Alvarezsaurus
| Key | Value |
|---|---|
| Name Meaning | “Alvarez’s lizard” |
| Location | Argentina |
| Time Period | c. 85 million years ago (Late Cretaceous) |
| Length | 4 ft (1.2 m) |
| Weight | 6 lb (3 kg) |
| Locomotion | Biped |
| Diet | Insectivore |
| Described | 1991 (Bonaparte) |
| Geological Formation(s) | Bajo de la Carpa |
| Valid Species | Alvarezsaurus calvoi (type) |
Phylogeny: Dinosauria > Saurischia > Theropoda > Neotheropoda > Tetanurae > Avetheropoda > Coelurosauria > Maniraptora > Alvarezsauroidea > Alvarezsauridae
Overview: Coelurosaurs, the theropod lineage from which birds evolved, diverged relatively early in the history of dinosaurs, at least having done so by the Early Jurassic. From there, they would soon diversify into many distinct clades and families, some of them quite unusual in comparison to most other theropods. Alvarezsaurus is the namesake of one such group. It’s classified as a member of the family Alvarezsauridae, a part of the larger superfamily Alvarezsauroidea. These coelurosaurs are grouped into the Maniraptora, which made them closely related to birds. Indeed, some have mistaken the remains of these animals for birds themselves. They were typically quite tiny as far as non-avian dinosaurs go, with fragile bones. Measuring more than a meter long, Alvarezsaurus was actually one of the larger alvarezsauroids. Alvarezsauroids as a whole may’ve first evolved in the Late Jurassic, but reached their peak during the Cretaceous Period.
Alvarezsaurus itself is based on partial remains. Known bones include some vertebrae, parts of the pelvis, lower leg bones, part of the shoulders and bones from the hand. Based on these remains, we know it was probably similar in appearance to most other alvarezsaurids, being a slender and agile creature. The skull isn’t known, but those of its relatives usually sported large eye sockets and narrow jaws lined with needle-like teeth. Alvarezsaurus may’ve been adapted for going after small prey, specifically insects and grubs. Alvarezsaurids often had remarkably tiny arms and, in many cases, only a single claw on each hand. The forelimbs of this genus may’ve been somewhat less reduced in size, given its status as a more basal member of the Alvarezsauridae. Alvarezsaurus is known from Argentina’s Bajo de la Carpa Formation, dated to eighty-five million years ago. Named in 1991, its generic name honors the late Argentine historian Gregorio Álvarez.