Maniraptoran Dinosaurs

Maniraptora ("Hand Snatchers") is a clade of theropod dinosaurs containing birds and all species related closer to birds than to Ornithomimus velox. They are characterized by long arms and by the semi-lunate (half-moon shaped) carpal bone in their wrist. This bone allows them to fold their arms or wings in against their bodies. Many maniraptors in the fossil record show indications of being partially or fully feathered, although this evidence does not exist for all extinct species in the clade. Maniraptora is often broken down into six groups; Therizinosauria, Dromaeosauridae, Avialae, Alvareszauria, Troodontidae, and Oviraptorosauria. Let's look at what these groups are, where they originated, and how they spread across the globe millions of years ago.

Therizinosauria are characterized by small heads and long necks. The smallest species were about 6-7 feet long, but the largest grew to be around 30-33 feet in length. Many of them possessed elongate claws, with the most extreme example being seen in Therizinosaurus cheloniformis, the taxa which gave the group their name. These claws were likely used for defense or possibly to rake in vegetation for feeding. Research indicates the group was mostly if not wholly herbivorous. The earliest known therizinosaur lived in the Early Jurassic of China roughly 200 million years ago.

Dromaeosauridae is probably best known through Velociraptor mongoliensis, featured in the 1993 film Jurassic Park. The smallest dromaeosaurs were around 2 feet long, but the largest species could exceed 20 feet. This group is known for the sickle-shaped "killing claw" on their second toe, long arms compared to other theropods, and for exceptionally stiff tails which were thought to have been used for balance and agility. All known species were either carnivorous, piscivorous, or insectivorous. The earliest known dromaeosaur fossils are tentatively identified from the Early Jurassic of India, roughly 180 million years ago.

Avialae is the group within Maniraptora containing modern birds and species more closely related to birds than to Dromaeosauridae and Troodontidae. The smallest avialian is the extant bee hummingbird at just over 2 inches long, but the largest known species were the 12-foot tall North and South Giant Moa which went extinct 600 years ago. They were and remain a diverse group, comprised of true birds and birdlike dinosaurs with long tails and teeth. Like with modern birds, extinct avialians were known from a variety of ecosystems and had varied diets, showing a high capacity for adaptation. The most famous extinct avialian is the Late Jurassic Archaeopteryx lithographica. The earliest known avialian comes from the Middle Jurassic of China, roughly 160 million years ago.

Alvarezsauria are characterized by small, toothed beaks and powerful arms bearing a large thumb and thumb claw with the other digits being reduced. It is thought that these adaptations helped them to dig insects out of stumps or dirt mounds. Alvarezsaurids ranged from about 1 to 5 feet tall, although many known species are rather fragmentary, and larger and more complete specimens may at some point be found. The most well preserved and studied species is Mononykus olecranus. The earliest known alvarezsaurid lived in the Middle Jurassic of China approximately 161 million years ago.

Troodontids are very similar in appearance and are closely related to dromaeosaurs. They are sometimes grouped with them in the classification Deinonychosuria. They differ in having longer legs, shorter arms, and more teeth than their "raptor" relatives. These teeth are also more diverse in type, suggesting that troodontids had a more varied diet. While Troodontids also possessed a sickle claw, it tended to be smaller and sometimes less curved than those belonging to Dromaeosauridae. The smallest Troodontids were about 1 foot long, and the largest known species were around 10 feet in length. Troodontidae gets its name from a species formerly known as Troodon formosus, but now referred to as Latenavenatrix mcmasterae. The oldest known Troodontid lived in the Late Jurassic of North America, some 151 million years ago, however, a 2023 study on some teeth from the UK may push this range back if accepted by the scientific community.

Oviraptorosauria are defined by their powerful beaks and boxy heads. The name comes from the species Oviraptor philoceratops, which was found on top of a clutch of eggs. While it was eventually determined that the eggs were the animals own, it was initially thought that it was stealing them. Thus, the name Oviraptor which means, "egg thief." There are arguments and evidence for omnivory, herbivory, and carnivory in this group of dinosaurs. The smallest oviraptorosaurs were likely the pigeon sized Scansoriopterygids. This group of Oviraptorosaurs had a long and oddly positioned first digit of the hand, and in at least two species, this digit served as the framework for membranous bat-like wings. This feature separates them from other Oviraptorosaurs which had hands with normal fingers and showy feathers. The largest Oviraptorosaur hails from China and was around thirty feet long. The earliest known oviraptorosaur lived in the Late Jurassic of China, roughly 125 million years ago.

This series of interactive maps show how the six groups of Maniraptorans spread and diversified during the Jurassic and Cretaceous periods. Bear in mind that the fossil record is both incomplete and constantly being updated. There are places these animals lived but where no fossils exist or have not yet been found to record their history. Perhaps one day soon, some of these gaps will be filled and new maps will have to be made to record new research.

As you scroll through the maps, please refer to the web-app below to visualize how the continents shifted during the discussed time periods.

At the end of the Cretaceous, a six-mile-wide meteor struck the Yucatan Peninsula, and the resulting fallout caused the extinction of roughly 75% of life on earth. This included all dinosaurs except for birds. These animals, the last Maniraptoran dinosaurs, continued to spread and diversify and today over 10,000 species exist across every continent from pole to pole.

Thank you.