Fossil Friday: Morrolepis, Leptolepis, and Hulettia

Hulettia hide in the fronds of a drifting conifer branch. Leptolepis and Morrelepis search the plant for insects and algae.
Morrolepis peers through murky water to see if anything tasty might be on the floating plant, which makes the hiding Hulettia nervous. Leptolepis leaves for a quieter part of the lake.

Species: Morrolepis schaefferi (mo-roe-lep-is shay-fur-eye)

cf. Leptolepis sp. (lep-toe-lep-is)

Hulettia hawesi (hew-let-ee-ah haw-sigh)

What it means: Morrolepis = Fish scale from the Morrison Formation

Leptolepis = Delicate scale

Hulettia = From Hulett, Wyoming

Other Species: M. aniscowitchi, M. andrewsi

Leptolepis has 17 recognized species at this time.

H. americana

Where I live: Colorado, USA – The Morrison Formation

When to find me: The Late Jurassic period, about 150 million years ago.

My favorite food: Anything that’ll fit in our mouths, which could be plants that fall in the water, algae, insects, snails, tadpoles, or smaller fish.

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, frogs, turtles, other fish, and pterosaurs that patrol the skies!

Fun Facts:

  • I could not find the original description for Morrolepis, so the translation for it’s name is a best-guess. Morro is a Spanish word meaning an animal snout or the nose of a vehicle. Lepis is Latin for fish scale. Perhaps the name refers to the unusual placement of the eye near the end of the blunt snout. Morro can also mean a small hill or point of land, borrowing from the Spanish. It is unlikely to be from the Greek because the Greek word is moros, with only one r instead of two. If anyone has access to Kirkland’s original description from 1998, then please enlighten us on the etymology behind the name. There is one last possibility, and the one I think most likely. Simply borrowing Morro from the Morrison Formation, the first place this fish was discovered, which makes the name “Fish from the Morrison Formation”.
  • Leptolepis comes from Ancient Greek leptos (thin, slender, delicate) + lepis (fish scale). The cf. is an abbreviation of the Latin word conferre, which means “to compare to” or “confer”. It is often used for newly discovered species in the modern day, or poorly preserved fossil species. Basically, the best guess is that it’s a species of Leptolepis, and so we can compare it with other species of Leptolepis to make educated guesses on its place in the environment. However, the fossil does not preserve defining characteristics, and so remains an undetermined species. This is shown with the abbreviated sp. at the end of its name.
  • Fossils of the genus Leptolepis have been found in both marine and freshwater environments spanning from the Middle Triassic Period until the Late Cretaceous. They are found all over the world in parts of Eurasia, North America, Africa, and Australia. Most look a bit like modern herring, and fossils suggest that they lived in schools. The Morrison species has an unusually deep body compared to other Leptolepis.
  • Hulettia gets its name from Hulett, Wyoming, a town near the Morrison Formation. Both species are known from the Morrison, but H. americana is closer to the Rocky Mountains, and H. hawesi is known from the Fruita and Rabbit Valley localities of the Morrison, which are both in Western Colorado.
  • All three fish are found in the Rabbit Valley site of the Morrison, which was a large lake during the Jurassic. It is speculated that this was a low area where water collected into ponds during the wet season, and eventually grew into a large, shallow, mud-bottomed lake as the water table rose underground. It sustained not only these three fish, but also several species of large lungfish, frogs, freshwater snails, and tiny crustaceans like shrimp. Surely many turtles and other animals benefitted from it as well, even if we may not find direct fossil evidence for it.

Fossil Finds:

Morrolepis – Several partially complete and fragmentary specimens. Most in the Morrison, but a few found in other places such as Kazakhstan.

cf. Leptolepis – A single, nearly complete skeleton from Rabbit Valley, Colorado. For other species there are many, many fossils from all over the globe.

Hulettia – Many fossils, most of which only preserve an outline of the very thick scales.


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

Skrzycka, Roksana. (2014). Revision of two relic actinopterygians from the Middle or Upper Jurassic Karabastau Formation, Karatau Range, Kazakhstan. Alcheringa: An Australasian Journal of Palaeontology. 38. 10.1080/03115518.2014.880267.

“Leptolepis.” Wikipedia,

“Hulettia.” Wikipedia,

9 thoughts on “Fossil Friday: Morrolepis, Leptolepis, and Hulettia

  1. It is interesting to note that scales are just an outgrowth of the skin. Scales have a tough outer layer and a soft inside called a pulp. So if a fish or snake has an injury to its scales and some are removed it will draw blood. In fish that don’t have scales other means of protection are necessary such as leathery skin or thick slime layers. There is also a disease in humans called Ichthyosis vulgaris or the “fish scale disease” which is a genetic mutation. So apparently through mutations fish developed scales from a softer bodied precursor.

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    1. Fish are pretty cool. It’s especially interesting to see the different ways they adapted in prehistoric times. We still have a few remnants of unusual body plans and strategies, such as the few surviving lungfish and hagfish, for example, but in the past there was so much variety! In the Morrison Formation the most common fish were several species of lungfish, so I’ll be featuring those at some point. 😀 Thank you for stopping by! 🙂

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  2. This was unexpected. I’m glad I got to learn about two fish I have never heard of (I’ve known Leptolepis for some time now). I can see their obscurity, which is a large reason to why this is the case. I do really wish that these fish get more mentions. Everything Dinosaur revealed the final three CollectA figures. They all look great to me. I want to know your thoughts.

    Liked by 1 person

    1. Thank you, I’m glad you like them!

      I’m excited to see that CollectA got a new Dilophosaurus out so quickly after the new paper! Now I’ll have to decide whether to get CollectA’s model or Safari’s newer Dilophosaurus. Even more exciting than that (if that’s possible) is that gorgeous ammonite! I’ll definitely need to add that to my little collection at some point. 😀


      1. I am sure you can get both, one to represent Picasso and the other to represent his “special friend.” Can you give me a hint on the next COTM?


        1. Haha, that’s a thought. I may repaint the CollectA one to match Picasso’s colors. 😀 I’m not a huge fan of the current colors or clown feet. Some people complain about Safari’s tripod and semi-tripod poses, but I actually prefer the tip of a tail or claw touching the ground for stability instead of making the feet so huge that it’s clownish. Or they could just make a base like what Safari did for their Giganotosaurus. 🙂

          One more hint before tomorrow’s critter of the month…He really likes to climb, and he likes to play fetch. He’s not very good at fetch, but he still likes to play. 😀


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