Rhizosmilodon
| Rhizosmilodon | ||||||||||||
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Jaw parts of Rhizosmilodon fiteae |
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| Temporal occurrence | ||||||||||||
| Lower Pliocene | ||||||||||||
| approx. 5 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Rhizosmilodon | ||||||||||||
| Wallace & Hulbert , 2013 | ||||||||||||
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Rhizosmilodon is a genus of the extinct saber-toothed cats (Machairodontinae) that has so far only been documented by individual fragments of the lower jaw and parts of the limbs of the species Rhizosmilodon fiteae from Florida . The fossils come from a phosphate mine in the Upper Bone Valley Formation near Fort Meade in Florida. They are assigned to the so-called Palmetto Fauna or Whidden Creek Local Fauna, which lived in what is now central Florida about five million years ago.
Rhizosmilodon , like other saber-toothed cats, was a carnivore that likely actively hunted and killed its prey. It was probably a small to medium-sized mammal, with a range of prey similar to that of the puma . The habitat in central Florida likely consisted of floodplain and floodplain areas with a mosaic of forests with closed canopies, more open woodland and open grassy areas.
The first bones of the species were assigned to the species Megantereon hesperus as the first finds on the American double continent in 1983 . In 2013, based on new finds, the assignment was revised and the first scientific description of Rhizosmilodon fiteae as a separate species within the likewise new genus Rhizosmilodon .
features
The description of Rhizosmilodon fiteae as an independent species was based on several dentition fragments, and the species was also assigned the remains of several limb bones from the same site.
Features of the teeth and dentition fragments
The holotype UF 124634 (UF stands for Florida Museum of Natural History , University of Florida , Gainesville , and names the storage location of the fossils) is a part of the right lower jaw with preserved symphysis as well as the canine tooth (C1) and the first molar (M1); between these are the tooth sockets (alveoli) of the premolars P3 and P4, the teeth themselves are missing. A fragment of the left lower jaw with preserved premolars P3 and P4 and the molar M1 was selected as the paratype UF 135626. In addition to these two lower jaw parts, other finds from the same site were assigned to the species. These are mainly a few other fragments of the lower jaw with teeth and partially preserved symphysis and tooth fan parts (UF 22890, UF 223796, UF 212381, UF 272337).
Numerous features of the existing teeth and some of the lower jaw bones are given as diagnostic features of the species on the basis of the fragments available. The symphysis of the lower jaw is almost vertical and the lower jaw has a slight indentation to adapt to the greatly elongated canines of the upper jaw. The incisors are small but not lying. At least the lower canines are large, but clearly flattened on the sides; they have moderate, rounded teeth. The second premolar (P2) is missing, P3 is elongated, but only about two thirds as large as the last premolar (P4), which is enlarged like a blade; P3 and P4 are not connected and are not in a line and P4 is not in a direct line with the first molar (M1). The arrangement of the cusps on the tooth crowns of the premolars and molars appears typical . For example, P3 lacks the front cusp and the rear cusp is only slightly formed. The front cusp at P4 is also small. The first molar is as strong as that of Smilodon .
Features of the limb bones
In addition to the described parts of the jaw, several bones and parts of the limbs were assigned to the species based on their size, although they were not found directly with the jaw fragments. It is a full left femur (UF 133938), the lower ( distal ) end of a right femur (UF 65686), the distal portion of a left spoke (UF 123836), a complete left shinbone (tibia) (UF 133939) and the upper ( proximal ) piece of a right tibia (UF 212380).
For the first description of Rhizosmilodon fiteae , only the two thigh bones were described in more detail. The pronounced elongation of the middle part of the joint gnar (epicondyles) and the very straight pectoral ridge, which does not fit the typically curved deltoid ridge of most Panthera species and allows an assignment to the saber-toothed cats, are considered typical of the species. Further details of the bones such as the curved shaft and the overall strong structure of the bones as well as the structure of the articular knots and foramina suggest a relationship to Smilodon . The existence of another, as yet undescribed, closely related species besides Rhizosmilodon fiteae from the area to which these bones could belong is assumed to be improbable.
Feature reconstruction
Although only a few skeletal components are known of Rhizosmilodon fiteae , a relatively well-founded reconstruction of the entire animal is possible. In this case, the paleontologists benefit greatly from the species that are classified as close relatives, i.e. above all from known saber-toothed cats and also from cats of similar size and stature living today. By comparing characteristics, many characteristics can be assumed as plesiomorphies , i.e. characteristics already present in the common parent species - including above all the posture and design of the limbs as well as the general body structure and posture.
On the basis of the existing thigh and shin bones, it was possible to extrapolate the weight of the cat by comparing the bones with those of cats living and extinct today. According to this estimate, Rhizosmilodon fiteae reached a weight of about 56 to 85 kilograms and thus corresponded to a puma ( Puma concolor ) or jaguar ( Panthera onca ) living today . The size also overlaps with the estimates for the extinct smaller Smilodon gracilis .
Characteristics compared with other species
Since Rhizosmilodon fiteae was described as an independent species and genus, the existing and reconstructed characteristics had to be compared with other potentially closely related species and genera in the first description in order to prove the independence and derive a phylogenetic classification.
The assignment to the Smilodontini, to which the genera Smilodon and Megantereon are placed in addition to Rhizosmilodon , is based on the perforation of the cutting surfaces of the canines, which affects all teeth in representatives of the Machairodontini. The vertical symphysis of the mandible as well as the position of the teeth P3, P4 and M1 to one another as well as the formation of the individual teeth enable assignment to this relationship. However , Rhizosmilodon differs from the genera Smilodon and Megantereon by its own characteristics. These are also specific tooth features such as the specifically moderate and rounded shape of the teeth on the lower canine. This is also present in Smilodon gracilis , but much more pronounced in other species of Smilodon ( Smilodon fatalis , Smilodon popular ); on the other hand, Megantereon has no perforation and has probably been lost. The indentation in the lower jaw as an adaptation to the enlarged canines of the upper jaw is only slightly pronounced compared to Smilodon . Further features with clear differences concern the formation of the tooth cusps on the premolars and molars.
Location and chronological order
The fossils for the first description come from a phosphate mine near Fort Meade in Polk County in central Florida, other finds from the adjacent regions in Hardee and Hillsborough Counties . The fossil-bearing layers of this region are assigned to the Upper Bone Valley Formation in Florida , the animals contained in the so-called Palmetto fauna and the Whidden Creek Local Fauna. This is chronologically classified in the late Hemphillium , a period of the North American mammal fauna that overlaps with the early Pliocene , the Zancleum . The fossils contained in this layer are estimated to be around five million years old.
While most of the fossil remains of vertebrates in the Upper Bone Valley Formation are collected at isolated sites and a targeted search for further fossils is not worthwhile, the mine of Gardinier Inc. near Fort Meade is an exception. Since 1989, thousands have been able to use this mine Vertebrate fossils are found in a layer only 0.8 meters thick over an area of about 2000 square meters, the largest known concentration of fossils in the area.
Way of life and paleoecology
No data are available on the way of life and ecology of the species, however, similar to other fossil big cats, it can be reconstructed by comparing it with recent species. Like other saber-toothed cats, Rhizosmilodon will have been a carnivore, likely actively hunting and killing its prey. According to its size, these were probably small to medium-sized mammals, the range of prey was similar to that of the recent puma ( Puma concolor ). It is possible that Rhizosmilodon, due to its comparatively small size, could climb trees and hide its prey from larger predators or packs.
The composition of the palmetto fauna suggests that the species is found on the seashore. In addition to terrestrial vertebrates, the fossil layers also contain numerous fossils of marine life such as cartilaginous fish, bony fish, turtles and whales. The habitat in Central Florida's Bone Valley was likely comprised of humid floodplain and floodplain areas, the vegetation of which consisted of a mosaic of closed-canopy forests, more open woodland, and open grassy areas. In total, fossils of 33 different mammal species were identified in the Whidden Creek Local Fauna, including 11 species of predator. There are around 900 fossils, around five percent of which are predators. In addition to Rhizosmilodon with Machairodus coloradensis, another saber-toothed cat, Lynx rexroadensis and an unconfirmed representative of the genus Pseudaelurus , dogs ( Borophagus , Carpocyon , Eucyon and Vulpes ), bears ( Agriotherium , Plionarctos ) and small bears , martens and scunks are among the cats . The rest of the mammal fossils come mainly from odd-toed ungulates (approx. 33%), even-toed ungulates (approx. 37%) and whales (approx. 16%). Overall, the Palmetta fauna is one of the most species-rich ecosystems in North America at this time, with the large number of larger herbivores being particularly noteworthy.
Taxonomy
Find history and effects on the system
The first known fossil of a comparatively small saber-toothed cat from the Palmetto fauna, a mandibular fragment (UF 22890), was used in 1983 to assign the find to Megantereon hesperus . The fossil was also assigned to the genus Megantereon as the oldest find worldwide and based on this description, the genus, which otherwise occurs mainly in Eurasia and Africa, was founded in North America.
Megantereon hesperus was described by Gazin in 1933 as Machairodus hesperus on the basis of a right mandibular fragment from Twin Falls County in Idaho and assigned to the genus Megantereon in 1970 by Schultz and Martin . Through the discovery in Florida, the thesis was developed that the genus, contrary to the previously valid Eurasian or African origin, developed in North America and that Megantereon hesperus is the oldest representative of the same. According to this thesis, it was assumed from North America that the genus spread to Eurasia and Africa about 3.5 million years ago in the early Villa Franchian in the Middle Pliocene, which corresponds to the oldest occurrences of the genus in Europe in Les Etouaires , France. Some later editors adopted these theses, including Martinez-Navarro & Palmqvist (1995) in an investigation of the fossils of Megantereon whitei in Spain.
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Systematics of the saber-tooth cats according to Berta & Galiano 1983
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The assignment of the North American fossils from Florida to the genus Megantereon , however, led to confusion and criticism even before the description of Rhizosmilodon . The paleontologist Alan H. Turner questioned the assignment in 1987 and suggested alternatively the assignment to a still unknown species of the widespread genus Dinofelis , which is no longer part of the saber-toothed cats, or to the more original genus Paramachairodus . Even John Paul Hodnett favored a classification of this fossil in the genus paramachairodus because they the Fund he describes a paramachairodus resembled from northern Arizona. At the same time, he argued with his find also for an origin of the Smilodontini in North America by assigning Paramachairodus to the tribe. Wallace & Hulbert 2013, in their first description of Rhizosmilodon as an answer to Hodnett, very clearly show the differences between the Paramachairodus and Rhizosmilodon he described . Webb et al. (2008) also show that the description as Machairodus cannot be correct and show that, according to newly found material, it must be a species related to Smilodon and Machairodus , but different from both. One of the authors, Richard C. Hulbert, was one of the first to describe Rhizosmilodon .
Current system
In 2013 there was a revision of the assignment and the first scientific description of Rhizosmilodon fiteae as a separate species within the likewise new genus Rhizosmilodon on the basis of a lower jaw found in 1990 and other bones that are assigned to the species.
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Phylogenetic systematics of saber-tooth cats according to Wallace & Hulbert 2013
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According to the first description, the genus Rhizosmilodon is classified at the base of the Smilodontini tribe on the basis of the existing characteristics and compared there with a taxon consisting of the genera Smilodon and Megantereon . The system results from an analysis of a matrix of characteristics of known saber-tooth cats. With an age of about five million years, the fossils represent the oldest fossils of the tribe, therefore Rhizosmilodon lived before the other representatives of the Smilodontini.
Concrete comparisons of features primarily concern the characteristics of individual teeth. In the Rhizosmilodon , for example, as the first representative of the Smilodontini, the teeth on the canines were moderate and rounded, as was the case with the earliest and smallest representative of the Smilodon genus , Smilodon gracilis . Within the genus it was expressed in Smilodon fatalis and Smilodon popular to a clear and sharp perforation, while it was lost in the genus Megantereon . The indentation of the lower jaw as an adaptation to the enlarged canines of the upper jaw is clear compared to more original species of the taxon such as Promegantereon or Paramachaerodus and similarly strong as in Machairodus , whose enlarged canines were flattened; Compared to Smilodon and Megantereon with strong and very large upper canines, however, it is only slightly pronounced.
This development would mean that the Smilodontini tribe and the genera originated in North America, where all three genera were able to develop and later immigrated from Megantereon to Eurasia and Africa.
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Alternative systematics of the saber-tooth cats according to Wallace & Hulbert 2013
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In addition to the hypothesis preferred by the authors , according to which rhizosmilodon faces a common taxon of smilodon and megantereon as a sister species, it is alternatively assumed that rhizosmilodon and smilodon form a common taxon and megantereon faces this. The formation of the lower jaw indentation and the imperforate canines could stand for such a hypothesis. In this case, the emergence of the Smilodontini tribe with Megantereon as the most original genus in Eurasia or Africa and a double immigration to North America would be likely.
Naming
The scientific name of the genus Rhizosmilodon is based on a combination of the Greek word rhizo , which means 'root', and the already existing generic name Smilodon . In the naming as the "root of the Smilodon", the position of the genus at the base of the Smilodontini and thus the origin of the known genus Smilodon is reflected by the first description .
The species name Rhizosmilodon fiteae, the only previously described species within the genus, is derived from the name of the paleontologist Barbara Fite, who donated the paratype from her private collection.
supporting documents
- ↑ a b c d e f g h i j k l m n o p q r s t u v w Steven C. Wallace, Richard C. Hulbert Jr .: A New Machairodont from the Palmetto Fauna (Early Pliocene) of Florida, with Comments on the Origin of the Smilodontini (Mammalia, Carnivora, Felidae). In: PLoS One. 8 (3), 2013, p. E56173. doi: 10.1371 / journal.pone.0056173
- ↑ Rhizosmilodon fiteae . - Profile on the Florida Museum of Natural History website; Retrieved September 29, 2013.
- ↑ Tanya Lewis: 5-Million-Year-Old Saber-Toothed Cat Fossil Discovered. LiveScience, March 15, 2013. Accessed September 29, 2013.
- ↑ Bruce J. MacFadden, Nikos Solounias, Thure E. Cerling: Ancient Diets, Ecology, and Extinction of 5-Million-Year-Old Horses from Florida. In: Science. 283 (5403), February 5, 1999, pp. 824-827. doi: 10.1126 / science.283.5403.824
- ^ A b c d S. David Webb, Richard C. Hulbert Jr., Gary S. Morgan, Helen F. Evans: Terrestrial mammals of the Palmetto Fauna (early Pliocene, latest Hemphillian) from the Central Florida Phosphate District. In: X. Wang, LG Barnes (Ed.): Geology and Vertebrate Paleontology of Western and Southern North America. In: Natural History Museum of Los Angeles County Science Series. No. 41, 2008, pp. 293-312.
- ↑ a b c d Annalisa Berta. Henry Galiano: Megantereon hesperus from the late Hemphillian of Florida with remarks on the phylogenetic relationships of machairodonts (Mammalia, Felidae, Machairodontinae). In: Journal of Paleontology. 57, 1983, pp. 892-899. ( Abstract , JSTOR )
- ↑ Alan Turner: Megantereon cultridens (Cuvier) (Mammalia, Felidae, Machairodontinae) from the Pliocene-Pleistocene deposits of Africa and Eurasia, with comments on dispersal and the Possibility of a New World origin. In: Journal of Paleontology. 61, 1987, pp. 1256-1268. ( JSTOR )
- ↑ John-Paul Hodnett: A machairodont felid (Mammalia; Carnivora; Felidae) from the latest Hemphillian (late Miocene / early Pliocene) Bidahochi Formation, northeastern Arizona. In: PaleoBios. 29, 2010, pp. 76-91.
- ^ Alan Turner, Mauricio Antón: The big cats and their fossil relatives. Columbia University Press, New York 1997, p. 57.
literature
- Steven C. Wallace, Richard C. Hulbert Jr .: A New Machairodont from the Palmetto Fauna (Early Pliocene) of Florida, with Comments on the Origin of the Smilodontini (Mammalia, Carnivora, Felidae). In: PLoS One. 8 (3), 2013, p. E56173. doi: 10.1371 / journal.pone.0056173
- Annalisa Berta, Henry Galiano: Megantereon hesperus from the late Hemphillian of Florida with remarks on the phylogenetic relationships of machairodonts (Mammalia, Felidae, Machairodontinae). In: Journal of Paleontology. 57, 1983, pp. 892-899. ( Abstract , JSTOR )
Web links
- Rhizosmilodon fiteae . - Profile on the Florida Museum of Natural History website
- Rhizosmilodon fiteae • A New Machairodont from the Palmetto Fauna (Early Pliocene) of Florida, with Comments on the Origin of the Smilodontini (Mammalia, Carnivora, Felidae) . - Blog post in the blog "Species New to Science"
- Tanya Lewis: 5-Million-Year-Old Saber-Toothed Cat Fossil Discovered. LiveScience, March 15, 2013. Accessed September 29, 2013.
