gephyrosaurids (the distinction isnât huge, mostly that gephyrosaurids have completely pleurodont teeth). The anatomy of Diphydontosaurus was unexpected compared to modern tuataras, which are so often described as âliving fossilsâ unchanged since the Mesozoic. In fact, certain features of Diphydontosaurus and other early sphenodonts reveal that the modern tuatara is actually pretty derived compared to its ancestors, especially so in the skull, including the loss of its external ears, its shearing teeth and the ability to chew food. Diphydontosaurus really just goes to show you canât judge a 200 million year old clade by its sole extant member, eh?
~ By Scott Reid
Sources under the CutÂ
