Fylax

Fylax (meaning "keeper") is a genus of hadrosauroid ornithopod from the Late Cretaceous Figuerola Formation of Spain. The genus contains a single species, Fylax thyrakolasus, known from a nearly complete left dentary.^[1]

Fylax Temporal range: Late Cretaceous, 66.052–66 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Holotype dentary from multiple angles
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Clade:	†Ornithischia
Clade:	†Ornithopoda
Clade:	†Hadrosauromorpha
Genus:	†Fylax Prieto-Márquez & Carrera Farias, 2021
Species:	†F. thyrakolasus
Binomial name
†Fylax thyrakolasus Prieto-Márquez & Carrera Farias, 2021

Discovery and naming

Reconstructed skeleton with the preserved dentary in white

The holotype of Fylax, IPS-36338, a left dentary, was discovered in the early 1990s. It was found in the Figuerola Formation in Lleida province, northeastern Spain. It was initially described in 1999.^[2]

In 2021, Albert Prieto-Márquez and Miguel Ángel Carrera Farias described the dentary as belonging to a new genus of hadrosauroid dinosaur. The generic name, Fylax, comes from the modern Greek, fýlax (keeper), and the specific name, thyrakolasus, comes from the Greek thýra (gate) and kólasi (hell), thus creating the combination "keeper of the gates of hell” in reference to the proximity of this taxon to the Cretaceous-Paleogene mass extinction event.^[1]

Classification

Prieto-Márquez and Carrera Farias recover Fylax as the sister taxon to Tethyshadros, in a derived position in the Hadrosauromorpha, making it one of the latest surviving non-hadrosaurid hadrosauromorphs. Their cladogram is shown below:

Hadrosauromorpha	Jeyawati Eolambia Protohadros Tanius Bactrosaurus Gilmoreosaurus Lophorhothon Penelopognathus Telmatosaurus Claosaurus Fylax Tethyshadros Plesiohadros Eotrachodon Hadrosauridae