Creodonta

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Creodonta
Temporal range: Early Paleocene to Late Miocene 63.3–10  Ma
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(Suspected Late Cretaceous origin for Hyaenodonta, but unconfirmed by fossils yet) [1] [2]
Colorado Creodonta.JPG
Various creodonts of the Eocene of Colorado, United States. From top: Tritemnodon , Patriofelis , Machaeroides , and Sinopa
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Mirorder: Ferae
Order:† Creodonta
Cope, 1875 [3]
Families
Synonyms
list of synonyms:
  • Creodontia
  • Creodontidae (Winkler, 1893) [4]
  • Creodontiformes (Kinman, 1994) [5]
  • Creodontina (Pearse, 1936) [6]
  • Creophaga (Kretzoi, 1945) [7]
  • Hyaenodontia (Romer, 1966) [8]
  • Paracarnivora (Kretzoi, 1929) [9]
  • Pseudocreodi (Matthew, 1909) [10]
  • Subdidelphia (Trouessart, 1879) [11]

Creodonta ("meat teeth") is a former order of extinct carnivorous placental mammals that lived from the Early Paleocene (or Late Cretaceous) to the Late Miocene epochs in North America, Eurasia, 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 hyaenodonts, not a natural group. Oxyaenids are first known from the early Paleocene of North America, [12] while hyaenodonts hail from the late Paleocene, or Late Cretaceous, of Europe. [13] [14] [15]

Contents

Creodonts were the dominant carnivorous mammals from 55 to 35 million years ago, peaking in diversity and prevalence during the Eocene. [16] The first large, obviously carnivorous mammals appeared with the radiation of the oxyaenids in the late Paleocene. [17] During the Paleogene, "creodont" species were the most abundant terrestrial carnivores in the Old World. [18] In Oligocene Africa, hyaenodonts were the dominant group of large flesh-eaters, persisting until the middle of the Miocene.

"Creodont" groups had an extensive range, both geographically and temporally. They are known from the late Paleocene through the late Oligocene in North America, the early Eocene through late Oligocene in Europe, from the late Paleocene through late Miocene in Asia, and from the late Paleocene to the late Miocene in Africa. [19] While most were small-to-medium sized mammals, among their number was Sarkastodon , one of the largest mammalian land predators of all time, weighing an estimated 800 kg, though this may have been an overestimate. [20] The last genus, Dissopsalis , went extinct about 10  million years ago. [21]

Most modern paleontologists agree both "creodont" families are related to Carnivora, but are not their direct ancestors. It is still unclear how closely the two families are related to each other. In general, classification is complicated by the fact that relationships among fossil mammals are usually decided by similarities in the teeth, but the teeth of hypercarnivorous species may evolve similar shapes through convergent evolution, to deal with the mechanics of eating meat. [22]

"Creodonts" share with the Carnivora, and many other predatory mammal clades, the carnassial shear , a scissors-like modification of upper and lower cheek teeth that was used to slice muscle tissue. This adaptation is also seen in other clades of predatory mammals.

Systematics and history

"Creodonta" was coined by Edward Drinker Cope in 1875. [3] Cope included the oxyaenids and the viverravid Didymictis but omitted the Hyaenodontidae. In 1880. he expanded the term to include families Miacidae (including Viverravidae), Arctocyonidae, Leptictidae (now Pseudorhyncocyonidae), Oxyaenidae, Ambloctonidae and Mesonychidae. [23] Cope originally placed creodonts within the Insectivora. In 1884, however, he regarded them as a basal group from which both carnivorans and insectivorans arose. [24]

Hyaenodontidae was not included among the creodonts until 1909. [25] William Diller Matthew regarded Creodonta as a suborder of order Carnivora, divided in three groups:

Over time, various groups and species were removed from this order. It stabilized in the mid-20th century as representing oxyaenids, hyaenodonts, mesonychids, and arctocyonids, [26] which were understood as the major groups of flesh-eating placental mammals that were not members of the Carnivora. It became increasingly clear that arctocyonids were a wastebasket taxon and mesonychids might be more closely related to ungulates. By 1969, Creodonta contained only the oxyaenids and the hyaenodontids. [27]

More recently, "Creodonta" had been considered to be a nonvalid polyphyletic assemblage of carnivorous placental mammals (and not a natural group), and members of Creodonta being sister taxa to Carnivoramorpha (carnivorans and their stem-relatives) within clade Pan-Carnivora (in mirorder Ferae), split in two groups: order Oxyaenodonta as one group and order Hyaenodonta plus its stem-relatives (genera Altacreodus and Simidectes ) in the other. [28] [29] [30] [31] [32] However, some phylogenetic analysis recover them as a natural group, such as a phylogenetic analysis of Paleocene mammals published in 2015 that supported the monophyly of Creodonta, and placed the group as relatives of clade Pholidotamorpha (pangolins and their stem-relatives). [33]

Polly has argued that the only available synapomorphy between oxyaenids and hyaenodontids is a large metastylar blade on the first molar (M1), but he believes that that feature is common for all basal eutheria. [34] Separating Oxyaenidae from Hyaenodontidae would also comport with biogeographic evidence, since the first oxyaenid is known from the North American early Paleocene and the first hyaenodontids are from very late Paleocene of North Africa. [17]

Complicating this arrangement is the tentative endorsement by Gunnell [19] of the erection of a third family, Limnocyonidae. [35] The group includes taxa that were once considered oxyaenids, such as Limnocyon , Thinocyon [25] and Prolimnocyon . [36] Wortman had even erected a subfamily of Limnocyoninae within the oxyaenids. [37] Van Valen nests the same subfamily (including Oxyaenodon ) within Hyaenodontidae. [27] Gunnell is agnostic whether Limnocyonidae is a group within Hyaenodontidae (although a sister group to the rest of hyaenodontids) or entirely separate. [19]

According to Gunnell, the defining features of the oxyaenids include: A small braincase low in the skull. The occiput wide at base and narrowing dorsally (to give it a triangular shape). The lacrimal bone makes a semicircular expansion on the face. The mandibles have heavy symphysis. M1 and m2 form the carnassials, while M3/m3 are absent. The manus and pes are plantigrade or subplantigrade. The fibula articulates with the calcaneum, and the astragalus articulates with the cuboid bone. The phalanges are compressed and fissured at the tip. [19]

Likewise, Gunnell's list of defining features of hyaenodontids includes: Long, narrow skull with a narrow basicranium and a high narrow occiput. The frontal bones are concave between the orbital regions. M2 and m3 form the carnassials. M3 is present in most species, while m3 is always present. Manus and pes range from plantigrade to digitigrade. The fibula articulates with the calcaneum, while the astragalar-cuboid articulation is reduced or absent. Terminal phalanges are compressed and fissured at the tip. [19]

The limnocyonids had the following features according to Gunnell: M3/m3 were reduced or absent, other teeth were unreduced. The rostrum was elongated. The animals themselves were small to medium-sized. [19]

Morphology

Dentition

Among primitive creodonts the dental formula is 3.1.4.33.1.4.3, but later forms often had reduced numbers of incisors, premolars and/or molars. [38] The canines are always large and pointed. The lateral incisors are large, while the medial incisors are usually small. [19] Premolars are primitive, with one primary cusp and various secondary cusps. [18]

Creodonts have two or three pairs of carnassial teeth. One pair performed the largest cutting function (either M1/m2 or M2/m3). [19] This arrangement is unlike modern carnivorans, which use P4 and m1 for carnassials. [39] This difference suggests convergent evolution among meat-eaters, with a separate evolutionary history and an order-level distinction, [40] given that different teeth evolved as the carnassials both between creodonts and carnivorans, and between oxyaenids and hyaenodonts. Carnassials are also known in other flesh-eating mammal clades, such as in the extinct bat Necromantis , as well as highly unrelated taxa such as the flesh-eating marsupial Thylacoleo .

Different molars were involved in the two major groups of creodonts. In the Oxyaenidae, M1 and m2 that form the carnassials. Among the hyaenodontids, it is M2 and m3. Unlike most modern carnivorans, in which the carnassials are the sole shearing teeth, other creodont molars have a subordinate shearing functions. [25] The difference in which teeth form the carnassials is a major argument for the polyphyly of Creodonta.

Comparison of Carnivoran and Creodont Carnassials.png
Comparison of carnassial teeth of wolf and typical hyaenodontid and oxyaenid
Teeth of Middle Eocene Bridger Basin Creodonts.png
Upper teeth of creodonts from Middle Eocene Bridger Basin, Wyoming
Teeth of Creodonts.png
Sinopa fossils: (1) Right upper cheek teeth, P2-M2; (2) Left ramus of mandible (p2-m2); (3) Right ramus of mandible (c-m2)

Cranium

Creodonts had long, narrow skulls with small brains. The skull narrowed considerably behind the eyes, producing a distinct splanchnocranium and neurocranium segments of the cranium. They had large sagittal crests and usually broad mastoids (which were probably derived features for the group). [19] Many creodonts had proportionately large heads. [18] In basal forms, the auditory bullae was not ossified. Generally the temporal fossae were very broad. [19]

Machaeroides eothen.JPG
Skull of oxyaenid Machaeroides eothen
Sarkastodon scull AMNH.jpg
Lateral outline and front view of skull of Sarkastodon mongoliensis
SarkastodonDB.jpg
Head of Sarkastodon mongoliensis
Apterodon macrognathus skull2.svg
Lateral (A) and dorsal (B) views of the skull of the hyaenodontid Apterodon macrognathus by Henry Fairfield Osborn
Hyaenodon horridus skull.jpg
Skull of Hyaenodon horridus
Limnocyon verus 2.jpg
Skull of Limnocyon verus

Postcranial skeleton

Creodonts had generalized postcranial skeletons. Their limbs were mesaxonic (with the axis of the foot provided by the middle of their five digits). Their method of locomotion ranged from plantigrade to digitigrade. The terminal phalanges were fused claws. [19]

Within oxyaenids, many taxa within the family remained adaptations. Hyaenodonts, on the other hand, showed transition from plantigrade to digitigrade throughout their evolutionary history. [41] [42]

Patriofelis-mount.jpg
Mount of oxyaenid Patriofelis ferox from the American Museum of Natural History
Patriofelis22DB.jpg
Reconstruction of Patriofelis ferox
Sinopa from Matthew.png
Mounted skeleton of the hyaenodontid Sinopa rapax from Bridger Basin

Size

Creodonts ranged in size from the size of a small cat to the 800 kilograms (1,800 lb) Sarkastodon , however this has been considered to possibly be an overestimate. [20] Its dimensions were described as 50% greater than the Patriofelis to which it bore many similarities. [43] Other large creodonts include Megistotherium , Hyainailouros , and Simbakubwa . [44] [45] [20] [46] The largest North American hyaenodonta, as well as creodont, was Hemipsalodon , which could’ve weighed 430–760 kilograms (950–1,680 lb). [47]

The larger oxyaenids, however, were not known until late in the Paleocene which saw a radiation of oxyaenids, [17] such as the puma-sized Dipsalidictis and the probably bone-crushing scavenger Dipsalodon . [48] On the other hand, the largest known hyaenodonts didn’t appear until the early Miocene. [44]

Certain creodonts ( Arfia , Prolimnocyon and Palaeonictis ) seem to have experienced the dwarfing phenomenon during the Paleocene-Eocene Thermal Maximum seen in other mammal genera. A proposed explanation for this phenomenon is that the increased carbon dioxide levels in the atmosphere directly affected carnivores through increased temperature and aridity and also indirectly affected them by reducing the size of their herbivorous prey through the same selective pressures. [49]

Biology

Diet and feeding

Early creodonts (both oxyaenids and hyaenodontids) displayed the tribosphenic molars common for basal therians. Small forms had somewhat strong postmetacrista-metastellar crests [50] suggesting that they were probably opportunistic feeders, eating such things as eggs, birds, small mammals, insects and possibly plant matter as well, [19] possibly like extant viverrids. [38] Larger forms had greater shearing capacity and the capacity increased over time. Arfia, one of the most common carnivorous mammals in early Eocene North America, developed a more open trigonid on M3 over the course of the Early Eocene, increasing the shearing ability of the carnassials. [50] A similar development can be seen by comparing Oxyaena , Prototomus and Limnocyon with the smaller, more generalized feeders among the creodonts. [19] However, however some of the last oxyaenids, such as Patriofelis and Machaeroidinae, showed adaptations towards hypercarnivory. [51] [52] Similarly, some of the youngest hyaenodonts in the Miocene, have shown extreme specialization towards hypercarnivory. [53] [54]

Extinction

Creodonts, as a whole, began to experience a decline in the Eocene, [55] with oxyaenids going extinct during the middle Eocene. [56] [57] Some experts suggested their extinction was due to competition with nimravids, [57] however other experts disagree with this hypothesis. [58] [56] The excellent fossil records within North America show that oxyaenids were declining prior to the appearance of replacement taxa such as nimravids. [59] In addition, the last records of machaeroidines predate the earliest records of nimravids. [57] [60] Instead, climatic changes towards the late Eocene played a role in their extinction, as during the towards the late Eocene the climate of the planet began to cooling, resulting in more arid, open environments. [59] [56] Because of their low mobility, oxyaenids went extinct because they weren’t adapted towards the temperate, open forest habitats. [56]

Hyaenodonts, the last group of creodonts, also experienced a decline in Eurasia and North America during the Eocene, [58] in North America only a few species of Hyaenodon persisted into the Oligocene. [55] During the Miocene, Afro-Arabia hyaenodonts experienced a massive decline after the early Miocene and went extinct by the late Miocene. [54] Many experts have argued that the extinction of hyaenodonts was due to competition with carnivorans. [54] [55] [58] [44] [61] [62] Some experts argued that carnivorans outcompeted hyaenodonts in mesocarnivore niches which forced hyaenodonts to become more specialized hypercarnivores. [55] [54] Lang et al. (2021) suggested carnivorans played a role in their extinction of hyaenodonts due to the adaptive potential of their carnassials. [61] Serio et al. (2024) found that creodont disparity showed a degree of morphological differentiations until the middle Eocene, when disparity from carnivorans increased. They argued this suggests that carnivorans competitively replaced hyaenodonts. [62] Borths and Stevens (2019) suggested that large hyainailourines may have went extinct because of loss of diversity of large herbivores and competition with gregarious carnivorans that had larger, more complex brains. [44]

However, not all experts agree that carnivorans played a role in the extinction of hyaenodonts. [63] [64] [65] Christison et al. (2021) conducted a study on hyaenodonts, and carnivoran dietary niches in the Cypress Hills Formation. Their results showed that only the smallest hyaenodonts in the faunal assemblage had any significant dietary overlap with smaller carnivorans, while larger carnivorans and hyaenodonts were extremely distinct from one another, with the study concluding that it was highly unlikely that the extinction of hyaenodonts in North America can be attributed to competition with carnivorans. Instead, they argued the extinction of hyaenodonts may have been because of the preferences of large prey, such as brontotheres, in addition to the inability to adapt to more open environments due to their relatively short legs. [63]

References

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  2. ↑ Borths, Matthew R.; Stevens, Nancy J. (2017). "The first hyaenodont from the late Oligocene Nsungwe Formation of Tanzania: Paleoecological insights into the Paleogene-Neogene carnivore transition". PLOS ONE. 12 (10) e0185301. Bibcode:2017PLoSO..1285301B. doi: 10.1371/journal.pone.0185301 . PMC   5636082 . PMID   29020030.
  3. 1 2 Cope, Edward Drinker (1875). "On the Supposed Carnivora of the Eocene of the Rocky Mountains". Proceedings of the Academy of Natural Sciences of Philadelphia. 27: 444–449.
  4. ↑ T. C. Winkler (1893.) "De Gewervelde Dieren van Het Verleden." Palaeontologische Studiën in Telyer's Museum 1-291
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  36. ↑ Matthew, William Diller; Granger, Walter (1915). "A revision of the Lower Eocene Wasatch and Wind River faunas". Bulletin of the American Museum of Natural History. 34: 4–103. hdl:2246/1373. In this paper the authors rename Marsh's Limnocyon protenus as Didymictis protenus and include it among the miacids
  37. ↑ Wortman, J. Lewis (July 1902). "Studies of Eocene Mammalia in the Marsh Collection, Peabody Museum". American Journal of Science. pp. 17–23.
  38. 1 2 Denison, Robert Howland (October 1937). "The Broad-Skulled Pseudocreodi". Annals of the New York Academy of Sciences. 37 (1): 163–255. Bibcode:1937NYASA..37..163D. doi:10.1111/j.1749-6632.1937.tb55483.x. S2CID   129936019. (Subscription or payment required.)
  39. ↑ Feldhamer, George A.; Drickamer, Lee C.; Vessey, Stephen H.; Merritt, Joseph F.; Krajewski, Carey (2015). Mammalogy: Adaptation, Diversity, Ecology. Baltimore: Johns Hopkins University Press. p.  356. ISBN   978-0-8018-8695-9.
  40. ↑ Turner, Alan; Antón, Mauricio (2004). Evolving Eden: An Illustrated Guide to the Evolution of the African Large-Mammal Fauna. New York: Columbia University Press. p. 77. ISBN   978-0-231-11944-3.
  41. ↑ Solé, Floréal; Amson, Eli; Borths, Matthew; Vidalenc, Dominique; Morlo, Michael; Bastl, Katharina (2015-09-23). Friedman, Matt (ed.). "A New Large Hyainailourine from the Bartonian of Europe and Its Bearings on the Evolution and Ecology of Massive Hyaenodonts (Mammalia)". PLOS ONE. 10 (9) e0135698. doi: 10.1371/journal.pone.0135698 . ISSN   1932-6203. PMC   4580617 . PMID   26398622.
  42. ↑ Borths, M. R.; Stevens, N. J. (2019). "Simbakubwa kutokaafrika, gen. et sp. nov. (Hyainailourinae, Hyaenodonta, 'Creodonta,' Mammalia), a gigantic carnivore from the earliest Miocene of Kenya" . Journal of Vertebrate Paleontology. 39 (1) e1570222. Bibcode:2019JVPal..39E0222B. doi:10.1080/02724634.2019.1570222. S2CID   145972918.
  43. ↑ Granger, Walter (April 21, 1938). "A Giant oxyaenid from the Upper Eocene of Mongolia" (PDF). American Museum Novitates. pp. 1–5.
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