Ankylosaurus
| Ankylosaurus | |
|---|---|
| |
| Cast of Ankylosaurus skull (AMNH 5214) in front view, Museum of the Rockies | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Thyreophora |
| Clade: | †Ankylosauria |
| Family: | †Ankylosauridae |
| Subfamily: | †Ankylosaurinae |
| Tribe: | † Ankylosaurini
|
| Genus: | †Ankylosaurus Brown, 1908 |
| Species: | †A. magniventris
|
| Binomial name | |
| †Ankylosaurus magniventris Brown, 1908
| |
Ankylosaurus
Possibly the largest-known
Ankylosaurus is a member of the family Ankylosauridae, and its closest relatives appear to be Anodontosaurus and Euoplocephalus. Ankylosaurus is thought to have been a slow-moving animal, able to make quick movements when necessary. Its broad muzzle indicates it was a non-selective browser. Sinuses and nasal chambers in the snout may have been for heat and water balance or may have played a role in vocalization. The tail club is thought to have been used in defense against predators or in intraspecific combat. Specimens of Ankylosaurus have been found in the Hell Creek, Lance, Scollard, Frenchman, and Ferris formations, but it appears to have been rare in its environment. Although it lived alongside a nodosaurid ankylosaur, their ranges and ecological niches do not appear to have overlapped, and Ankylosaurus may have inhabited upland areas. Ankylosaurus also lived alongside dinosaurs such as Tyrannosaurus, Triceratops, and Edmontosaurus.
History of discovery
In 1906, an
The skeletal reconstruction accompanying the 1908 description restored the missing parts in a fashion similar to
Brown had collected 77 osteoderms while excavating a
In 1910, another AMNH expedition led by Brown discovered an Ankylosaurus specimen (AMNH 5214) in the Scollard Formation by the Red Deer River in Alberta, Canada. This specimen included a complete skull, mandibles, the first and only tail club known of this genus, as well as ribs, vertebrae, limb bones, and armor. In 1947 the American fossil collectors Charles M. Sternberg and T. Potter Chamney collected a skull and mandible (specimen CMN 8880, formerly NMC 8880), 1 kilometer (5⁄8 mile) north of where the 1910 specimen was found. This is the largest-known Ankylosaurus skull, but it is damaged in places. A section of caudal vertebrae (specimen CCM V03) was discovered in the 1960s in the Powder River drainage, Montana, part of the Hell Creek Formation. In addition to these five incomplete specimens, many other isolated osteoderms and teeth have been found.[12][10]
In 1990, American paleontologist Walter P. Coombs pointed out that the teeth of two skulls assigned to A. magniventris differed from those of the holotype specimen in some details, and though he expressed a "considerate temptation" to name a new species of Ankylosaurus for these, he refrained from doing so, as the range of variation in the species was not completely documented. He also raised the possibility that the two teeth associated with the holotype specimen perhaps did not belong to it, as they were found in matrix within the nasal chambers.[13] The American paleontologist Kenneth Carpenter accepted the teeth as belonging to A. magniventris in 2004, and that all the specimens belonged to the same species, noting that the teeth of other ankylosaurs are highly variable.[10]
Most of the known Ankylosaurus specimens were not scientifically described at length, though several paleontologists planned to do so until Carpenter redescribed the genus in 2004.
Description
Ankylosaurus was the largest-known ankylosaurine dinosaur and possibly the largest ankylosaurid.[12] In 2004 Carpenter estimated that the individual with the largest-known skull (specimen CMN 8880), which is 64.5 centimeters (2 ft 1+1⁄2 in) long and 74.5 cm (2 ft 5+1⁄4 in) wide, was about 6.25 m (20 ft 6 in) long and had a hip height of about 1.7 m (5 ft 7 in). The smallest-known skull (specimen AMNH 5214) is 55.5 cm (1 ft 9+3⁄4 in) long and 64.5 cm (2 ft 1+1⁄2 in) wide, and Carpenter estimated that it measured about 5.4 m (17 ft 9 in) long and about 1.4 m (4 ft 7 in) tall at the hips.[10] The English paleontologist Roger B. J. Benson and colleagues estimated the weight for AMNH 5214 at 4.78 metric tons (5.27 short tons) in 2014.[14]
In 2017, based on comparisons with more complete ankylosaurines, Arbour and Mallon estimated a length of 7.56 to 9.99 m (24 ft 9+1⁄2 in to 32 ft 9+1⁄2 in) for CMN 8880, and 6.02 to 7.95 m (19 ft 9 in to 26 ft 1 in) for AMNH 5214. Though the latter is the smallest specimen of Ankylosaurus, its skull is still larger than those of any other ankylosaurins. A few other ankylosaurs reached about 6 m (20 ft) in length. Because the vertebrae of AMNH 5214 are not significantly larger than those of other ankylosaurines, Arbour and Mallon considered their upper range estimate of nearly 10 meters (33 ft) for large Ankylosaurus too long, and suggested a length of 8 m (26 ft) instead. Arbour and Mallon estimated a weight of 4.78 t (5.27 short tons) for AMNH 5214, and tentatively estimated the weight of CMN 8880 at 7.95 t (8.76 short tons).[12]
Skull
The three known Ankylosaurus skulls differ in various details; this is thought to be the result of
The snout region of Ankylosaurus was unique among ankylosaurs, and had undergone an "extreme" transformation compared to its relatives. The snout was arched and truncated at the front, and the nostrils were elliptical and were directed downward and outward, unlike in all other known ankylosaurids where they faced obliquely forward or upward. Additionally, the nostrils were not visible from the front because the
Specimen AMNH 5214 has 34–35
Postcranial skeleton
The structure of much of the skeleton of Ankylosaurus, including most of the
The
Armor
A prominent feature of Ankylosaurus was its armor, consisting of knobs and plates of bone known as osteoderms, or scutes, embedded in the skin. These have not been found in articulation, so their exact placement on the body is unknown, though inferences can be made based on related animals, and various configurations have been proposed. The osteoderms ranged from 1 centimeter (1⁄2 in) in diameter to 35.5 cm (14 in) in length, and varied in shape. The osteoderms of Ankylosaurus were generally thin walled and hollowed on the underside. Compared to Euoplocephalus, the osteoderms of Ankylosaurus were smoother. Many smaller osteoderms and ossicles probably occupied the space between the larger ones, as in other ankylosaurids. The osteoderms covering the body were very flat, though with a low keel at one margin. In contrast, the nodosaurid Edmontonia had high keels stretching from one margin to the other on the midline of its osteoderms. Ankylosaurus had some smaller osteoderms with a keel across the midline.[12][10]
Like other ankylosaurids, Ankylosaurus had cervical half-rings (armor plates on the neck), but these are known only from fragments, making their exact arrangement uncertain. Carpenter suggested that when seen from above, the plates would have been paired, creating an inverted V-shape across the neck, with the midline gap probably being filled with small ossicles (round bony scutes) to allow for movement. He believed the width of this armor belt was too wide to have fitted solely on the neck, and that it covered the base of the neck and continued onto the shoulder region. Arbour and the Canadian paleontologist Philip J. Currie disagreed with Carpenter's interpretation in 2015 and pointed out that the cervical half-ring fragments of the holotype specimen did not fit together in the way proposed by Carpenter (though this could be due to breakage). They instead suggested that the fragments represented the remains of two cervical half-rings, which formed two semi-circular plates of armor around the upper part of the neck, as in the closely related Anodontosaurus and Euoplocephalus.[10][15] Arbour and Mallon elaborated on this idea, describing the shape of these half-rings as "continuous U-shaped yokes" over the upper part of the neck, and suggested that Ankylosaurus had six keeled osteoderms with oval bases on each half-ring.[12]
The first osteoderms behind the second cervical half-ring would have been similar in shape to those in the first half-ring, and the osteoderms on the back probably decreased in diameter hindwards. The largest osteoderms were probably arranged in transverse and longitudinal rows across most of the body, with four or five transverse rows separated by creases in the skin. The osteoderms on the flanks would probably have had a more square outline than those on the back. There may have been four longitudinal rows of osteoderms on the flanks. Unlike some basal ankylosaurs and many nodosaurs, ankylosaurids do not appear to have had co-ossified pelvic shields above their hips. Some osteoderms without keels may have been placed above the hip region of Ankylosaurus, as in Euoplocephalus. Ankylosaurus may have had three or four transverse rows of circular osteoderms over the pelvic region, which were smaller than those on the rest of the body, as in Scolosaurus. Smaller, triangular osteoderms may have been present on the sides of the pelvis. Flattened, pointed plates resemble those on the sides of the tail of Saichania, and may have been distributed similarly on Ankylosaurus. Osteoderms with oval keels could have been placed on the upper side of the tail or the side of the limbs. Compressed, triangular osteoderms found with Ankylosaurus specimens may have been placed on the sides of the pelvis or the tail. Ovoid, keeled, and teardrop-shaped osteoderms are known from Ankylosaurus, and may have been placed on the forelimbs, like those known from Pinacosaurus, but it is unknown whether the hindlimbs bore osteoderms.[10][12]
The tail club (or tail knob) of Ankylosaurus was composed of two large osteoderms, with a row of small osteoderms at the midline, and two small osteoderms at the tip; these osteoderms obscured the last tail vertebra. As only the tail club of specimen AMNH 5214 is known, the range of variation between individuals is unknown. The tail club of AMNH 5214 is 60 cm (23+1⁄2 in) long, 49 cm (19+1⁄2 in) wide, and 19 cm (7+1⁄2 in) tall. The club of the largest specimen may have been 57 cm (22+1⁄2 in) wide. The tail club of Ankylosaurus was semicircular when seen from above, similar to those of Euoplocephalus and Scolosaurus but unlike the pointed club osteoderms of Anodontosaurus or the narrow, elongated club of Dyoplosaurus. The last seven tail vertebrae formed the "handle" of the tail club. These vertebrae were in contact, with no cartilage between them, and were sometimes co-ossified, which made them immobile. Ossified tendons attached to the vertebrae in front of the tail club, and these features together helped strengthen it. The interlocked
Classification
Brown considered Ankylosaurus so distinct that he made it the type genus of a new family, Ankylosauridae, typified by massive, triangular skulls, short necks, stiff backs, broad bodies, and osteoderms. He also classified Palaeoscincus (only known from teeth), and Euoplocephalus (then only known from a partial skull and osteoderms) as part of the family. Due to the fragmentary condition of the remains, Brown was unable to fully distinguish between Euoplocephalus and Ankylosaurus. Having for comparison only a few, incomplete members of the family, he believed the group was part of the suborder Stegosauria.[2] In 1923 Osborn coined the name Ankylosauria, thereby placing the ankylosaurids in their own suborder.[19]
Ankylosauria and Stegosauria are now grouped together within the clade Thyreophora. This group first appeared in the Sinemurian age, and survived for 135 million years until disappearing in the Maastrichtian. They were widespread and inhabited a broad range of environments.[10][6] As more complete specimens and new genera have been discovered, theories about ankylosaurian interrelatedness have become more complex, and hypotheses have often changed between studies. In addition to Ankylosauridae, Ankylosauria has been divided into the families Nodosauridae, and sometimes Polacanthidae (these families lacked tail clubs). Ankylosaurus is considered part of the subfamily Ankylosaurinae (members of which are called ankylosaurines) within Ankylosauridae.[20] Ankylosaurus appears to be most closely related to Anodontosaurus and Euoplocephalus.[21] The following cladogram is based on a 2015 phylogenetic analysis of the Ankylosaurinae conducted by Arbour and Currie:[15]
Because Ankylosaurus and other Late Cretaceous North American ankylosaurids were grouped with Asian genera (in a
Paleobiology
Feeding
Like other ornithischians, Ankylosaurus was herbivorous. Its wide muzzle was adapted for non-selective low-browse cropping,[10] although not to the extent seen in some related genera, especially Euoplocephalus.[12][22] Though ankylosaurs may not have fed on fibrous and woody plants, they may have had a varied diet, including tough leaves and pulpy fruits.[23] Ankylosaurus probably fed on abundant ferns and low-growing shrubs. Assuming it was endothermic, Ankylosaurus would have eaten 60 kilograms (130 pounds) of ferns per day, similar to the amount of dry vegetation a large elephant would consume. The requirements for nutrition could have been more effectively met if Ankylosaurus ate fruit, which its small, cusp-like teeth and the shape of its beak seem well adapted for, compared to for example Euoplocephalus. Certain invertebrates, which the small teeth may have been adapted for handling, could also have provided supplemental nutrition.[12]
Fossils of Ankylosaurus teeth exhibit wear on the face of the crown rather than on the tip of the crown, as in nodosaurid ankylosaurs.[10] In 1982 Carpenter ascribed to baby Ankylosaurus two very small teeth that originate from the Lance and Hell Creek Formations and measure 3.2 to 3.3 mm (1⁄8 to 17⁄128 in) in length, respectively. The smaller tooth is heavily worn, leading Carpenter to suggest that ankylosaurids in general or at least the young did not swallow their food whole but employed some sort of chewing.[16] Since adult Ankylosaurus did little chewing of its food, it would have spent less time in the day foraging than an elephant.[12] Based on the broadness of the ribcage, the digestion of unchewed food may have been facilitated by hindgut fermentation like in modern herbivorous lizards, which have several chambers in their enlarged colon.[10]
In 1969, paleontologist Georg Haas concluded that despite the large size of ankylosaur skulls, the associated musculature was relatively weak. He also thought jaw movement was limited to up and down movements. Extrapolating from this, Haas suggested that ankylosaurs ate relatively soft non-abrasive vegetation.[24] Later research on Euoplocephalus indicates that forward and sideways jaw movement was possible in these animals, the skull being able to withstand considerable forces.[25] A 2016 study of the dental occlusion (contact between the teeth) of ankylosaur specimens found that the ability for backwards (palinal) jaw movement evolved independently in different ankylosaur lineages, including Late Cretaceous North American ankylosaurids like Ankylosaurus and Euoplocephalus.[22]
The retracted position of the nostrils of Ankylosaurus were compared to those of
Airspaces and senses
In 1977, paleontologist Teresa Maryańska proposed that the complex sinuses and nasal cavities of ankylosaurs may have lightened the weight of the skull, housed a nasal gland, or acted as a chamber for vocal resonance.[10][27] Carpenter rejected these hypotheses, arguing that tetrapod animals make sounds through the larynx, not the nostrils, and that reduction in weight was minimal, as the spaces only accounted for a small percent of the skull volume. He also considered a gland unlikely and noted that the sinuses may not have had any specific function.[10] It has also been suggested that the respiratory passages were used to perform a mammal-like treatment of inhaled air, based on the presence and arrangement of specialized bones.[27]
A 2011 study of the nasal passages of Euoplocephalus by paleontologist Tetsuto Miyashita and colleagues supported their function as a heat and water balancing system, noting the extensive blood vessel system and an increased surface area for the
According to Carpenter, the shape of the nasal chambers of Ankylosaurus indicate that airflow was unidirectional (looping through the lungs during inhalation and exhalation), although it may also have been bidirectional in the posterior nasal chamber, with air directed past the olfactory lobes.[10] The enlarged olfactory region of ankylosaurids indicates a well-developed sense of smell.[28] Though hindwards retraction of the nostrils is seen in aquatic animals and animals with a proboscis, it is unlikely either possibility applies to Ankylosaurus, as the nostrils tend to be reduced or the premaxilla extended. In addition, though the widely separated nostrils may have allowed for stereo-olfaction (where each nostril senses smells from different directions), as has been proposed for the moose, little is known about this feature.[12] The position of the orbits of Ankylosaurus suggest some stereoscopic vision.[10]
Limb movements
Reconstructions of ankylosaur forelimb musculature made by Coombs in 1978 suggest that the forelimbs bore the majority of the animal's weight, and were adapted for high force delivery on the front feet, possibly for food gathering. In addition, Coombs suggested that ankylosaurs may have been capable diggers, though the hoof-like structure of the manus would have limited fossorial activity. Ankylosaurs were likely to have been slow-moving and sluggish animals,[29][30] though they may have been capable of quick movements when necessary.[17]
Growth
The squamosal horns of the largest Ankylosaurus specimen are blunter than those of the smallest specimen, which is also the case in Euoplocephalus, and this may represent ontogenetic variation (related to growth development).[12] Studies of specimens of Pinacosaurus of different ages found that during ontogenetic development, the ribs of juvenile ankylosaurs fused with their vertebrae. The forelimbs strongly increased in robustness while the hindlimbs did not become larger relative to the rest of the skeleton, further evidence that the arms bore most of the weight. In the cervical half-rings, the underlying bone band developed outgrowths connecting it with the underlying osteoderms, which simultaneously fused to each other.[31] On the skull, the middle bone plates first ossified at the snout and the rear rim, with ossification gradually extending towards the middle regions. On the rest of the body, ossification progressed from the neck backward in the direction of the tail.[32]
Defense
The osteoderms of ankylosaurids were thin in comparison to those of other ankylosaurs, and appear to have been strengthened by randomly distributed cushions of
The tail club of Ankylosaurus seems to have been an active defensive weapon, capable of producing enough of an impact to break the bones of an assailant. The tendons of the tail were partially ossified and were not very elastic, allowing great force to be transmitted to the club when it was used as a weapon.[10] Coombs suggested in 1979 that several hindlimb muscles would have controlled the swinging of the tail, and that violent thrusts of the club would have been able to break the metatarsal bones of large theropods.[30]
A 2009 study estimated that ankylosaurids could swing their tails at 100 degrees laterally, and the mainly
In 1993, Tony Thulborn proposed that the tail club of ankylosaurids primarily acted as a decoy for the head, as he thought the tail too short and inflexible to have an effective reach; the "dummy head" would lure a predator close to the tail, where it could be struck.[38] Carpenter has rejected this idea, as tail club shape is highly variable among ankylosaurids, even in the same genus.[10]
Paleoenvironment
Ankylosaurus existed between 68 and 66 million years ago, in the final, or Maastrichtian, stage of the Late Cretaceous Period. It was among the last dinosaur genera that appeared before the Cretaceous–Paleogene extinction event. The type specimen is from the Hell Creek Formation of Montana, while other specimens have been found in the Lance and Ferris Formations in Wyoming, the Scollard Formation in Alberta, and the Frenchman Formation in Saskatchewan, all of which date to the end of the Cretaceous.[39][40][12]
Fossils of Ankylosaurus are rare in the
With its low center of gravity, Ankylosaurus would have been unable to knock down trees like modern elephants do. It was also incapable of chewing bark and thus unlikely to have practiced bark stripping. As an adult, Ankylosaurus does not appear to have congregated in groups (though some ankylosaurs appear to have congregated when young). It is therefore improbable that Ankylosaurus was able to modify the landscape of its ecosystem in the way elephants do;
The formations where Ankylosaurus fossils have been found represent different sections of the western shore of the
Cultural significance
Carpenter noted in 2004 that Ankylosaurus has become the archetypal member of its group, and the best-known ankylosaur in popular culture, perhaps due to a life-sized reconstruction of the animal being featured at the 1964 World's Fair in New York City.[10] Arbour and Mallon called Ankylosaurus an "iconic" dinosaur in 2017, and noted that the World's Fair sculpture, as well as the American artist Rudolph Zallinger's 1947 mural The Age of Reptiles and other later popular depictions, showed Ankylosaurus with a tail club, following the first discovery of the feature in 1910.[12]
Many traditional popular depictions show Ankylosaurus in a squatting posture and with a huge tail club being dragged over the ground. Modern reconstructions show the animal with a more upright limb posture and with the tail held off the ground. Likewise, large spines projecting sideways from the body (similar to those of nodosaurid ankylosaurs) are present in many traditional depictions, but are not known from Ankylosaurus itself.[5] The armor of Ankylosaurus has often been conflated with that of Edmontonia (earlier referred to as Palaeoscincus); in addition to Ankylosaurus being depicted with spikes, Edmontonia has also been depicted with an Ankylosaurus-like tail club (a feature nodosaurids did not have), including in a mural by the American artist Charles R. Knight from 1930.[12] Ankylosaurus has been featured in the Jurassic Park franchise, where they are depicted as attacking with their tails and running, abilities that have been criticized as unlikely by paleontologists.[46][47][48]
See also
References
Notes
- ^ Pronounced /ˌæŋkəloʊˈsɔːrəs/ ANG-kə-loh-SOR-əs[1]
Citations
- ^ "Ankylosaurus". Merriam-Webster.com Dictionary.
- ^ hdl:2246/1435.
- ^ Creisler, B. (July 7, 2003). "Dinosauria Translation and Pronunciation Guide A". Archived from the original on August 18, 2010. Retrieved September 3, 2010.
- ISBN 978-0-19-910207-5.
- ^ ISBN 978-0-375-82419-7.
- ^ a b Coombs, W. (1978). "The families of the ornithischian dinosaur order Ankylosauria" (PDF). Journal of Paleontology. 21 (1): 143–170. Archived from the original (PDF) on July 8, 2015. Retrieved July 8, 2015.
- ISBN 978-1408119068.
- JSTOR 2455817.
- ISBN 978-0-253-33964-5.
- ^ doi:10.1139/e04-043.
- hdl:2246/1464.
- ^ .
- ^ ISBN 978-0-521-43810-0.
- PMID 24802911.
- ^ S2CID 214625754.
- ^ a b Carpenter, K. (1982). "Baby dinosaurs from the Late Cretaceous Lance and Hell Creek formations and a description of a new species of theropod". Rocky Mountain Geology. 20 (2): 123–134.
- ^ S2CID 84505681.
- PMID 26332595.
- hdl:2246/3267.
- S2CID 86002282.
- .
- ^ S2CID 55372674.
- .
- hdl:2246/2609.
- ISBN 978-0-253-33964-5.
- PMID 37880323.
- ^ a b Maryanska, T. (1977). "Ankylosauridae (Dinosauria) from Mongolia" (PDF). Palaeontologia Polonica. 37: 85–151. Archived from the original (PDF) on July 12, 2020. Retrieved July 25, 2015.
- ^ PMID 21954840. Archived from the original(PDF) on September 24, 2015.
- JSTOR 1303969.
- ^ JSTOR 1304004.
- S2CID 130610291.
- S2CID 129291148.
- S2CID 86333501.
- JSTOR 1303019..
- doi:10.1139/e82-058.
- PMID 19707581.
- PMID 34824329.
- ^ Thulborn, T. (1993). "Mimicry in ankylosaurid dinosaurs". Records of the South Australian Museum. 27: 151–58.
- ISBN 978-0-520-24209-8.
- ^ ISBN 978-0-520-24209-8.
- ISBN 978-0-12-226810-6.
- ISBN 978-0-12-226810-6.
- ISBN 978-0-12-226810-6.
- ISBN 978-0-12-226810-6.
- ^ Bigelow, P. "Cretaceous 'Hell Creek Faunal Facies'; Late Maastrichtian". Archived from the original on December 26, 2009. Retrieved March 24, 2014.
- ^ "We asked a paleontologist how accurate Jurassic World really is..." Wired UK. 2015. Retrieved August 29, 2023.
- ^ Waxman, Olivia B. (2018). "The real scientific history behind the Jurassic Park dinosaurs". Time. Retrieved August 29, 2023.
- ^ Dorsch, Rita (2022). "Everything the Jurassic Park franchise gets wrong about paleontology". Looper. Retrieved August 29, 2023.
External links
