Microvenator

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Caenagnathidae

Genus: Microvenator

Species: Microvenator celer

Introduction

Microvenator was a small carnivorous or omnivorous dinosaur that lived in North America in the Early Cretaceous period. The specimen was first described from a partial skeleton that was later thought to be a juvenile. Microvenator has been an important fossil from an evolutionary standpoint, considered the earliest appearance of the oviraptorosaurid dinosaurs in North America.

During the Triassic and Early to Middle Jurassic, the landmasses of the world were united into a single supercontinent known as Pangaea. The supercontinent split apart during the Jurassic, resulting in two supercontinents : Gondwana, in the south, and Laurasia in the north.

Over the course of the Jurassic and the Early Cretaceous, the supercontinents continued to split due to tectonic movement. After the landmasses split apart, dinosaur groups on each landmass radiated into many different species. Microvenator was a member of a highly successful group of bipedal dinosaurs that occupied every continent during the Cretaceous.

Classification

Scientists use two basic methods to classify organisms into different groups. Linnaean taxonomy creates groups based on overall physical similarity, which includes the categories of life still used today, including placing organisms into kingdoms, phylums, classes, etc.

An alternate, more dynamic method, called “cladistics,” attempts to create groups that better represent the evolutionary connections between species. Cladistic analysis traces the presence of key traits between species and hypothesizes groups called “clades,” containing the organisms that share a characteristic with their common ancestor. For instance, in 2017 Matthew Baron and his colleagues posited a common ancestor for therapods and ornithischians, and proposed they be reclassified together into a new clade, Ornithoscelida. Species and groups are thereby divided by the addition of novel characteristics not present in their relatives.

Using cladistic analysis and Linnaean taxonomy, paleontologists have placed Microvenator into a suborder known as the Theropoda, which were typically bipedal, carnivorous animals, though a few became omnivorous or herbivorous. More specifically, Microvenator is placed in the infraorder Oviraptorosauria, which includes smaller bipedal predators that were closely related to birds and are distinguished by their bird-like features.

Anatomy

Microvenator was a small carnivore, measuring 1.2 to 3 meters (4 to 10 feet) long and standing approximately 0.8 meters (2.5 feet) tall, with a light build and an estimated weight of 6.4 kilograms (14 pounds), approximately the weight of a small dog.

The animal was bipedal, with shorter forearms. Both rear and front limbs terminated in three digits, with small claws. The animal had a small head with forward facing eyes and possibly a small toothless beak. Because Microvenator was a relative of the oviraptorosaurids, the animal may have been covered in feathers, like some other members of the group.

Though there is no current evidence to suggest the coloration of Microvenator, the species lived in an environment filled with many types of dinosaurian predators and may have been cryptically colored to avoid predation.

Intelligence

While the EQ value for Microvenator has not been calculated, the oviraptorosauria had larger brains than most dinosaurs and may therefore have been more intelligent than the average dinosaur. Microvenator lived in an environment filled with a number of dangerous predators and may have needed advanced intelligence to avoid predators.

Reproduction and Population

Microvenator is one of only a few oviraptorosaurs found in North America, though many representatives of the group have been found in deposits from the arid Gobi Desert in Asia. No Microvenator eggs or juvenile specimens have been found, and paleontologists are uncertain about the animal's reproductive behavior.

Oviraptorosaurs related to Microvenator have been found in close association with nests of eggs, and a specimen of the closely related species Oviraptor philoceratops was found in a position suggesting that the animal brooded its eggs like many modern birds. This may indicate that oviraptorosaurs were warm-blooded, like birds, and used their body heat to raise the temperature of their eggs. Microvenator may also have brooded its eggs like its relatives, but fossil evidence has not yet been found to confirm this hypothesis.

Diet

Like other oviraptorosaurs, Microvenator was most likely a predator, hunting insects, small mammals, reptiles, amphibians, and smaller dinosaurs. Its short beak would have been used to bite and rend flesh, similar to modern birds of prey. Like other Oviraptorosaurs, Microvenator had grasping arms, which could have been used to help capture small, elusive prey.

Behavior

Little is known about the behavior of Microvenator. Paleontologists have suggested that some oviraptorosaurids may have lived and/or hunted cooperatively. However, this theory is still under investigation, and there is no current evidence that Microvenator displayed any social behavior.

Judging from its size and the composition of other area fauna, Microvenator probably behaved similarly to other small carnivores living in diverse, predator-rich environments.

Habitat and Other Life Forms

During the Early Cretaceous, the climate varied widely across the landmass that would later form North America. While some areas were arid and dry, there were other areas featuring high moisture and warm temperatures that created lush forests. Cycads, conifers, and other gymnosperms were common. Ferns were still a dominant form of low-lying vegetation. The first angiosperms began to appear during this time and would soon spread around the world.

A wide variety of reptiles, amphibians, and small mammals shared Early Cretaceous North America with Microvenator and other dinosaurs, many similar to extant species. Though the first birds appeared in the Early Cretaceous, the skies were still dominated by flying reptiles, or pterosaurs, which ranged from small insect eaters to large predators.

The sauropods, large herbivorous dinosaurs that dominated the Jurassic, were still common in North America in the Early Cretaceous, including species like Venenosaurus. There were also a variety of ankylosaurs, large armored herbivores known for their spiked and clubbed tails, including Hoplitosaurus. Microvenator was not the only theropod in the Early Cretaceous but shared its environment with dromeosaurs or “raptors” like Deinonychus and Utahraptor .

Research

Microvenator was first discovered in Late Cretaceous sediment in Montana in the United States. The species was described by paleontologist John Ostrom in 1970. The first Microvenator bones were found with teeth that seemed to be oversized for the dinosaur's skull. These teeth were later found to belong to Deinonychus, a much larger bipedal predator that shared the animal's range.

In 1986, the fragments of Microvenator were reexamined in light of new discoveries, and the species was placed in the Maniraptora clade. (Maniraptora are characterized by such features as a half-moon shaped bone in the wrist, three-fingered hands, and a breast bone [the only dinosaurs with such a bone].) In addition to Microvenator celer, another species, Microvenator chagyabi, was posited to belong the genus.

Microvenator is the earliest known representative of the oviraptorosaurids and the maniraptora in North America and has been instrumental in helping paleontologists gain a clearer picture of how the group diversified and spread through Laurasia. Species of oviraptorosaurids flourished in other parts of Laurasia, specifically areas in modern-day Mongolia.

Researchers like Matt Lamanna and his team have classified Microvenator as a basal caenagnathid rather than a basal oviraptorosaur, as previously proposed. This would mean it evolved between the earliest oviraptorosaurs and the later oviraptorids. There remains speculation over the diets of caenagnathids like Microvenator, which some hypothesizing plant consumption alone while others argue for a carnivorous diet.

Comparison with other extinct archosaurs found Microbenator lacked articulation between the trunk vertebrae that was common in larger dinosaurs.

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