An Introduction

The clade Alvarezsauria is a group of small-bodied Ancient Aardvarks: [10] maniraptoran dinosaurs. The first known alvarezsaurid, Alvarezsaurus calvoi, was discovered in partial remains in the late 20th century, and named by Jose F. Bonaparte. A. calvoi was uncovered in Argentina, but today alvarezsaurs are known to have ranged across the Americas, Asia, and Meet the Alvarezsaurs Europe.[10] It is currently estimated that members of this Eggs and Bones clade existed between the Late Jurassic and the Cretaceous. This feather covered bird-like dinosaur is known for its insect based diet and especially its unique hooked The recently discovered Bonapartenykus forelimbs. These highly derived and powerful arms evolved ultimus represents a new genus of of throughout the clade Alvarezsauridae, giving these Alvarezsaurs. A 70 million year old pocket [12] Stunted But Strong dinosaurs a predatory advantage. of fossilized bones and two eggs of this Bird-Brained? species have been discovered in Argentina. This is the first time Alvarezsaurs have strangely powerful Using a cast of a skull from the species Alvarezsaurus bones and egg remains forearms, with one large thumb claw and the Ceratonykus oculatus, researchers have been found in close proximity. other two digits highly reduced. They are reconstructed an alvarezsaurian brain. Prehistoric Delicacies Though evidence of brooding behavior radically transformed from the typical Their analysis revealed that this has been found for other theropod theropod forelimb, which is longer, with three dinosaur had acute hearing and dinosaurs, no conclusion can yet be [10] functional digits and grasping ability. Given excellent eyesight, with intelligence drawn for Alvareszsaurs as no indication their highly specialized nature, it has been comparable to living birds. Additionally, of a nest was found at the site. It’s difficult to determine the relationship of C. oculatus had a complex cerebellum, possible that these two eggs were still [3] alvarezsaurs to other theropods. Recently a part of the brain that governs being carried by B. ultimus.[13] discovered species Xiyunykus and Bannykus coordination, balance, and motor have filled in the time gap in their control. Its structure may indicate that cerebellum [5] Diagram of evolutionary history, solidifying the clade as this dinosaur’s ancestors were arboreal Fossil wood, Horseshoe Canyon Formation fossil site[13] members of Maniraptora and documenting [1] (living in trees).[1] the development of their unique forelimbs. Alvarezsaurs display adaptations characteristic of living The transition was very gradual and occurred myrmecophages (animals that eat insects living in colonies, in a “mosaic” fashion (piece-by-piece, with such as ants and termites). They have small, simple teeth, parts modified at different rates). The narrow beaks, and a reduced chewing power. While ants olecranon process is elongated, the arm were likely uncommon during the Cretaceous and shortens and becomes more powerful, and mound-building termites are not known to exist until the the thumb claw grows in size as the other Eocene, fossilized wood from the Late Cretaceous shows [12] fingers are increasingly stunted. evidence of boring from wood-nesting termites. Alvarezsaurs may have used their powerful arms to rip open [12] logs of wood in search of prey.[5]

fossil eggs

olecranon process

Alvarezsaurus calvoi [9] Need For Speed

Alvarezsaurs were highly cursorial Shuvuuia deserti [4] (running specialists) with long Arctometatarsus of hindlimbs, narrow metatarsals, and basal parvicursorine muscles concentrated towards the Xixianykus zhangi [11] trunk of the body.[10] Parvicursorines, a highly derived group of alvarezsaurids, Smaller Than You Think are known to have evolved for very swift running. They display an extreme version of the arctometatarus, an Alvarezsaurs aren’t the giants we picture when we think of adaption of the foot in which the [10] theropod dinosaurs — some were as small as chickens. middle metatarsal (III) is pinched between its neighbors (II and IV), Feathered Friends allowing for greater speed and improved turning ability; in Despite being closely related to birds, parvicursorines, the upper portion of the feathers on the Alvarezsaur do not metatarsal III is completely absent.[10] give it flying capabilities. Their Alvarezsaurs may have used their feathers are similar to those of extreme running ability to escape modern birds as they were tested to predators, or to efficiently cover contain the protein beta-keratin. ground to forage for food.[11] Biochemical analysis allowed scientist [8] (background image) to confirm this in decayed feathers. Therefore, it is fair to assume that [6] Alvarezsaur had an entire coat of Allison Stafford, Josh Jackson, Leigh feathers, rather than just a few.[7] [2] Papadopoulos, Tristan Knapp GEOL 204 The Fossil Record Spring 2019, Section 0104