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Mymoorapelta

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Mymoorapelta
Temporal range: Late Jurassic, 155–150 Ma
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Cast in Wyoming Dinosaur Center
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: †Ornithischia
Clade: †Thyreophora
Clade: †Ankylosauria
Clade: †Euankylosauria
Family: †Nodosauridae
Genus: †Mymoorapelta
Kirkland et Carpenter, 1994
Type species
†Mymoorapelta maysi

Mymoorapelta (Meaning "Vannetta Moore and Pete and Marilyn Mygatt's shield" after a combination of the names of the discoverers of the Mygatt-Moore Quarry that fossils were originally collected from, and pɛltə "shield") is a monospecific genus of nodosaurid ankylosaur, a group of heavily armored, herbivorous, quadrupedal dinosaurs, from the Late Jurassic (Kimmeridgian-Tithonian, around 155 to 150 million years ago) Morrison Formation (Brushy Basin Member) of western Colorado and central Utah, USA. Few specimens are known, but the most complete one is the holotype individual from the Mygatt-Moore Quarry that includes many osteoderms, a partial skull, vertebrae, and other bones. It was initially described by James Kirkland and Kenneth Carpenter in 1994. Along with Gargoyleosaurus, it is one of the earliest known nodosaurids.

Mymoorapleta is one of the smaller known nodosaurids, with the estimated length of the largest specimen only reaching 3 metres (9.8 ft). It had a narrow snout and almost triangular skull in dorsal view with two large horns pointing backwards from the brow, and two horns below these that pointed backwards and down on the jugal. Five different armor types have been observed in Mymoorapelta, ranging from elongated, sharp spines affixed to the side of the body to a giant sacral shield composed of tiny osteoderms, called ossicles, that covered the top of the pelvis. In contrast to the club-tailed ankylosaurids, the tail bore spikes that Mymoorapleta likely used for defense.

Mymoorapelta was a low browser in the Morrison ecosystem, feeding on cycads and conifers, in contrast to the high-browsing Apatosaurus known from the same quarries. Other dinosaur groups were also present, including the herbivorous ornithopod Nanosaurus and Camptosaurus, and the giant plate-backed Stegosaurus. The large theropod Allosaurus has also been found in association with the animal, and we have evidence that it preyed on Mymoorapelta.

Discovery and naming

Map of the location of Mygatt-Moore Quarry, where Mymoorapelta fossils were first discovered.

The Mygatt-Moore Quarry was first discovered in March of 1981 by hikers Vanetta Moore and Pete and Marilyn Mygatt in Mesa County, west-central Colorado. The quarry's strata come from the Brushy Basin Member of the Morrison Formation, which dates to the Upper Jurassic.[1][2] It was not until 1990 that fossils of Mymoorapelta were discovered in the quarry, and since then over 160 elements have been found scattered over 25 metres (27 yd) of the 150-square-metre (1,600 sq ft) quarry.[3][1] A few of these elements are part of a single adult individual and were described by American paleontologists James Kirkland and Kenneth Carpenter in 1994. This specimen (MWC 1815) would be designated the holotype of the species and includes a left ilium (hip bone) with preserved bitemarks.[1] Kirkland and Carpenter named the species Mymoorapelta maysi, the generic name deriving from the names of Marilyn Mygatt and the Moores, who had discovered the quarry, and the Greek root pelta, meaning “shield”, due to the preserved armor.[1] The specific name is after Chris Mays, the president of the Dinamation International Corporation and Society, who funded the initial excavation of the Mygatt-Moore Quarry.[1][3] Mymoorapelta was the first Jurassic ankylosaur named from North America, with the closely related Gargoyleosaurus being named four years later in 1998.[4][1] Other parts of the type specimen that were excavated from the quarry include several dorsal and caudal (tail) vertebrae, ribs, isolated limb bones, and many osteoderms, including the signature triangular cervical spine of basal ankylosaurs.[5][3][1] Some osteoderms which have been found in the quarry and referred to Mymoorapelta come from a higher stratigraphic layer, suggesting that a second individual is preserved.[3]

Left ilium of the holotype (MWC 1815)

In 1998, a partial skeleton referred to Mymoorapelta was described by Kirkland et al from Cactus Park, Colorado, though at the time the fossil was still undergoing fossil preparation.[5] The skeleton preserved natural molds and body fossils of the sacrum, caudal vertebrae, chevrons (bones attached to the underside of the tail vertebrae in dinosaurs), pes (foot), and many pieces of the dermal armor, including parts of the sacral shield, which was a type of armor that would cover the top of the pelvis. Though skull material was mentioned to be preserved it is still in preparation and undescribed.[6][1] Some of the material, namely from the pes and sacral shield, was preserved in articulation making it the only known articulated specimen of the taxon.[5] In a 2010 abstract, Kirkland and colleagues mentioned the discovery of many more elements of Mymoorapelta at Mygatt-Moore Quarry including a nearly complete skull and every postcranial element except the pubis and femur.[5][7][3] All of the fossils found at Mygatt-Moore Quarry and Cactus Park are currently deposited in the Dinosaur Journey Museum of Western Colorado in Fruita.[3][1] 2015 saw the presentation of an abstract by Katie Tremaine et al that mentions a new Mymoorapelta specimen unearthed at Hanksville-Burpee Quarry near Hanksville, Utah.[8] The specimen includes one individual preserving: 24 osteoderms, three ribs, one vertebra, and a femur, though more material has yet to be excavated. The discovery of a single, dorsal osteoderm that had been collected from the Peterson Quarry outside of Albuquerque, New Mexico was described in 2016.[9] The osteoderm is morphologically similar to Mymoorapelta, however it is stratigraphically closer to Gargoyleosaurus.[9]

Description

Diagram illustrating the size of Mymoorapelta.

Mymoorapelta is one of the smallest ankylosaurs known and the smallest known quadrupedal dinosaur from the Morrison Formation. However, few individuals have been found and only a portion of the known material has been described in detail. The Cactus Park specimen is the largest described individual, with a 1998 estimate of 3 metres (9.8 ft) long.[5] Body mass estimates based on the type specimen are around 300–562 kilograms (661–1,239 lb).[10][6][11]

Skull and dentition

Skull of the similar Gargoyleosaurus, also from the Morrison Formation.

The skull specifically has not been described in detail, but the preserved morphology (external anatomy) is very similar to that of Gargoyleosaurus from the same formation.[7] It had a narrow snout and almost triangular shaped skull in dorsal (top) view with two, large horns pointing backward from the back of the head on the brow, and two horns below these that pointed backward and down on the jugal (cheek bone). A preserved jugal described in 1998 has a wedge-shaped, armored morphology and projects ventrolaterally like in ankylosaurids but not nodosaurids.[5] The premaxillae (bones at the tip of the snout) of Gargoyleosaurus, a taxon that closely resembles Mymoorapelta, possess a narrow, toothed, and trapezoidal muzzle.[12] In the back of the skull, the quadrate-articular area has an oval mandibular glenoid faces slightly medially, and is subtly longest anteroposteriorly. The articular surface's distal surface of the quadrate, especially on the medial condyle, is robust and elongate anteroposteriorly. In all ankylosaurs, the jaw joint is placed ventral to the occlusal plane. The coronoid process is very well developed in nodosaurids and the jaw joint (joint connecting the skull to the jaw bone) is well depressed in turn, which corresponds to a higher relative bite force.

Most ankylosaurs bear homodonty (variation in tooth morphology), but not in Gargoyleosaurus in the premaxillary, maxillary, and dentary teeth, which show subtle morphological differences. Ankylosaur teeth are compressed labiolingually and phylliform, with an apical cusp and secondary cusps along the mesial and distal edges. Nodosaurid teeth are blade-like, larger, and usually more complex than the basic cusps of ankylosaurids. Nodosaurid teeth have a larger crown, a rough enamel surface, confluent fluting with grooves of the marginal cusps, and a crenelated cingulum. The wear facets on Ankylosaur teeth vary greatly, but in nodosaurids they are usually more extensive and steeply inclined than in ankylosaurids, demonstrating underlying patterns of shape-constrained function. In early nodosaurids like Gargoyleosaurus and Gastonia, the pterygoid complex is not yet well developed anteroposteriorly and mediolaterally, but in later species are much wider, with more robust lateral wings, and anteroposteriorly more expanded than in basal forms, reaching the level of the distal quadrate condyles. This suggests relatively more developed pterygoid muscles in later nodosaurids than in ankylosaurids, reflecting a more efficient jaw adductor system in nodosaurids than typical ankylosaurids. The mandibular adductor chamber and the coronoid process are relatively taller in nodosauirds than in ankylosaurs, suggesting differences in the size and jaw adductor attachment of muscles.[12]

Postcrania

A dorsal vertebra in anterior view at the Dinosaur Journey Museum, Fruita.

Cervical (neck) vertebrae are known from Mymoorapelta, though many of them have not been fully researched or excavated. In the cervicals, the faces (ends) of the centra are wider than tall and display a "heart-shaped" morphology. The centra overall are short anteroposteriorly with lengths that are around equal to the centra's widths. The neural spines are short and thick with round, circular neural canals. A deep, tear-shaped fossa (or small opening in bone) is present between the postzygapophyses.[5] Several dorsal (back, sometimes referred to as thoracic) vertebrae are known from Mymoorapelta and are unique when compared to those of Cretaceous nodosaurids. The centra are cylindircal, more elongate posteriorly, and less compressed laterally compared to those of other nodosaurids like Sauropelta and Dracopelta. The anterior dorsals are unique in that they bear a triangular pit between the prezygapophyses. The prezygapophyses are also much more elongate at the anterior end of the vertebra, while the postzygapophyses are truncated at the posterior end. The left and right postzygapophyses are divided by a large groove. The mid dorsal vertebrae differ in that they are rounded ventrally and have a weak keel at the bottom. All of the dorsal vertebrae'ds transverse processes do not ascend steeply and are instead gradually heightened, as in basal ankylosaurs but not nodosaurids. Mymoorapelta has 13 ribs, all of which have triangular cross-sections and a weak T-shape, in contrast to other ankylosaurs. Mymoorapelta is also one of the few ankylosaurs with 4 sacral ribs, a trait shared with only 3 other taxa.[5][13]

The caudal (tail) vertebrae of Mymoorapelta and other nodosaurids are longer than wide, and dorsoventrally (top-bottom) flattened in comparison to anterior caudals. The neural spines are reduced relative to the anterior caudals, and the haemal spine takes on a rounded, hatchet-shaped appearance. The prezygapophyses (a part of the transverse processes) are short and extend past the anterior edge of the centra by only 25% or less. This trait is only present in nodosaurids and basal anklosaurs, but in taxa like Liaoningosaurus and ankylosaurids they overlap by at least 50% of its length to make them more fused together. Mymoorapelta lacks tail club handles or tail club knobs, as in other nodosaurids, giving them less ankylosis. In the caudal vertebrae overall, the transition from anterior to posterior caudals is less abrupt compared to ankylosaurids, which have an abrupt transition at the midcaudals. These features would give the tail more flexibility, which is unique to nodosaurids compared to the strongly fused tails of ankylosaurids.[14] The vertebral centra are much shorter compared to Gargoyleosaurus and the neural spines are shorter in Mymoorapelta.[5] Mymoorapelta, like other dinosaurs, preserves chevrons along the undersides of the caudal vertebrae. In Mymoorapelta and many other ankylosaurs, the chevrons are strongly fused to the lower posterior part of the centra and the haemal arches extend parallel to the elongate vertebral centra. Extension of these arches is greater anteriorly than posteriorly, forming a continuous boney structure underneath the haemal canal. One of the preserved posterior chevrons measures 9.1 centimetres (3.6 in) and is strongly recurved posteriorly.[1][5]

The scapular spine forms a vertical ridge opposite the glenoid in Mymoorapelta as in ankylosaurids and an indeterminate ankylosaur scapula found in the nearby Dry Mesa Quarry. In the pelvic region, Mymoorapelta displays an intermediate of some features between basal and more derived ankylosaurs. The ischium is bent as in other nodosaurids and polacanthines, indicating that a straight ischium is a derived feature in ankylosaurids. In the forelimbs, the ulna has a broad, massive olecranon process that preserved rugosities. The coronoid process develops about 1/3rd the way down the ulna’s shaft, compared to 1/4th as in Stegopelta and Polacanthus. In the pes (foot), the genus preserves short, wide metapodials with long phalanges. The distal phalanges look triangular and pointed in side view, contrary to other nodosaurids like Edmontonia.[1][5]

Armor

Three of the thin, triangular plates on display at the Dinosaur Journey Museum, Fruita.

A prominent feature of Mymoorapelta was its armor mostly consisting of large spiked osteoderms (bony armor) protruding from the lateral and dorsal sides of the body. These have not been found in articulation, so their exact placement on the body is unknown, though their position can be surmised based on the well preserved skeletons of nodosaurids and other ankylosaurs. In Mymoorapelta, there are five different preserved armor types: an elongated spine with a large, hollow base; a thin triangular plate with a narrower, asymmetrical base; a small bladelike spine with a rounded, solid base; isolated, flat, keeled scutes; and scutes fused into a single plate of armor.[5][1] The large spine is assumed to have extended from the base of the neck outward laterally and the point curving posteriorly.[5][1] Evidence from Borealopelta also supports the extension of the spike by a large keratin sheath.[15] Further down the body, the aforementioned thin triangular plates, of which eight are known, are preserved similarly to those in Polacanthus.[16][1] It was theorized by Kirkland and Carpenter that the largest of these plates were attached to the proximal part of the tail, and protruded laterally along the sides of the body and a specimen preserved one at 11 centimetres (4.3 in).[5][1] A single, small triangular plate was reported in 1994 and it preserves a thin, bladelike morphology, though its position is unknown.[1] Twelve of the keeled, flat scutes were recovered from Mymoorapelta in 1994, preserving a keeled oval shape and an external surface bearing uniform, weak pitting, and a privation of neurovascular grooves (the system that controls blood flow and homeostasis) and foramina (small openings within bones).[1] In the internal structure of the scutes, half of the space is made up of trabecular bone while the rest of thick external and basal cortices.[17]

Lastly, a small fragment of dermal armor preserves a rosette formed by a large central scute surrounded on all sides by smaller ossicles.[5][1] This piece of armor comes from the sacral shield, a large plate of small, connected armor across the sacrum and pelvis for protection. A more complete sacral shield was preserved in the Cactus Park specimen, with estimates placing the complete sacral shield at 70 centimetres (28 in) for a 50 centimetres (20 in) wide pelvis.[5][1] The sacral shield also preserves two middle rows of larger scutes with seven large scutes preserved in each row.[5] Mymoorapelta preserves a category 2 sacral shield, which is characterized by bosses (keeled osteoderms) bordering tubercles (elevated knobs) as well as rosettes (a large osteoderm surrounded by smaller osteoderms, forming a flower-like arrangement) of coossified osteoderms. This category of sacral shield is mostly found in the "polacanthids",[18][19] but the status of this group is in a flux and the trait is also known in some ankylosaurids like Shamosaurus.[20][21][19] The category 2 shield is most similar to that of category 3, though the latter preserves polygonal osteoderms lacking rossettes.[19] Victoria Arbour et al (2011) however suggested that category 1 shields could simply be an ontogenetic stage of category 2, as they have very similar morphology but are not co-osiffied, an ontogenetic trait present in extant armored animals like armadillos and alligators.[19][22][23] On the upper surface of the back and tail, the skin was covered in small osteoderms, sometimes referred to as ossicles, in-between larger plates of armor as inferred by Sauropelta,[24] though ossicles themselves are not known confidently outside of the sacral shield in Mymoorapelta.[5][1] The armor of Mymoorapelta differs from those in Gargoyleosaurus in that the former has solid conical armor compared to the thin-walled armor of the latter.[4]

Paleobiology

Diet and feeding

A life restoration of the closely related Gargoyleosaurus.

Mymoorapelta, like its relatives, was a low browsing herbivore in its ecosystem that likely fed on the cycads and conifers of the time due to the lack of complex grasses in the Jurassic.[25] Mymoorapelta, like its relatives, was a low browsing herbivore in its ecosystem that likely fed on the cycads and conifers of the time due to the lack of complex grasses in the Jurassic.[25] Nodosaurids like Mymoorapelta had narrow snouts, an adaptation seen today in animals that are selective browsers as opposed to the wide muzzles of grazers.[26][12] In ankylosaurs, the Jurassic and mid-Cretaceous forms with narrow and pointed muzzles were apparently the most selective feeders like extant mammalian browsers. This is in stark contrast to later ankylosaurs, which were adapted to bulk feeding of less nutritious foods. The preservation of complete hyobranchial apparatuses in taxa like the ankylosaurid Pinacosaurus and the nodosaurid Edmontonia demonstrate that ankylosaurs had fleshy, muscular tongues that could assist with feeding on plants low to the ground.[27][12] Tongue protrusion and prehension is not confidently known, but at least in later ankylosaurids, lingual food manipulation could have been used, like in giraffes, to crop food. The preservation of cheek plates in Edmontonia and Panoplosaurus provide evidence for fleshy cheeks and chewing created a fleshy cheek which covered the tooth rows for defense and to prevent food loss when eating.[28] Tooth occlusion is not directly preserved in Mymoorapelta or its close relative Gargoyleosaurus, but it has been found in Cretaceous nodosaurids. The earliest evidence of nodosaurid occlusion is in Sauropelta, which had basic occlusion that demonstrate that the power strokes went in a vertical direction. In contrast to later nodosaurids, tooth-tooth contact was incidental or local when present and a biphasial jaw mechanism was lacking in Mymoorapelta and Gargoyleosaurus.[12] In wear patterns overall, ankylosaurs demonstrate more variable wear patterns than the contemporary ceratopsids and hadrosaurids of the Cretaceous. Though ankylosaurs may not have fed on fibrous and woody plants, they may have had a varied diet, including tough leaves and pulpy fruits.[27]

Habitat preference

Due to competition with Diplodocid sauropods, Mymoorapelta and its ecological group seems more adapted for open environments.[29] Mymoorapelta has a very limited known distribution, known only from two sites in Western Colorado in addition to the Hanksville-Burpee and potential Albuqurque specimens.[1][5][8][9] This could possibly be due to Mymoorapelta's preference for a specific variety of plant that it fed on, constricting its possible distribution. The Hanksville-Burpee specimen's taphonomy suggests that the individual had died inland, contrary to the coastal distribution previously inferred for nodosaurids.[8][30][31]

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,[32][33] though they may have been capable of quick movements when necessary.[34] Mymoorapelta specifically preserves very short limbs with even shorter distal limb elements, in contrast to the longer distal limb elements known in other nodosaurids but alike ankylosaurids and Polacanthus.[7]

Classification

Mymoorapelta is one of the basalmost known genera of Nodosauridae an extinct family of medium to large, heavily built, quadrupedal, herbivorous dinosaurs, possessing small, leaf-shaped teeth which first evolved in the Late Jurassic (ca. 155 mya) and went extinct in the Late Cretaceous (ca. 66 mya) during the famous Cretaceous–Paleogene extinction event. Nodosaurids were in the group Euankylosauria with the similar family Ankylosauridae, although ankylosaurids evolved more recently in the Early Cretaceous and several distinct anatomical characteristics; nodosaurids lacked mace-like tail clubs and had flexible tips instead, many nodosaurids had spikes projecting outward from their shoulders, and two armored neck half-rings, among other traits. Many nodosaurids had spikes projecting outward from their shoulders. A third proposed family, Polacanthidae, was erected for several genera that were similar to nodosaurids but had more fragile armor and a different distribution, though it has seen little support from phylogenetic analyses in recent years and is in a state of flux.[35][20][36] Euankylosauria encompassed all members of Ankylosauria except for the clade Parankylosauria, which is a smaller group known exclusively from a few taxa that lived in the Cretaceous of Gondwana, rather than Laurasia where Euankylosaurs were endemic to. Ankylosauria and Stegosauria are now grouped together within the clade Thyreophora. This whole 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.[37][38] The suborder name Ankylosauria was first erected by American paleontologist and fossil hunter Barnum Brown in 1923 for his genus Ankylosaurus and several other ankylosaurs that had been named earlier, though fossils of ankylosaurs have been known since the early 19th century with genera like Palaeoscincus, Polacanthus, and Hylaeosaurus.[39][20] Nodosauridae was named in 1890 by Othniel Charles who designated the Cretaceous genus Nodosaurus as the type genus based on the heavy dermal armor, solid bones, large forelimbs, and ungulate feet preserved it preserves.[40][41]

Below is a reproduced phylogenetic analysis of the Victoria Arbour et al. matrix, the reference phylogeny of Ankylosauria following Madzia et al., that represents the detailed internal and basic external phylogeny of Ankylosauria:[42][43]

Thyreophora

When Mymoorapelta was originally named, James Kirkland and Kenneth Carpenter placed the taxon as a potential Nodosaurid, though at that time there were few taxa to compare the material to. The phylogenetic placement was changed in 1998 when it was considered closer to the European Polacanthidae,[5] though this has been doubted.[7][13][8] Vickaryous et al. (2004) considered it Ankylosauria incertae sedis,[44] while a cladistic analysis performed by Thompson et al. (2011) suggests that Mymoorapelta is a basal nodosaurid as originally theorized by Kirkland and Carpenter.[20] A 2010 phylogenetic analysis utilizing undescribed material resulted with Mymoorapelta as the sister taxon to Gargoyleosaurus in their own group outside of Polacanthidae, Nodosauridae, and Ankylosauridae.[7] The 2018 phylogenetic analysis of Rivera-Sylva and colleagues is used below, placing it as a basal nodosaurid, with relationships within Panoplosaurini and Struthiosaurini collapsed for simplicity.[36] Mymoorapelta here is in a clade including Sauroplites and Dongyangopelta that is the most basal group within the family, while Gargoyleosaurus is more advanced, further proving their distinction.[36] Alternatively, Mymoorapelta may be an ankylosaur outside both Nodosauridae and Ankylosauridae.[45]

Tail anatomy of ankylosaurs, F is Mymoorapelta
Nodosauridae

Paleoecology

The Morrison Formation is a sequence of shallow marine and alluvial sediments which, according to radiometric dating, ranges between 156.3 million years old (Ma) at its base, to 146.8 million years old at the top, which places it in the late Oxfordian, Kimmeridgian, and early Tithonian stages of the Late Jurassic period. This formation is interpreted as a semiarid environment with distinct wet and dry seasons. The Morrison Basin where dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west. The deposits from their east-facing drainage basins were carried by streams and rivers and deposited in swampy lowlands, lakes, river channels and floodplains. This formation is similar in age to the Solnhofen Limestone Formation in Germany and the Tendaguru Formation in Tanzania. In 1877, this formation became the center of the Bone Wars, a fossil-collecting rivalry between early paleontologists Othniel Charles Marsh and Edward Drinker Cope.

Illustration of the theropods Ceratosaurus and Allosaurus fighting over food in the Mygatt-Moore Quarry.

Mygatt-Moore Quarry has been interpreted as an attritional accumulation of dinosaur fossils at a permanent waterhole, allowing it to become one of the most fossil abundant sites in the United States. The site notably preserves a menagerie of Jurassic fossils, with plants, pollen, coprolites, and even skin impressions preserved alongside dinosaur fossils. Plant fossils are abundant in the quarry, with horsetails, cycadophytes, gingkoes, Czekanowskiales, and many different conifers represented by leaf, wood, and pollen fossils.[3] Invertebrates represented in the quarry include gastropods and most notably, fossils of fossil crayfish.[3] As for vertebrates, three different kinds of fish have been described from the quarry in astonishing quality, and the dinosaur fossils are the most common in the quarry. Allosaurus fragilis, a large carnivorous theropod, and Apatosaurus, a large diplodocid sauropod, are the two most common dinosaurs in the quarry, with Mymoorapelta being the third most common at the site.[3] Fossils of several other dinosaurs are known from the quarry, including the theropod Ceratosaurus, sauropod Camarasaurus, and potentially the small ornithischian Nanosaurus. The Morrison Formation in total is interpreted as a semiarid environment with distinct wet and dry seasons, and flat floodplains.[6] Vegetation varied from river-lining forests of conifers, tree ferns, and ferns (gallery forests), to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.[6]

Fossils of Mymoorapelta and the theropod Allosaurus from the Mygatt-Moore Quarry preserving bite marks alongside other bones found with feeding traces were described by Drumheller et al (2020).[46] Unlike the others, the fossils of Mymoorapelta and Allosaurus have left striations that, when measured to determine denticle width, produced tooth and body size extrapolations greater than any known specimen of Allosaurus or Ceratosaurus, the two large predators known for osteological remains from the quarry. The extrapolations are instead coherent either with an unusually large specimen of Allosaurus, or a separate large taxon like Torvosaurus or Saurophaganax, both of which are not known from the quarry. The result either increases the known diversity of the site based on ichnological evidence alone, or represents powerful evidence of cannibalism in Allosaurus. Based on the position and nutrient value associated with the various skeletal elements with bite marks, it is predicted that while Mymoorapelta was either predated upon or scavenged shortly after death, Allosaurus was scavenged some time after death.[46]

See also

References

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  2. ^ Sullivan, Sharon. "Huge dinosaur bone unearthed at quarry". www.aspentimes.com. Retrieved 2022-08-18.
  3. ^ a b c d e f g h i Foster, J., Hunt-Foster, R., Gorman, M., Trujillo, K., Suarez, C., McHugh, J., ... & Schoenstein, H. (2018). Paleontology, taphonomy, and sedimentology of the Mygatt-Moore Quarry, a large dinosaur bonebed in the Morrison formation, western Colorado—implications for Upper Jurassic dinosaur preservation modes. Geology of the Intermountain West, 5, 23-93.
  4. ^ a b Carpenter, K., Miles, C. and Cloward, K. (1998). "Skull of a Jurassic ankylosaur (Dinosauria)." Nature 393: 782–783.
  5. ^ a b c d e f g h i j k l m n o p q r s t Hunt, A. P., & Scheetz, R. D. (1998). Ankylosaur (Dinosauria) specimens from the Upper Jurassic Morrison Formation The Upper Jurassic Morrison Formation: An Interdisciplinary Study: Denver Museum of Natural History, Denver, USA: May 26-28, 1994, 22, 145-177.
  6. ^ a b c d Foster, J. (2007). Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. pp. 327–329. ISBN 978-0-253-34870-8.
  7. ^ a b c d e Kirkland, J. I., Hunt-Foster, R. K., Foster, J. R., & Loewen, M. (2010). Newly recovered skeletal elements of the Late Jurassic dinosaur Mymoorapelta from its type locality in the Morrison Formation permits re-evaluation of ankylosaur phylogeny. Journal of Vertebrate Paleontology, 30, 116A.
  8. ^ a b c d Tremaine, K., D’Emic, M., Williams, S., Hunt-Foster, R.K., Foster, J., and Mathews, J., (2015), Paleoecological implications of a new specimen of the ankylosaur Mymoorapelta maysi from the Hanksville-Burpee Quarry, latest Jurassic (Tithonian) Morrison Formation (Brushy Basin Member) [abs.]: Journal of Vertebrate Paleontology Program and Abstracts, p. 226.
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  10. ^ Farlow, James O.; Coroian, Dan; Currie, Philip J.; Foster, John R.; Mallon, Jordan C.; Therrien, François (2022-07-11). ""Dragons" on the landscape: Modeling the abundance of large carnivorous dinosaurs of the Upper Jurassic Morrison Formation (USA) and the Upper Cretaceous Dinosaur Park Formation (Canada)". The Anatomical Record: ar.25024. doi:10.1002/ar.25024. ISSN 1932-8486. PMID 35815600. S2CID 250422526.
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