Miacis cognitus
Encyclopedia
Miacis cognitus is the only species of the diverse genus Miacis that is regarded as belonging to the crown-group Carnivora
, within the Caniformia
. The type specimen or holotype
was discovered in Reeve's bonebed
, western Texas
, in the Chambers Tuff Formation in 1986. The University of Texas holds this specimen. It is the only confirmed fossil of this species.
s, viverrids, herpestid, and the famously few-toothed felids. Most member of Miacoidea
have forty four teeth, so this advanced species has already lost two bottom premolars. Though the upper canines
are missing, these teeth can be reconstructed due to the foramen for the tooth root remaining intact. These canines were not particularly long or short, though they were not stout or shaped for great stress. The molars of this species were small and not suited for grinding large amounts of material. The premolars show carnassial
form that makes carnivorans unique and were good for slicing rather than crushing or grinding.
still appears much like Oligocene M. cognitus. In skull morphology
alone, the African palm civet
, Nandinia binotata takes the prize of looking most like its distant relative. Considering the morphology of the entire body, various species of civet
, and herpetids are pretty close to what the living animal would have resembled. The most similar in body type would be between Viverridae's binturong (without the shag of hair) and the fossa
of Eupleridae
.
The holotype of Miacis cognitus was made available to the University of Texas High-Resolution X-ray
CT Facility for scanning by Dr. Timothy Rowe of The University of Texas at Austin
, Department of Geological Sciences. The specimen was scanned by Richard Ketcham on 3 December 2007 along the coronal axis for a total of 1010 slices. Each 1024×1024-pixel slice is 0.08551 mm thick, with an interslice spacing of 0.08551 mm and a field of reconstruction of 40 mm.
Surface views allow one to roll
, pitch
, and yaw
the specimen to see the fossil as though you were holding it in your hand. A second series is much more in depth slice movies, with coronal, transverse, and sagittal slices of the fossil. The last series is a dynamic cutaway from coronal, transverse, and sagittal angles as well.
as many small carnivorans are today.
s open and powerful competition to fill them. Species who previously had needed to be small and hide as a way of life suddenly had the requirement released and there was a strong pressure to get big and successful. The Paleocene
was a period of struggle in which animals that had been occupied with avoiding being eaten by dominant species, namely the dinosaurs, were suddenly competing against each other to become the next dominant organism. Most mammals were small, many the size of rabbits, few exceeding the size of cats. The competition between the two groups of predatory mammals, the creodonts and the Carnivoramorpha
, resulted in the better adapted creodonts occupying the position of top predators. As the Eocene continued, they were the dominant hunters and the carnivorans remained relatively small, staying out of the way. Miacis lived during this period. Miacis belongs to the stem-group Carnivoramorpha
that began to diversify during the middle and late Oligocene. Two major lineages appeared, the feliformes
(cats, hyenas, civets, palm civets, etc.) and the caniformes
(dogs, bears, pinnipeds, skunks, ferrets, etc.). The tables began to turn and the creodonts were struggling during the late Oligocene when the carnivorans, while small, were well off. Open niches left by extinct predators were quickly filled by the small carnivorans, and they became larger and more diverse until their peak in the Miocene when the last of the creodonts had died out.
Reeves bonebed is well known for it oreodonts, especially Bathygenys
. This oreodont, related to modern llamas, is very common in the formation, and being small for an oreodont at about thirteen pounds, it would have been hunted by Miacis regularly. The creodont Hyaenodon
was also present in the fossil bed, and it is probably that this larger creodont hunted the larger oreodont Merycoidodon
who, at over two hundred pounds, would have killed attacking Miacis. The large brontothere Menodus
would have been far too large for Miacis, and if anything would have been a danger for the small carnivore. Miacis would have avoided this species completely to avoid injury from massive perissodactylid. The medium-sized herbivores Agriochoerus
, Hyracodon
, Mesohippus
and Leptotragulus
, were again probably Hyaenodon prey and Miacis would have left it alone completely. Leptomeryx
inhabited the same range and was smaller. Its young would have been ample prey, and the adults might have been tackled. The rodent
Ardynomys was of perfect size and would have been hunted by Miacis. Within the region, there were many smaller rodents, and with so many animals in the area that were too large for Miacis to kill, it is likely that the small animal, somewhere between the size of a cat and a begal, would have been a prolific rodent hunter and a hunter of Bathygenys.
Carnivora
The diverse order Carnivora |Latin]] carō "flesh", + vorāre "to devour") includes over 260 species of placental mammals. Its members are formally referred to as carnivorans, while the word "carnivore" can refer to any meat-eating animal...
, within the Caniformia
Caniformia
Caniformia, or Canoidea , is a suborder within the order Carnivora. They typically possess a long snout and non-retractile claws . The Pinnipedia evolved from caniform ancestors and are accordingly assigned to this group...
. The type specimen or holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
was discovered in Reeve's bonebed
Reeve's Bonebed
Reeve's Bonebed is a geological formation in Presidio County, Texas, with the coordinates of 29.9° N, 104.2° W. It consists of fossiliferous sedimentary rock dating from the late Eocene and early Oligocene. It is well known for its vertebrate fossils, hence the name "bone bed"...
, western Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
, in the Chambers Tuff Formation in 1986. The University of Texas holds this specimen. It is the only confirmed fossil of this species.
Fossil
The holotype is missing the mandible, upper canines, and zygomatic arch. The remainder of the skull is damaged, but relatively intact.Teeth
It preserves the old style of many teeth, probably having forty two as compared to a modern carnivoran in the low thirties. With the later species of Miacis, the size of the certain teeth were decreasing, namely the foremost premolars. These teeth would eventually be lost all together, resulting in the fewer number of teeth seen in most modern carnivorans, especially feliforms, including extant hyenaHyena
Hyenas or Hyaenas are the animals of the family Hyaenidae of suborder feliforms of the Carnivora. It is the fourth smallest biological family in the Carnivora , and one of the smallest in the mammalia...
s, viverrids, herpestid, and the famously few-toothed felids. Most member of Miacoidea
Miacoidea
Miacoidea is paraphyletic superfamily that had been traditionally divided into two families of carnivores: Miacidae and Viverravidae. Miacoids were primitive carnivores which lived during the Paleocene and Eocene Epoch about 33-65 million years ago...
have forty four teeth, so this advanced species has already lost two bottom premolars. Though the upper canines
Maxillary canine
The maxillary canine is the tooth located laterally from both maxillary lateral incisors of the mouth but mesial from both maxillary first premolars...
are missing, these teeth can be reconstructed due to the foramen for the tooth root remaining intact. These canines were not particularly long or short, though they were not stout or shaped for great stress. The molars of this species were small and not suited for grinding large amounts of material. The premolars show carnassial
Carnassial
Carnassials are large teeth found in many carnivorous mammals, used for shearing flesh and bone in a scissor- or shear-like way. In the Carnivora, the carnassials are the modified last upper premolar and the first molar, but in the prehistoric creodonts, the carnassials were further back in the...
form that makes carnivorans unique and were good for slicing rather than crushing or grinding.
Comparison to modern species
The skull of M. cognitus is long and low. Their modern-day relatives have often changed greatly, but there are several species whose osteologyOsteology
Osteology is the scientific study of bones. A subdiscipline of anatomy, anthropology, and archeology, osteology is a detailed study of the structure of bones, skeletal elements, teeth, morphology, function, disease, pathology, the process of ossification , the resistance and hardness of bones , etc...
still appears much like Oligocene M. cognitus. In skull morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
alone, the African palm civet
African Palm Civet
The African palm civet , also known as the two-spotted palm civet, is a small mammal, with short legs, small ears, a body resembling a cat, and a long lithe tail as long as its body. Adults usually weigh . It is native to the forests of eastern Africa, where it usually inhabits trees...
, Nandinia binotata takes the prize of looking most like its distant relative. Considering the morphology of the entire body, various species of civet
Civet
The family Viverridae is made up of around 30 species of medium-sized mammal, including all of the genets, the binturong, most of the civets, and the two African linsangs....
, and herpetids are pretty close to what the living animal would have resembled. The most similar in body type would be between Viverridae's binturong (without the shag of hair) and the fossa
Fossa (animal)
The fossa is a cat-like, carnivorous mammal that is endemic to Madagascar. It is a member of the Eupleridae, a family of carnivorans closely related to the mongoose family . Its classification has been controversial because its physical traits resemble those of cats, yet other traits suggest a...
of Eupleridae
Eupleridae
The family Eupleridae is a group of carnivorans endemic to Madagascar and comprising 10 known species in seven genera. Probably the best known species is the Fossa , in the subfamily Euplerinae...
.
Digital morphology and CT scanning
The information core for the Digital Morphology library is generated using a state-of-the-art high-resolution X-ray computed tomographic (X-ray CT) scanner. This instrument is comparable to a conventional medical diagnostic CAT scanner, but with greater resolution and penetrating power. The CT scanner was custom built and optimally designed to explore the internal structure of natural objects and materials at mega- and microscopic levels. This instrument is at the center of The University of Texas High-Resolution X-ray Computed Tomography Facility (UTCT), a designated NSF-supported Multi-User Facility. Now in its seventh year, UTCT has scanned hundreds of rocks, meteorites, fossils, and modern organisms, providing unique data and visualizations for a wide range of interests in education and research.The holotype of Miacis cognitus was made available to the University of Texas High-Resolution X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
CT Facility for scanning by Dr. Timothy Rowe of The University of Texas at Austin
Austin
Austin is the capital of the U.S. state of Texas.Austin may also refer to:-In the United States:*Austin, Arkansas*Austin, Colorado*Austin, Chicago, Illinois*Austin, Indiana*Austin, Minnesota*Austin, Nevada*Austin, Oregon...
, Department of Geological Sciences. The specimen was scanned by Richard Ketcham on 3 December 2007 along the coronal axis for a total of 1010 slices. Each 1024×1024-pixel slice is 0.08551 mm thick, with an interslice spacing of 0.08551 mm and a field of reconstruction of 40 mm.
Surface views allow one to roll
Aircraft principal axes
An aircraft in flight is free to rotate in three dimensions: pitch, nose up or down about an axis running from wing to wing), yaw, nose left or right about an axis running up and down; and roll, rotation about an axis running from nose to tail. The axes are alternatively designated as lateral,...
, pitch
Aircraft principal axes
An aircraft in flight is free to rotate in three dimensions: pitch, nose up or down about an axis running from wing to wing), yaw, nose left or right about an axis running up and down; and roll, rotation about an axis running from nose to tail. The axes are alternatively designated as lateral,...
, and yaw
Aircraft principal axes
An aircraft in flight is free to rotate in three dimensions: pitch, nose up or down about an axis running from wing to wing), yaw, nose left or right about an axis running up and down; and roll, rotation about an axis running from nose to tail. The axes are alternatively designated as lateral,...
the specimen to see the fossil as though you were holding it in your hand. A second series is much more in depth slice movies, with coronal, transverse, and sagittal slices of the fossil. The last series is a dynamic cutaway from coronal, transverse, and sagittal angles as well.
Lifestyle
Though only the skull of Miacis cognitus is known, there is a great deal of inference that can be applied to the species based on the knowledge of its relatives, whose fossil records are more intact. M. cognitus was most likely an arboreal. It was an omnivore that ate anything from amphibians to birds to eggs to small mammals. It would have been lean and slender, with a tail to aid it in balancing. It was likely very agile and claws that were probably retractable aided in its climbing. Because of the configuration of its legs, it was not well suited for sprints, instead it would have ambushed. Still a small animal hiding the wake of creodonts, it would have preferred hiding to being out in the open and it may have been nocturnal or crepuscularCrepuscular
Crepuscular animals are those that are active primarily during twilight, that is during dawn and dusk. The word is derived from the Latin word crepusculum, meaning "twilight." Crepuscular is, thus, in contrast with diurnal and nocturnal behavior. Crepuscular animals may also be active on a bright...
as many small carnivorans are today.
Evolution
The mass extinction of the K-T event left many ecological nicheEcological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
s open and powerful competition to fill them. Species who previously had needed to be small and hide as a way of life suddenly had the requirement released and there was a strong pressure to get big and successful. The Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
was a period of struggle in which animals that had been occupied with avoiding being eaten by dominant species, namely the dinosaurs, were suddenly competing against each other to become the next dominant organism. Most mammals were small, many the size of rabbits, few exceeding the size of cats. The competition between the two groups of predatory mammals, the creodonts and the Carnivoramorpha
Carnivoramorpha
Carnivoramorpha are a clade of mammals that includes the modern order Carnivora and its closest extinct relatives in the Miacoidea , but excludes the creodonts. The order Creodonta are a sister taxon to the Carnivoramorpha dating back 58.7 million years ago...
, resulted in the better adapted creodonts occupying the position of top predators. As the Eocene continued, they were the dominant hunters and the carnivorans remained relatively small, staying out of the way. Miacis lived during this period. Miacis belongs to the stem-group Carnivoramorpha
Carnivoramorpha
Carnivoramorpha are a clade of mammals that includes the modern order Carnivora and its closest extinct relatives in the Miacoidea , but excludes the creodonts. The order Creodonta are a sister taxon to the Carnivoramorpha dating back 58.7 million years ago...
that began to diversify during the middle and late Oligocene. Two major lineages appeared, the feliformes
Feliformia
The Feliformia are a suborder within the order Carnivora and includes cats , hyenas, mongooses, civets and related taxa. The other suborder of Carnivora is Caniformia...
(cats, hyenas, civets, palm civets, etc.) and the caniformes
Caniformia
Caniformia, or Canoidea , is a suborder within the order Carnivora. They typically possess a long snout and non-retractile claws . The Pinnipedia evolved from caniform ancestors and are accordingly assigned to this group...
(dogs, bears, pinnipeds, skunks, ferrets, etc.). The tables began to turn and the creodonts were struggling during the late Oligocene when the carnivorans, while small, were well off. Open niches left by extinct predators were quickly filled by the small carnivorans, and they became larger and more diverse until their peak in the Miocene when the last of the creodonts had died out.
Ecology
Bathygenys
Bathygenys is an extinct genus of terrestrial herbivore of the family Merycoidodontidae , endemic to North America during the Late Eocene-Early Oligocene subepochs existing for approximately ....
. This oreodont, related to modern llamas, is very common in the formation, and being small for an oreodont at about thirteen pounds, it would have been hunted by Miacis regularly. The creodont Hyaenodon
Hyaenodon
Hyaenodon is an extinct genus of Hyaenodonts, a group of carnivorous creodonts of the family Hyaenodontidae endemic to all continents except South America, Australia and Antarctica, living from 42—15.9 mya, existing for approximately .-Morphology:Some species of this genus were amongst the largest...
was also present in the fossil bed, and it is probably that this larger creodont hunted the larger oreodont Merycoidodon
Merycoidodon
Merycoidodon is an extinct genus of terrestrial herbivore of the family Merycoidodontidae, subfamily Merycoidodontinae ,...
who, at over two hundred pounds, would have killed attacking Miacis. The large brontothere Menodus
Menodus
Menodus giganteus is a species of brontothere. The best known specimen is a mounted skeleton in the Field Museum of Natural History.According to one source , M. giganteus is merged into the genus Megacerops....
would have been far too large for Miacis, and if anything would have been a danger for the small carnivore. Miacis would have avoided this species completely to avoid injury from massive perissodactylid. The medium-sized herbivores Agriochoerus
Agriochoerus
Agriochoerus is an extinct genus of terrestrial herbivore of the family Agriochoeridae, endemic to North America. Agriochoerus and other agriochoerids possessed claws, which is rare within Artiodactyla....
, Hyracodon
Hyracodon
Hyracodon is an extinct genus of mammal.It was a lightly built, pony-like mammal of about 1.5 m long. Hyracodons skull was large in comparison to the rest of the body...
, Mesohippus
Mesohippus
Mesohippus is an extinct genus of early horse. It lived some 40 to 30 million years ago from the late Eocene to the mid-Oligocene...
and Leptotragulus
Leptotragulus
Leptotragulus is a small extinct genus of Artiodactyla, of the family Protoceratidae, endemic to North America from the Eocene epoch 40.2—33.9 Ma, existing for approximately .-Taxonomy:...
, were again probably Hyaenodon prey and Miacis would have left it alone completely. Leptomeryx
Leptomeryx
Leptomeryx is an extinct genus of ruminant of the family Leptomerycidae, endemic to North America during the Eocene through Oligocene 38—24.8 Mya, existing for approximately .-Taxonomy:...
inhabited the same range and was smaller. Its young would have been ample prey, and the adults might have been tackled. The rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
Ardynomys was of perfect size and would have been hunted by Miacis. Within the region, there were many smaller rodents, and with so many animals in the area that were too large for Miacis to kill, it is likely that the small animal, somewhere between the size of a cat and a begal, would have been a prolific rodent hunter and a hunter of Bathygenys.