Microvenator

In North America, dinosaur fossils are found in profusion in rocks dated to the late Triassic, late Jurassic, and late Cretaceous Periods. However, much of the rest of the Mesozoic Era’s time scale contains much sparser remains. The middle part of the Cretaceous Period, from about 120 to 90 million years ago, is one of these times where we don’t know nearly as much as we would like to. Dinosaur species which are commonly associated with mid-Cretaceous North America include the wolf-sized raptor Deinonychus, the large meat-eater Acrocanthosaurus, the long-necked sauropod Astrodon, the ornithopod Tenontosaurus, and the armored dinosaur Sauropelta. However, there were others which are not well-known, and this particular article concerns one of these lesser-known dinosaurs – Microvenator.

In 1933, the famous paleontologist Barnum Brown was exploring the rocks of the Cloverly Formation in Wheatland County, located in central Montana, when he discovered a partial skeleton. Although the bones were small, there were also found several large teeth nearby, which Brown assumed belonged to the same animal. Barnum Brown provisionally named it Megadontosaurus, “big tooth lizard”, although he never actually officially published the name. It wasn’t until the discovery of Deinonychus in the 1960s by Prof. John Ostrom of Yale University that it was realized that a mistake had been made. It was shown that these teeth actually belonged to Deinonychus while the skeleton belonged to some other animal. As a result, you couldn’t exactly call this creature “big tooth lizard”. So in the year 1970, Prof. John Ostrom gave this skeleton the name Microvenator celer, which in Latin means “the speedy little hunter” (1).

The holotype is currently in the collections of the American Museum of Natural History (collections ID code: AMNH 3041). Based upon the size of the bones, it is estimated that this animal reached just 4 feet long. However, it has been proposed that the remains found represent a juvenile, and that the adult was substantially larger, possibly reaching 10 feet long. However, this is the only skeleton which we have of this animal, and until more remains are discovered, the claim that it was much larger when fully grown is merely speculation. A single neck vertebra (collections ID code: USNM 546292) which is larger than the vertebrae seen in the holotype has been ascribed to Microvenator, but this cannot be determined to be 100% true (2).

In John Ostrom’s 1970 description of the animal, he claimed that Microvenator was a coelurosaur, thus placing it in the same family as the late Jurassic carnivores Coelurus and Ornitholestes. However by the late 1980s, Microvenator’s phylogenic position was re-evaluated, and it was concluded that it was actually an oviraptorosaurian, and more specifically, that it was a member of the family Caenagnathidae, placing it in the same theropod family as Caenagnathus and Anzu. Most sources today maintain this identification, although a few still state that the remains are too fragmentary for us to know exactly where Microvenator fits into the dinosaur tree (3).

Below is a drawing that I made of Microvenator. The skull is largely hypothetical – only the front half of one side of the lower jaw was found, so the rest is conjecture based upon what we know of other caenagnathid oviraptorosaurian dinosaurs. Since Microvenator is often stated to have been a primitive member of the caenagnathid family, I gave it a skull with longer jaws compared to other caenagnathids, and I also gave it a longer tail as well. This drawing was made with No. 2 pencil and No. 3 pencil on printer paper, and followed up with A LOT of touching up on my computer. Keep your pencils sharp, everyone.

Microvenator. © Jason R. Abdale (July 20, 2021).

Source citations:

  1. Randy Moore, Dinosaurs by the Decades: A Chronology of the Dinosaur in Science and Popular Literature. Santa Barbara: Greenwood, 2014. Page 188; Mark A. Norell, Eugene S. Gaffney, and Lowell Dingus, Discovering Dinosaurs in the American Museum of Natural History. New York: Alfred A Knopf, 1995. Pages 126-127; Peter J. Mackovicky and Hans-Dieter Sues (1998), “Anatomy and phylogenetic relationships of the Theropod Dinosaur Microvenator celer from the Lower Cretaceous of Montana”. American Museum Novitates. Number 3240 (August 27, 1998). Pages 1-2.
  2. Peter J. Mackovicky and Hans-Dieter Sues (1998), “Anatomy and phylogenetic relationships of the Theropod Dinosaur Microvenator celer from the Lower Cretaceous of Montana”. American Museum Novitates. Number 3240 (August 27, 1998). Page 1; Matthew P. J. Oreska, Matthew T. Carrano, and Katherine M. Dzikiewicz (March 2013), “Vertebrate Paleontology of the Cloverly Formation (Lower Cretaceous), I: Faunal Composition, Biogeographic Relationships, and Sampling”. Journal of Vertebrate Paleontology, volume 33, issue 2. Page 277.
  3. John H. Ostrom (1970), “Stratigraphy and paleontology of the Cloverly Formation (Lower Cretaceous) of the Bighorn Basin area, Wyoming and Montana”. Bulletin of the Yale Peabody Museum of Natural History, bulletin 35 (August 1970). Pages 71, 76; Currie, Philip J.; Russell, Dale A. (1988). “Osteology and relationships of Chirostenotes pergracilis (Saurischia, Theropoda) from the Judith River (Oldman) Formation of Alberta, Canada”. Canadian Journal of Earth Science, volume 25, issue 7 (July 7, 1988). Pages 972-986; Peter J. Mackovicky and Hans-Dieter Sues (1998), “Anatomy and phylogenetic relationships of the Theropod Dinosaur Microvenator celer from the Lower Cretaceous of Montana”. American Museum Novitates. Number 3240 (August 27, 1998). Page 1.

Bibliography:



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