It was a relatively small hadrosaur, measuring approximately 5 m (16 ft) in length and 600 kg (1,300 lb) in body mass, which has been explained as an instance of insular dwarfism.

[1] In 1895 some peasants presented Ilona Nopcsa, the daughter of their lord, with a dinosaur skull they had found at the estate Săcele in the district Hunedoara (then named Hunyad) in Transylvania.

Ilona had an elder brother, Ferenc or Franz Nopcsa von Felső-Szilvás who was inspired by the find to become a paleontology student at the University of Vienna.

Fragmentary hadrosauroid material from Spain, France and Germany, that had been referred to Orthomerus, is now often assigned to Telmatosaurus, but an identity is hard to prove; the same is also true of many Romanian fragments and eggs.

[6] A juvenile Telmatosaurus examined by Dumbrava et al.[7] bears a large non-cancerous tumor called an ameloblastoma on its lower jaw.