Spinolestes
| Spinolestes | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Temporal occurrence | ||||||||||||
| Upper Barremium | ||||||||||||
| 129.4 to 126.3 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Spinolestes | ||||||||||||
| Martin , Marugán-Lobón , Vullo , Martín-Abad , Luo & Buscalioni , 2015 | ||||||||||||
Spinolestes is an extinct genus of early mammals that lived in the Lower Cretaceous around 127 to 125 million years ago. It belongs to the family of the Gobiconodontidae within the group of the Eutriconodonta , whose representativesappeared quite diversein the Mesozoic and were the largest known mammals at that time. The genus is only known from one - almost complete - skeleton. This was discovered in the fossil depositof Las Hoyas in central Spain . The animal that has the species name Spinolestes xenarthrosusreceived, reached the size of a present-day mouse and probably lived on the edge of water, where it predatory food. The preservation of the skeleton is extremely good and also shows parts of the soft tissue cover in the form of skin and hair, as well as individual internal organs are drawn. This made it possible to show that the subdivision of fur, typical of today's mammals, into outer hair and woolen hair was developed by the early representatives of the Mesozoic era. In addition, special hair formations in the form of spikes can be detected, as well as cornified skin flakes. Another special feature in skeleton construction are additional joint surfaces on the vertebrae, which strengthen the spine more firmly. The genus was scientifically described in 2015.
features
Spinolestes was a mouse to rat-sized animal with a reconstructed body weight of 52 to 72 g, making it a medium-sized representative among the mammals of the Mesozoic Era . So far, only one skeleton is known to lie on the left side, with the exception of the skull, which rests on the forehead, disarticulated from the rest of the body. The skull measured a total of 35.8 mm in length, the width between the zygomatic arches was 17.5 mm. It was only slightly stretched, but had a strong, rounded rostrum . The closed zygomatic arch was relatively straight and less expansive. It was mainly formed by the arched process of the temporal bone and extended roughly to the glenoid fossa for the mandibular joint. The glenoid pits were laterally elongated, but not trough-shaped. The articular surfaces of the occiput were large, oval in shape. The lower jaw was relatively short at 28.7 mm, but built robustly. The angular process was missing at the posterior end, a noticeable characteristic of the eutriconodonta , the region was clearly rounded and provided with strong bony ridges. The Meckel's cartilage , which is absorbed in the lower jaw in the higher mammals , was ossified in Spinolestes as in other eutriconodonts. It was long and curved in the shape of a clasp and had a blunt end. The development of Meckel's cartilage indicates that the middle ear was characteristically connected to the lower jaw via this; however, it is not recorded. The articular process showed a rotation in relation to the crown process and the body of the mandible, the mandibular joints were oval and wide. The dentition still had the original structure of the early mammals with an increased number of molars . The tooth formula was as follows: So a total of 40 teeth were formed. However, at the time of death, the animal was in the process of exchanging the posterior teeth from the deciduous dentition to the permanent dentition. The deciduous teeth, characteristic of the Gobiconodontidae and unlike other mammals, had developed ontogenetic predecessors of the molars, which are generally referred to as molar-shaped . The incisors were smaller at the top than at the bottom and were not in a closed row. The innermost of each had a conical shape and was the largest, in the lower jaw it stood obliquely forward ( procumbent ), which is a characteristic feature of the triconodonts. The teeth became smaller towards the canine . The canine tooth itself had an incisiform shape . The posterior premolars and molars showed three pointed cusps ( tricuspid ) on the chewing surface , of which the middle one had the most prominent shape.
The spine comprised 16 thoracic, 7 lumbar, 3 sacrum and 22 caudal vertebrae, cervical vertebrae are not known. The vertebrae formed a series with a length of 8.3 cm, the caudal spine was 10.7 cm long and thus comprised about half the total body length. Of the 23 vertebrae, there were a total of 20 ribs that were two-headed and round in cross-section. From the 9th and 10th to the 16th and 17th vertebrae, there were additional articular surfaces on the transverse processes , so-called xenarthrals or secondary joints, which are a defining feature for the secondary articular animals of South America, but occasionally also in other mammals not closely related to the secondary articulated animals occur. Spinolestes and the other gobiconodontids, for example, lacked the teat process (processus mammillaris), which forms one of the typical xenarthral connections in secondary articulated animals. The caudal vertebrae were relatively short at the base of the tail, but elongated backwards and became slimmer. Some of the anterior caudal vertebrae had doubled transverse processes. The vertebral arches were relatively long and oriented forward. The shoulder girdle was generally similar to that of the Theria and was equipped with a broad, triangular shoulder blade . The shoulder bone was set very high, the acromion, a prominent muscle attachment point, was directed forward and downward. Another appendix was on the rear edge. In addition, a collarbone of robust and curvy shape was developed. The humerus , which was 19.7 mm long, had a hemispherical joint head that had no neck attachment. The lower part of the shaft was rotated around 40 ° counterclockwise. At the elbow joint, the joint surface for the ulna and the radius were separated from each other, which is a rather primitive feature, and there were also prominent attachment points for the arm muscles. The ulna and radius were not fused together, the upper articular process of the ulna, the olecranon , had a massive but short shape and only took up about 20% of the length of the total bone, which was 20.1 mm. In contrast to the clearly modern design of the shoulder girdle, the pelvis, in accordance with other eutriconodonts, had a rather primitive structure; its three bones were not fused to the acetabulum. The pouch bone , distinctive for the marsupials , appeared as a broad, triangular formation. The femur was 22.7 mm long, the joint head sat on a distinct neck. The large rolling mound reached about the height of the head of the femur, the small rolling mound, on the other hand, was not prominent. Both the tibia and fibula had a round shaft and were approximately the same size. There was no bony connection between them. A fabella was also formed on the knee joint . The hands had five rays, the individual finger bones were rather short and thick. Each finger beam ended in claw-like limbs that were not very curved and only moderately narrowed at the sides. There were also small notches on the sides into which the horn attachments clicked. The foot is disarticulated in the found skeleton and scattered around the skull.
Reference
The only known skeleton of Spinolestes came to light in the fossil deposit of Las Hoyas around 20 km east of the city of Cuenca in the province of the same name in central Spain . The fossil site is located in the Iberian Mountains in the eastern part of the Iberian Peninsula , in the highlands of Serranía de Cuenca , which in turn can be divided into several secondary basins, one of which is Las Hoyas. The oldest continental deposits of the Serranía de Cuenca consist of sandstones and limestones that belong to the Lower Cretaceous and are discordant over central Jurassic limestones of marine origin. The terrestrial sediments can be assigned to two formations, whereby the lower El Collado formation is only slightly exposed. Much more extensive are the deposits of the La Huérguina Formation , which are up to 400 m thick and correspond to a total of four layers or subunits. The exceptional site Las Hoyas belongs to the second layer (counting from the bottom), which is called Rambla de Las Cruces II . It consists of a series of finely layered limestones ( plate limestone ), which go back to one or more former lakes or a flood plain in an originally low relief landscape.
The Las Hoyas fossil site was discovered in 1985. The find material from the finely laminated deposits is characterized by an extraordinarily good preservation and is made up of several thousand trace and body fossils. The proven organisms include bacteria, fungi, algae, protists, plants and animals and belong to a total of more than 130 genera. Both invertebrates and vertebrates are represented among the animals ; they are often found in the anatomical association with only minimal traces of displacement. Overall, the arthropods dominate, making up almost 45% of the total finds. Particularly noteworthy is the insect fauna , which is one of the most significant of the Mesozoic Era. Vertebrates identified so far include fish , amphibians , scaled reptiles and archosaurs . Las Hoyas gives, among other things, an insight into the early development of birds ; in addition to these, ornithomimosaurs and allosaurs are particularly represented among the dinosaurs . Spinolestes is the first known mammal at the site. In addition, Las Hoyas is also known for the excellent preservation of soft tissue , which is present in the form of feathers , skin remnants, stomach contents or lumps. With the help of the rich flora and fauna community, a subtropically influenced landscape can be reconstructed, which was characterized by coniferous plant communities. From a biostratigraphic point of view, a classification in the outgoing Barremium can be assumed about 127 to 125 million years ago.
Paleobiology
Tradition of the soft tissues
The skeleton of Spinolestes from Las Hoyas shows an extraordinarily good preservation of the soft tissue . This is due to the action of microbiotic processes, whereby the organic components were passed on as a result of the storage of phosphates . Particularly noteworthy are remnants of the skin and the coat that can be seen in individual areas of the body and head. Among other things, a covering of outer hair was preserved in the crown area , the neck and the shoulder , which also extends over the back and the tail. Possibly it was a kind of mane that continued as a stripe on the back. On the other hand, thick woolly hair has been handed down on the rest of the body . The division of the fur into top and woolen hair, which is typical today for mammals and occurs in both monotones , marsupials and higher mammals , was therefore already pronounced in the early mammals of the Mesozoic Era. Individual remnants of skin from the middle back area reveal characteristic wrinkles, in which there are hair follicles from which outer and woolen hairs sprout like bundles. In the follicles, partially egg-shaped structures can be detected, which can be interpreted as hair roots. The individual hairs are also structurally preserved. The hairs of the top hair are about 3 to 5 mm long and have a diameter of 20 to 35 μm. They are covered externally (on the cuticle ) with individual scales that form an irregular pattern. Split hair shows a medullary canal, which is not continuous, but divided into individual chambers. The hair cortex is wide and consists of spindle-shaped cells. The wool hair, on the other hand, is significantly thinner and shorter. Your cuticle is covered with scales arranged in a ring. On individual hairs, noticeable thickenings of about 1 mm in length occur in certain areas of the shafts. In modern comparison, they resemble certain hair diseases caused by fungal infections, such as dermatophytosis , but this phenomenon could also be caused by post-mortem processes.
The significantly thicker hairs that occur in the pelvic area and have a diameter of 80 to 130 μm should be emphasized. They consist of several fused tubes, each of which is scaled on the outside and has a medulla on the inside. The tubes probably represent single hairs that have grown together to form spines. These proto-spines form a dense vegetation in which thicker and thinner ones alternate. The orientation of the spines is not uniform, but random or irregular. In addition, scale-like skin formations were detected in the back area, each around 4 mm long and with an oval or rounded outline. Assuming that they were originally covered by a layer of keratin , these structures could represent flakes of skin that covered the body randomly, but together with the proto-spines formed a homogeneous matrix.
A part of the body outline can be seen on the back and neck due to the tracing of the soft tissue. The line of the back is almost completely preserved, the formation of the head can be seen in front despite the displacement of the skull. The shape of the left ear, which was 17.5 mm long and 8.5 mm wide and had a semi-oval shape, was also preserved, the auricle may have been bare. Inside the anterior thorax there is a sediment-filled body around 11 mm long, which is interpreted as a remnant of the lungs due to its position . This view is supported by numerous branched tubes, which obviously represent the bronchial system through which the air flow is directed to the alveoli . A reddish spot of 20 mm behind the lungs, on the other hand, is regarded as an indication of the liver , the striking color being due to the accumulation of iron in the organ. Indirectly, the presence of the diaphragm in Spinolestes can be inferred from the position of the lungs and the liver as well as the arched space between them, which runs convexly from the lower end of the third rib to the rib attachment of the 15th rib on the spine . The mammalian diaphragm developed with its function as a respiratory muscle together with the animals' increasingly good and persistent running characteristics; the early reference in Spinolestes suggests that the structure had already existed in Mesozoic mammals.
Way of life
Spinolestes probably lived mostly terrestrially. This is indicated by the relatively short phalanxes of the hand and the only slightly curved terminal phalanges, which exclude a more arboricolous locomotion. The general structure of the musculoskeletal system suggests that Spinolestes, like his close relative Gobiconodon, rather moved by walking. The comparatively relatively broad end links of the fingers, however, support a ditch in the ground, which is also indicated by the numerous raised surfaces on the arm bones, which suggest strong foreleg muscles. However, the olecranon , which is remarkably short in relation to the length of the ulna, speaks against an exclusively fossorial (underground burrowing) way of life of Spinolestes , whose relation to one another is in the lower range of that of recent burrowing animals. According to this, the representatives of Spinolestes occasionally pawed or scratched the ground for food. Among other things, the tail could have had a supporting effect on the body, which is often the case in today's burrowing animals and is to be assumed in Spinolestes due to the shape and formation of the caudal vertebrae . The secondary joints of the thoracic and lumbar vertebrae, which serve to strengthen the spine, are also noteworthy. Such formations occur today among other things in the South American articulated animals , they have also been proven in individual fossil forms, for example in the likewise Mesozoic Fruitafossor from the Morrison Formation of Colorado . Like today's armadillos and anteaters , Fruitafossor's skeleton structure was clearly adapted to digging in the ground, with the more strongly crossed spine promoting this way of life. Analogous to the secondary articulated animals, Fruitafossor has a homodontic dentition, the teeth of which, as in the secondary articulated animals, no longer have any tooth enamel ; Both represent an extreme specialization. Spinolestes differs significantly in these features and is more similar to today's members of Scutisorex , an African shrew species that also has secondary joints on the spine, but has normal, heterodontic teeth. The animals inhabit swampy palm forest areas and feed on insect larvae. The animals seek their food by wedging themselves between the trunk of the trees and the palm fronds lying on the ground and by prying away the fronds with the help of their reinforced back. For Spinolestes , based on the anatomical features, a similar way of life can be assumed, the distinctive pointed-humped teeth of the Gobiconodontidae advocate a general carnivorous to omnivorous diet.
In the structure and the only local formation of the spines on the rear, Spinolestes again shows similarities with today's spiny mice , and the hair formation may also have had a similar function. The spines can easily be stripped off in the spiny mice, which plays a role in escape behavior. As a result, an animal can escape relatively easily if bitten from behind, while the predator only retains the spines in its mouth. The skin flakes of Spinolestes could have had a similar protective function .
Systematics
|
Internal systematics of the eutriconodonta according to Martin et al. 2015
|
Spinolestes is a genus of the family of gobiconodontidae within the now-extinct group of eutriconodonta . The Eutriconodonta were represented quite variedly in the Mesozoic Era and included the largest known mammals at that time. They are named after their prominent feature, the three - arranged in a row - cusps on the chewing surfaces of the molars. However, this feature is rather original and also occurs in other, not closely related forms (for this reason, the term Triconodontidae was introduced by Othniel Charles Marsh in 1887, which united numerous primeval mammals with three-pointed teeth). In the Eutriconodonta, the teeth are clearly narrowed laterally. Overall, the representatives of the eutriconodonts were relatively sturdy and, according to the design of the teeth with the sharp-edged tips or cusps on the chewing surface, represented predatory animals. The geological findings indicate that they mainly lived near water. The eutriconodonta are sometimes placed at the base of the crown group of mammals or viewed as its sister group, but they could also stand at the side of a group of Multituberculata , Gondwanatheria and the crown group of mammals. Within the Eutriconodonta, several families are distinguished, one of which is the Gobiconodontidae. These are mainly passed down from the Lower Cretaceous of central and eastern Asia and northern America. So far only a few finds from Spain and England in the form of isolated teeth have been reported in Europe. The Gobiconodontidae have a robust skull as well as an obliquely protruding inner incisor in the lower jaw. The cusps of the lower molars are in one line, but are at an angle to each other in the upper molars. A special feature of the group can be found in the atypical change of teeth of the posterior teeth from molar-shaped predecessors of the posterior molars in the deciduous dentition to the permanent molars. Spinolestes forms within the Gobiconodontidae a closer family group with Gobiconodon and Repenomamus , two significantly larger representatives.
The first scientific description of Spinolestes took place in 2015 by Thomas Martin and research colleagues. The holotype (specimen number MCCM LH30000) includes the only skeleton from Las Hoyas in Spain to date, which is distributed over four individual plates, which, when put together, are a total of 30 by 20 cm. The name Spinolestes is composed of the Latin word spinosus for "thorny" or "prickly" as a reference to the spiky hair on the rear part and the Greek word λέστης ( lestes ) for "robber" or "thief", the latter is often added to the name predatory mammals. The only known species is Spinolestes xenarthrosus . The specific epithet refers to the secondary joints formed on the thoracic and lumbar vertebrae and consists of the Greek names ξένος ( xenos ) for “foreign” and ἄρϑρον ( arthron ) for “joint”.
Individual evidence
- ^ Zhe-Xi Luo: Developmental patterns in Mesozoic evolution of mammal ears. Annual Review of Ecology, Evolution, and Systematics 42, 2011, pp. 355-380
- ↑ a b c d e f g h i j k Thomas Martin, Jesús Marugán-Lobón, Romain Vullo, Hugo Martín-Abad, Zhe-Xi Luo and Angela D. Buscalion: A Cretaceous eutriconodont and integument evolution in early mammals. Nature 526, 2015, pp. 380-384
- ↑ a b A. D. Buscalioni and MA Fregenal-Martínez: A holistic approach to the palaeoecology of Las Hoyas conservation deposit (La Huérguina Formation, Lower Cretaceous, Iberian Ranges, Spain). Journal of Iberian Geology 36 (2), 2010, pp. 297-326
- ↑ José Luis Sanz, JF Bonaparte and A. Lacasa: Unusual Early Cretaceous birds from Spain. Nature 331, 1988, pp. 433-435
- ↑ José Luis Sanz and AD Buscamoni: A new Bird from the Early Cretaceous of Las Hoyas, Spain, and the Early Radiation of Birds. Palaeontology 35 (4), 1992, pp. 829-845
- ↑ José Luis Sanz, Luis M. Chiappe, Bernardino P. Pérez-Moreno, Angela D. Buscalioni, José J. Moratalla, Francisco Ortega and Francisco J. Poyato-Ariza: An Early Cretaceous bird from Spain and its implications for the evolution of avian flight. Nature 382, 1996, pp. 442-445
- ↑ Bernardino P. Pérez-Moreno, José Luis Sanz, Angela D. Buscalioni, José J. Moratalla, Francisco Ortega and Diego Rasskin-Gutman: A unique multitoothed ornithomimosaur from the Lower Cretaceous of Spain. Nature 370, 1994, pp. 363-367
- ^ A b Francisco Ortega, Fernando Escaso and José L. Sanz: A bizarre, humped Carcharodontosauria (Theropoda) from the Lower Cretaceous of Spain. Nature 467, 2010, pp. 203-206
- ↑ Jesús Marugán-Lobón and Romain Vullo: Feather diversity in the Barremian (Early Cretaceous) of Las Hoyas, Spain. Comptes Rendus Palevol 10, 2011, pp. 219-223
- ↑ a b Derek EG Briggs, Philip R. Wilby, Bernardino P. Pérez-Moreno, José Luis Sanz and Marian Fregenal-Martinez: The mineralization of dinosaur soft tissue in the Lower Cretaceous of Las Hoyas, Spain. Journal of the Geological Society 154, 1997, pp. 587-588
- ↑ José L. Sanz, Luis M. Chiappe, Yolanda Fernández-Jalvo, Francisco Ortega, Begoña Sánchez Chillón, Francisco J. Poyato-Ariza and Bernardino P. Pérez-Moreno: An Early Cretaceous pellet. Nature 409, 2001, pp. 998-999
- ↑ José Luis Sanz, Sylvie Wenz, Alfonso Yebenes, Richard Estes, Xavier Martínez Delclòs, Emiliano Jiménez-Fuentes, Carmen Diéguez, Angela D. Buscalioni, Luis Javier Barbadillo and Luis Vía: An Early Cretaceous faunal and floral continental assemblage: Las Hoyas fossil site (Cuenca Spain). Geobios 21 (5), 1988, pp. 611-635
- ^ Farish A. Jenkins and Charles R. Schaff: The Early Cretaceous mammal Gobiconodon (Mammalia, Triconodonta) from the Cloverly Formation in Montana. Journal of Vertebrate Paleontology. 8 (1), 1988, pp. 1-24
- ^ Zhe-Xi Luo and John R. Wible: A Late Jurassic Digging Mammal and Early Mammalian Diversification. Science 308. 2005, pp. 103-107
- ^ A b Zofia Kielan-Jaworowska, Richard L. Cifelli and Zhe-Xie Luo: Mammals from the Age of Dinosaurs. Origins, Evolution, and Structure. , Columbia University Press, New York 2004, pp. 216-248
- ↑ David W. Krause, Simone Hoffmann, John R. Wible, E. Christopher Kirk, Julia A. Schultz, Wighart von Koenigswald, Joseph R. Groenke, James B. Rossie, Patrick M. O'Connor, Erik R. Seiffert, Elizabeth R. Dumont, Waymon L. Holloway, Raymond R. Rogers, Lydia J. Rahantarisoa, Addison D. Kemp, and Haingoson Andriamialison: First cranial remains of a gondwanatherian mammal reveal remarkable mosaicism. Nature 515, 2104, pp. 512-517
- ^ Gloria Cuenca − Bescós and José I. Canudo: A new gobiconodontid mammal from the Early Cretaceous of Spain and its palaeogeographic implications. Acta Palaeontologia Polonica 48 (4), 2003, pp. 575-582
- ↑ Steven C. Sweetman: A gobiconodontid (Mammalia, Eutriconodonta) from the Early Cretaceous (Barremian) Wessex Formation of the Isle of Wight, southern Britain. Palaeontology 49 (4), 2006, pp. 889-897
Web links
- University of Bonn: Ursula probably suffered from hair disease. October 14, 2015