Miomachairodus

Miomachairodus is an extinct genus of large saber-toothed cats of the subfamily Machairodontinae. It is known from Miocene-age fossils in China and Turkey and persisted until the Late Miocene (early Vallesian).^[1] Miomachairodus may have coexisted with the barbourofelid Barbourofelis in its North American range.

Fossil record

Fossils have been found in the Vallesian-age Bahe Formation in Shaanxi, China, and Yeni Eskihisar in Anatolia. This Turkish site is of Miocene age and is well known for its pollen studies.^[2]

Morphology

Miomachairodus was generally small, and the canines already began to show the flattening that would soon advance into the distinct "saber-tooth" design of the more advanced machairodonts. Miomachairodus was not the ancestor to all machairodonts; this title most likely rested with Pseudaelurus. This genus is thought to be ancestral to both machairodontinae and felini, the clades of saber-toothed and conical-toothed (modern) felids.

Comparison to Relatives

the knobby skull of Homotherium, distinctly Homotheriini, resembling Machairodus but with shorter canines and a mandible that is more stout.

A sister taxon of Miomachairodus is the more well known Machairodus. Of the several species of widespread Machairodus, M. giganteus is probably the most well known. The fossil record is well established in its wide range of Eurasia. Pseudaelurus ogygia stood at 58 cm at the shoulder,^[3] and its ancestor Miomachairodus advances little in size, but between Miomachairodus and its descendants of the tribe Homotherini (one of three machairodont tribes; including Machairodus and Homotherium), they grow to massive sizes, surpassing the modern lion. Most Machairodus species reach 120 cm shoulder height, and Homotherium reaches 110 cm, when compared to the 95 cm shoulder height of the modern Bengal tiger. Machairodus rivals in size among the cats only Smilodon populator of South American Pleistocene.

The Machairodus was a massive creature with a tail of medium length that did not reach the ground while standing, large ribcage, stout body, and especially strong forequarters. Its skull was long, canines of moderate length for a machairodont, making it a very good representative of the group. Sexual dimorphism displayed itself in males that were much larger and, unusual for carnivores, the main killing apparatus, the canines, were shaped differently and were surely not capable of exactly the same method of killing. Male canines were shorter and much more stout, while females were long and thin. The question of the specific usage of the canines is still in limbo, and Machairodus offers a good deal of suggestion as to how they were used, giving support to the usually inadequate claim that they were used for show, not for killing, though the hypothesis is still generally discarded. Machairodus was also in the leagues of the extreme carnivores, or hypercarnivores who could consume little but meat, and generally fresh meat at that, so scavenging was usually out of the range of means of sustenance. It has been thought that Machairodus hunted in groups, along with Homotherium, who are strangely linked to juvenile Mammoth remains.

Ecology

Bahe Formation

Species that Miomachairodus would probably have encountered in this region of China would have certainly been reptiles such as Emydidae and Testudo. Both are turtles and Miomachairodus was not suited for killing them in any way. Only species with exceptionally strong jaw bites, such as the modern Crocuta, the spotted hyena of Africa, could have torn open the shell to retrieve the meat on the inside. These species would have been left alone. Another unwelcoming creature would have been Erinaceus. Members of this genus still live today, and we generally call them hedgehogs. Most species can, but will not, eat them for risk of injury caused by the spines, which are, as with porcupines, modified hair, but nevertheless painful and possibly opening the animal up to infection from an open sore. The rhinocerid Dicerorhinus was also located in this region at this time. Members of this species still exist, though may not for much longer: the remaining member is the critically endangered Sumatran Rhinoceros, or Asian one-horned Rhino as it is technically called. During the Miocene, this genus was likely to be small, but probably still too much of a feat for a lone Miomachairodus, though if it worked in groups as its descendants showed, it might have been able to take the young or the injured. Hipparion was probably prime prey for Miomachairodus at this locality. It was small and light-footed, and though the morphology of Miomachairodus suggests it did not partake on long chases, it probably used the cover of trees, foliage, and shadows during dusk and at night to creep up on herds of Hipparion and capture one in the short struggle that is typical of felines. The suid Chleuastochoerus was again probably another very good candidate for prey of Miomachairodus. Even modern pigs are primitive in form, and Miocene Cheleuastochoerus looked much like the modern pigs we consume in the modern world in their low forms, two toes per foot, and lack of extreme defense besides tusks that can kill if the predator is too inexperienced or lame to subdue the animal quickly. The giraffid Paleotragus looked much like the modern okapi, Okapia johnstoni. Paleotragus was a common prey for many predators of the Miocene, and its descendant lineage which became the Okapia did not change much and as felines took to the adaptive radiation of later eras, the lineage became common prey for felines living in the region it inhabited. During the Miocene, there were two species of Paleotragus: P. primaevus, who had no ossicones and was smaller, at just under two meters at the shoulder, and P. germaini who bore the ossicones later giraffe and okapi males would bear. Miomachairodus might have been too small to take on Paleotragus alone, but if they acquired the adaptation of grouping, it was likely that this animal, too, fell on their list of prey.

Yeni Eckihisar

The other predators noted here, including the large hyaenids Thalassictis and Proticititherium,^[2] probably meant that here, Miomachairodus was increasingly nocturnal to avoid its diurnal relatives. The fauna was likely widely different, and behavioral aspects might have been noted. Solitary lives could be inferred because smaller prey must have been taken, and as smaller prey was taken, each individual needed more land to support itself and the population was likely more spread out than it was in the Bahe region. It probably preyed more on amphibians and small reptiles, along with small rodents and birds, not often taking the larger fauna that would have been seen in the Bahe regions.

Dinocrocuta of the Greek localities.

Ouranopithecus of the Greek localities.

Greece

Though none of their fossil beds have provided Miomachairodus, the region of Greece during the middle Miocene is close to Turkey and displays a similar habitat. Aliveri (Evia island) in Greece shows a rich micromammalian fauna but with few large mammals. The island of Chios is known for its middle Miocene faunas from the beginning of the 1940s when the first large mammals have been described from a clay pit near Thymiana village. Of the two Vallesian periods (early, or MN9, and late, or MN10) only the late is represented by the formations of Greece.

Because of the Greek fossil beds' proximity with those in Turkey providing Miomachairodus fossils, inference of similar ecosystems and species to some degree may be taken for the purposes of comparison when good fossil records are absent. The fossil beds in Greece during the middle and late Miocene uncovered more hyaenids, such as the large Dinocrocuta^[4] who probably would have forced Miomachairodus, if it existed in this region, back into a nighttime hunting style and avoidance of direct competition. Here, the Miocene primate Mesopithecus of the family Cercopithecidae, or the old world monkeys, of which there are plenty of members alive today, from Papio, the baboon, to Semnopithecus including langurs. These primates would have been ideal for hunting of this semi-arboreal forest machairodont, and whether alone or in groups, hiding from Dinocrocuta or dealing well with the large carnivore and playing a more active role as a dominate predator in the ecosystem, it would be likely that Miomachairodus would have hunted Mesopithecus. The rhinocerid Dicerorhinus (whose local fossils might mistakenly been identified, actually being the first appearance of Brachypotherium in Europe) was probably not a good candidate for the lone Miomachairodus, although good prey for Dinocrocuta. The small rodent Pogonomys was present in this region and would likely have been small prey for Miomachairodus. The early hominid Ouranopithecus appeared briefly in this region during the late Miocene and could have been prey for Miomachairodus and Dinocrocuta.

Lifestyle

Since the fossil record is so scarce for this species, it is hard to tell exactly what this animal would have acted like or how it might have hunted. With species like Smilodon fatalis, it is relatively easy to at least make hypothesis about social life, to infer that the presence of terrible injuries that healed indicated hunting large animals and a strong social structure that cared for the wounded. With this species that had no modern descendants, the inferences on its life are at best guesses based on more well known extinct relatives such as the Homotheriini tribe.

Behavior

As a felid, it probably experienced some degree of sexual dimorphism, most likely with the males being larger. It would have been territorial and might have sprayed its range with urine like modern cats, telling the marker's age, gender, and if it is a female, estrus cycle. Fighting would have been limited, but unlike many other animals, there would probably have been no elaborate fighting ritual: a fight would consist of blood actually being drawn and injuries that, if one was ganged up on as seen in the modern lion, could be fatal. But these fights, for that reason, would be scarce and would probably be concerned with territorial disputes and mating rights. Biting with the incisors could have been suitable, but the canines were growing more fragile, and a rough jerk from the opponent while being bitten could break a canine off completely, as seen with Smilodon and Machairodus, so this was a risk probably not taken. Vocalizations would have been limited, and the main form of communicating would have been scent left in markers, and possibly visual if two came into contact. Motions of the tail and ears along with general body positioning would have been utilized for these purposes.

Breeding

Most feline species have young in a select period of time if the seasons are defined enough, but if this animal lived in a warm, forested environment when food was available year round, it might have had offspring at any time in the year. Modern feline cubs of the larger species, specifically Panthera are kicked out between one and two years of age, but there is recent evidence that long teeth that the machairodonts were known for took longer to develop and species such as Barbourofelis, Smilodon, and especially Machairodus, and cubs might have had to stay with their mothers until three, possibly even four years of age, depending on the individual mother's tolerance or readiness to mate again. Numerous Machairodus skulls are found with mature canines still erupting, and until then, they would be unable to hunt for themselves. If the start of long sabres for Miomachairodus meant a longer time until cubs were independent, they might be staying with their mothers for a full year longer than modern cats.

Hunting

The specialization of the dentition of Miomachairodus would have meant a limited number of prey items. Fewer teeth that were primarily slicing premolars and not crushing molars meant that grass or anything with cellulose would not have been on the menu. The specialization of diet, from omnivore eating mostly meat, to obligatory carnivore eating almost nothing but meat, takes its toll on an individual. Certain machairodont groups crossed the boundary from normal obligatory carnivore, including all of today's cats, to the category of hypercarnivore. Machairodonts such as the Homotheriini group are placed in this league because their dentition denies them eating nothing but meat, and probably fresh, so scavenging is unlikely for Miomachairodus. This increasing dependency on meat meant that hunting would occupy more time and an any injury could have led to an inability to hunt and starvation.

References

• Jordi Augusti: Mammoths, Sabertooths and Hominids 65 Million Years of Mammalian Evolution in Europe, Columbia University Press, 2002. ISBN 0-231-11640-3
• Lars W. van den Hoek Ostende, Michael Morlo & Doris Nagel (July 2006). "Fossils explained 52 Majestic killers: the sabre-toothed cats". Geology Today 22 (4): 150. doi:10.1111/j.1365-2451.2006.00572.x. 

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