Mesembriornis is a genus of intermediate-sized phorusrhacids that grew up to in height. They represent a well-distinct lineage of terror birds, differing from the massive large groups and the smaller Psilopterinae. In general proportions, they most resembled the Patagornithinae which flourished somewhat earlier, mainly to the south of the range of Mesembriornis. Fossils of the terror bird have been found in Montehermosan deposits of the Monte Hermoso Formation, as well as the Andalgala Formation and Chapadmalal Formation in Argentina.
Mesembriornis is a genus of intermediate-sized phorusrhacids that grew up to in height. They represent a well-distinct lineage of terror birds, differing from the massive large groups and the smaller Psilopterinae. In general proportions, they most resembled the Patagornithinae which flourished somewhat earlier, mainly to the south of the range of Mesembriornis. Fossils of the terror bird have been found in Montehermosan deposits of the Monte Hermoso Formation, as well as the Andalgala Formation and Chapadmalal Formation in Argentina.
== Taxonomy and discovery == Mesembriornis was first described by Argentine paleontologist Francisco Moreno during the "Argentine Bone Wars" between him and Florentino Ameghino in 1889 based on a cervical vertebral centrum along with the proximal section of a right tibiotarsus and fibula (MLP-140-142), the species name being Mesembriornis milneedwardsi. The genus name, Mesembriornis, means "southern bird" after its discovery in the southern Argentina, while the specific name is after French paleontologist Alphonse Milne-Edwards. In the same paper, Moreno erected a new genus and species of what he thought to be a fossil stork, Paleociconia australis, based on a distal left tarsometatarsus. This species has since been synonymized with Mesembriornis milneedwardsi, and Moreno also unknowingly assigned a femur of M. milneedwardsi to another one of his taxa, Driornis pampeanus. All of the fossils were collected from the Monte Hermoso Formation strata of the town of Monte Hermoso in Buenos Aires Province, Argentina. 2 years later in 1891, Moreno and his colleague Alcides Mercerart described two more Mesembriornis species that are now seen as synonymous with the large Phorusrhacid Phorusrhacos, the species being Mesembriornis studeri and Mesembriornis quatrefragesi, the former species' type specimen notably included skull and mandible material.
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