''Periptychus'' is an extinct genus of

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

belonging to the family

Periptychidae Periptychidae is a family of Cretaceous–Paleocene placental mammals, known definitively only from North America. The family is part of a radiation of early herbivorous and omnivorous mammals formerly classified in the extinct order " Condylart ...

. It lived from the Early to Late

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

and its

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

remains have been found in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

Description

This animal was of medium size and could exceed one meter in overall length; ''Periptychus'' is supposed to have weighed about 23 kilograms. ''Periptychus'' was an unusual mammal that combined a number of rather specialized dental, cranial, and postcranial features with a relatively generalized skeletal structure.

Skull

The shape of the skull of ''Periptychus'' was almost identical to that of early

Eutheria Eutheria (from Greek , 'good, right' and , 'beast'; ), also called Pan-Placentalia, is the clade consisting of Placentalia, placental mammals and all therian mammals that are more closely related to placentals than to marsupials. Eutherians ...

, although it was more robust. The snout of ''Periptychus'' was moderately elongated and tall, and tapered anteriorly without a rostral constriction. The

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

of the rostrum of this animal was very similar to that found in related genera such as '' Carsioptychus'' or '' Ectoconus''; the snout was not elongated as in other

condylarth Condylarthra is an informal group – previously considered an Order (biology), order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs. They are considered early, primitive ungulates and is now largely consid ...

s such as '' Arctocyon'', but it was longer than that of

pantodonts Pantodonta is an extinct suborder (or, according to some, an Order (biology), order) of eutherian mammals. These herbivorous mammals were one of the first groups of large mammals to evolve (around 66 million years ago) after the K-T boundary, en ...

such as ''

Pantolambda ''Pantolambda'' (Greek: "all" (pantos), "lambda" (lambda), in a reference to the shape of upper premolars, similar to the Greek letter lambda) is an extinct genus of Paleocene pantodont mammal. ''Pantolambda'' lived during the middle Paleocene, a ...

''. In lateral view, the dorsal surface of the skull of ''Periptychus'' was relatively flat compared to the more domed morphology found in ''Pantolambda''. The zygomatic arches of ''Periptychus'' were wide and protruded laterally. The skull was small and low, with well-developed nuchal and sagittal ridges. The latter, in particular, was robust and provided a substantial insertion point for the temporal muscles along the entire length of the cranial box. The paired nasal bones were very elongated and went to form a wide, flat "roof" over the rostrum. The

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

was characterized by an unusual pitted surface, just above the tooth row; these holes, concentrated mainly above the

premolar The premolars, also called premolar Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...

s and around the infraorbital foramen, varied in shape and size: some were circular and others ovoid, and did not exceed 0.7 millimeters in diameter. In the living animal, these holes probably housed a network of capillaries that supply blood to the jaws and were connected to the vibrissae. The

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

of ''Periptychus'' was particularly robust; the paired dental bones were co-ossified toward the end, and went to form a high mandibular

symphysis A symphysis (, : symphyses) is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint. # A symphysis is an amphiarthrosis, a slightly movable joint. # A growing together o ...

that extended from the

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...

s to the ventral limit of the mandible, at the level of the anterior margin of the second inferior premolar. The ascending ramus of the mandible was rather high in relation to the mandibular body, and went to form a rounded, high and wide coronoid process. The dentition of ''Periptychus'' was distinctive: the premolars were larger than the

molars The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ...

and possessed highly expanded central cusps, while the molars were highly

bunodont The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone tooth ...

and possessed bulbous cusps compressed at the apex. The

dental enamel Tooth enamel is one of the four major Tissue (biology), tissues that make up the tooth in humans and many animals, including some species of fish. It makes up the normally visible part of the tooth, covering the Crown (tooth), crown. The other ...

was strongly crenulated with well-aligned ridges, typical of all periptychids but reaching their maximum development in ''Periptychus.'' The

canine Canine may refer to: Zoology and anatomy * Animals of the family Canidae, more specifically the subfamily Caninae, which includes dogs, wolves, foxes, jackals and coyotes ** ''Canis'', a genus that includes dogs, wolves, coyotes, and jackals ** Do ...

was relatively small and single-rooted.

Postcranial skeleton

The postcranial skeleton of ''Periptychus'' was that of a robust, strong-footed animal with a

plantigrade 151px, Portion of a human skeleton, showing plantigrade habit In terrestrial animals, plantigrade locomotion means walking with the toes and metatarsals flat on the ground. It is one of three forms of locomotion adopted by terrestrial mammals. ...

gait. The

lumbar vertebrae The lumbar vertebrae are located between the thoracic vertebrae and pelvis. They form the lower part of the back in humans, and the tail end of the back in quadrupeds. In humans, there are five lumbar vertebrae. The term is used to describe t ...

were robust and dorsoventrally compressed. The caudal vertebrae were also robust, rod-like; the tail must have been rather long and heavy, although not as long as that of ''Ectoconus.'' The forelimbs were mainly characterized by a

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

that was rather short compared to

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

and

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

, with a hemispherical head equipped with large low tuberosities; the humerus also had a wide and elongated deltopectoral region and a region for the insertion of the ''teres major'' muscle that was rather small. Expanded medial and lateral entepicondyles were also present, and the humerus-radial joint was open. The ulna was rather straight and gracile, with a posterior bulge of the

diaphysis The diaphysis (: diaphyses) is the main or midsection (shaft) of a long bone. It is made up of cortical bone and usually contains bone marrow and adipose tissue (fat). It is a middle tubular part composed of compact bone which surrounds a centr ...

, while the

olecranon The olecranon (, ), is a large, thick, curved bony process on the proximal, posterior end of the ulna. It forms the protruding part of the elbow and is opposite to the cubital fossa or elbow pit (trochlear notch). The olecranon serves as a lever ...

was massive and formed an almost rectangular projection at the proximal part of the ulna. The radius was robust compared to the ulna. The

carpus In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carpal ...

was wide and had an enlarged central bone. The hand had five fingers, and the number of

phalanges The phalanges (: phalanx ) are digit (anatomy), digital bones in the hands and foot, feet of most vertebrates. In primates, the Thumb, thumbs and Hallux, big toes have two phalanges while the other Digit (anatomy), digits have three phalanges. ...

was the generalist number for mammals (2-3-3-3). The bones of the fingers were rather short and compact, and ended in nail-like

hoof The hoof (: hooves) is the tip of a toe of an ungulate mammal, which is covered and strengthened with a thick and horny keratin covering. Artiodactyls are even-toed ungulates, species whose feet have an even number of digits; the ruminants with ...

phalanges. The ilium of ''Periptychus'' was slender and elongated, and in dorsal view was concave in the central area. The

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

was typical of a robustly built animal, and it had strong

trochanter A trochanter is a tubercle of the femur near its joint with the hip bone. In humans and most mammals, the trochanters serve as important muscle attachment sites. Humans have two, sometimes three, trochanters. Etymology The anatomical term ' ...

s; a third trochanter was present. The greater trochanter was high but did not extend beyond the head of the femur. The

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

was also strong, but somewhat elongated, while the

fibula The fibula (: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. ...

was small. The foot of ''Periptychus'' was

, pentadactylous and paraxonic in structure, with wide toes well spaced apart, much like those of the hand. The

astragalus Astragalus may refer to: * ''Astragalus'' (plant), a large genus of herbs and small shrubs *Astragalus (bone) The talus (; Latin for ankle or ankle bone; : tali), talus bone, astragalus (), or ankle bone is one of the group of foot bones known ...

was dorsoventrally compressed, and its joint was wedged between the tibia and fibula, allowing the latter to make contact with the

calcaneus In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel; : calcanei or calcanea) or heel bone is a bone of the Tarsus (skeleton), tarsus of the foot which constitutes the heel. In some other ...

. A tibial bone was present, sandwiched between the tendons of the posterior tibial muscle. The phalanges of the tarsus were almost identical to those of the hand, but were slightly larger.

Classification

''Periptychus'' was first described by

Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontology, paleontologist, comparative anatomy, comparative anatomist, herpetology, herpetologist, and ichthyology, ichthyologist. Born to a wealthy Quaker fam ...

1881 Events January * January 1– 24 – Siege of Geok Tepe: Russian troops under General Mikhail Skobelev defeat the Turkomans. * January 13 – War of the Pacific – Battle of San Juan and Chorrillos: The Chilean army ...

, based on fossil remains found in

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

in deposits dating to the Middle Paleocene. The fossils were very fragmentary including a part of a jaw with teeth and belonging to a juvenile specimen, which Cope did not recognize as such and assigned it to

Creodonta Creodonta ("meat teeth") is a former order of extinct carnivorous placental mammals that lived from the early Paleocene to the late Miocene epochs in North America, Europe, Asia and Africa. Originally thought to be a single group of animals ance ...

. In the same year Cope described a jawbone, also from New Mexico, and described it as ''Catathleus rhabdodon''. Only later, through the discovery of more complete remains, did it become clear that the two forms were synonymous and belonged to the same species. To the genus ''Periptychus'' was then also ascribed by Cope himself the species ''P. coarctatus,'' which is slightly older and perhaps ancestral to the

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

. Fossils of ''Periptychus'' have since also been found in

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

and

Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...

. ''Periptychus'' is the eponymous genus of the family

, a family of archaic mammals that developed immediately after the Cretaceous-Tertiary extinction event, and produced a variety of forms of different sizes. In particular, ''Periptychus'' would appear to be a derived member of the group.

Paleobiology

''Periptychus'' was endowed with many features such as the broad facial region, high sagittal and nuchal ridges, dentition with enlarged premolars and highly developed enamel that indicate a

durophagous Durophagy is the eating behavior of animals that consume hard-shelled or exoskeleton-bearing organisms, such as corals, shelled mollusks, or crabs. It is mostly used to describe fish, but is also used when describing reptiles, including fossil t ...

diet, based on dense, fibrous plants. The postcranial skeleton of ''Periptychus'' indicates that this animal was plantigrade, adapted to move slowly over the ground; it was also capable, on occasion, of making rapid movements. Despite its robust structure, ''Periptychus'' retained a fairly high degree of movement capacity in its legs: they were very powerful but did not make very rapid movements. The flexor and extensor muscles in the hands and fingers were highly developed, indicating that this animal was probably capable of climbing and digging.

References

*E. D. Cope. 1881a. Mammalia of the lower Eocene beds. American Naturalist 15:337-338 *E. D. Cope 1881b. On some mammals of the Lower Eocene beds of New Mexico. Proc Am Philos Soc. 19: 484-495. *E. D. Cope. 1883. On some fossils of the Puerco Formation. Proc Acad Nat Sci;35: 168-170. *O. C. Marsh. 1894. Description of artiodactyls of the Tertiary. American Journal of Science 48(285):259-275. *G. G. Simpson. 1936. Additions to the fauna of the Puerco, Lower Paleocene. Am Mus Novit;849:1-12. *W. D. Matthew. 1937. Paleocene faunas of the San Juan Basin, New Mexico. Transactions of the American Philosophical Society 30:1-510. *J. A. Schiebout. 1974. Vertebrate paleontology and paleoecology of the Black Peaks Paleocene Formation, Big Bend National Park, Texas. Bulletin of the Texas Memorial Museum 24:1-88. *L. M. Van Valen. 1978. The beginning of the mammalian age. Evolutionary Theory 4:45-80. *J. K. Rigby. 1980. Swain Quarry of the Fort Union Formation, Middle Paleocene (Torrejonian), Carbon County, Wyoming: geologic setting and mammalian fauna. Evolutionary Monographs 3:1-178 *T. E. Williamson. 1996. The beginning of the mammal era in the San Juan Basin, New Mexico; biostratigraphy and evolution of Paleocene mammals of the Nacimiento Formation. Bulletin of the New Mexico Museum of Natural History and Science 8:1-141. *T. J. D. Halliday, P. Upchurch, and A. Goswami. 2017. Resolving relationships of Paleocene placental mammals. 92:521-550 {{Taxonbar, from=Q60978042 Periptychidae Paleocene mammals of North America Paleogene United States Fossils of the United States Puercan Torrejonian Tiffanian Fossil taxa described in 1881 Prehistoric placental genera Taxa named by Edward Drinker Cope