Namachloris

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Namachloris
Temporal occurrence
Bartonian (Upper Eocene )
41.3 to 38 million years
Locations
Systematics
Higher mammals (Eutheria)
Afrotheria
Afroinsectiphilia
Tenrecus (Afrosoricida)
Gold mole (Chrysochloridae)
Namachloris
Scientific name
Namachloris
Pickford , 2015

Namachloris is an extinct genus of the golden mole family thatlivedin southern Africa in the Upper Eocene around 41 to 38 million years ago. It is one of the earliest known representatives of the gold mulle and the best-documented ever. The finds cover almost the entire skeleton, including the characteristic third forearm bone, which was first documented for an extinct form of the golden mole, and some complex hand structures. They come from a travertine area inthe restricted area in the south of Namibia , their discovery dates back to 2013. The fossils can be used to reconstruct an animal that was slightly larger than today's golden mole rat . The special design of the forelimbs suggests good burrowing properties, according to which Namachloris evidently pursued a similar underground way of life as the species today. The arrangement of the fossils in spherical concentrations is interpreted as the remains of birds of prey . Thegenus was first described in 2015.

features

Namachloris was a small representative of the golden mole , which was slightly larger than today's desert golden mole ( Eremitalpa ). The skull was short, pointed at the front and wide at the back, as with today's gold mullets, it reached its greatest width in the area of ​​the skull. The occiput was strongly rounded and had strong, widely spaced articular surfaces, and there was a small sagittal ridge on the parietal bones . The zygomatic arch was fully developed, but slender, but increased in solidity towards the rear. The orbit was only slightly developed by a small indentation on the skull, the infraorbital foramen in front of the anterior border of the orbit was elongated and lay above the first and second molars. The nasal bone had no adhesions with the middle jawbone or the upper jaw , but with the frontal bone . On the median jawbone, strong bony bulges appeared on the side of the nostrils. The tympanic membrane at the base of the skull was relatively large. The cochlea was very coiled with its 3 to 3.5 revolutions and thus resembled that of today's gold mulle, which has a total turn of up to 1200 °. Some surviving ossicles like the anvil also had individual swellings. The hammer was built normally with a small, rounded head. Its weight of 0.48 mg is less than that of any recent representative of the golden mole.

Noticeable on the lower jaw was the angled process, which ran downwards at an angle to below the lower edge of the body of the lower jaw and ended there straight. It may have been in contact with the hyoid bone, as with the recent gold mole . The mandibular joint sat on an almost horizontal, rearward-oriented process slightly above the occlusal plane, was rounded and was located in a clearly defined glenoid pit on the underside of the skull. Among the two front premolar and the first molar was in each case a mental foramen formed. The bit included as with many modern gold Mullen total of 40 teeth with the following dental formula : . In the front teeth there were only a few differences to the more recent forms, so the inner upper and the second lower incisor were each significantly larger than the others. There was a short diastema behind the inner upper incisor, which was shaped like a column and pointed slightly inwards . The canine tooth was also enlarged in the lower jaw . The anterior premolars only had a small cusp on the chewing surface, which gave them a nail-like shape and were not molarized, so they did not resemble the molars. The rearmost premolar, on the other hand, had several cusps and almost reached the size of the molars. The rear molars had three main cusps ( tricuspid ). They also showed themselves to be extremely zalambdodont , that is, the ectolph, one of the main shear folds on the occlusal surface, formed the shape of a "V", at the tip of which there were two of the main cusps (the paraconus and the metaconus). These stood close together and were fused together at the base. In contrast to other zalambdodont mammals as well as today's gold mole, the protoconus, the third main cusp, dominated the tooth crown with its extremely wide design. On the lower molars there was a very large talonid, a deep protrusion of the chewing surface, in which the protoconus of the upper molars engages when the teeth are closed. The third molar, which is greatly reduced in size or not developed at all in today's Goldmullen, was barely reduced in size in Namachloris , which underlines the primeval status of the shape. The length of the row of teeth from the last premolar to the last molar was 4.9 mm in the upper jaw and 4.6 mm in the lower jaw.

In all Goldmullen the anterior musculoskeletal system has clear adjustments to a digging way of life. In Namachloris, the collarbone had the shape of a razor with a rod-like extension that was connected to one of the two processes of the acromion on the shoulder blade . The first rib was extremely short and wide like a paddle. It resembled that of today's gold mulle and thus indicates that the circumference of the anterior chest was already significantly reduced in Namachloris . The humerus had a massive shape and had an extremely extensive lower joint end (elbow joint), the width of which corresponded to the length of the entire bone. This widening took place mainly through the lateral stretching of the inner epicondyle and the thickening of the outer joint role (capitulum). The outer epicondyle protruded steeply above the capitulum as a vertical bone wall. A strong bone ridge ran along the shaft of the humerus as a muscle attachment point (deltopectoral ridge). The most noticeable characteristic of the ulna was the extremely elongated extension of the upper joint ( olecranon ), which was laterally narrowed and so leaf-like and was also clearly curved. On the underside of the equally robust spoke there was a prominent pit at the lower end, which is spanned by a bony bridge in today's Goldmullen, but which was missing in Namachloris . According to today's Goldmullen, Namachloris also had a "third" forearm bone, which is an ossified tendon of the flexor digitorum profundus muscle , a flexor muscle of the forearm. In contrast to today's gold mole, whose “flexor” bones are more tubular, Namachloris's showed a noticeable swelling on the inside around the middle of the shaft, on which there were joint surfaces for the connection with the ulna and the radius. In addition, the lower end was widened and ended in three button-like swellings, on which parts of the wrist were probably directed. The triplex bone, which forms the third finger ray, is a distinctive structure of the gold mulle's hand. The triplex bone consists of the corresponding third metacarpal bone and the first and second phalanx, which are firmly fused together. In Namachloris , the proportion of the first phalanx in the triplex bone reached about the length of the metacarpal bone and exceeded that of the second phalanx. In today's gold mole, however, the triplex bone is more reduced so that the first phalanx is no longer visible. Another characteristic formation occurs in the gold mole on the second finger ray, in which the large polygonal bone , the small polygonal bone and the second metacarpal bone are also fused together (the so-called trapezium-trapezoid-metacarpal-II complex or "ttm" or "totem." "-Bone). In Namachloris, this had a complex surface of humps and depressions that clicked into the corresponding structures of the triplex bone and thus gave the two finger beams a stable connection. The end links of the fingers were split and could accommodate strong claws. The end of the joint hung over on the back.

The posterior musculoskeletal system, on the other hand, is less specialized in the gold mole. The pelvis corresponded to that of today's representatives, in contrast to this, a roughened surface appeared on the surface of the ischium near the acetabulum , which possibly served as a starting point for a reinforced supraspinous ligament , which helps stabilize the spine; however, such a structure is unusual for small mammals. The thighbone of Namachloris was narrowed in front and behind, and the head, which sat on a short neck, reached the same height as the Great Rolling Hill. A third rolling hill was prominently located in the middle of the shaft, the shaft in turn was noticeably curved laterally. The lower joint (knee joint) was also flattened, but this did not appear quite as clearly as in today's desert gold mole. The tibia and fibula were fused together above and below. The strong lateral curvature of the shin along the upper shaft section created a wide opening between the two lower leg bones. The ankle joint at the lower end of the two bones was designed similarly to that of today's gold mullets and had a concave joint facet that articulated with a spherical joint on the heel bone . There was also a small, flat joint head on the ankle bone , which steered with a flat joint dent on the shin bone. On the other bones of the foot, such as the metatarsal bones , there were mostly only a few deviations from today's forms of the gold mole.

Fossil site

Namachloris is known from around 120 fossil units, which include partial skeletons as well as skull remains, mandibular fragments, isolated teeth and almost all parts of the body skeleton. It is the so far best documented fossil representative of the gold mole. All finds come from the northern restricted area in the south of Namibia . They came to light on the so-called Eocliff , a fossil deposit at the western foot of the Klinghardt Mountains . Today the region is characterized by the dry, desert-like climate of the Namib and is located in the middle of a rather flat undulating plain in the coastal hinterland ( Plain Namib ). The Eocliff deposit is a semicircular, 150 m diameter and 15 m high travertine and tufa block that rises like a dome over the landscape and is supported by sediments of the Ystervark carbonatite formation . The underlying formation consists of limestones (slab and sintered limestones), between which deposits of volcanic origin are interposed , the radiometric age of which dates between 45 and 40 million years and thus to the Middle to Upper Eocene ( Lutetium to Bartonium ). The travertine originated from a nearby source, which drew its limestone wealth from the sediments of the Ystervark carbonatite formation. Originally it was probably much wider, as there is a shallow depression about 1.5 km to the east, which is also filled with fossil-bearing travertine and is called Eoridge . The deposits in the depression can be traced back to a former swamp area, which may have been the drainage basin of the source of Eocliff . The travertines and limestone tuffs are partially silicified , which happened during the building of the sediment block . Since this silicification also influenced the lying limestones of the Ystervark carbonatite formation, it can be concluded that a one-off process during the exit of the bartonium. In the larger regional context, the silicified limestone deposits are covered by marine formations. These go back to an influence of the sea to which the area of ​​today's Namib was subject at the end of the Eocene ( Priabonian ) around 38 million years ago.

The Eocliff site was discovered in 2013. Before that, there were already first indications of very fossil-rich deposits in the restricted area, which are stored in the calcareous sediments of the Ystervark carbonatite formation, but are somewhat older. The Eocliff finds are very extensive and include innumerable plant remains from individual plant parts to complete algae mats and smaller vertebrates . The latter are represented with a range of several thousand bone elements, which in addition to isolated scaled crawfish , snakes and birds mainly represent mammals . For example, Namagale , Sperrgale and Arenagale from travertine could be described, three early representatives of the Tenreks , the former being close to the otter shrews , the latter two to the hedgehog treks . With Namaloris an early member of the primates is also proven, which belongs to the line of development of the Loris . Further finds can be referred to the elephants and rodents . The taphonomic difference to the nearby site of Eoridge is striking , as it not only shows much more frequent remains of aquatic life in the form of freshwater snails, but also fossils of larger mammals, for example early snails and members of the family of the Anthracotheriidae , which may have been associated with the Hippos are more closely related. Both sites have in common the occurrence of rodents and elephants, who have high-crowned molars and thus indicate that open landscapes must have existed in the area. They show that the dense forests that were still predominant in the Middle Eocene gradually thinned out and gave way to open landscapes, thus leading to the extremely arid conditions that have prevailed in the Namib since the Miocene . The age classification made on the basis of geological data is not shared by some paleontologists , as the fauna association also allows a significantly younger age for Eocliff and Eoridge . This relates, for example, to the presence of the anthracotheria, which only appear in Africa in the transition from the Eocene to the Oligocene . Due to some proven rodents and hyrax, a position in the Miocene would also be possible.

Paleobiology

The extensive finds of Namachloris provide an insight into the way of life of this early representative of the golden mole. The skeleton shows some special adaptations that are reminiscent of today's gold mulle. The front limbs in particular are highly specialized and were probably adapted to a digging way of life, as is the case with today's gold mole. This is not only supported by the strong long bones with their distinctive muscle attachment points and some formations that are typical of fossilized (underground) animals, such as the extremely wide elbow joint on the humerus, the elongated upper articular process on the ulna ( olecranon ) or the enlarged and clearly curved ones The end links of the fingers, here especially on the third ray, which had massive, curved claws. In addition, there are further reinforced joint connections, for example between the "flexor" bone and the two other forearm bones or between the triplex bone on the third and the ttm bone on the second finger ray and from these to the forearm. This created an extremely stable chain of bone elements that reached from the shoulder blade to the terminal phalanges of the second and third fingers and allowed for powerful movement of the front leg. Due to the often deeply arched joint surfaces with partially lateral lips or ridges, it can be concluded that mainly forward and backward movements of the arms were supported, less inward or outward turning. The strongly curved end phalanx of the middle finger with the front notch indicates a curved, narrow claw with sharp upper and lower edges. This could cut through soft sediment with the predominant forward and backward movement of the arm and thus ensured effective locomotion. Namachloris was therefore adapted to very loose subsoil, similar to today's desert gold mole ( Eremitalpa ), which "swims" through the soft sand. The additional raised edges at the nasal openings on the middle jawbone are an indication that Namachloris already had a leathery nasal pad. This is typical of today's gold mole and is also used when digging underground. In terms of the structure of the teeth, Namachloris showed only a few functional differences to the recent gold mole rats, so that a basically similar diet based on invertebrates can be assumed.

The Namachloris finds on the Eocliff have been handed down in individual small concentrations of a few centimeters in length, often in connection with other small vertebrates: These concentrations probably go back to the burrows of birds of prey or owls that nested in the trees near the source. Even today, owls are the most important predators of the golden mole. Complete bulges on the Eocliff usually contain one or two skeletons, but most of them have decayed through natural processes. Longer transport through water can be ruled out, as hardly any traces of displacement can be seen on the fossils. On Eocliff young adult animals dominate (in which the last or next to last molar has not yet erupted), pups are completely absent. This picture also corresponds to the present-day conditions in gold mole rats captured by birds of prey.

Systematics

Namachloris is an extinct genus from the golden mole family (Chrysochloridae). The golden mole represent small, endemic animals native to Africa , which occur in narrowly defined landscapes due to their underground way of life and strong specialization. They inhabit open, partly desert-like regions, savannah landscapes and forest areas. Its current main area of ​​distribution is in southern Africa, a few representatives can also be found in the eastern or central part of the continent. The closest relatives are the Tenreks (Tenrecidae), with which the Goldmulle are in the order of the Afrosoricida . Both groups probably separated as early as the transition from the Upper Cretaceous to the Paleocene around 65 million years ago. Gold mulle are rarely known to have been fossilized . Besides the genera Diamantochloris and Damarachloris from the Middle Eocene of Namibia , Namachloris possibly represents one of the oldest fossil representatives of the family. Earlier, early forms of the gold mole or their close relatives from the Lower Oligocene of Egypt and the Lower Miocene of East Africa were known. The early appearance of the three genera in southern Africa could indicate a possible origin of the entire family in this region. In addition, it dates before the molecular-genetic date of the greater diversification of the family in the course of the Oligocene, around 28.5 million years ago. This very primeval position within the gold mole also points to some very primitive features, for example the slightly differently structured teeth with the rearmost molar that is not reduced in size or the lack of the bony bridge at the lower end of the spoke, which is found in the desert gold mole and occurs with Cape Goldmull or their extinct relatives. In addition, the structure of the middle ear indicates a position of Namachloris outside the crown group of the golden mole.

The genus Namachloris was first scientifically described by Martin Pickford in 2015 . The holotype (specimen number GSA Na 1) is a complete skull with lower jaw as well as associated body skeleton parts such as scapula fragments, the humerus, the ulna, parts of the pelvis, a third phalanx and metapodia. The finds come from the Eocliff site number 7. The name Namachloris is derived on the one hand from the term Nama , which means something like "desert" or "wasteland" in the local language, on the other hand from chloris , which means the Greek goddess of flowers whose Roman counterpart is Flora . The Greek word χλωρός ( chlōrós ), which can be translated as “light green” or “fresh” , also refers to chloris . The word is reminiscent of the greenish shimmering skin of today's belt mole and is often used as an addition to scientific terms. The only known species is Namachloris arenatans . The specific epithet consists of the Latin words arena for "sand" and natans for "swimming" (from natare for "swimming"), thus referring to the supposed sand-swimming way of life of Namachloris .

literature

  • Martin Pickford: Late Eocene Chrysochloridae (Mammalia) from the Sperrgebiet, Namibia. Communications of the Geological Survey of Namibia 16, 2015, pp. 153–193

Individual evidence

  1. ↑ a b c d e f g h Martin Pickford: Late Eocene Chrysochloridae (Mammalia) from the Sperrgebiet, Namibia. Communications of the Geological Survey of Namibia 16, 2015, pp. 153–193
  2. ↑ a b c Matthew J. Mason, Nigel C. Bennett and Martin Pickford: The middle and inner ears of the Palaeogene golden mole Namachloris: A comparison with extant species. Journal of Morphology 279 (3), 2018, pp. 375-395, doi: 10.1002 / jmor.20779
  3. ^ A b Robert J. Asher: Recent additions to the fossil record of tenrecs and golden moles. Afrotherian Conservation 15, 2019, pp. 4–13
  4. ↑ a b c Martin Pickford, Brigitte Senut, Helke Mocke, Cécile Mourer-Chauviré, Jean-Claude Rage and Pierre Mein: Eocene aridity in southwestern Africa: timing of onset and biological consequences. Transactions of the Royal Society of South Africa 69 (3), 2014, pp. 139-144
  5. ↑ a b Martin Pickford: Cenozoic Geology of the Northern Sperrgebiet, Namibia, accenting the Palaeogene. Communications of the Geological Survey of Namibia 16, 2015, pp. 153–193
  6. ↑ Martin Pickford, Brigitte Senut, Jorge Morales and Israel Sanchez: Fossiliferous Cainozoic Carbonates of the Northern Sperrgebiet. Memoir of the Geological Survey of Namibia 20, 2008, pp. 25-42
  7. ↑ Martin Pickford: Late Eocene Potamogalidae and Tenrecidae (Mammalia) from the Sperrgebiet, Namibia. Communications of the Geological Survey of Namibia 16, 2015, pp. 114–152
  8. ↑ Martin Pickford: Late Eocene Lorisiform Primate from Eocliff, Sperrgebiet, Namibia. Communications of the Geological Survey of Namibia 16, 2015, pp. 194–199
  9. ↑ Laurent Marivaux, El Mabrouk Essid, Wissem Marzougui, Hayet Khayati Ammar, Sylvain Adnet, Bernard Marandat, Gilles Marzeraud, Rodolphe Tabuce and Monique Vianey Liaud: A new and primitive species of Protophiomys (Rodentia, Hystricognathi) from the Djebel middle Eocene el Kébar, Central Tunisia. Palaeovertebrata 38 (1), 2014, p. E2
  10. ^ Hesham M. Sallam and Erik R. Seiffert: New phiomorphic rodents from the latest Eocene of Egypt, and the impact of Bayesian "clock" -based phylogenetic methods on estimates of basal hystricognath relationships and biochronology. PeerJ 4, 2016, p. E1717 doi: 10.7717 / peerj.1717
  11. ^ Gary N. Bronner: Family Chrysochloridae Golden-moles. In: Jonathan Kingdon, David Happold, Michael Hoffmann, Thomas Butynski, Meredith Happold and Jan Kalina (eds.): Mammals of Africa Volume I. Introductory Chapters and Afrotheria. Bloomsbury, London, 2013, pp. 223-225
  12. Jump up ↑ Robert W. Meredith, Jan E. Janečka, John Gatesy, Oliver A. Ryder, Colleen A. Fisher, Emma C. Teeling, Alisha Goodbla, Eduardo Eizirik, Taiz LL Simão, Tanja Stadler, Daniel L. Rabosky, Rodney L. Honeycutt, John J. Flynn, Colleen M. Ingram, Cynthia Steiner, Tiffani L. Williams, Terence J. Robinson, Angela Burk-Herrick, Michael Westerman, Nadia A. Ayoub, Mark S. Springer, and William J. Murphy: Impacts of the Cretaceous Terrestrial Revolution and KPg Extinction on Mammal Diversification. Science 334, 2011, pp. 521-524
  13. ↑ Martin Pickford: Chrysochloridae (Mammalia) from the Lutetian (Middle Eocene) of Black Crow, Namibia. Communications of the Geological Survey of Namibia 16, 2015, pp. 105–113
  14. ^ Martin Pickford: New Chrysochloridae (Mammalia) from the middle Eocene of Black Crow, Namibia. Communications of the Geological Survey of Namibia 21, 2019, pp. 40–47
  15. ↑ C. Gilbert, PC O'Brien, G. Bronner, F. Yang, A. Hassanin, MA Ferguson-Smith and TJ Robinson: Chromosome painting and molecular dating indicate a low rate of chromosomal evolution in golden moles (Mammalia, Chrysochloridae) . Chromosome Research 14, 2006, pp. 793-803
  16. ^ Robert J. Asher and D. Margaret Avery: New Golden Moles (Afrotheria, Chrysochloridae) from the Early Pliocene of South Africa. Palaeontologia Electronica 13 (1), 2010, p. 3A ( [1] )