Chilecebus

Chilecebus
Temporal occurrence
Lower Miocene
20.1 million years
Locations
South America ( Chile )
Systematics
Primates (Primates) Dry- nosed primates (Haplorrhini) Monkey (anthropoidea) New World Monkey (Platyrrhini) incertae sedis Chilecebus
Scientific name
Chilecebus
Flynn , Wyss , Charrier & Swisher , 1995

Chilecebus is an extinct genus of primates from the New World monkey group. The only known find so far consists of a skull that wasfoundin central Chile anddatedto the Lower Miocene around 20 million years ago. It is a very small representative of the New World monkeys that lived active during the day and ate herbivorous food. Also noticeable is the small, yet complex brain, which structurally differs somewhat from that of today's New World monkeys. This was based on Chilecebus be shown in conjunction with other extinct primates that brain development proceeded much more complex than originally suspected. The genus was scientifically introduced in 1995. One species, Chilecebus carrascoensis ,is currentlyrecognized.

features

Chilecebus was a small representative of the New World monkeys . Body weight reconstructions vary between 430 and 1870 g, depending on the calculation method used and the assessment basis. In relation to the proportions of the skull, however, a range between 580 and 720 g is more likely to be assumed, which roughly corresponds to the weight of today's marmosets . So far, the shape is only known from a skull. This was flat arched in profile and short. It did not have a trained crest , which is typical of early New World monkeys , but one does occur in some early African monkeys . The egg-shaped orbit was relatively small and measured around 9.1 mm in diameter. It showed itself to be more or less closed by a bony septum that was extended backwards, a characteristic of numerous dry-nosed monkeys .

The dentition was slightly reduced compared to the full dentition of the higher mammals . The upper row of teeth consisted of two incisors , a canine , three premolars and three molars per half of the jaw, so the upper dentition consisted of a total of 18 teeth. The left and right rows of teeth together formed a V, the opening reaching back thus reflecting the expanding palate . The incisors were of the same size, spatulate and slanted forward ( procumbent ), more clearly than was the case with Homunculus . The canine was only small in size, which is particularly evident when one takes into account the sexual dimorphism that is common in primates . It was separated from the posterior incisor by a very short diastema only 1 mm wide . The tooth gap is markedly shorter than that of Homunculus . Typical of New World monkeys, Chilecebus had a second premolar (P2) that preceded the rear row of teeth. This had only one large hump on the chewing surface and was anchored to the jaw by one or two roots. The two posterior premolar teeth (P3 and P4) were significantly larger and were characterized by a large main cusp (Paraconus) and a small secondary cusp (Protoconus). Unlike Carlocebus and Soriacebus , but consistent with numerous recent New World monkeys, no hypoconus occurred. The two shear edges in front of and behind the main hump (prepara- and postparacrista) reached about the same dimensions. The first two molars (M1 and M2) were square in outline, which stands out from the more rounded teeth in Branisella . On the cheek side, the metaconus protruded beyond the paraconus on the first molar; the ratio was reversed on the second molar. On the first molar in particular, the paraconus sat very far forward, so that the parastyle was missing. The tongue-sided hypoconus was well developed and more pronounced than in Branisella . The last molar was clearly smaller and oval in shape. The most striking feature here was the missing metaconus, which distinguishes Chilecebus from Branisella , Dolichocebus and Homunculus , among others . However, there was a small swelling on the rear, steeply sloping shear edge of the paraconus, which may correspond to the metaconus. The molars were generally low-crowned ( brachyodont ) and increased in size from front to back. The anterior premolar measured 1.75 mm in length and 3.50 mm in width, the corresponding dimensions of the second molar were 3.00 and 4.55 mm. The last molar was again significantly smaller with a length of 2.41 mm and a width of 3.87 mm.

Fossil finds

The only known find of Chilecebus so far , a largely complete skull without a lower jaw, was discovered in the Abanico formation . The Abanico Formation is located in central Chile and extends for several hundred kilometers in a north-south direction parallel to the main chain of the Andes . It reaches a thickness of 1000 to 2000 m and is composed of continental, mostly volcanic and pyroclastic deposits. The period of origin of the rock unit probably extends from the Paleogene to the Early Neogene . The region had already been visited by Charles Darwin during his trip with the HMS Beagle in the 1830s, during which he also technically named the exposed rock units in his notes , but there was no knowledge of fossil finds from the Abanico formation. A team of scientists led by John J. Flynn of the American Museum of Natural History discovered the first mammal remains during mapping work in 1988 in the area around Termas del Flaco . Subsequent work on site led to the discovery of two rich fossil sites , known as Tapado Fauna and Tinguiririca Fauna , which belong to the Eocene and the Oligocene , respectively . In 1994, two younger fossil bearing areas were observed in outcrops along the Río Las Leña around 60 km north of Termas del Flaco. The finds were embedded in a hard matrix of volcanic rocks. A total of around 200 objects came to light, most of which include rodents and South American ungulates (mainly Typotheria ). but underneath was also the skull of Chilecebus . Using argon-argon dating, an age value of around 20.09 ± 0.27 million years could be obtained directly from the rock that also contained the primate skull. This corresponds to the section of the Lower Miocene (locally stratigraphically Colhuehuapium ).

Paleobiology

The brain volume of Chilecebus was originally given as about 6.6 to 7.5 cm³. Computed tomographic examinations were able to determine the dimensions more precisely. According to these, the volume was an estimated 7.86 cm³, which corresponds to a weight of around 7.96 g. In relation to a presumed body weight of around 600 g, the encephalization quotient is around 1.1. This is lower than most of today's New World monkeys and also the non-hominine Old World monkeys, and when compared in size, it roughly corresponds to that of the goblin tarsier . However, it exceeds the value of some other fossil primates, such as Aegyptopithecus , a parent group representative of the Old World monkeys, or the more original Proteopithecus . The computed tomographic analyzes revealed a relatively complex structure of the Chilecebus brain . It was in top view of oval shape with a length of 34.1 and a maximum width of 25.9 mm. The front end was narrower than the rear. In side view it was flat and so resembled the brain of the also extinct New World monkey Dolichocebus . Compared to Aegyptopithecus , the anterior section did not bulge as much; in general, the lower part of the brain in Chilecebus was more voluminous than the upper part, while in Aegyptopithecus the opposite was the case. The central longitudinal furrow divided the cerebrum into two halves. In addition, the distinctive furrowing of the cerebral cortex was present. A total of seven pairs of furrows could be determined. The resulting individual brain regions were of different sizes, since the temporal lobe, for example, took up about 40% of the side surface of the brain. This can also be seen in the areas for the sense of sight and smell . In relation to body size, Chilecebus' eye windows are relatively small with a diameter of 9 mm. The optic foramen , the point of passage of the optic nerve into the optic canal , is comparatively small in proportion, it takes up an area of ​​about 1.57 mm². The relationship between the size of the eye window and that of the foramen opticum (the so-called foramen opticum index or OFI) provides information about the light sensitivity of a living being, as it reflects the number of photoreceptors in the retina , which are connected to each other via a ganglion . As a rule, nocturnal monkeys have large eyes and a proportionally smaller optic foramen, resulting in a low optic foramen index and thus a high number of connected photoreceptors. This intensifies the sensitivity to light, but at the same time reduces the eyesight. Expressed in absolute terms, the foramen opticum index is accordingly between 1.0 and 1.2. In diurnal monkeys, whose index ranges from 1.2 to 4.7, it is usually the other way round (smaller eyes, proportionally larger foramen opticum, lower number of connected photoreceptors and thus low light sensitivity compared to high eyesight). For Chilecebus an index of 2.4 can be given, which is in the size range of diurnal monkeys. However, in comparison to today's diurnal monkeys , Chilecebus had particularly small eye windows and consequently small eyes, which probably leads to lower eyesight. The result is similar to some old world monkeys such as Parapithecus or Aegyptopithecus , so that it can be assumed that this was the original condition in early primates. The high visual acuity of diurnal monkeys seems to have developed independently within the Old and New World monkeys. The extent of the olfactory sense can in turn be derived from the size of the olfactory bulb , an extension on the endbrain . Diurnal monkeys with their improved eyesight often have a less developed sense of smell and thus a smaller olfactory bulb than nocturnal monkeys, in which the sensitivity to smells is more finely defined. The olfactory bulb in Chilecebus had a diameter of slightly more than 3 mm and took up a volume of 11.1 mm³, making it relatively smaller than in other dry-nosed primates . In contrast to today's monkeys, Chilecebus does not show a negative correlation between a poorly developed sense of smell and a better developed sense of sight or vice versa. According to this, both sensory abilities developed independently of one another within the monkeys and are not directly causally related. The findings of Chilecebus and some other early primates show that the brain within the primates group did not increase uniformly in volume and specialization, but that the individual brain regions changed more like a mosaic.

The structure of the inner ear in turn makes it possible to obtain further information about the biological ability of a living being. The width and orientation of the semicircular canals allow conclusions to be drawn about agility; the number of turns of the cochlea provides information about hearing ability. So far, only a few studies in primates have been carried out on both. Chilecebus has 2.5 turns, the value lies within the range of variation of the primates, it is lower than in some capuchin monkeys and spider monkeys , but higher than in the finger animal . Sometimes the number of revolutions is associated with the perception of certain frequency ranges or improved tactile perception . The semicircular canals in Chilecebus are built in a more generalized way, so it is possible that the animals were less agile than, for example, today's lion tamarins or marmosets . A swinging, swinging or fast climbing movement can also be ruled out for Chilecebus . Other peculiarities are the short but wide anterior and the elongated posterior arcade in Chilecebus , which is not known in New World monkeys, but occurs in early Old World monkeys. The position of the semicircular canals in relation to one another and their rotation are also designed differently in Chilecebus than in the recent primates examined so far. Nothing can currently be said about any biological functions or taxonomic implications.

The small body size, the protruding front set of teeth and the features of the low-crowned molars with voluminous cusps suggest that Chilecebus was largely herbivorous or fruit-eating.

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

Chilecebus is a genus from the order of the primates (Primates). Within this, the genus belongs to the group of New World monkeys (Platyrrhini), which are mainly tree-living monkeys from the tropical and subtropical areas of South and Central America . The New World monkeys habitually differ from the Old World monkeys by their relatively wider nose, their average smaller body size and the generally developed tail. The latter can be used as a gripping member in some forms . Several families of New World monkeys can be distinguished, the most important of which are the sakia monkeys (Pitheciidae), the spotted monkeys ( Atelidae), the capuchin monkeys (Cebidae) and the marmosets (Callitrichidae). As a rule, the sakia monkeys are regarded as the sister group of all other New World monkeys, which has also been proven molecular-genetic . The oldest fossil record of the New World monkeys dates back to Perupithecus from the Peruvian area of ​​the Amazon basin in the transition from the Eocene to the Oligocene around 35 million years ago.

The exact position of Chilecebus within the New World monkey system is currently not clear. The mixture of modern and antiquated features can be emphasized as remarkable. In some cases, the form is regarded as belonging to a tribe group of the New World monkeys, which includes numerous extinct representatives of the Oligocene and Miocene and which may also be classified as an independent family, the Homunculidae. This goes back to Florentino Ameghino from the year 1894, but according to overwhelming opinion it does not form a self-contained unit. Other authors group Chilecebus in turn with the capuchin-like or with the spiked-tailed monkeys and thus classify the genus in the lines of today's species.

The deviating assignments result from two competing hypotheses on the phylogenesis of the New World monkeys: On the one hand there is the Long Lineage Hypothesis or Morphological Stasis Hypothesis , according to which the extinct Miocene genera can be incorporated as original representatives into the crown group of the New World monkeys. On the other hand, the Stem Platyrrhine Hypothesis or Successive Radiation Hypothesis assumes that the primeval forms are to be viewed as part of a basal radiation phase. Both views are currently controversial. The molecular genetic studies on recent New World monkeys, which are sometimes used to underpin the respective view, are, however, not unambiguous and can be interpreted in various ways, as they are based on different calibration models. Accordingly, the proponents of the Long Lineage Hypothesis assume the splitting of today's New World monkeys 29 to 31 million years ago, those of the Stem Platyrrhine Hypothesis assume a fanning out from around 20 million years ago. With regard to the varying systematic allocation depending on the phylogenetic model, Chilecebus is one of the few exceptions, as in a study from 2019 some proponents of the Stem Platyrrhine Hypothesis also classify the form as a core group representative of the Capuchin species.

The first scientific description of Chilecebus was submitted by a research team led by John J. Flynn in 1995 and appeared in the journal Nature . It is based on the only skull find so far from the Abanico formation in central Chile (copy number SGOPV 3213). It is kept in the Museo Nacional de Historia Natural de Chile in Santiago de Chile . The generic name Chilecebus is on the one hand a reference to the country of origin of the skull, on the other hand the addition cebus is often used in New World monkeys (at the same time it is the generic name of the unhealed Capuchin ). Chilecebus carrascoensis is the only recognized species. The specific epithet refers to Gabriel Carrasco, a fossil collector who was involved in field research by Flynn and his team and who discovered the primate skull.

The current range of the New World monkeys includes the tropical South America and extends to the 29th southern parallel. The Chilecebus find lies at around 34 ° south latitude and is therefore outside of today's occurrence. It thus complements the occurrence of the fossil known representatives in the south. Primate finds here further south are from the Santa Cruz Formation in Patagonia , but they date a little more recently. In addition, he extends the find area in a westerly direction into the area of ​​today's Andes , from where no primate fossils were previously known. In principle, evidence of New World monkeys in the Andean region is rare. Another find dates back to 2003 and concerns an ankle bone , which was discovered on the Río Cisnes at about 44 ° south latitude. Its exact systematic assignment is unclear. At 16.4 million years old, it belongs to the Middle Miocene and is therefore a little younger than the Chilecebus skull .

literature

• John J. Flynn, Andre R. Wyss, Reynaldo Charrier, and Carl C. Swisher: An Early Miocene anthropoid skull from the Chilean Andes. Nature 373, 1995, pp. 603-607, doi: 10.1038 / 373603a0
• 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

Individual evidence

1. ^ ^{A b} Karen E. Sears, John A. Finarelli, John J. Flynn, and André 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
2. ↑ ^{a b c d e f} John J. Flynn, Andre R. Wyss, Reynaldo Charrier and Carl C. Swisher III: An Early Miocene anthropoid skull from the Chilean Andes. Nature 373, 1995, pp. 603-607
3. ^ André R. Wyss, John J. Flynn, A. Norell, Carl C. Swisher III, Michael J. Novacek, Malcolm C. McKenna and Reynaldo Charrier: Paleogene Mammals from the Andes of Central Chile: A Preliminary Taxonomic, Biostratigraphic, and Geochronologic Assessment. American Museum Novitates 3098, 1994, pp. 1-31
4. ↑ John J. Flynn, Raynaldo Charrier, Darin A. Croft, Ralph Hitz and André R. Wyss: The Abanico Formation of the Chilean Andes: an exceptional Eocene-Miocene record of South American mammal evolution. Journal of Vertebrate Paleontology 23 (3 suppl.), 2003, p. 50A
5. ^ John J. Flynn, Darin A. Croft, Ralph Hitz and André R. Wyss: The Talpado Fauna (? Casamayoran SALMA), Abanico Formation, Tinguiririca valley, Central Chile. Journal of Vertebrate Paleontology 25 (3 suppl.), 2005, p. 57A
6. ↑ Darin A. Croft, Reynaldo Charrier, John J. Flynn and André R. Wyss: Recent additions to knowledge of Tertiary mammals from the Chilean Andes. I Simposio - Paleontología en Chile, Libro de Actas, 2008, pp. 91-96
7. ^ Richard F. Kay and Christopher Kirk: Osteological Evidence for the Evolution of Activity Pattern and Visual Acuity in Primates. American Journal of Physical Anthropology 113, 2000, pp. 235-262
8. ↑ 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
9. ^ Xijun Ni, John J. Flynn and André R. Wyss: The bony labyrinth of the early platyrrhine primate Chilecebus. Journal of Human Evolution 59 (6), 2010, pp. 595-607
10. ^ Xijun Ni, John J. Flynn and André R. Wyss: Imaging the inner ear in fossil mammals: High-resolution CT virtual reconstructions. Palaeontologie Electronica 15 (2), 2012, p. 18A ( [1] )
11. ↑ 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
12. ^ ^{A b} 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
13. ↑ ^{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
14. ↑ 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
15. ↑ 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
16. ↑ 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
17. ↑ 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
18. ↑ 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] )
19. ^ 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
20. ^ Alfred L. Rosenberger: Evolutionary Morphology, Platyrrhine Evolution, and Systematics. The Anatomical Record 294, 2011, pp. 1955-1974
21. ↑ 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
22. ^ ^{A b} Richard F. Kay, Lauren A. Gonzales, Wout Salenbien, Jean-No € el Martinez, Siobh> to B. Cooke, Luis Angel Valdivia, Catherine Rigsby and Paul A. Baker: Parvimico materdei gen. Et sp. nov .: A new platyrrhine from the Early Miocene of the Amazon Basin, Peru. Journal of Human Evolution 134, 2019, p. 102628
23. ^ 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
24. ↑ 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
25. ^ 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
26. ↑ 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
27. ^ Marcelo F. Tejedor: New fossil primate from Chile. Journal of Human Evolution 44, 2003, pp. 515-520