Fossil Friday: Rhadinosteus, Enneabatrachus, and Unidentified Frog.

Little Enneabatrachus seems amused on her ginkgo branch. Rhadinosteus puffs up in a huff, offended that an unnamed frog is so obliviously close to his burrow.
Little Enneabatrachus seems amused on her ginkgo branch. Rhadinosteus puffs up in a huff, offended that an unnamed frog is so obliviously close to his burrow.

Species: Rhadinosteus parvus (rad-ih-no-stee-us par-vus)

Enneabatrachus hechti (in-ee-ah-baa-track-us hek-tie)

Indeterminate Pelobatid (peh-low-bat-id)

What it means: Rhadinosteus = Small slender bone

Enneabatrachus = Frog from Quarry 9

Other Species: None

Where I live: Utah, USA – The Morrison Formation

When to find me: The Late Jurassic period, about 155-148 million years ago.

My favorite food: Anything that’ll fit in our mouths, which could be insects, insect larvae, worms, snails, and even tiny fish fry if we can catch one!

Tiny Morrison frogs next to an American quarter, because everyone has a quarter on hand for comparison right? It's 24.5 mm in diameter.

My neighborhood: The Morrison Formation covers a huge expanse of land with a variety of different habitats teaming with life. Most of it was very much like the Serengeti of modern day Africa, only with prairies of drought-tolerant ferns and cycad relatives instead of grass. Dense woodlands of tall conifers like the modern araucaria, ginkgoes, and tree ferns would only lie in places of plentiful water such as the few permanent rivers. Other areas had far more sparse and shrubbier vegetation like the open woodlands of acacia trees in the Serengetti.

Life in this environment would’ve adapted to long months of harsh drought, followed by a few months of monsoon that flooded the rivers. Many of the larger herbivores may have migrated like the herds in Africa do today, while most carnivores stayed behind to feast on the dead and dying, or else become opportunistic hunters of less traditional diets for lean times, such as fish or turtles in the rivers.

A few of my neighbors: First let me share the plant-eating giants…

  • Long-necked sauropods like Apatosaurus, Brachiosaurus, Camarasaurus, Diplodocus, Barosaurus, Suuwassea, Supersaurus, Haplocanthosaurus, and Dystrophaeus.
  • Armored dinosaurs like Stegosaurus, Hesperosaurus, Mymoorapelta, and Gargoyleosaurus.
  • Two-legged ornithopods like Dryosaurus, Camptosaurus, and Nanosaurus

Monstrous meat-eaters in the neighborhood include dinosaurs like Allosaurus, Torvosaurus, Ceratosaurus, Saurophaganax, Marshosaurus, Ornitholestes, Coelurus, Elaphrosaurus, Tanycolagreus, Stokesosaurus, and Koparion.

Plus there are all the other creatures that might eat me…countless lizards, crocodile relatives on land and water, mammals, turtles, large fish, and pterosaurs that patrol the skies!

Fun Facts:

  • Rhadinosteus fossils are known from the Rainbow Park site in Dinosaur National Monument, in Utah, so it can’t be proven that the encounter pictured above would happen. More fossils are needed to know how far a range the frogs lived, but it’s possible!
  • The Mexican burrowing frog, or Burrowing frog, is the only member left from the group of frogs known as rhinophrynids (rie-no-frin-id), the group Rhadinosteus was a part of. The burrowing frog is a specialized digger and ant eater, but Rhadinosteus was a much older member of the group and was more of a generalist.
  • Enneabatrachus comes from Ancient Greek ennea (nine) + bátrachus (frog). It was named after Quarry 9 at Como Bluff, Wyoming. A second specimen has been described from Dinosaur National Monument.
  • Enneabatrachus was a member of a group of frogs still alive today, the discoglossids. Modern members of the family include painted frogs and midwife toads, and between the two the painted frogs are the oldest and closest relatives of Enneabratachus.
  • The unnamed frog is also from Quarry 9. It is known from a single ilium, a bone from the pelvis, which only tells us that it is probably from a group of frogs known as pelobatids. (Though another paper suggests it might be a discoglossid like Enneabatrachus)
  • Pelobatids are a group of frogs commonly known as spadefoot toads, and they thrive in many regions of North America, Africa, Europe, and Asia. Some are more adapted to dryer regions, and burrow in the ground with their hind feet, while others live in forests near streams and are not burrowers.

Fossil Finds:

Rhadinosteus – Several partial and nearly complete skeletons found together on several slabs of rock. These specimens were in the middle of metamorphosis, and not yet adult frogs.

Enneabatrachus – A few bones, most notably an ilium (pelvic bone) only a few millimeters long. A second specimen has been described from Dinosaur National Monument.

Pelobatidae indent. – A single ilium slightly larger than Enneabatrachus.


Foster, John. Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press, 2007

Henrici, Amy C. “A New Pipoid Anuran from the Late Jurassic Morrison Formation at Dinosaur National Monument, Utah.” Journal of Vertebrate Paleontology, vol. 18, no. 2, 1998, pp. 321–332. JSTOR, Accessed 30 May 2021.

Cannatella, David. 1995. Discoglossidae. Discoglossid frogs. Version 01 January 1995 (under construction). in The Tree of Life Web Project,

3 thoughts on “Fossil Friday: Rhadinosteus, Enneabatrachus, and Unidentified Frog.

  1. Haha, I love the added part of the title: “…and unidentified frog.” And Enneabatrachus’s face is priceless. 😛 I think it’s so cool to see all the varieties of wildlife that surrounded the other more well-known prehistoric critters. I mean, normally I didn’t think of frog/dino interactions in the Morrison formation, but now I can’t help imagining it!

    Also, I just wanted to say that you made those Gingko leaves look so satisfyingly slurpy. 😀

    Can’t wait till the next Fossil Friday!


    1. Haha, thank you! I’m learning a lot with these little illustrations. I really like how they help fill in the rest of the picture and show how much variety to life there really was.

      I must say I was rather proud of my rotting ginkgo leaves, right up to the point one of my kids came up and asked me if they were banana peels lol. At least I got the rotting slurpiness down! 😀


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s