Purgatorius

of Alberta. Purgatorius contains at least five valid species distributed throughout the early Paleocene of western North America. Buckley proposed a new species for the Simpson Quarry fossils, P. titusi, but several subsequent studies considered his species a junior synonym of P. unio. The youngest known Purgatorius fossils are teeth similar to P. unio and P. pinecreeensis found at Horsethief Canyon, a site in Garfield County, Montana dated to the Torrejonian 1 age. Further excavations have yet to reveal any more Purgatorius fossils at Harbicht Hill, and it is possible that P. ceratops is instead a tooth from a eutherian unrelated to Purgatorius. Garbani Channel is from the Puercan 3 land mammal age. P. janisae has the most complete remains of any Purgatorius species, including numerous teeth, maxilla fragments, and lower jaws. One lower jaw fossil contains three preserved molars, three preserved premolars, and empty sockets for a premolar and canine. Isolated incisors are also known from Garbani Channel, along with Purgatorius ankle bones (astragali and calcanei). Molar teeth of P. janisae have been found at the Harley's Point, a site which is Puercan 1 in age. This would make P. janisae the joint-oldest species of Purgatorius, alongside P. mckeeveri. Purgatorius coracis Purgatorius fossils were first reported from the Ravenscrag Formation of Saskatchewan in 1984, as the first Purgatorius fossils found outside of Montana. These fossils received their own species, P. coracis, in 2011. The species name coracis is Latin for raven, in reference to the Ravenscrag Formation. The mammal fauna at the same site as P. coracis resemble Puercan 2 mammals found further south, though magnetostratigraphy may support an age as old as Puercan 1. Purgatorius pinecreeensis P. pinecreensis is the second Purgatorius species from the Ravenscrag Formation of Saskatchewan. Its teeth have lower, broader cusps and a larger talonid basin than other Purgatorius species, suggesting a greater ability to crush and grind tough food items such as seeds. Purgatorius mckeeveri P. mckeeveri was described in 2021 based on jaw fragments and isolated molar teeth from Harley's Point, a Tullock Member site in Garfield County, Montana. Harley's Point is the oldest site to preserve Purgatorius fossils, from the Puercan 1 land mammal age at the very start of the Paleocene. It dates to at least 65.844 Ma (million years ago), a maximum of 208 thousand years after the asteroid impact which ended the Cretaceous period at 66.052 Ma. Some calibrations place it even closer to the K-Pg boundary, 105–139 thousand years after the impact (65.946–65.912 Ma). P. mckeeveri also occurs at Garbani Channel. The species name mckeeveri honors Frank McKeever, a Garfield County resident who assisted fieldwork in the 1960s, as well as the McKeever family who more recently supported excavations at Harley's Point. ==Description of remains==

Postcanine dentition of P. unio is documented by 13 dentulous, fragmentary mandibles, a fragmentary maxillary and more than 50 isolated teeth from Garbani Locality 80 km west of Purgatory Hill. P. ceratops is represented by an isolated lower molar found at Harbicht Hill, McCone County. The report of the occurrence of Purgatorius in the Late Cretaceous was based on an isolated, worn molar found in a channel filling that contains early Puercan fossils. It is also abundantly represented in Pu 2-3 local faunas in the northwestern interior, suggesting that it came into the area between 64.75 and 64.11 Mya. Fragmentary dentition from the Garbani Channel fauna from Purgatorius janisae shows that the lower dental formula was 3.1.4.3. Dentition The type specimen of P. unio, a damaged upper molar, is essentially identical to teeth found at the Garbani Locality. Data from this sample support Van Valen and Sloan's identification of topotypic lower molars, and also demonstrate that the lower dentition of P. unio includes seven postcanines. The alveolus for the single root of P1, crown unknown, is smaller than those for the canine or P2. The second lower pre- molar is smaller than P3; both are two- rooted. The fourth lower premolar is submolariform. A metaconid is lacking, although on some teeth slight thickenings of the enamel are present in this region. Talonid cusps are slightly differentiated. The first and second lower molars are approximately the same length (M1, average length x=- 1.93 mm, N- 13; M2, x=2.00 mm, N- 9); M. is longer (x= 2.32 mm, N -7). Widths of talonids of M1.2 vary from less than to greater than widths of trigonids. Hypoconulid of M. is enlarged, salient, and on some teeth incipiently doubled by addition of a lingual cusp. The proximate cause of the tall protocone found in Purgatorius may have been a lingual bias in activator expression during the bud stage of dental development, which would have stablished a buccolingual growth axis. Ankle bones Bones from the ankle are similar to those of primates, and were suited for a life up in trees. ==Classification==

For many years, there has been debate as to whether Purgatorius is a primitive member of the primates or a basal member of the Plesiadapiforms. Several characters of the dentition of Purgatorius, which includes its incisor morphology, can ally it with later plesiadapiforms. The prism cross sections are highly variable with circular, horseshoe and irregular shapes, while the prisms of cheek teeth are radially arranged. Similar results had been obtained in previous studies with far fewer species. ==References==