Gustafsonia

Last updated

Gustafsonia
Temporal range: 39–33  Ma
Miacisreconstructedskull2.png
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Amphicyonidae
Genus: Gustafsonia
Tomiya & Tseng, 2016
Species:
G. cognita
Binomial name
Gustafsonia cognita
(Gustafson, 1986)
Synonyms
Miacis cognitus

Gustafsonia is an extinct genus of carnivoran belonging to the family Amphicyonidae (a bear dog). The type species, Gustafsonia cognita, was described in 1986 by Eric Paul Gustafson, who originally interpreted it as a miacid and named it Miacis cognitus. It was subsequently considered to be the only species of the diverse genus Miacis that belonged to the crown-group Carnivora, within the Caniformia, [1] and it was ultimately assigned to the family Amphicyonidae. [2] The type specimen or holotype was discovered in Reeve's bonebed, western Texas, in the Chambers Tuff Formation in 1986. [3] The University of Texas holds this specimen. It is the only confirmed fossil of this species.

Contents

Morphology

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 most modern carnivorans 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 hyenas, viverrids, herpestid, and the famously few-toothed felids. Most members 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.

drawing of the original holotype Miacisfossil.png
drawing of the original holotype
The African palm civet (Nandinia binotata), a modern species resembling Gustafsonia cognita in skull morphology. Nandinia binotata, Manchester Museum.jpg
The African palm civet (Nandinia binotata), a modern species resembling Gustafsonia cognita in skull morphology.

Comparison to modern species

The skull of G. cognita is long and low. In skull morphology, the African palm civet, Nandinia binotata takes the prize of looking most like its distant relative.

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 Gustafsonia cognita 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. [4]

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.

a facial profile of Gustafsonia cognita Miacisfinal.jpg
a facial profile of Gustafsonia cognita

Evolution

The mass extinction of the Cretaceous–Paleogene extinction event left many ecological niches open, allowing various mammalian lineages to move into them during the Paleocene. Contrary to popular belief, many mammals such as the pantodonts and mesonychians became large quickly during the Paleocene rather than remaining small for longer, but this also caused other lineages to remain small to avoid competition, including the creodonts (which are likely not a natural group) and the Carnivoramorpha. As the Eocene continued, some of the creodonts, known as the oxyaenids, became larger and competed with the mesonychians as the dominant hunters in Laurasia; the carnivoramorphs and the other group of “creodonts”, the hyaenodonts, remained relatively small, staying out of the way. At this point, the crown-group Carnivora began to diversify during the middle and late Eocene, when two major lineages appeared-the feliforms (cats, hyenas, civets, palm civets, etc.) and the caniformes (dogs, bears, pinnipeds, skunks, ferrets, amphicyonids, etc.). Gustafsonia, being an early amphicyonid, is a caniform. Around this time, the formerly dominant oxyaenids and mesonychians began to decline as a result of climatic changes; open niches left by these predators were quickly filled by some of the carnivorans, namely the feliform nimravids, and by the hyaenodonts; hyaenodonts would remain successful in various predatory niches until the end of the Middle Miocene, but the carnivorans were much more diverse, becoming the dominant group of land predators in Laurasia by the start of the Miocene and fully taking over once hyaenodonts entered terminal decline in the Late Miocene.

Ecology

the local, large oreodont Merycoidodon Merycoidodon gracilis.jpg
the local, large oreodont Merycoidodon
the medium-sized equid Mesohippus Mesohippus.jpg
the medium-sized equid Mesohippus

Reeves bonebed is well known for its 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. [5]

Related Research Articles

<span class="mw-page-title-main">Carnivora</span> Order of mammals

Carnivora is an order of placental mammals that have specialized in primarily eating flesh, whose members are formally referred to as carnivorans. The order Carnivora is the fifth largest order of mammals, comprising at least 279 species on every major landmass and in a variety of habitats, ranging from the cold Polar regions of Earth the hyper-arid region of the Sahara Desert to the open seas. They have a very large array of different body plans with a wide diversity of shapes and sizes.

<span class="mw-page-title-main">Amphicyonidae</span> Extinct family of carnivores

Amphicyonidae is an extinct family of terrestrial carnivorans belonging to the suborder Caniformia. They first appeared in North America in the middle Eocene, spread to Europe by the late Eocene, and further spread to Asia and Africa by the early Miocene. They had largely disappeared worldwide by the late Miocene, with the latest recorded species at the end of the Miocene in Africa. They were among the first carnivorans to evolve large body size. Amphicyonids are colloquially referred to as "bear-dogs".

<span class="mw-page-title-main">Caniformia</span> Suborder of mammals

Caniformia is a suborder within the order Carnivora consisting of "dog-like" carnivorans. They include dogs, bears, raccoons, and mustelids. The Pinnipedia are also assigned to this group. The center of diversification for the Caniformia is North America and northern Eurasia. Caniformia stands in contrast to the other suborder of Carnivora, the Feliformia, the center of diversification of which was in Africa and southern Asia.

<span class="mw-page-title-main">Creodonta</span> Former order of extinct flesh-eating placental mammals

Creodonta 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 ancestral to the modern Carnivora, this order is now usually considered a polyphyletic assemblage of two different groups, the Oxyaenids and the Hyenodonts, not a natural group. Oxyaenids are first known from the Palaeocene of North America, while hyaenodonts hail from the Palaeocene of Africa.

<span class="mw-page-title-main">Mesonychia</span> Extinct taxon of carnivorous ungulates

Mesonychia is an extinct taxon of small- to large-sized carnivorous ungulates related to artiodactyls. Mesonychians first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely when the last genus, Mongolestes, became extinct in the early Oligocene. In Asia, the record of their history suggests they grew gradually larger and more predatory over time, then shifted to scavenging and bone-crushing lifestyles before the group became extinct.

<i>Hyaenodon</i> Extinct genus of mammals

Hyaenodon ("hyena-tooth") is an extinct genus of carnivorous placental mammals from extinct tribe Hyaenodontini within extinct subfamily Hyaenodontinae, that lived in Eurasia and North America from the middle Eocene, throughout the Oligocene, to the early Miocene.

<span class="mw-page-title-main">Carnassial</span> Mammal tooth type

Carnassials are paired upper and lower teeth modified in such a way as to allow enlarged and often self-sharpening edges to pass by each other in a shearing manner. This adaptation is found in carnivorans, where the carnassials are the modified fourth upper premolar and the first lower molar. These teeth are also referred to as sectorial teeth.

<span class="mw-page-title-main">Miacidae</span> Extinct family of carnivores

Miacidae is a former paraphyletic family of extinct primitive placental mammals that lived in North America, Europe and Asia during the Paleocene and Eocene epochs, about 65–33.9 million years ago. These mammals were basal to order Carnivora, the crown-group within the Carnivoraformes.

<i>Miacis</i> Extinct genus of carnivores

Miacis is an extinct genus of placental mammals from clade Carnivoraformes, that lived in North America from the early to middle Eocene.

<span class="mw-page-title-main">Eupleridae</span> Family of carnivores

Eupleridae is a family of carnivorans endemic to Madagascar and comprising 10 known living species in seven genera, commonly known as euplerids, Malagasy mongooses or Malagasy carnivorans. The best known species is the fossa, in the subfamily Euplerinae. All species of Euplerinae were formerly classified as viverrids, while all species in the subfamily Galidiinae were classified as herpestids.

<span class="mw-page-title-main">Carnivoramorpha</span> Clade of carnivores

Carnivoramorpha is a clade of placental mammals of clade Pan-Carnivora from mirorder Ferae, that includes the modern order Carnivora and its extinct stem-relatives.

<span class="mw-page-title-main">Feliformia</span> Suborder of carnivores

Feliformia is a suborder within the order Carnivora consisting of "cat-like" carnivorans, including cats, hyenas, mongooses, viverrids, and related taxa. Feliformia stands in contrast to the other suborder of Carnivora, Caniformia.

<i>Dissopsalis</i> Extinct family of mammals

Dissopsalis is a genus of teratodontine hyaenodonts of the tribe Dissopsalini. The older species, D. pyroclasticus, lived in Kenya during the middle Miocene, while the type species, D. carnifex, lived in Pakistan and India during the middle to late Miocene.

<span class="mw-page-title-main">Ursoidea</span> Superfamily of mammals

Ursoidea is a superfamily of arctoid carnivoran mammals that includes the families Subparictidae, Amphicynodontidae, and Ursidae. The last family includes the extant lineages of bears, as well as the extinct Hemicyoninae and Ursavinae.

<i>Asiavorator</i> Extinct genus of carnivores

Asiavorator is an extinct genus of civet-like carnivoran belonging in the family Stenoplesictidae. It was endemic to Asia and lived during the Eocene and Oligocene epochs.

<i>Mentoclaenodon</i>

Mentoclaenodon is an extinct genus of arctocyonid ungulate mammals.

<i>Pterodon</i> (mammal) Extinct genus of mammals

Pterodon is an extinct genus of hyaenodont in the family Hyainailouridae, containing five species. The type species Pterodon dasyuroides is known exclusively from the late Eocene to the earliest Oligocene of western Europe. The genus was first erected by the French zoologist Henri Marie Ducrotay de Blainville in 1839, who said that Georges Cuvier presented one of its fossils to a conference in 1828 but died before he could make a formal description of it. It was the second hyaenodont genus with taxonomic validity after Hyaenodon, but this resulted in taxonomic confusion over the validities of the two genera by other taxonomists. Although the taxonomic status of Pterodon was revised during the late 19th and early 20th centuries, it became a wastebasket taxon for other hyaenodont species found in Africa and Asia. Today, only the type species is recognized as belonging to the genus while four others are pending reassessment to other genera.

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". A few invertebrate fossils are also present.

<span class="mw-page-title-main">Hyaenodonta</span> Extinct order of mammals

Hyaenodonta is an extinct order of hypercarnivorous placental mammals of clade Pan-Carnivora from mirorder Ferae. Hyaenodonts were important mammalian predators that arose during the early Paleocene in Europe and persisted well into the late Miocene.

<i>Angelarctocyon</i> Extinct genus of carnivores

Angelarctocyon is an extinct genus of Amphicyonidae, which belongs to the order Carnivora.

References

  1. Spaulding, M.; Flynn J.J.; Stucky, R.K. (2010) Anew basal Carnivoramorphan (Mammalia) from the ‘Bridger B’ (Black’s Fork Member, Bridger Formation, Bridgerian NALMA, Middle Eocene) of Wyoming, USA. Paleontology 53: 815-832. doi : 10.1111/j.1475-4983.2010.00963.x
  2. Susumu Tomiya; Zhijie Jack Tseng (2016). "Whence the beardogs? Reappraisal of the Middle to Late Eocene Miacis from Texas, USA, and the origin of Amphicyonidae (Mammalia, Carnivora)". Royal Society Open Science. 3 (10): 160518. Bibcode:2016RSOS....360518T. doi:10.1098/rsos.160518. PMC   5098994 . PMID   27853569.
  3. "Miacis cognitus Gustafson 1986 (carnivoran)". Paleobiology Database. Archived from the original on March 25, 2012.
  4. Digimorph (Digital morphology). "Miacis cognitus, extinct carnivoran".
  5. University of Texas, Austin. "Reeves bonebed". Archived from the original on 2011-09-29. Retrieved 2024-02-10.