Fossil Friday: Macelognathus

Species: Macelognathus vagans (Ma-keh-log-nay-thus vay-gans)

What it means: Unknown

Other Species: none

Where I live: Western U.S.A.- The Morrison Formation

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

My favorite food: Meat! I’m a carnivore.

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

There are also giant, meat-eating monsters to worry about, including dinosaurs like Torvosaurus, Ceratosaurus, Saurophaganax, Marshosaurus, Stokesosaurus, Ornitholestes, Coelurus, Tanycolagreus, Elaphrosaurus, and Koparion.

Not to mention the countless lizards, crocodile relatives on land and water, mammals, frogs, turtles, fish, and all the pterosaurs flying in the sky!

Fun Facts:

  • Othniel Charles Marsh described Macelognathus in 1884.
  • A portion of the lower jaw was the only fossil found at the time. The front of the jaw had a flat, hard palate with no teeth, but plenty of sockets for teeth in the back half of the jaw. Marsh proposed the toothless front half had a beak.
  • Unfortunately Marsh did not explain the meaning of the name Macelognathus, so I will make my best educated guess. The end of the name may sound familiar. We can find it in the name Compsognathus, which means “pretty jaw.” Gnathus is ancient Greek for jaw. The first half of the name must then describe the jaw found for Macelognathus. The closest match I could find was mákella, which is ancient Greek for a pick-axe, or any digging tool like a hoe or spade. In fact, a spade or shovel is a perfect match for the shape of the toothless front portion of the jaw. Perhaps the name Macelognathus means “shovel jaw”.
  • Macelognathus was first thought to be a relative to turtles, but since then many have debated which family it would join for a family reunion. Dinosauria, Reptilia, Ornithischia (plant-eating dinos), Hypsilophodontidae (small, two-legged vegetarian dinos with beaks), and finally Crocodilians. More recent fossil finds place Macelognathus in a group closely related to crocodiles known as Sphenosuchia.
  • Kayentasuchus is a close relative from the Kayenta Formation in New Mexico, and a relative from the Morrison Formation is Hallopus. Fossil finds of both Hallopus and Macelognathus are so incomplete, that these might be the same animal. More fossils are needed to compare the two and find out more.

Fossil Finds: Some fragmentary parts of the skull and jaw, a few vertebrae, partial pelvis, and parts of the limb bones.


Göhlich, Ursula & Chiappe, Luis & Clark, James & Sues, Hans-Dieter. (2005). The systematic position of the Late Jurassic alleged dinosaur Macelognathus (Crocodylomorpha: Sphenosuchia). Canadian Journal of Earth Sciences. 42. 307-321. 10.1139/e05-005.

Marsh, Othniel Charles. A new order of extinct reptiles (Macelognatha). American Journal of Science Apr 1884, s3-27 (160) 341; DOI: 10.2475/ajs.s3-27.160.341

Abdale, Jason R. (2020) “Macelognathus.” Dinosaurs and Barbarians,

Donnegan, James, et al. A new Greek and English lexicon. Boston: Hilliard, Gray, 1834.

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

“Macelognathus.” Wikipedia,

5 thoughts on “Fossil Friday: Macelognathus

    1. Your articles are always very well researched, and I enjoy reading them! 🙂 I did read the original papers as well, just to make sure and double check all the sources, but your article was very helpful as a starting point. There aren’t very many places you can find out about Macelognathus! 🙂

      Liked by 1 person

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