Homunculus (genus)

from Wikipedia, the free encyclopedia
Homunculus
Lower jaw of Homunculus (holotype, lost)

Lower jaw of Homunculus ( holotype , lost)

Temporal occurrence
Lower to Middle Miocene
17.4 to 16.3 million years
Locations
Systematics
Primates (Primates)
Dry- nosed primates (Haplorrhini)
Monkey (anthropoidea)
New World Monkey (Platyrrhini)
incertae sedis
Homunculus
Scientific name
Homunculus
Ameghino , 1891

Homunculus is an extinct genus of primates from the New World monkey group . She lived in the transition from the Lower to the Middle Miocene 18 to 16 million years ago in the southern part of South America . All previous fossil remains wererecoveredin the Santa Cruz Formation in Patagonia , the rock unit represents the southernmost region of discovery of a monkey on the continent. The material consists of skulls, remains of teeth and individual parts of the limbs. They belong to a medium-sized representative of the New World monkey, which differs from today's species by individual primitive features. The animals had a relatively small brain and their hearing was well developed. The males and females may have formed small groups. Sub- tropical forests or those that were influenced by seasonal changesserved as habitat. In these the animals moved by climbing trees and doing their activities in daylight. The diet consisted of hard seeds and soft leaves and fruits . The first finds came to light at the end of the 19th century, and shortly afterwards the genus was scientifically introduced. Two species are currently recognized, but the fossil record known so far suggests more. There is a controversial discussion aboutthe systematic position, but it also includes other early New World monkeys.

features

Homunculus was a medium-sized representative of the New World monkey, of which mainly skull material, but also individual parts of the musculoskeletal system are known. The skull was around 6.6 cm long and 2.4 to 2.8 cm wide, and the height of the facial area below the eyes varied from just 1.0 to 1.2 cm. The rostrum was more preferred ( prognath ) in Homunculus than in today's New World monkeys, which resulted in a more expansive middle jawbone . In contrast, the bones of the jumper monkeys and the night monkeys are rather shortened. In Homunculus, the nasal bone showed very wide in the area of ​​the nasal opening. The frontal bone was not bulging and the interocular region was relatively wide. The orbita was about the same size as that of today's jumping monkeys. The absolute dimensions were 1.2 to 1.4 cm both in height and in width. In contrast to the night monkeys or the extinct Tremacebus , it was not enlarged. As a result , some paranasal sinuses such as the maxillary sinus expanded significantly in Homunculus , which are reduced in the night monkeys because the space is taken up by the large eyes. The edge of the orbit was also completely closed. At the pterion (a region to the side of the eyes in the human skull) the sphenoid and frontal bone met in some skulls of Homunculus and formed a common bone suture . This is more similar to the Old World monkeys, since in today's New World monkeys the suture of the parietal bone and the cheekbone runs here. Other skull finds in Homunculus showed the peculiarities of platyrrhine skulls, so that the feature as a whole must be classified as more polymorphic. The occipital scale of the occiput was steeply inclined to the eye-ear level . This is typical for almost all New World monkeys with the exception of the squirrel monkeys , as the scales of these monkeys are very acute.

Lower jaw of Homunculus

The lower jaw of Homunculus was broad, but less deep and robust than many of today's leaf-eating New World monkeys. It had a horizontal bone body that deepened towards the rear, and looked a bit compressed in a longitudinal view. In its general form, there were similarities to the lower jaw of today's night monkeys and to some jumper monkeys, but in the latter it is more massive. However, it differed from that of the sakia monkeys , in which the horizontal bone body is significantly higher in front, and from that of the capuchin monkeys with its more elongated shape and more balanced profile line. The two branches of Homunculus converged in a V-shape and merged in a closed, firmly fused symphysis . Here the chin tilted about 50 ° in relation to the front teeth. The mental foramen lay below the anterior premolar, roughly above the center of the bone. The ascending branch was wide, the angled process discharged far back. The corolla protruded steeply and was slightly curved backwards like a hook. The articular process was lower, but still well above the occlusal plane of the teeth. Its rear edge formed a steep edge. The joint head was narrowed in front and behind, but strongly arched. On the outside there was only a shallow masseteric fossa . Inside, the mandibular foramen opened at the end of a sharply delimited groove roughly at the level of the alveolar plane of the premolars.

The front set of teeth had two incisors per arch in the upper and lower rows . The upper inner incisor was spatulate, the outer one was narrower. The lower incisors had narrow and moderately high crowns. They protruded slightly forward and formed a closed row with a position well in front of the canine . There was no pronounced diastema for this . Both the upper and lower canines rose just a little over the edge of the posterior teeth. In terms of their size, they were largely similar to those of the jumper monkeys or night monkeys and were not enlarged as with the Bartsakis or the capuchin monkeys or reduced as with the marmosets . Like almost all New World monkeys, and unlike the Old World monkeys, there was a second premolar, which marks the beginning of the back row of teeth. The upper premolars were characterized by a large main cusp, the paraconus, and the two posterior premolar teeth also had a well-developed protoconus and, in addition, a hypoconus, which was particularly large on the last premolar tooth. The hypoconus is absent in recent New World monkeys. On the lower anterior premolar there was an occasional grinding facet that was created by the upper canine when the dentition closed. On the upper rear molars, three roots were formed on the first molar and two roots on the second molar. The two front upper molars had four main cusps with a paraconus higher on the cheek side than the metaconus (although the feature is less clear on the first molar than on the second). Both stood wide apart with elongated shear ledges in between. On the side of the tongue, the large hypoconus assumed a slightly inward position in relation to the protoconus. In addition to these four main humps, there was also a small side hump, the paraconule. Its appearance is considered to be an original characteristic that is no longer developed in today's New World monkeys, with the exception of the jumping tamarin . A cingulum (a low bulge of enamel) snuggled to the inside and outside of the teeth, the inside being more clearly developed. The hypoconus was absent on the last molar and the paraconus was very large, while the metaconus was very small. The lower molars each had two roots, which also includes the rearmost molar. The characteristic is also found in other early New World monkeys such as Branisella or Carlocebus , in most of today's representatives, with the exception of howler monkeys , this tooth is single-rooted. The chewing surface was shaped by four bumps. Sometimes there was an additional fifth cusp, the paraconid, on the foremost molar; it is reduced in modern New World monkeys. The expression of the hypoconulid, a small side hump in the middle of the tooth, can also be seen as strikingly primeval. The upper row of teeth from the second incisor to the last molar was 2.7 cm long, the molars took up 1.1 cm. Usually the foremost molar was the largest.

From the postcranial skeleton the humerus , the radius and the thighbones have been described, which due to the proportions to the skull can be compared with today's New World monkeys to homunculus . They largely resemble the corresponding limb bones of the recent representatives of the New World monkeys, but have individual peculiarities. The upper joint end and the shaft were significantly wider and more robust than in today's forms. A strong deltopectoral ridge ran around the shaft as an attachment point for the arm muscles, which is somewhat reminiscent of the lemurs . Another ridge towards the lower end acted as the starting point for the brachioradialis muscle . It was extended further upwards than most of today's New World monkeys. At the lower end of the humerus ( elbow joint ) there was a cylindrical joint roll (trochlea) with an only slightly raised center line. The laterally attached capitulum was round and wider at the top than at the bottom. The outer as well as the inner epicondyle both appeared rather large, especially the inner one was pulled out to the side. On the total of 11.2 cm long thigh bone, the large rolling hill hung prominently above the front shaft and was also very wide. Furthermore, a noticeable bone ridge ran between the large and small rolling hills. The articular surface of the femoral head also lengthened backwards. A deep patellar pit appeared at the lower end of the femur, stretched upward and with a lip on one side. The end of the joint was narrow on the sides, but thickened in front and behind.

Fossil finds

The known fossil finds of Homunculus come from the Santa Cruz Formation in Patagonia . This formation is one of the most significant early Neogene fossil sites in South America . Their deposits extend between Lake Buenos Aires in the north and the Río Turbio in the south, approximately between the 50th and 52nd parallel south. The most important outcrops are lined up like a string of pearls on the Atlantic coast in the Argentine province of Santa Cruz between the Río Coyle and Río Gallegos . However, individual significant sites are also further north of the Río Coyle and inland. On the Atlantic coast, the Santa Cruz Formation reaches a thickness of around 240 m and is composed of two almost equal sub-units: the Estancia La Costa layer element in the horizontal and the Estancia La Angelina layer element in the hanging wall. Both series of deposits consist largely of clay , clay / silt and sandstones with a few interposed layers of pyroclastic sediments . The lower, rather fine-grained sediments go back to a former estuary , which gradually gave way to a flood plain. The upper, coarse-grained deposits were largely created under fluvial influence. Various radiometric dating methods give the Santa Cruz Formation an age of 18 to 16 million years, which corresponds to the transition from the Lower to the Middle Miocene .

The discovery of the wealth of fossils in the Santa Cruz Formation dates back to the middle of the 19th century, but more intensive research did not begin until the 1880s to 1890s and is inextricably linked with the names Carlos and Florentino Ameghino . For more than 100 years in the focus of scientific research, a good two dozen fossil layers can be differentiated within the rock formation. The fossil records go in the thousands and are composed of almost all higher groups of vertebrates . Subordinate remains of invertebrates and plants could also be detected. Outstanding is the mammal community consisting of marsupials and especially representatives of higher mammals such as collateral articulated animals , rodents and South American ungulates . The importance of the mammal finds is expressed in the chronostratigraphic stage of the Santacruzian , for which the Santa Cruz Formation was the inspiration and which as a section in the development of the South American Land Mammal Ages (SALMA) the period before 17.5 covers up to 16.3 million years. The geological and palaeontological data allow a landscape to be reconstructed, which consisted of wide, open savannah areas interspersed with alluvial and gallery forests . These were exposed to a subtropical climate with a relatively high annual precipitation of 1000 to 1500 mm compared to today. The then missing blockade by the Andes , which only unfolded later, enabled the passage of strong westerly winds.

Significant finds of Homunculus were made by Carlos Ameghino during his expeditions to the Santa Cruz Formation between 1891 and 1894. These include jaw and skull fragments as well as individual elements of the body skeleton. A left partial skull with the preserved eye window (copy number MACN -A 5968) from the coastal discovery site Puesto estancia La Costa (then known as Corrigüen Aike ) advanced to the iconic fossil that represented the entire primate genus. The same site also contained an almost complete lower jaw (MACN-A 5757), which was possibly associated with a femur as well as an ulna and a radius . Other finds, such as several remains of the lower jaw or isolated teeth, were brought to light by Carlos Ameghino at the Monte Observación site, which is also close to the coast . For two further mandibular fragments he only gave an approximate position with Río Gallegos, while a third mandibular fragment in its original position is controversial. The latter, however, still had parts of the deciduous dentition and thus represents an early evidence of a young animal in research history. Only a few years later, between 1898 and 1904, André Tournouër visited the Santa Cruz Formation several times and discovered, among other things, a lower jaw fragment near the Río Coyle .

After these important early discoveries, new fossil remains of Homunculus did not come to light until almost 90 years later . These were made in 1988 during an expedition by Stony Brook University in New York and the Museo Argentino de Ciencias Naturales Bernardino Rivadavia . The material, composed of individual teeth and two lower jaw fragments, was stored at the Monte Observación site . Independently of this, an investigation by the Universidad de Córdoba south of the Río Coyle revealed a skull roof ( CORD -PZ 1130) from the Puesto estancia La Costa site . Another primate remnant in the form of a facial skull ( MPM -PV 5000) came to light during a third simultaneous expedition of a research group in transit to Antarctica in Killik Aike Norte . In 2003, major on-site investigations began as a joint project between Duke University and the Museo de La Plata , in which numerous international researchers were also involved. The field research continues to this day. An early success was the discovery of three skulls of Homunculus (MPM-PV-3501 to 3503) plus individual long bones in Puesto estancia La Costa and Killik Aike Norte , later the skull of a young individual was added (MPM-PV 3505). The areas further away from the coast are also increasingly in focus. Between 2014 and 2017, various remains of the lower jaw and individual teeth were recovered from the Barrancas Blancas and Segundas Barrancas Blancas outcrops on the Río Santa Cruz and also on the Río Bote . The intensive excavation activities led to the fact that the finds from Humunculus grew to more than half a dozen skulls including that of a young animal and numerous individual teeth as well as various elements of the musculoskeletal system.

Paleobiology

Body size and brain volume

Various skeletal elements can be used to calculate the body weight of Homunculus . Based on the thigh bone, a weight of 1.9 to 2.5 kg can be assumed. The overall dimensions of the skull lead to a presumed weight of 1.9 to 2.4 kg, which can be confirmed by using the lower first molar; here comparative sizes of 1.9 to 2.7 kg result. With reference to the first upper molars, values ​​of 2.5 to 3.4 kg have been calculated. The slightly higher weights may be related to the hypertrophy of the upper molars. If the last dimensions are left out, Homunculus is likely to have had the size of today's Sakis or Uakaris . Outside the range of variation given here, a body weight of 3 kg can be assumed based on the anterior molar of an extremely large lower jaw of Homunculus .

For two skull casts, the brain volume is around 20 cm³. This is relatively small compared to body size and is below the values ​​of today's New World monkeys. The poorly developed frontal lobe in Homunculus has a significant influence on the small brain size . For the early Miocene New World monkey Chilecebus , too , a very small brain volume with an even smaller body size was determined. It is therefore likely that the New World monkeys developed larger brain volumes in relation to body size in the course of their tribal history, for which various factors with a nutritional and sociobiological background are responsible. This also corresponds to the findings within the Old World monkeys .

Locomotion

In the proportions of its limbs, Homunculus largely resembles today's New World monkeys. Based on the structure of the long bones, conclusions can be drawn about the mode of locomotion. The overhanging large roll mound on the thigh bone acts as the starting point of the vastus lateralis muscle , which represents a powerful knee extensor . The lower joint end, which is narrow at the sides and thickened at the front and back, extends the lever arm of the knee extensor muscles, among other things. The deep patellar pit counteracts the strong mechanical stress on the kneecap that occurs when the legs are extended. All these characteristics are typical of jumping locomotion in New World monkeys and can be found, for example, in Sakis and Satan monkeys . The same can be seen in the humerus . Its robust construction with the distinctive bone ridges such as the deltopectoral ridge and the wide and characteristically shaped lower joint end ( elbow joint ) speaks for a high degree of freedom of movement of the forearm, which is ultimately also indicated by the strong and quite strikingly curved spoke . The stretched and laterally directed inner epicondyle of Homunculus can accordingly be observed in numerous climbing primates, while in ground-dwelling species it is oriented backwards. In contrast, the articular surface of the trochlea does not expand upwards in any of the humerus of Homunculus . Such an enlarged joint surface is typical for numerous primates, such as marmosets or lemurs , and, as a so-called “clasp facet”, enables vertical climbing with wide-reaching arms (here the coronary process of the ulna presses against it when the arms are extended). Together with the conspicuous shape of the capitulum, it can be concluded that the elbow joint is obviously mostly bent rather than stretched when moving. The entire configuration also indicates a rather extensive olecranon on the ulna, which has not yet been recorded in fossil form. An elongated olecranon increases the leverage of the forearm muscles. A larger part of the characteristics mentioned can be traced back to a tree-dwelling way of life and does not occur in today's ground-living primates. In sum, there are only few indications of a swinging, swinging or vertically climbing movement in Homunculus . Rather, the primate form should have been walking on four legs.

The relatively large semicircular canals of the inner ear indicate a very agile animal such as today's jumper monkeys, but less fast than squirrel monkeys or tamarins . The semicircular canals are also at right angles to each other. The entire organ of equilibrium allowed head movements of around 135 ° per second, which corresponds to the order of magnitude of modern lemurs such as bamboo lemurs and various sifakas .

Diet

The lower jaw and skull show hardly any strong muscle attachment points compared to today's New World monkeys of the same size due to the lack of a crest , the little pronounced temporal lines and the weakly protruding zygomatic arch . Added to this is the relative prognathism of the snout of Homunculus , which outperforms other New World monkeys. This resulted in long loading arms but short lever arms for the masticatory muscles, which leads to largely poorly developed masticatory muscles with reduced bite force. Due to the completely overgrown symphysis , however, there was in principle the possibility of providing considerable muscle strength, especially on the side opposite the chewing movement. The extensive articular surface connecting the lower jaw with the underside of the skull also indicates that the incisors can compensate for repetitive force discharges when chewing or biting .

The spatulate upper and narrow as well as protruding lower incisors could be used in conjunction with the relatively small canine to crack hard fruits and seeds, as in the sakis. In contrast to the Sakis with their larger canines and stronger roots there, these did not pierce the food in Homunculus . However, a tree-bark-scraping function for extracting tree sap is also conceivable for the front set of teeth, as is the case with the tufted monkey . On the relatively large molars, there are comparatively extensive shear and cutting edges. These are suitable for chopping leafy food or soft fruits, in accordance with the corresponding teeth of woolly monkeys or howler monkeys . New World monkeys, which mainly eat hard-shelled seeds and fruits, have shorter cutting edges on their molars. They also have a more massive tooth enamel , which is not the case with Homunculus . The recent, leaf-eating New World monkeys also have larger tooth roots on the molars than hard-seed-consuming species, a feature that also occurs in Homunculus . The teeth of Homunculus, which are often more heavily chewed, lead to the assumption that the soft plant food contained more fibers and thus produced greater abrasion. Accordingly, despite poorly developed chewing muscles, the food in the mouth was crushed by means of strong chewing movements, which on the one hand caused the large tooth roots and on the other hand the noticeable abrasions. The overall finding thus points to a predominant diet of hard-shelled seeds by means of the front teeth, while the rear dentition advocates the consumption of softer fruits and leaves. This functional separation is possibly based on a seasonally changing food supply. For these reasons, a life in tropical rainforests can be ruled out for Homunculus . Seasonally influenced forests or those in peripheral locations such as gallery forests come into consideration as possible habitats . The feeding behavior of Homunculus is likely to have largely corresponded to today's jugular monkeys in the Atlantic coastal forests .

Gender dimorphism

Today's New World monkeys have variably developed canine teeth between the individual sexes with a strong dimorphism in the howler monkeys and a small one in some jumper monkeys and the night monkey . The different characteristics are partly related to the way of life, whereby a strong canine tooth dimorphism refers to the dominance struggles of the males for the mating privilege and a territorial behavior, while a low canine tooth dimorphism indicates a life in sometimes monogamous groups. In the fossil material of Homunculus there are only a few variations in the size of the canines, provided that the previous find material represents both sexes, consequently no particular dimorphism can be identified. From this it could be concluded that fights among the males were rather unusual and that there was no selection for strong canines. There was then less competition between the individual individuals of the respective sexes and possibly more between the various groups or couples. In this characteristic, the extinct primate representative more clearly resembles the jumping monkey or the night monkey.

Sensory perception and sounds

The size of the orbit compared to the skull refers Homunculus to the diurnal primates. The view is supported by the almost closed orbital rim, which among other things stabilizes the surrounding connective tissue and thus protects the eye from excessive movements of the masticatory muscles . The better protected eyeball was able to develop a stronger visual acuity , which is in principle higher in diurnal primates than in nocturnal primates. In addition, the foramen opticum as the point of passage of the optic nerve into the canalis opticus is relatively large in Homunculus and lies within the range of variation of today's diurnal New World monkeys. It can therefore be assumed that the extinct primate form had a central fovea with a high number of cone-shaped light receptors . In contrast, the infraorbital foramen is greatly reduced. This is where the sub-eye nerve runs , which transmits sensory impulses from the vibrissae of the snout region to the brain. A small under-eye hole is therefore connected to less well-developed whiskers, which in turn speaks for a more daylight-active life. Ultimately, the olfactory fossa through which the olfactory bulb runs is also comparatively small in Homunculus . In contrast, today's night monkeys have a large orbit, a large infraorbital foramen, and a large olfactory fossa.

The lower jaw, which becomes deeper towards the rear, finds its counterpart in the jugular and night monkeys and is related to the sac-like enlargements of the larynx ( laryngeal air sacs ), which occur in many, but not all, primates and to produce powerful sounds as part of the ritualized Serve territorial behavior. This allows small groups to spread out relatively widely and stay connected via phonetic communication, which in turn is effective in less productive landscapes. Perceived frequency ranges can be reconstructed using the anatomy of the ear. In principle, today's dry- nosed primates (old and new world monkeys) have more pronounced hearing for lower frequency ranges, while wet-nosed primates (lemurs and loris) are more specialized in higher frequencies. Within the dry-nosed primates, Old World monkeys can perceive low frequencies better than New World monkeys. The human-like on the other hand are not very sensitive to higher frequencies. In Homunculus , the eardrum at the entrance to the middle ear has an area of ​​23.8 mm², which roughly corresponds to that of today's spring tamarin , but which is smaller than Homunculus . Many of today's primates also have more extensive eardrums than homunculus in relation to their body size . The size of the footplate of the stapes (or the oval window to the inner ear in which the footplate is anchored) can be used as a further value . Both are about 0.6 mm² in Homunculus , which is slightly less than in numerous recent primates. The cochlea of the inner ear delivers very precise results , as, for example, the number of its revolutions and its total length are directly related to the perception of low-frequency sounds. In Homunculus, the cochlea has three complete turns with a total length of the turns of 24.6 mm. The revolution value is in the range of today's New World monkeys, but above that of numerous wet-nosed primates with less than three turns. In all three traits, Homunculus had good sensitivity to both lower and higher sounds. Low-frequency tones around 250  Hz were perceived at a sound pressure between 24 and 36  dB (for comparison: Old World monkeys 12 to 19 dB, New World monkeys 24 to 26 dB, Lemurs and Loris 32 to 48 dB). In the higher range, the threshold of frequencies around 32 kHz was around 13 dB (for comparison: Old World monkeys 22 to 39 dB, New World monkeys 8 to 14 dB, Lemurs and Loris 7 to 23 dB). Homunculus thus largely corresponds to today's New World monkeys. The hearing ability of the New World monkeys was thus already largely developed in the Lower / Middle Miocene, but was further refined in the subsequent period.

Systematics

Internal systematics of the New World monkeys according to the Long Lineage Hypothesis according to Silvestro et al. 2019
 Platyrrhini  

 Perupithecus (†)


   

 Scalatavus (†)


   

 Lagonimico (†)


   

 Canaanimico (†)


   
  Pitheciidae  



 Homunculus (†)


   

 Carlocebus (†)



   

 Callicebinae



   

 Xenotrichini (†)


   

 Mazzonicebus (†)


   

 Soriacebus (†)


   

 Pitheciinae






   

 Branisella (†)


   
  Atelidae  

 Chilecebus (†)


   

 Atelinae


   

 Stirtonia (†)


   

 Alouattinae





   
  Cebidae  

 Panamacebus (†)


   


 Dolichocebus (†)


   

 Saimiriinae



   

 Kilikaike (†)


   

 Cebinae





   

 Callitrichidae


  Aotidae 

 Tremace bus (†)


   

 Aotinae












Template: Klade / Maintenance / Style

shortened; In addition to the recent groups, only the fossil forms from the Eocene to the Lower Miocene are shown

Internal systematics of the New World monkeys according to the Stem Platyrrhine Hypothesis according to Marivaux et al. 2016
 Platyrrhini  

 Perupithecus (†)


   

 Branisella (†)


   
  "Homunculidae"  


 Carlocebus (†)


   

 Homunculus (†; including Kilikaike )



   

 Mazzonicebus (†)


   

 Canaanimico (†)


   

 Soriacebus (†)





   


 Dolichocebus (†)


   

 Tremace bus (†)



   

 Chilecebus (†)


   

 Xenotrichini (†)


   
  Pitheciidae  

 Callicebinae


   

 Pitheciinae



   
  Atelidae  

 Atelinae 


   

 Stirtonia (†)


   

 Alouattinae




   


 Aotidae


  Cebidae 

 Cebinae


   

 Saimiriinae + Panamacebus (†)




  Callitrichidae  

 Lagonimico (†)


   

 Saguinini + Callitrichini












Template: Klade / Maintenance / Style

shortened; In addition to the recent groups, only the fossil forms from the Eocene to the Lower Miocene are shown

Homunculus is a genus from the order of the primates (Primates). Within this the genus belongs to the group of the New World monkeys (Platyrrhini). These are mostly tree-living monkeys that inhabit the tropical and subtropical areas of South and Central America . Outwardly, they differ from the Old World monkeys by their relatively wider nose, their average smaller body size and the generally trained tail, which in some forms can be used as a grasping organ . The New World monkeys comprise several families , of which the sakia monkeys (Pitheciidae), the spotted monkeys ( Atelidae), the capuchin monkeys (Cebidae) and the marmosets (Callitrichidae) are the most important. As a rule, the sakia monkeys are considered to be the sister group of all other New World monkeys, which can be proven by molecular genetics . The earliest fossil record of the New World monkeys comes with Perupithecus from the Peruvian area of ​​the Amazon basin and dates to the transition from the Eocene to the Oligocene around 35 million years ago.

The systematic position of Homunculus is currently not clear. Sometimes the form is not assigned to a specific family and its status is shown as incertae sedis . It then belongs to a group of early Patagonian forms that functions as the parent group of the New World monkeys (some of these are classified in an independent family, the Homunculidae, which was introduced by Florentino Ameghino in 1894 ). Other authors group Homunculus within the sakia monkeys, the spotted monkeys or the Capuchin-like (sometimes with the Homunculinae in the rank of a subfamily or as Homunculini in the rank of a tribe ).

The different assignments go back to two competing hypotheses on the phylogenesis of the New World monkeys: on the one hand the Long Lineage Hypothesis or Morphological Stasis Hypothesis , according to which the extinct Miocene genera can be classified as original representatives in the crown group of the New World monkeys, on the other hand the Stem Platyrrhine Hypothesis or Successive Radiations Hypothesis that classifies the primeval forms as part of a basal radiation phase. Both views are currently controversial. The molecular genetic studies on recent New World monkeys used to underpin the respective view are inconclusive because they are based on different calibration models. According to this, the proponents of the Long Lineage Hypothesis put the splitting of today's New World monkeys 29 to 31 million years ago, that of the Stem Platyrrhine Hypothesis around 20 million years ago.

Taxonomy and research history

Florentino Ameghino

The first scientific description of Homunculus comes from Florentino Ameghino in 1891. He made it shortly after the discovery of the first finds by his brother Carlos Ameghino in the Santa Cruz Formation . Florentino Ameghinos introduction of Homunculus meant the oldest record of New World monkeys in South America and only the second record of an extinct primate on the continent after Peter Wilhelm Lund's name of Protopithecus from the Pleistocene of Brazil in 1840. The first description of Homunculus is based on some mandibular fragments, from where a right branch of the jaw with the symphysis and the teeth from the second incisor to the first molar is the holotype (copy number MACN -A 634). He comes from the region of the Río Gallegos . Florentino Ameghino did not provide any further details, but it is assumed that the find came from its north side and was possibly brought to the surface from Killik Aike Norte . The object has been lost for several decades, which is why in 2008 a neotype (specimen number MACN-A 5757) was determined from the Puesto estancia La Costa site a little further to the north with an almost complete lower jaw, but whose teeth have been more heavily chewed . Florentino Ameghino was the only species to name H. patagonicus . Provisionally he addressed the new primate form as lemur-like , but, in his opinion, saw them as very modern features in a direct line of development to humans and their closer relatives.

In the same year, Florentino Ameghino named Anthropops perfectus, referring to a lower jaw with more V-shaped arches and a wider symphysis than in comparison to Homunculus . The find came to light in the coastal area of ​​the Santa Cruz Formation without specifying a precise find region. Three years later he again introduced Pitheculus australis using a left lower jaw fragment from Monte Observación . Both are placed today with H. patagonicus . The primate form Ecphantodon ceboides , which was established by Alcides Mercerat in 1891 independently of Florentino Ameghino's publications on the Santa Cruz Formation, is to be regarded as problematic , which is based on a fragmented lower jaw with molar. The description is kept brief and not illustrated, Florentino Ameghino equated the species with H. patagonicus in the same year without giving reasons for it. Since the find has been lost and no further details are available, most scientists today follow this assessment.

Hans Bluntschli , who, shortly after the death of Florentino Ameghino in 1912 during a stay in Argentina, saw his collection and in 1931 presented an extensive new description of the primate remains, postulated the species H. ameghinoi , which, however, is largely not recognized. The species H. imago , also named by Florentino Ameghino in 1894 , for which he used a thigh bone and a cubit, is most likely not a primate form. On the other hand, Florentino Ameghino at the same time referred a right molar tooth to Stilotherium grande , a representative of the marsupials. More than 80 years later, Philip Hershkovitz recognized a primate's milk tooth in the find and named the shape H. grandis . It is now classified as synonymous with H. patagonicus . Carlos Rusconi named another species with H. harringtoni in 1933. Established on the basis of an almost complete skull from the Argentine province of Chubut, it dates to the Lower Miocene and is therefore somewhat older than Homunculus . In 1974, Hershkovitz established the new genus Tremacebus for him , as the shape with its significantly larger eye windows differs markedly from Homunculus . In the 1980s, John Fleagle brought individual isolated teeth from the Pinturas formation in connection with Homunculus , but moved them in 1990 to the genus Carlocebus, which he had established . The Pinturas Formation is also open in the Argentine province of Santa Cruz and corresponds in age to the lower sections of the Santa Cruz Formation.

In 2019 led Richard F. Kay and Jonathan MG Perry with H. vizcainoi one another kind, the supporting documentation from the Río Santa Cruz comes. Mention should also be made of a facial skull and an upper jaw fragment from the Killik Aike Norte site of the Santa Cruz Formation, which in 2006 a research team led by Marcelo F. Tejedor used as the basis for establishing the new genus Killikaike with the species K. blakei . Due to the short face and the size of the skull, the authors suspected a closer relationship with the capuchin monkeys . Other scientists saw this more critically in the following time and classified the form as identical to Homunculus and its nominate form , while H. blakei is again recognized by individual researchers as an independent species within the genus Homunculus . Accordingly, three species could exist with H. patagonicus , H. vizcainoi and H. blakei . Other previously unnamed species are accepted from the Puesto estancia La Costa site due to an atypically robust lower jaw and from the Río Bote due to a single molar .

So far, two distinct species can be distinguished within the genus:

Here H. patagonicus represents the type species and is the larger of the two representatives.

meaning

The fossil remains of Homunculus are found around the 51st degree of southern latitude and represent the southernmost of a primate species found in America. Today's New World monkeys reach their limit of expansion at the 29th degree of southern latitude. The genus Homunculus is embedded in a group of early New World monkeys from Patagonia, which appeared around 20 million years ago with Tremacebus and Dolichocebus and disappeared from the fossil record with Proteropithecia around 15.5 million years ago . After this point in time, no more monkeys from southern South America are recorded. Compared to the rather sparse finds of the other Miocene genera of Patagonia, the rich remains of Homunculus allow the best insight to date into the biological adaptations of an early New World monkey.

literature

  • Richard F. Kay, Jonathan MG Perry, Michael Malinzak, Kari L. Allen, E. Christopher Kirk, J. Michael Plavcan, and John G. Fleagle: Paleobiology of Santacrucian primates. In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (Eds.): Early Miocene Paleobiology in Patagonia: High-Latitude Paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 306-330
  • Marcelo F. Tejedor and Alfred L. Rosenberger: A neotype for Homunculus patagonicus Ameghino, 1891, and a new Interpretation of the Taxon. PaleoAnthropology 2008, pp. 68-82

Individual evidence

  1. ↑ Ethan L. Fulwood, Doug M. Boyer and Richard F. Kay: Stem members of Platyrrhini are distinct from catarrhines in at least one derived cranial feature. Journal of Human Evolution 100, 2016, pp. 16-24
  2. ↑ a b c Adan Tauber: Homunculus patagonicus Ameghino, 1891 (Primates, Ceboidea), Mioceno Temprano, de la costa Atlantica Austral, prov. De Santa Cruz, Republica Argentina. Academia Nacional de Ciencias Córdoba, Argentina Miscelanea 82, 1991, pp. 1–32 ( [1] )
  3. ↑ a b c R. F. Kay, SF Vizcaino, AA Tauber, MS Bargo, BA Williams, C. Luna and MW Colbert: Three newly discovered skulls of Homunculus patagonicus support its position as a stem platyrrhine and establish its diurnal arboreal folivorous habits. American Journal of Physical Anthropology 126 (S40), 2005, p. 127
  4. ↑ a b Richard F. Kay, JG Fleagle, TRT Mitchell, Matthew Colbert, Tom Bown and Dennis W. Powers: The anatomy of Dolichocebus gaimanensis, a stem platyrrhine monkey from Argentina. Journal of Human Evolution 54, 2008, pp. 323-382
  5. ↑ a b c d e f g h i Marcelo F. Tejedor and Alfred L. Rosenberger: A neotype for Homunculus patagonicus Ameghino, 1891, and a new Interpretation of the Taxon. PaleoAnthropology 2008, pp. 68-82
  6. ↑ a b c d e f g Jonathan MG Perry, Richard F. Kay, Sergio F. Vizcaíno and M. Susana Bargo: Oldest known cranium of a juvenile New World monkey (Early Miocene, Patagonia, Argentina): Implications for the taxonomy and the molar eruption pattern of early platyrrhines. Journal of Human Evolution 74, 2014, pp. 67-81
  7. ↑ a b c Hans Bluntschli: Homunculus patagonicus and the associated fossil finds from the Santa Cruz strata of Patagonia. a morphological revision based on the original pieces in the Ameghino collection at La Plata. Morphologisches Jahrbuch 67, 1931, S-811-892
  8. ↑ a b c John Fleagle and Richard Kay: A new humerus of Homunculus from the Santa Cruz Formation (Early-Middle Miocene, Patagonia). Journal of Vertebrate Paleontology 26 (3suppl.), 2006, p. 62A
  9. ↑ a b c d e f g h i j k l m n o p q r s Richard F. Kay, Jonathan MG Perry, Michael Malinzak, Kari L. Allen, E. Christopher Kirk, J. Michael Plavcan and John G. Fleagle: Paleobiology of Santacrucian primates. In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (Eds.): Early Miocene Paleobiology in Patagonia: High-Latitude Paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 306-330
  10. ↑ Sergio F. Vizcaíno, M. Susana Bargo, Richard F. Kay, Richard A. Fariña, Mariana Di Giacomo, Jonathan MG Perry, Francisco J. Prevosti, Néstor Toledo, Guillermo H. Cassini and Juan C. Fernicola: A baseline paleoecological study for the Santa Cruz Formation (late-early Miocene) at the Atlantic coast of Patagonia, Argentina. Palaeogeography, Palaeoclimatology, Palaeoecology 292, 2010, pp. 507-519
  11. ↑ Sergio D. Matheos and M. Sol Raigenborn: Sedimentology and paleoenvironment of the Santa Cruz Formation. In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (eds.): Early Miocene paleobiology in Patagonia: High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 59-82
  12. ↑ José I. Cuitiño, Juan Carlos Fernicola, Matthew J. Kohn, Robin Trayler, Maximiliano Naipauere, M. Susana Bargo, Richard F. Kay and Sergio F. Vizcaíno: U-Pb geochronology of the Santa Cruz Formation (early Miocene) at the Río Bote and Río Santa Cruz (southernmost Patagonia, Argentina): Implications for the correlation of fossil vertebrate localities. Journal of South American Earth Sciences 70, 2016, pp. 198-210
  13. ↑ Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo: Background for a paleoecological study of the Santa Cruz Formation (late Early Miocene) on the Atlantic Coast of Patagonia. In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (eds.): Early Miocene paleobiology in Patagonia: High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 1-22
  14. ↑ Juan Carlos Fernicola, José I. Cuitiño, Sergio F. Vizcaíno, M. Susana Bargo and Richard F. Kay: Fossil localities of the Santa Cruz Formation (Early Miocene, Patagonia) prospected by Carlos Ameghino in 1887 revisited and the location of the Notohippidian. Journal of South American Earth Sciences 52, 2014, pp. 94-107
  15. ^ In A. Croft: What Constitutes a Fossil Mammal Community in the Early Miocene Santa Cruz Formation? Journal of Vertebrate Paleontology 33 (2), 2013, pp. 401-409
  16. ^ Adán A. Tauber: Paleoecología de la Formación Santa Cruz (Mioceno inferior) en el extremo sudeste de la Patagonia. Ameghiniana 34, 1997, pp. 517-529
  17. ↑ Richard F. Kay, Sergio F. Vizcaíno and M. Susana Bargo: A review of the paleoenvironment and paleoecology of the Miocene Santa Cruz Formation. In: Sergio F. Vizcaíno, Richard F. Kay and M. Susana Bargo (eds.): Early Miocene paleobiology in Patagonia: High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, New York, 2012, pp. 331-365
  18. ^ A b Philip Hershkovitz: More on the Homunculus Dpm4 and M1, and Comparisons With Alouatta and Stirtonia (Primates, Platyrrhini, Cebidae). American Journal of Primatology 7, 1984, pp. 261-283
  19. ↑ Nelson M. Novo, Marcelo F. Tejedor and Laureano R. González-Ruiz: Previously unknown fossil platyrrhines (Primates) of Patagonia from the Tournouër collection at the Muséum national d'Histoire naturelle, Paris. Geodiversitas 40 (22), 2018, pp. 529-535
  20. ^ JG Fleagle, GA Buckley and ME Schloeder: New Primate Fossils from Monte Observación, Santa Cruz Formation (Lower Miocene), Santa Cruz Province, Argentina. Journal of Vertebrate Paleontology 8 (3suppl.), 1988, p. 14A
  21. ^ A b Marcelo F. Tejedor, Adán A. Tauber, Alfred L. Rosenberger, Carl C. Swisher III and María E. Palacios: New primate genus from the Miocene of Argentina. PNAS 103 (14), 2006, pp. 5437-5441
  22. ↑ Jonathan MG Perry, Richard F. Kay, Sergio F. Vizcaino and Susana M. Bargo: First cranial material of a juvenile monkey from the Tertiary of South America: cranial anatomy and dental eruption sequence. Journal of Vertebrate Paleontology 28 (3suppl.), 2008, p, 127A
  23. ^ A b c d e Richard F. Kay and Jonathan MG Perry: New primates from the Río Santa Cruz and Río Bote (Early-Middle Miocene), Santa Cruz Province, Argentina. Publicación Electrónica de la Asociación Paleontológica Argentina 19 (2), 2019, pp. 230-238
  24. ^ Karen E. Sears, John A. Finarelli, John J. Flynn and Andre R. Wyss: Estimating body mass in New World “monkeys” (Platyrrhini, Primates), with a consideration of the Miocene platyrrhine, Chilecebus carrascoensis. American Museum Novitates 3617, 2008, pp. 1-29
  25. ↑ Xijun Ni, John J. Flynn, André R. Wyss and Chi Zhang: Cranial endocast of a stem platyrrhine primate and ancestral brain conditions in anthropoids. Science Advances 5, 2019, p. Eaav7913, doi: 10.1126 / sciadv.aav7913
  26. ↑ Richard Kay and Michael Malinzak: New data on encephalization in Miocene New World monkeys: implications for anthropoid brain evolution. Journal of Vertebrate Paleontology 28 (3suppl.), 2008, p, 99A
  27. ↑ a b Dionisios Youlatos and Jeff Meldrum: Locomotor Diversification in New World Monkeys: Running, climbing, or clawing Along Evolutionary branches. The Anatomical Record 294, 2011, pp. 1991-2012
  28. ↑ Timothy M. Ryan, Mary T. Silcox, Alan Walker, Xianyun Mao, David R. Begun, Brenda R. Benefit, Philip D. Gingerich, Meike Köhler, László Kordos, Monte L. McCrossin, Salvador Moyà-Solà, William J Sanders, Erik R. Seiffert, Elwyn Simons, Iyad S. Zalmout, and Fred Spoor: Evolution of locomotion in Anthropoidea: the semicircular canal evidence. Proceedings of the Royal Society B 279, 2012, pp. 3467-3475
  29. ^ A b Jonathan MG Perry, Richard F. Kay, Sergio F. Vizcaíno, and M. Susana Bargo: Tooth Root Size, Chewing Muscle Leverage, and the Biology of Homunculus patagonicus (Primates) from the late early Miocene of Patagonia. Ameghiniana 47 (3), 2010, pp. 355-371
  30. ↑ Jonathan Perry and Matthew Colbert: Tooth root size and chewing muscle leverage in Homunculus, a Miocene primate from Patagonia. Journal of Vertebrate Paleontology 26 (3suppl.), 2006, p, 110A
  31. ↑ a b c Alfred L. Rosenberger, Marcelo F. Tejedor, Siobhán B. Cooke and Stephen Pekar: Platyrrhine ecophylogenetics in space and time. In: PA Garber, A. Estrada, JC Bicca-Marques, EW Heymann EW and KB Strier (eds.): South American primates: comparative perspectives in the study of behavior, ecology and conservation. New York, Springer, 2009, pp. 69-113
  32. ↑ Richard Kay, Abraham Lincoln, Matthew Colbert and Michael Malinzak: Brain size, activity pattern, and visual acuity in Homunculus patagonicus, an Early Miocene stem platyrrhine: the mosaic evolution of brain size and visual acuity in Anthropoidea. Journal of Vertebrate Paleontology 26 (3suppl.), 2006, p, 83A
  33. ^ Mark N. Coleman, Richard F. Kay, and Matthew W. Colbert: Auditory Morphology and Hearing Sensitivity in Fossil New World Monkeys. The Anatomical Record 293, 2010, pp. 1711-1721
  34. ^ Mark N. Coleman and Matthew W. Colbert: Correlations Between Auditory Structures and Hearing Sensitivity in Non-Human Primates. Journal of Morphology 271, 2010, pp. 511-532
  35. ↑ Daniele Silvestro, Marcelo F. Tejedor, Martha L. Serrano-Serrano, Oriane Loiseau, Victor Rossier, Jonathan Rolland, Alexander Zizka, Sebastian Höhna, Alexandre Antonelli and Nicolas Salamin: Early Arrival and Climatically-Linked Geographic Expansion of New World Monkeys from Tiny African Ancestors. Systematic Biology 68 (1), 2019, pp. 78-92
  36. ↑ a b c Laurent Marivaux, Sylvain Adnet, Ali J. Altamirano-Sierra, Myriam Boivin, François Pujos, Anusha Ramdarshan, Rodolfo Salas-Gismondi, Julia V. Tejada-Lara and Pierre-Olivier Antoine: Neotropics provide insights into the emergence of New World monkeys: New dental evidence from the late Oligocene of Peruvian Amazonia. Journal of Human Evolution 97, 2016, pp. 159-175
  37. ↑ Horacio Schneider and Iracilda Sampaio: The systematics and evolution of New World primates - A review. Molecular Phylogenetics and Evolution 82, 2015, pp. 348-357, doi: 10.1016 / j.ympev.2013.10.017
  38. ↑ F. Dumas and S. Mazzoleni: Neotropical primate evolution and phylogenetic reconstruction using chromosomal data: Italian Journal of Zoology 84 (1), 2017, pp. 1-18, doi: 10.1080 / 11250003.2016.1260655
  39. ↑ Xiaoping Wang, Burton K. Lim, Nelson Ting, Jingyang Hu, Yunpeng Liang, Christian Roos and Li Yu: Reconstructing the phylogeny of new world monkeys (platyrrhini): evidence from multiple non-coding loci. Current Zoology, 2018, pp. 1-10, doi: 10.1093 / cz / zoy072
  40. ↑ Mariano Bond, Marcelo F. Tejedor, Kenneth E. Campbell Jr., Laura Chornogubsky, Nelson Novo and Francisco Goin: Eocene primates of South America and the African origins of New World monkeys. Nature 520 (7548), 2015, pp. 538-541
  41. ↑ a b Florentino Ameghino: Enumération synoptique des espèces de mammifères fossiles des formations éocènes de Patagonia. Buenos Aires, 1894, pp. 1–196 (pp. 9–11 and 102) ( [2] )
  42. ^ Richard F. Kay: Biogeography in deep time - What do phylogenetics, geology, and paleoclimate tell us about early platyrrhine evolution? Molecular Phylogenetics and Evolution 82, 2015, pp. 358-374
  43. ^ Alfred L. Rosenberger: Evolutionary Morphology, Platyrrhine Evolution, and Systematics. The Anatomical Record 294, 2011, pp. 1955-1974
  44. ↑ Marcelo F. Tejedor: Sistemática, evolución y paleobiogeografía de los primates Platyrrhini. Revista del Museo de La Plata Sección Zoología 20 (176), 2013, pp. 20-39
  45. ^ Alfred L. Rosenberger: Platyrrhines, PAUP, parallelism, and the Long Lineage Hypothesis: A reply to Kay et al. (2008). Journal of Human Evolution 59, 2010, pp. 214-217
  46. ↑ Jessica W. Lynch Alfaro, Liliana Cortés-Ortiz, Anthony Di Fiore and Jean P. Boubli: Comparative biogeography of Neotropical primates. Molecular Phylogenetics and Evolution 82, 2015, pp. 518-529
  47. ^ S. Ivan Perez, Marcelo F. Tejedor, Nelson M. Novo and Leandro Aristide: Divergence Times and the Evolutionary Radiation of New World Monkeys (Platyrrhini, Primates): An Analysis of Fossil and Molecular Data. PLoS ONE 8 (6), 2013, p. E68029, doi: 10.1371 / journal.pone.0068029
  48. ↑ Jason A. Hodgson, Kirstin N. Sterner, Luke J. Matthews, Andrew S. Burrell, Rachana A. Jani, Ryan L. Raaum, Caro-Beth Stewart, and Todd R. Disotell: Successive radiations, not stasis, in the South American primate fauna. PNAS 106 (14), 2009, pp. 5534-5539
  49. ↑ Florentino Ameghino: Nuevos restos de mamiferos fosiles decubiertos par Carlos Ameghino en el eoceno inferior de la Patagonia austral. - Especies nuevas, adiciones y correcciones. Revista Argentina de Historia Natural 1, 1891, pp. 289–328 ( [3] )
  50. ↑ a b c Florentino Ameghino: Los monos fósiles del eoceno de la república Argentina. Revista Argentina de Historia Natural 1, 1891, pp. 383–397 ( [4] )
  51. ↑ Alcides Mercerat: Sobre la presencia de restos de monos en el eoceno de Patagonia. Revista del Museo de La Plata 2, 1891, pp. 73–74 ( [5] )
  52. ↑ Carlos Rusconi: Nuevos restos de monos fósiles del TERCIARIO antiguo de la Patagonia. Anales de la Sociedad Científica Argentina 116, 1933, pp. 286–289 ( [6] )
  53. ↑ Philip Hershkovitz: A new genus of Late Oligocene monkey (Cebidae, Platyrrhini) with notes on postorbital closure and platyrrhine evolution. Folia Primatologica 21, 1974, pp. 1-35
  54. ^ John G. Fleagle: New fossil platyrrhines from the Pinturas Formation, southern Argentina. Journal of Human Evolution 19, 1990, pp. 61-85