Ankylosauria

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Ankylosauria
Skeleton of Euoplocephalus

Skeleton of Euoplocephalus

Temporal occurrence
Middle Jurassic to Upper Cretaceous ( Callovian to Maastrichtian )
166.1 to 66 million years
Locations
  • worldwide
Systematics
Ornithodira
Dinosaur (dinosauria)
Pelvic dinosaur (Ornithischia)
Thyreophora
Eurypoda
Ankylosauria
Scientific name
Ankylosauria
Osborn , 1923

The Ankylosauria (German also Ankylosaurier ; Latinization from ancient Greek ἀγκύλος ankýlos "crooked" and σαῦρος sauros "lizard") are a taxon (a systematic group) of the bird pelvic dinosaur (Ornithischia). They were four-legged, herbivorous dinosaurs , which were characterized by armor made of bone plates. They appeared in the Middle Jurassic , but had their peak in the Cretaceous period , when they spread around the world. A distinction is made between two sub-taxa, the Nodosauridae and the Ankylosauridae , whereby the internal systematics is controversial.

features

General

Most Ankylosauria reached lengths of four to six meters, the largest representatives such as Ankylosaurus were up to nine meters long, while the smallest representatives such as Struthiosaurus and Minmi only reached three meters. All ankylosauria had a broad, stocky torso with four short, powerful limbs. They moved exclusively quadruped (on all fours). The back legs were longer than the front legs, which brought the head into a position close to the ground.

Skull and teeth

Skull of Saichania

The skull of the ankylosauria was sturdy and massive, and sat on a short neck. One synapomorphism (a common derived trait) was that, unlike the original dinosaur skull , two skull windows - the pre- orbital window in front of the eye socket and the upper temporal window (in the temporal region ) - were closed. The top of the skull and sometimes the cheek region were provided with bulging, bony ornamentation. Some ankylosaurs even had armored eyelids . These animals were also characterized by two bony outgrowths behind the eye socket and in the cheek region. These were larger and more horn-like in the Ankylosauridae, while they were more rounded and blunt in the Nodosauridae. In the construction of the skull, the complex nasal cavities and paranasal sinuses , whose function is controversial, were also noticeable in many ankylosauria . In the more highly developed ankylosauria, a bony palate has formed. The two subgroups differed in the shape of the skull. In the Nodosauridae it was rather narrow and elongated, while in the Ankylosauridae it was wider and more massive. Accordingly, the snout of the Nodosauridae was narrower than that of the Ankylosauridae, which allows conclusions to be drawn about different diets.

The ankylosaurian brain must have been very small. Compared to body size, it was proportionally smaller than that of the stegosauria - of all dinosaurs, only the sauropods had smaller brains.

The teeth of the Ankylosauria were relatively small, they had a leaf-shaped, laterally compressed appearance. The primal representatives still had teeth on the premaxillary (the foremost part of the upper jaw), while the more highly developed species had a toothless hornbill. The teeth were arranged in two rows of teeth offset inwards, which suggests that there were cheeks.

Trunk skeleton and limbs

The spine of the ankylosauria consisted of 7 to 8 cervical vertebrae, 12 to 19 thoracic vertebrae, 3 to 4 sacral vertebrae fused to form the sacrum and 20 to 40 caudal vertebrae. The rearmost three to six thoracic vertebrae and the foremost one to three caudal vertebrae were fused with the sacrum to form the synsacrum, presumably to give the pelvis more stability. This was very wide and modified, among other things, by a rotated and horizontally expanded iliac bone , presumably to create more space for a voluminous digestive system. The acetabulum was not open like most dinosaurs, but cup-shaped. In the area of ​​the shoulder girdle , the elongated shoulder blade was conspicuous, which - especially in the Nodosauridae - had a bump-like outgrowth ( acromion ), which served as the attachment point for the strong muscles.

The limb bones were relatively thick and short, with the Nodosauridae presumably having somewhat slimmer limbs than the Ankylosauridae. The rear legs were always longer than the front legs and carried the main weight of the body. The feet were also short and strong. The forefeet are often not preserved, but most ankylosaurs probably had five toes. The hind feet were more variable and had three to five toes depending on the species. The toes of the front and rear feet were thick and ended in wedge-shaped claws.

Armor, spikes, and bones

Reconstruction of Edmontonia , a Nodosauridae. These were characterized by larger shoulder spines and a missing tail lobe.

Ankylosauria was characterized by armor made of bone plates ( osteoderms ) that covered the neck, the back and the top of the tail. These were embedded in the skin and are usually not preserved in situ in fossils , so that their exact shape and arrangement is often not precisely known.

The bone plates were arranged in numerous, sagittal (front to back) rows. Between the larger plates there were small plates that made for a gapless armor. Large, keeled plates were usually attached to the top of the neck. In the shoulder area, the plates were often woven into a crescent-shaped structure, especially in the Nodosauridae there were also spines. In the area of ​​the fuselage, the armor was variable depending on the type, in addition to flat plates there were also plates with keels or humps. In some ankylosaurs, the osteoderms were fused into a shield-like structure above the sacrum.

According to studies by Torsten Scheyer and P. Martin Sander, collagen fibers were incorporated into the bone plates, which formed three-dimensional interwoven mats. This achieved enormous stability with a comparatively low weight.

Bone lobe on the tail of Anodontosaurus

Many representatives of the Ankylosauridae, but not the Nodosauridae, had a bony club at the tip of their tail. This consisted of osteoderms fused with the caudal vertebrae and was supported and stiffened by ossified tendons . When moving, the leg of the bone was held just above the ground, but not dragged. While the rear part of the tail was stiff and immobile, the mobile, presumably strongly muscled front part of the tail was likely to have enabled the club to swing back and forth. The expression of these characteristics can be understood as a convergent development to the Glyptodontidae from the group of the secondary articular animals . The latter developed in the Paleogene and reached their greatest diversity with individual giant forms in the Pleistocene , but died out shortly afterwards.

Paleobiology

distribution and habitat

Well-preserved fossil remains are known from North America , Europe , Asia , Australia and the Antarctic ( Antarctopelta was the first dinosaur to be discovered on this continent), fragmentary remains from South America and New Zealand , among others , so that a worldwide distribution of these animals can be assumed.

There is also a variety of deposit locations. The majority of the finds indicate that these animals preferred humid habitats with lush vegetation such as river areas and coastal plains. Some fossils have also been discovered in marine sediments - the ankylosauria, like all dinosaurs, lived on land, in such cases the carcass was probably washed into the sea after death. According to some researchers, the complex nasal and sinus cavities could have been used to cool or humidify the air we breathe, thus allowing conclusions to be drawn about hot and dry habitats. However, these views are controversial.

Social behavior

Reconstruction of Minmi

Speculations about the social behavior of the Ankylosauria are, as with all animals known only from fossil finds, difficult. Even finds of the remains of several animals in one place do not have to indicate a group life, but can also be due to deposition technology. Most of the finds come from individual animals, so the majority of researchers assume that these animals lived alone or at most in small groups. The remains of numerous subadult (half-grown) individuals of Pinacosaurus were found together, which could be an indication that juveniles formed larger groups for protection.

Some physique features could indicate interaction with conspecifics. The large, backward-protruding spines in the shoulder area of ​​the Nodosauridae probably served less defensive purposes than display - the observation of a sexual dimorphism in the length of the spine also fits into this context . The tail lobe of the Ankylosauridae could also have been used in rival fights - for example for the mating privilege.

Locomotion and Defense

The physique and ego fossils (fossil footprints) show that ankylosauria only moved quadruped - they could not stand up on their hind legs. The heavy build and short limbs did not allow rapid locomotion. According to the calculations by RA Thulborn based on limb length and estimated body weight, these animals could not have reached more than 10 km / h, but usually only moved around 3 km / h.

Although the ankylosauria could not seek their salvation by fleeing in case of threat, their armor undoubtedly offered an effective defense against predators. It is conceivable that in an attack they would press themselves to the ground to protect their unarmored belly and rely on the protection of their bone-plate-covered top. In the case of the Ankylosauridae, the tail club was probably added as an active defense weapon, with which blows could be distributed on the legs of the attackers. According to one - albeit dubious - theory, the tail club could also have mimicked the head as a mimicry and thus lured predators away from the sensitive parts of the body.

nutrition

Model of an eating Euoplocephalus

Due to the structure of the teeth and the positioning of their head, it can be assumed that ankylosauria fed on plants close to the ground (up to about 1 meter in height). Fossilized stomach contents, which are made of plant material, have also been preserved from Minmi . Presumably these animals ate, for example, mosses , ferns , cycads or conifers , the representatives of the Upper Cretaceous probably also fed on the newly emerged Bedecktsamern . The broad claws, which are probably unsuitable for such activities, speak against the assumption sometimes expressed that these animals could also have dug for food in the ground. The more pointed mouth of the Nodosauridae suggests a more selective food intake, while the wide mouth of the Ankylosauridae was designed for unspecialized plucking of all accessible parts of the plant.

How effective the ankylosaurian chewing apparatus was is controversial. For a long time it was assumed that the jaws were only capable of simple up and down movements and were therefore unsuitable for thorough chewing. Microscopic and macroscopic examination of traces of wear at Euoplocephalus have shown that at least some ankylosauria also an on-and-forth movement - supplemented by a slight flexibility between the lower jaw and the front located predentary  were and thus to a more thorough chewing of food Healthy - . The bony palate found in the more highly developed ankylosaurs could also be a sign of this.

The wide torso and modified pelvis are signs that a bulky digestive system was present. It is conceivable that the fermentation took place with the help of symbiotic microorganisms in a multi-chambered stomach or in another section of the digestive tract.

Reproduction and development

The ankylosauria were probably egg-laying like all dinosaurs, but there are no egg finds that can be assigned to this group and, compared to other dinosaur groups, very few fossils of young animals are known. The completely preserved, 34 centimeter long fossil of a young animal has come down to us from Liaoningosaurus . This differs significantly from all other ankylosaurs in some features, including the armor on the belly and the huge teeth. It is unclear whether these were general characteristics of young animals or genus-specific characteristics.

Systematics and history of development

External system

The sister group of the Ankylosauria are the Stegosauria , which also had the bone plates, but which were arranged in two rows next to each other on the back. Ankylosauria and stegosauria together form the taxon Eurypoda . Together with some primitive representatives from the Lower Jurassic (for example Scutellosaurus and Scelidosaurus ), the Eurypoda form the taxon of the Thyreophora ("shield bearer"). However, this is not without controversy, according to the opinion of other researchers ( e.g. Kenneth Carpenter) Scelidosaurus is more closely related to the Ankylosauria than to the Stegosauria. Carpenter therefore summarizes Ankylosauria and Scelidosaurus as Ankylosauromorpha.

The Thyreophora are classified in the bird pelvic dinosaur (Ornithischia). A simplified cladogram that shows only the most important taxa looks like this:

 Dinosauria  

 Lizard dinosaur (Saurischia)


  Pelvic dinosaur (Ornithischia)  
  Thyreophora  

 primitive representatives


  Eurypoda  

 Ankylosauria


   

 Stegosauria




   

 Cerapoda ( Ornithopoda and Marginocephalia )




Internal system

The systematics of the ankylosauria is controversial. Traditionally, a distinction is made between two sub-taxa, the Ankylosauridae and the Nodosauridae . The Ankylosauridae are characterized, among other things, by a broad head and a tail lobe, while the Nodosauridae have, among other things, a narrow head, larger spines in the shoulder area and a conspicuous bulge in the shoulder blade (acromion). A group of animals, the Polacanthidae or Polacanthinae , combined features of both groups, and is therefore sometimes seen as a subfamily of the Ankylo and sometimes the Nodosauridae, other studies even see them as a separate taxon. But this is controversial - also because of the sparse remains of many genera.

Many finds cannot be clearly assigned to one of the groups and different systematics of the ankylosauria sometimes differ considerably from one another. The system described here largely follows M. Vickaryous et al. (2004), who do not recognize the Polacanthidae, have since included genera described. For comparison - where there are deviations - the system of K. Carpenter (2001) or the assignment by the person who first described it is shown in brackets after the name.

Development history

The oldest undoubted finds of the Ankylosauria come from the Middle Jurassic and are around 165 million years old. Individual genera such as Gargoyleosaurus and Mymoora are known from the Upper Jurassic , but they did not reach the greatest wealth of forms and genres until the Cretaceous period .

The history of development of the subgroups is difficult to reconstruct due to the uncertain assignment of many genera. In the opinion of K. Carpenter, the Polacanthidae in the Lower Cretaceous and the Nodosauridae in the Upper Cretaceous became extinct, so that at the end of the Cretaceous only the Ankylosauridae existed. These, along with all other non-avian dinosaurs, then disappeared during the mass extinction at the end of the Cretaceous Period. (For discussions of the reasons for this extinction, see Cretaceous-Tertiary Boundary and the Extinction of Dinosaurs .)

History of discovery and research

Model of Minmi , the first ankylosaur found in Australia

The oldest find of an ankylosaur was Hylaeosaurus , the remains of which were found in England and which, together with Iguanodon and Megalosaurus, was one of the animals for which Richard Owen coined the term dinosaur in 1842 . However, this find was very incomplete, as were other finds from the 19th century from Europe such as Polacanthus , Acanthopholis or Struthiosaurus , which formed a very imperfect picture of this group.

The oldest finds from North America were Nodosaurus (1889), Euoplocephalus (1902) and Ankylosaurus (1908). In 1923 Henry Fairfield Osborn coined the name Ankylosauria for this taxon. The oldest Asian find was Pinacosaurus from the 1930s.

It was only after the Second World War that more complete discoveries made the appearance of these animals more clearly recognizable, such as Talarurus and Saichania from Asia or Sauropelta and Silvisaurus from North America. In the 1980s, Minmi, the first Australian and Antarctopelta, the first Antarctic ankylosaurs were discovered. Finds from China have only been brought to light on a large scale since the 1990s, such as Tianzhenosaurus and Liaoningosaurus ; During the same period in North America, Gargoyleosaurus and Mymoorapelta, two important basal ankylosaurs, were found.

In addition to new discoveries and more detailed analyzes of old finds, cladistic and paleo-ecological studies have come to the fore since that time , which sought to fathom the development history or the presumed way of life and the interaction with other animals. In this context, Walter Coombs , Kenneth Carpenter and Matthew Vickaryous , among others , should be mentioned.

literature

Web links

Commons : Ankylosauria  - collection of images, videos and audio files

Individual evidence

  1. ^ Gregory S. Paul : The Princeton Field Guide To Dinosaurs. Princeton University Press, Princeton NJ u. a. 2010, ISBN 978-0-691-13720-9 , pp. 226-239, online .
  2. ^ Wilhelm Gemoll : Greek-German school and hand dictionary. 9th edition, reviewed and expanded by Karl Vretska ; with an introduction to the history of language by Heinz Kronasser. Freytag u. a., Munich a. a. 1965.
  3. ↑ Ben Creisler: Dinosauria Translation and Pronunciation Guide. Archived from the original on May 14, 2011 ; accessed on September 23, 2014 (English).
  4. ↑ Torsten M. Scheyer, P. Martin Sander : Histology of ankylosaur osteoderms: implications for systematics and function. In: Journal of Vertebrate Paleontology. Vol. 24, No. 4, 2004, ISSN  0272-4634 , pp. 874-893.
  5. ↑ Victoria M. Arbor and Lindsay E. Zanno: The evolution of tail weaponization in amniotes. Proceedings of the Royal Society B 285, 2018, S. 20172299 doi: 10.1098 / rspb.2017.2299
  6. ↑ Victoria M. Arbor and Lindsay E. Zanno: Tail Weaponry in Ankylosaurs and Glyptodonts: An Example of a Rare but Strongly Convergent Phenotype. The Anatomical Record, 2019 doi: 10.1002 / ar.24093
  7. ↑ a b c d Section “Paleoecology and Behavior” in Vickaryous et al. (2004), pp. 391-392.
  8. ↑ D. Fastovsky et al. (2005), p. 135.
  9. ↑ K. Carpenter: Nodosauridae
  10. ^ Richard A. Thulborn: Speeds and gaits of dinosaurs. In: Palaeogeography, Palaeoclimatology, Palaeoecology. Vol. 38, No. 3/4, 1982, ISSN  0031-0182 , pp. 227-256, doi: 10.1016 / 0031-0182 (82) 90005-0 .
  11. ↑ D. Fastovsky et al. (2005), pp. 137-139.
  12. ↑ D. Fastvosky et al. (2005), p. 135
  13. ↑ D. Fastovsky et al. (2005), p. 136.
  14. ↑ Kenneth Carpenter: Ankylosauromorpha in The Tree of Life Web Project
  15. ↑ after D. Fastovsky et al. (2005).
  16. ↑ Kenneth Carpenter: Polacanthidae in The Tree of Life Web Project
  17. ↑ Clifford A. Miles, Clark J. Miles: Skull of Minotaurasaurus ramachandrani, a new Cretaceous ankylosaur from the Gobi Desert. In: Current Science. Vol. 96, No. 1, 2009, ISSN  0011-3891 , pp. 65-70, digital version (PDF; 1.04 MB) .
  18. ↑ Victoria M. Arbor, Michael E. Burns, Robert M. Sullivan, Spencer G. Lucas, Amanda K. Cantrell, Joshua Fry, Thomas L. Suazo: A New Ankylosaurid Dinosaur from the Upper Cretaceous (Kirtlandian) of New Mexico with Implications for Ankylosaurid Diversity in the Upper Cretaceous of Western North America. PLoS ONE , 2014; 9 (9): e108804 doi: 10.1371 / journal.pone.0108804
  19. ↑ Victoria M. Arbor, Philip J. Currie and Demchig Badamgarav: The Ankylosaurid Dinosaurs of the Upper Cretaceous Baruungoyot and Nemegt formations of Mongolia. Zoological Journal of the Linnean Society, Volume 172, Issue 3, pp. 631-652, 2014, doi: 10.1111 / zoj.12185
  20. ↑ Michael E. Burns: Taxonomic utility of ankylosaur (Dinosauria, Ornithischia) osteoderms: Glyptodontopelta mimus Ford, 2000: a test case. In: Journal of Vertebrate Paleontology. Vol. 28, No. 4, 2008, pp. 1102-1109, doi: 10.1671 / 0272-4634-28.4.1102 .
  21. ↑ Kenneth Carpenter, Jeff Bartlett, John Bird, Reese Barrick: Ankylosaurs from the Price River Quarries, Cedar Mountain Formation (Lower Cretaceous), east-central Utah. In: Journal of Vertebrate Paleontology. Vol. 28, No. 4, 2008, pp. 1089-1101, doi: 10.1671 / 0272-4634-28.4.1089 .
  22. ↑ Lucy G. Leahey, Ralph E. Molnar, Kenneth Carpenter, Lawrence M. Witmer and Steven W. Salisbury: Cranial Osteology of the Ankylosaurian Dinosaur formerly known as Minmi sp. (Ornithischia: Thyreophora) from the Lower Cretaceous Allaru Mudstone of Richmond, Queensland, Australia. PeerJ . 3; e1475, 2015, doi: 10.7717 / peerj.1475
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