Research history Early history In 1804, the French naturalist
Georges Cuvier, having established the genus
Palaeotherium and some of its species (
P. medium and
P. magnum), recognized a third species,
Palaeotherium minus, based on some postcranial fossils from the
gypsum quarries of the outskirts of Paris (known as the
Paris Basin), although he did not elaborate further on them. In a later journal of the same year, he described a nearly completely skeleton from the quarries of the
French commune of
Pantin, originally found by the French naturalist
Auguste Nicholas de Saint-Genis. According to Cuvier, the quarry workers previously thought the skeleton to be of a ram, and it was presented as such in public newspapers. The French prefect
Nicolas Frochot later acquired it and brought it to the
National Museum of Natural History, France, where Cuvier was then able to observe that it must have been a skeleton of a
Palaeotherium species. He noted that the majority of the fossil bones were detached from others and/or damaged but that postcranial elements such as
scapulae,
humeri,
femora,
vertebrae, and
ribs were found. The naturalist also provided a figure of the skeleton within the journal. Of note is that the skeleton, confirmed to be of a pregnant female, has since been lost.165 In 1812, Cuvier published his drawing of a skeletal reconstruction of
P. minus based on known fossil remains of the species including the mostly complete skeleton. He also suggested theoretical lifestyles of several
Palaeotherium species. In particular, he suggested that
P. minus resembled a
tapir, was smaller than a sheep, and was
cursorial (adapted for running) based on the slender morphologies of its leg bones. Such a behaviour and small size would have differed from other species of
Palaeotherium, several of which according to Cuvier had stockier limbed bone builds. He also identified that
P. medium,
P. magnum,
P. minus,
P. crassum, and
P. curtum were all tridactyl, or three-toed. medium'' (right) as they appeared as part of the
Crystal Palace Dinosaurs sculptures of the
Crystal Palace Park "
P. minus" (=
Plagiolophus minor) was amongst the fossil mammal species represented as sculptures in the
Crystal Palace Dinosaurs attraction in the
Crystal Palace Park in the United Kingdom, open to the public since 1854 and constructed by English sculptor
Benjamin Waterhouse Hawkins. The
Plagiolophus sculpture is smaller than the
P. magnum and
P. medium sculptures and is in a sitting position unlike the other two. The models' resemblances to tapirs reflected early perceptions that the
palaeothere species resembled them in body plan appearances. Despite this, the sculptures differ from living tapirs in several ways, such as shorter plus taller faces, higher eye positions, slender legs, longer tails, and the presence of three toes on the forelimbs unlike the four toes of the forelimbs of tapirs. Hawkins and other workers seemingly used Cuvier's research for reference to the anatomy of
P. minor and reproduced its size and proportions accordingly. The
P. minor sculpture, sheep-sized, originally had a short head that probably measured about in length and had pointed ears, large eyes, long lips, a stocky proboscis, a muscular neck, and a short plus slender tail. It looks similar to the
P. medium sculpture overall but lacks skin details. Although the original head's form is poorly known, it appeared to have been longer and more robust than that of
P. medium. Within the later half of the 20th century, the original head was lost and replaced with a head cast of
P. medium. Because the size and form of the head made it difficult to attach to the
P. minor body normally, the back portion of the cranium was removed and the neck lengthened. This resulted in the sculpture appearing to look forward instead of upwards like before. The
P. minor sculpture lost its head twice more, once recently in 2014 when its head was tossed into a lake of the Crystal Palace by an unknown criminal and had to be recovered. In 1847, the French palaeontologist
Auguste Pomel erected the
Palaeotherium subgenus Plagiolophus, which he reclassified
P. minus to. The genus name derives from the
Ancient Greek words ("oblique") and ("crest") meaning "oblique crest". British palaeontologist
Richard Owen in 1848 wrote about a nearly complete lower jaw with both
deciduous (or milk teeth) and
permanent dental sets that was uncovered from the Eocene beds of
Hordle, England, by Alexander Pytts Falconer, observing that it had one less
premolar for a total of three of them than in other species of
Palaeotherium and erecting the genus
Paloplotherium and the species
Paloplotherium annectens based on the mandible. He then described a
cranium belonging to
Paloplotherium that similarly had nearly complete dentition but evolutionarily lost a premolar. After comparing the dentition to those of both
Palaeotherium and
Anoplotherium, he determined that the dentition of
Paloplotherium was similar to that of the former but differed mainly by the absence of the first premolar. He wrote that the permanent
dental formula of
Paloplotherium is for a total of 40 teeth.
Paloplotherium derives from the Ancient Greek words ("ancient"), ("arms"), and ("wild beast") meaning "ancient armed beast". Fraas had studied fossils of palaeotheres from Frohnstetten since 1851, assembling a complete skeleton of
P. minor using fossils from there in 1853. In 1853, Pomel listed in the genus
Plagiolophus multiple previously recognized species, namely
P. ovinus (reclassified from
Palaeotherium and emended from
P. ovinum),
P. minor, and
P. annectens (by extent
synonymizing Paloplotherium with
Plagiolophus). He also erected another species
P. tenuirostris. In 1862, Swiss palaeontologist
Ludwig Ruetimeyer established
P. minutus based on dental remains from the Swiss locality of
Egerkingen. Not all taxonomists agreed on
Paloplotherium as a synonymous genus. In 1865 for example, French palaeontologist
Jean Albert Gaudry recognized
Paloplotherium as valid genus instead of
Plagiolophus, grouping
P. minor,
P. ovinus, and
P. annectens into it and erecting another species
P. codiciense. In 1869, Swiss palaeontologists
François Jules Pictet de la Rive and
Aloïs Humbert wrote that
Palaeotherium,
Paloplotherium, and
Plagiolophus were all valid genera and erected two species for the latter:
P. siderolithicus using fossil molars from a museum collection and
P. valdensis based on a mandible that was smaller in proportion than that of
P. minor. In 1877, French naturalist
Henri Filhol erected
Paloplotherium Javalii based on fossil jaws including that from the fossil collection of the French official
Ernest Javal, who he named the species after. Ruetimeyer in 1891 erected another species
Paloplotherium magnum, stating that its size would have been that of
Palaeotherium magnum. In addition to the now-lost skeleton studied originally by Georges Cuvier in 1804, several other incomplete skeletons have been described by other palaeontologists. Skeletal elements were figured by Cuvier and later Blainville in 1839–1864, and the latter naturalist also figured skeletal elements from the French commune of
Monthyon surrounding the skeleton whose whereabouts are also unclear.
20th-21st century taxonomy In 1901, researchers
Charles Depéret and G. Carrière designated the species name
Paloplotherium lugdunense to fossil material originally from the fossil deposits from the French commune of
Lissieu. They said that the species was barely larger than
P. codiciense and that it was also known from the locality of Robiac. In 1902, Swiss palaeontologist
Hans Georg Stehlin erected
Paloplotherium Rütimeyeri, but he only wrote that it was known from Egerkingen and did not elaborate further on it. In 1904, Swiss palaeontologist
Hans Georg Stehlin synonymized
Paloplotherium magnum with
Palaeotherium castrense and erected two species of
Plagiolophus:
P. nouleti from a fossil mandible from the French commune of
Viviers-lès-Montagnes and
P. cartailhaci using fossils from the commune of
Peyregoux. In one of his
monographies, written the same year, Stehlin erected
Palaeotherium Rütimeyeri to replace the previous name
Paloplotherium Rütimeyeri (the former being formally defined from fossil material) and synonymized
Paloplotherium javali with
Plagiolophus fraasi. He also erected the species
P. cartieri based on Egerkingen fossils, arguing that its size was between
P. annectens and
P. minor plus that its fossils resembled those of
P. codidiciensis. In 1917, Depéret erected the species
P. oweni (also recognizing it by the name
P. annectens mut.
Oweni) from fossils in the commune of
Gargas, arguing that it was a more advanced species of
Plagiolophus based on the size and morphology of its premolars. He also reclassified "
Paloplotherium"
codiciense into its own genus
Paraplagiolophus. In 1965, French palaeontologist Jean Albert Remy erected the genus
Leptolophus, reclassifying
P. nouleti into the taxon. In 1986, British palaeontologist Jerry J. Hooker listed
Paloplotherium as a synonym of
Palaeotherium and listed
P. minor,
P. cartieri,
P. lugdunensis (emended name),
P. cartailhaci,
P. annectens,
P. fraasi, and
P. javalii as valid species, although he doubted that
P. javalii was distinct from
P. fraasi. He also erected
P. curtisi using fossils from fragmentary cranial remains from the
Barton Beds of the UK and recognized two subspecies:
P. curtisi curtisi and
P. curtisi creechensis. The species was named after an individual named R.J. Curtis, who found the specimens for the former subspecies. In 1989, palaeontologists
Michel Brunet and Yves Jehenne considered
Paloplotherium to be distinct from
Palaeotherium and erected for the former genus two additional species:
P. majus from the fossil collections of the
Quercy Phosphorites Formation and
P. ministri from the French commune of
Villebramar. Remy in 1994, however, rejected the claim by Brunet and Jehenne that
Paloplotherium was a distinct genus from
Plagiolophus, instead suggesting to convert the former into a
Plagiolophus subgenus. In 1994, Spanish palaeontologist Miguel Ángel Cuesta Ruiz-Colmenares erected two
Plagiolophus species, the first being
P. casasecaensis, named after the Spanish municipality of
Casaseca de Campeán within the
Duero Basin. The second species he recognized was
P. mazateronensis, also from the Duero Basin; it was named after the Mazaterón province in the municipality of
Soria. In 1997, another Spanish palaeontologist Lluís Checa Soler analyzed a dental specimen, stating his belief that it belonged to
Plagiolophus and that the species would be defined by its smaller size and primitive characteristics compared to other species. He proposed the name
P. plesiomorphicus but sought to not formally define it until more complete material assignable to the species was found. In 2000, Remy described a skull of a male
Plagiolophus individual that was within a sandstone block originally from the French department of
Vaucluse, assigning it the new species name
P. huerzeleri. The species was named after Johannes Hürzeler, Swiss palaeontologist and former director of the osteology department of the
Natural History Museum of Basel. Remy had also emended
P. majus to
P. major and suggested both
Plagiolophus and
Paloplotherium as valid subgenera for
Plagiolophus. Remy, in 2004, followed up by erecting
P. ringeadei, named after Ruch fossil deposit discoverer Michel Ringead and known by a skull of an adult female with cheek teeth, and
P. mamertensis, which was based on a left
maxilla from Robiac. He also listed
P. minutus and
P. plesiomorphicus both as
nomen dubia (doubtful taxon names with no distinguishing features). Remy reiterated both
Plagiolophus and
Paloplotherium as subgenera for
Plagiolophus and created a third subgenus,
Fraasiolophus. Some authors have also considered the Plagiolophinae to be a separate subfamily, while others group its genera into the Palaeotheriinae.
Plagiolophus has also been suggested to belong to the tribe
Plagiolophini, one of three proposed tribes within the Palaeotheriinae along with the
Leptolophini and
Palaeotheriini. Palaeotheriids are well-known for having lived in western Europe during much of the
Palaeogene but were also present in eastern Europe, possibly the Middle East, and, in the case of pachynolophines (or pachynolophs), Asia. The MP13 unit saw the appearances of later pachynolophines such as
Pachynolophus and
Anchilophus along with definite records of the first palaeotheriines such as
Palaeotherium and
Paraplagiolophus. The palaeotheriine
Plagiolophus has been suggested to have potentially made an appearance by MP12. It was by MP14 that the subfamily proceeded to diversify, and the pachynolophines were generally replaced but still reached the late Eocene. In addition to more widespread palaeothere genera such as
Plagiolophus,
Palaeotherium, and
Leptolophus, some of their species reaching medium to large sizes, various other palaeothere genera that were endemic to the Iberian Peninsula, such as
Cantabrotherium,
Franzenium, and
Iberolophus, appeared by the middle Eocene. }} }} }} }} }} }} }} }} }} }} }} }} }} }} }} }} }} As shown in the above phylogeny, the Palaeotheriidae is defined as a
monophyletic clade, meaning that it did not leave any derived descendant groups in its evolutionary history.
Hyracotherium sensu stricto (in a strict sense) is defined as amongst the first offshoots of the family and a member of the Pachynolophinae. "
H."
remyi, formerly part of the now-invalid genus
Propachynolophus, is defined as a sister taxon to more derived palaeotheriids. Both
Pachynolophus and
Lophiotherium, defined as pachynolophines, are defined as monophyletic genera. The other pachynolophines
Eurohippus and
Propalaeotherium constitute a
paraphyletic clade (or phylogenetic group excluding descendant lineages) in relation to members of the derived and monophyletic subfamily Palaeotheriinae (
Leptolophus,
Plagiolophus, and
Palaeotherium), thus making Pachynolophinae a paraphyletic subfamily clade in relation to the palaeotheriine descendants..
Inner systematics Unlike
Palaeotherium where many species have subspecies,
Plagiolophus only has one species with defined subspecies,
P. curtisi. All species of
Plagiolophus are classified in one of three subgenera. The following table defines the species and subspecies of
Plagiolophus and additional information about them: == Description ==