Patagornis is a genus of phorusrhacid ("terror bird"), an extinct clade of flightless birds, that lived in present-day Argentina during the Miocene age of the Neogene period. The taxonomic history of the genus is long and convoluted. It was described by Argentine paleontologists Francisco Moreno and Alcides Mercerat in 1891. The genus contains one species, P. marshi, named based on a premaxilla (frontmost beak bone) fragment and some incomplete postcranial remains. These fossils were unearthed by an expedition to strata (rock layers) of the Santa Cruz Formation in Santa Cruz Province, southern Argentina. This formation dates to the early-mid section of the Miocene, which makes it around 17.5 to 11.6 million years old. Also in 1891, Moreno's scientific rival, Argentine naturalist Florentino Ameghino, named his own genus and species, Tolmodus inflatus, on the basis of a premaxilla fragment as well. Ameghino also described several well-preserved specimens of Patagornis. After realizing that they came from the same taxon, paleontologists still opted to use the name Tolmodus over Patagornis despite the fact that, according to the rules of the ICZN, Patagornis marshi was the correct name. In 2003, Brazilian paleontologist Herculano Alvarenga and German paleontologist Elizabeth Höfling revalidated Patagornis as the correct name. Although, some scientists still use Tolmodus instead.
Patagornis is among the best-understood phorusrhacids. It is known from several well-preserved specimens, including skulls and nearly complete postcranial skeletons. It was around tall at the back and weighed about , much smaller than its giant relatives like Kelenken and Phorusrhacos but larger than the other phorusrhacid Psilopterus. Its skull is tall and elongated, similar to that of its kin Andalgalornis and Andrewsornis. The hindlimbs are relatively lethe and adapted for a cursorial (running) lifestyle, suggesting it was a pursuit predator. The taxonomy of Phorusrhacidae is in constant flux, but Patagornis is often regarded as being the type genus of its own subfamily, Patagornithinae. This subfamily includes the other phorusrhacids Andalgalornis and Andrewsornis, though some phylogenetic analyses (studies of the evolutionary relationships of organisms) have found it to be more closely related to phorusrhacines like Phorusrhacos.
Remains of Patagornis are exclusively known from the Miocene of southern Argentina, a region which was covered in grasslands, interspersed with forests, and contained a diverse array of reptiles, birds, and mammals when Patagornis lived. Fossils have also been recovered from the Cerro Boleadoras Formation, which dates to between 16.5 and 15.1 million years ago, and the older Monte León Formation. Patagornis potentially preyed on small-medium sized mammals such as the litoptern Thoatherium and the ground sloth Hapalops. Additionally, it may have competed with the carnivorous sparassodont marsupials Arctodictis and Prothylacinus for food.
History and taxonomy
Discovery and naming
The taxonomic history of Patagornis is muddled on account of the fragmentary nature of fossils, few of which overlap with others, little consensus between researchers, and competition between scientists. In the 19th century, scientific interest in the rich "Tertiary" (now Neogene) fossil sites of Argentina boomed. This included exploration by two teams of Argentine paleontologists; Florentino and Carlos Ameghino, who operated independently, and Francisco Pascasio Moreno and Alcides Mercerat of the Museo de La Plata (MLP). Their discoveries comprised thousands of fossils from Cenozoic fossil deposits throughout Patagonia and central Argentina. Initially, Moreno hired the Ameghinos as staff at the MLP in 1887; Florentino operated as a researcher and Deputy Director, while his brother conducted expeditions and assisted with preparation. However, the relationship between Moreno and Florentino Ameghino deteriorated, culminating in the Ameghinos' resignation from the MLP in 1888. Operating independently of any institutions until 1902, the Ameghinos competed with Moreno and the Museo de La Plata to discover and describe as many new fossils as they could. This led to the description of many genera and species based on fragmentary, undiagnostic, or poorly described material.
The first known discovery of Patagornis fossils was made by crews of the MLP during the late 1880s. The material, consisting of a mandibular symphysis (the area where the two mandibles meet) fragment, then thought to be from the premaxilla (the frontmost upper jaw bone), was collected from an unknown locality of the Santa Cruz Formation in Santa Cruz Province, southern Argentina. Although then believed to be from the Eocene period, nicknamed the "Pyrotherium Beds", it is now thought to date to the upper section of the middle Miocene epoch. This specimen (which was later deposited at the MLP under specimen number MLP-143-158) likely includes other elements from the same individual, consisting of: three vertebrae, sacrum fragments, scapula fragments, proximal (towards body) end of the left femur, distal (away from body) end of the right femur, sections of the right tibia, incomplete tarsometatarsi, unguals, and unidentified pieces.
In May 1891, Moreno and Mercerat scientifically described the remains and assigned them to a new genus and species of bird, which they named Patagornis marshi. The generic name Patagornis is a combination of Patagonia, where the fossils were discovered, and the Greek word ὄρνις (ornis), "bird". The specific name is in honor of American paleontologist Othniel Charles Marsh, who made his own discoveries of fossil birds in the American West. Later, the mandibular symphysis fragment (MLP-143) was selected as the lectotype (name-bearing) specimen of P. marshi. In the same paper, P. lemoinei and P. bachmanni were named as species of Patagornis. However, they were unearthed in lower Miocene rocks of the Monte León Formation and have since been moved to the genus Psilopterus. Moreno and Mercerat (1891) described a multitude of new phorusrhacid (then called stereornithine) genera and species, many of which were based on fragmentary or isolated fossils. This included Palaeociconia cristata, which was known only from two vertebrae and two unguals that had also been unearthed from layers of the Santa Cruz Formation. In 1933, Hungarian paleontologist Kálmán Lambrecht moved Palaeociconia cristata to another genus, Morenomerceraria. However, it is now considered a synonym of Patagornis marshi.
Florentino Ameghino and Tolmodus
Simultaneously, Moreno's rival, Florentino Ameghino, was conducting his own expeditions to Santa Cruz Formation strata. In August 1891, Ameghino scientifically described a new genus and species of phorusrhacid (then incorrectly spelled "phororhacid") bird (though at the time he believed it was a megalonychid sloth), Tolmodus inflatus, on the basis of a premaxilla fragment. The generic name Tolmodus derives from the Greek words τολμάω (tolmaó) "bold" and ὀδούς (odous) "tooth", based on the assumption that Tolmodus was a toothed mammal. The specific name inflatus comes from the Latin īnflō "blow" or "inflated" due to its large size. In 1895, Ameghino classified Tolmodus in Phorusrhacidae. Although it was named months before Tolmodus, the name Patagornis remained unused in scientific literature for over a century. Authors such as American paleontologist Bryan Patterson and Argentine naturalists Lucas Kraglievich and Ángel Cabrera used Tolmodus over Patagornis in several studies in the 20th century, despite the fact that Patagornis had precedent. Due to the fact that the name Patagornis was not used for over 100 years, according to Article 23 of the International Code of Zoological Nomenclature (ICZN), the name Tolmodus would take priority. However, in 2003 Brazilian paleontologist Herculano Alvarenga and German paleontologist Elizabeth Höfling opted to revalidate the name Patagornis and considered Tolmodus a junior synonym (the same taxon as a previously named taxon). The use of both Tolmodus and Patagornis is prevalent in scientific literature, with little consensus on what is the correct generic title.
In 1895, Ameghino published his most extensive description of phorusrhacids, including Phorusrhacos inflatus. One of these specimens included a nearly complete skeleton, among the best known from a phorusrhacid. In 1895 and 1896, Ameghino and Moreno sold much of their respective fossil bird collections to the Natural History Museum of London (NHMUK). This included the skeleton described by Ameghino, which was cataloged under NHMUK PV A 516. In 1899, British paleontologist Charles William Andrews described the skeleton in detail. By 1911, Ameghino had died and Moreno had retired, leaving behind a legacy of convoluted phorusrhacid taxonomy. Many European naturalists did not study Ameghino's or Moreno's taxa, especially their phorusrhacids, due to their confusing taxonomy. In the same 1895 paper, Ameghino named a new species of Phorusrhacos, P. modicus, on the basis of an associated humerus and tarsometatarsus that was found in strata of the Santa Cruz Formation in Santa Cruz Province. In 1967, American paleontologist Pierce Brodkorb stated that P. modicus was a synonym of Patagornis marshi, however it has also been considered a synonym of Psilopterus lemoinei or P. australis. Another specimen, a premaxilla fragment from the same site, was assigned to the rhea Opisthodactylus but is now believed to belong to Patagornis.
Later discoveries
At the close of the 19th century, American universities and institutions began taking an interest in the Neogene fauna of Patagonia. Inspired by Ameghino's papers and descriptions, these universities and institutions sought to establish their own collections of Santacrucian mammals and birds, including those of Phorusrhacos. Between 1896 and 1899, Princeton University students, under the leadership of American paleontologist John Bell Hatcher, led a series of expeditions to the same outcrops in Santa Cruz Province. Princeton was joined by the American Museum of Natural History on the last of these expeditions, altogether collecting a trove of new fossil bird and mammal material. Furthermore, in 1902, American professor William B. Scott ventured to the MLP and Ameghino's collections to photograph and review the taxa named prior by Ameghino, Moreno, and Mercerat. His studies, along with those of Hatcher, American paleontologist William John Sinclair, and others, culminated in a series of monographs that were published between 1903 and 1912 by Princeton University. Although they reviewed Ameghino's mammal taxa in detail, their description of some of the phorusrhacid remains was brief. In 1926, American paleontologist Marcus Farr traveled to the NHMUK in order to study the Ameghino collection, with the assistance of Dr. F. A. Bather, the museum's curator.