Johnson 1 Hope Johnson William Parker IFS 2087-0001 12 Nov 2015 Pinacosaurus: A Study Abstract When the dinosaurs roamed the earth, there were millions upon millions of species of dinosaurs, few of which left behind fossils for mankind to recover. One of which were the Pinacosaurus, which belonged to the Ankylosaurian family, underneath the umbrella of Ornithischian dinosaurs. They were split up into two different species, Pinacosaurus grangeri and Pinacosaurus mephistocephalus. Both were diagnosed in part by a shallow nasal vestibule with two or more paranasal apertures, a lacrimal, a quadrate condyle lying ventral to caudal margin of orbit, a strong craniolaterally divergent preacetabular process of the ilium and a pentadactyl manus. (Weishampel, 2004) They originated in the Late Cretaceous period, and were found in the Mongolia, northern China, and Djadokhta formations (Gregory, 2010). They lived in a desert habitat, and probably fed on vegetation along water courses and at oases, they contained a small club that was a high velocity weapon for use on small theropods. Moreover, their family, the armored ankylosaurs originated in Europe during the Early Jurassic, and waddled to Northern America, Asia, South America, and Antarctica by the end of the Cretaceous. (Farlow and Brett-Surman, 2012). The Pinacosaurus are the most well-known among the Ankylosaurs due to their many skeletal remains left behind in the deserts of Mongolia.
Johnson 2 Introduction The Pinacosaurus were divided into two different species, Pinacosaurus grangeri, and Pinacosaurus mephistocephalus. They are differentiated by the arrangement of the paranasal apertures, the shape of the lacrimal and the length of the deltopectoral chest of the humerus, which is short in P. grangeri. (Weishampel 2004). Pinacosaurids were very wide, short animals, with distinct features, living in the regions of Mongolia. However, the Pinacosaurus grangeri remains the best known Asian Ankylosaur, being represented by over 15 specimens, including a nearly complete skeleton, trunk osteoderms, and several well-preserved skulls (Hill, Witmer and Norell 2003). Both species lived in the Late Cretaceous, and were found typically in Mongolia, in the Djadokhta Formation, which yielded many fossils. (Farlow and Brett-Surman, 2012). The anatomical characteristics of the Pinacosaurus included very small heads, numerous nostril exits through the side of the snout, short spines along flanks of body and hips, with a small tail club to boot. Their habitat consisted of a desert environment with dunes and oases. They probably fed upon vegetation along water courses and at oases. Their small club was used as a high velocity weapon on small theropods. The intact skeletons of over a dozen large juvenile Pinacosaurus skeletons have been found grouped together, apparently killed at the same moment by a dune slide. The absence of the adult suggested that the growing armored dinosaurs were moving together as an independent gang, or in pods. The habitat probably lacked theropods large enough to attack adult Pinacosaurus (Gregory, 2010). Ankylosaurs, including the two species of the Pinacosaurus were believed to be herbivorous, not only because of their wide hips, and short legs leaving them close to the ground,
Johnson 3 but because the teeth are ill-suited for slicing flesh. The wear patterns of the teeth show tooth-totooth wear along the faces of the crowns in ankylosaurids. (Farlow and Brett-Surman, 2012). Discussion Pinacosaurs contain very distinct features, causing them to belong to their own genus, and even dividing them into two separate species. For instance, a specific ankylosaur discovered by Hill, Witmer, and Norell, turned out to be a juvenile P. grangeri because it contained such defining characteristics. It was found in southern Mongolia, in Ukhaa Tolgod, and had a complete skull with associated mandible and osteoderms that exhibits ankylosaurid characteristics. Ukhaa Tolgod is a location known for the well-preserved theropods, mammals and squamates, but until then had not yielded ankylosaur material. The skeleton had two pairs of osteodermal horns projecting from the quadratojugals and squamosals, a wide triangular skull, a premaxillary beak edge that is not continuous with the maxillary teeth row, an absence of premaxillary teeth. Moreover, it was identified as P. grangeri because of the presence of a large premaxillary sinus, a quadrate not co-ossified with the paroccipital process, several pairs of accessory openings in the narial region, and contains 5 pairs of openings in the narial region indicating that extensive morphological variability exists in the narial anatomy. The skeleton was furthermore identified as juvenile because of the small size of the skeleton, an incomplete fusion of secondary dermal ossifications to the skull roof, and exposing sutual boundaries (Hill, Witmer, and Norell 2003). Ankylosaurids, also contain very distinct behaviors and anatomical features. Of the 5 major skull openings typically seen in the dinosaurs, the Ankylosaurids have only three: External nares, orbit, and lateral temporal fenestra. The orbits in the Ankylosaurs moreover, tend to be circular or oval, and are often walled internally along the rear margin so as to separate the jaw-
Johnson 4 closing adductor muscles from the eyeball (Farlow and Brett-Surman 2012). In Pinacosaurus specifically, the external nares face outward, and the supraorbitals are sharp ridge-like structures over the orbit. (Farlow and Brett-Surman, 2012). The Ankylosaurs are also characterized by a low, wide body that is encased in armor embedded in the skin. The armor was probably formed within the skin in a manner similar to the crocodiles and armored lizards, by ossification of the cartilage nodules. (Farlow and Brett- Surman, 2012). In Pinacosaurus, the armor was grown from the neck and progressing down to the tail as growth occurs. As seen in the growth series for Pinacosaurus the body armor was nearly absent in the very youngest specimens known (about 1 m long), and were restricted to bands of neck armor. The tail club doesn t even appear until late in life, when the individual is over half-grown. (Farlow and Brett-Surman, 2012). The armor s direct use is unknown, with many varying reasons, the strongest possibility being self-defense and protection. In fact, it was even possible that the ankylosaurs could blush through their armor, showcasing a pink tint as a result of the infusion of blood under the horny covering of the armor. This is backed up by the fact that there are vascular grooves covering the surface of most ankylosaur armor, indicating there was a rich supply of blood being present. But in Pinacosaurus specifically, it was suggested the armor was used for thermoregulation, as they lived in the desert climate, where the days were boiling hot, and the night were below freezing. Moreover, Ankylosaurs were believed to be herbivores, because they consisted of short legs, and being built close to the ground, which probably restricted them to feed on plants or plant parts 2 meters or less from the ground. The type of plants they ate depended on where they lived, and the type of beak they had (Farlow and Brett-Surman 2012). Ankylosaur footprints were global, but most of the tracks are concentrated in coastal and floodplain deposits
Johnson 5 representing wet, well vegetated habitats. (Weishampel, 2004). These habitats allowed for lots of plants to chew on, and less competition for resources. However, the Pinacosaurus differed in that they lived in an arid climate, meaning they mostly lived along the oases, and water fronts, chewing on the vegetation. This could suggest that they lived with a higher competition for resources. They still remained mostly gregarious creatures, as several remains were found in pods. Such as the specific remains of the over dozen juveniles, found clustered, appearing to have been killed simultaneously by a dune slide (Gregory, 2010). Further proof they were herbivores, is the high mobility of the tongue, suggested by the large size of the throat bones (hyoids) that lay at the base of the tongue. This would allow ankylosaurs to push and roll a wad of vegetation around in the mouth while consuming it. They probably needed cheeks, and most likely were fleshy. (Farlow and Brett-Surman, 2012). The unworn teeth of ankylosaurs are shaped like tiny hands with fingers close together. Teeth are small compared to skull size. Moreover, the ankylosaur skull has a scoop-shaped beak at the front of the mouth, and the edge of the beak has a sharp rim around sides and front. It was probably covered with a keratinous beak much like a turtle. The unusual architecture of the skull, coupled with the small size of the individual teeth, led various experts to propose that diet was limited to nonabrasive plants (Weishampel, 2004). The broad beak of Ankylosaurs, suggested they also were general grazers, cropping low plants, instead of having a narrower beak which in turn suggests they eat specific plants, of specific heights. (Farlow and Brett-Surman, 2012.) To elaborate on the anatomy, the ankylosaur skull is different in that the skull is more wide than it is deep, unlike most other dinosaurs. This is due to the lateral expansion or bulging of the maxillary bones above the tooth row. The surface of the skull in many ankylosaurs is rough or knobby, which is the result of remodeling of the skull surface by skin with each bump
Johnson 6 being the site of a former scale. The ankylosaur skulls also typically have horns of sorts projecting from the rear corners. In the juveniles, such as that of the Pinacosaurus, the cranial sutures remain distinct, which is important for determining the skull bone homologies. (Farlow and Brett-Surman, 2012) In the case of a brain cavity, it shows that the forebrain region was rather small, including the olfactory lobes, so that even with a large nostril, the sense of smell was not very acute. In the midbrain region, the optical nerves were not very prominent suggesting the vision was not good either. These features could be compared to the rhinos of current times. The pituitary region is, however, large, indicating that the ankylosaurs could carry a lot of hormones. Also compared to living reptiles, the ankylosaurs had a brain about half the size that would be expected (Farlow and Brett-Surman, 2012). Moreover, Witmer reviewed the craniofacial pneumanticity and reasoned that the paranasal sinus cavities are best explained as an optimization of the skull architecture rather than as evolutionarily derived functional spaces (Weishampel, 2004) Figure 1, an image of the complete skeleton arrangement of the Pinacosaurus grangeri, demonstrates the short legs, and wide hips characteristic of the ankylosaurs.
Johnson 7 (Figure 1, P. Grangeri, Paul Gregory, Princeton Field Guide to Dinosaurs. 2010.) There remains to be more information found on the P. Grangeri than the P. Mephistocephalus, which suggests that there needs to be a realignment of the ontogeny, phylogeny, and whether or not those skulls could be from actual different species, or just different genders, or ages in life. For instance, more information could still be recovered from new fossils such as the club-tailed Ankylosaurus found in Bayan Mandahu in Mongolia, by local herdsmen. Experts were invited to examine the remains and classify it. The Bayan Mandahu rock formation itself is dated back 75 million to 120 million years, and was already known as one of the world s richest deposits for dinosaur fossils. It also was the one of the few sites in China that contains fossils of late Cretaceous Pinacosaurus (New Dinosaur Fossils).
Johnson 8 The information known about its habits, and lifestyle is thorough, and consistent with all that was found. The environment of the Pinacosaurus, and the herbivorous nature supported by its anatomical structure, is detailed and well-known. There could still be more information shown on how they lived, and what their diet consisted of, since they lived in the desert area, instead of wet humid areas that consisted of a lot of vegetation, like their ankylosaur counterparts. Conclusion Pinacosaurus, an armored Ankylosaurus, belonging to the umbrella taxa of the ornithischian dinosaurs, is split into two species, P. grangeri and P. mephistocephalus. They differed in the arrangement of the paranasal apertures, the shape of the lacrimal, and the length of the deltopectoral chest of the humerus, which is short in P. grangeri and long in P. mephistocephalus (Weishampel, 2004). They left behind several fossilized remains in Mongolia, northern China, Djadokhta formations, and the Baha Mandahu rock formation. The environment they lived in was a desert climate with dunes and oases, with a climate that has boiling hot temperatures, and below freezing nights, potentially using their armor for thermoregulation. They were believed to be herbivores, not only because of their body shape which consisted of large hips and short legs, leaving them close to the ground, but because of the shape of their teeth and the wear they had on the faces of the teeth. They also were believed to have lived during the late Cretaceous period, Late Santonian, and/or Early Campanian periods (Gregory, 2010). Moreover, they were also believed to be gregarious in nature, traveling in pods, as seen in the numerous clusters of remains found throughout Mongolia. They anatomically contained an armored plate, which originated at the neck, in early life, and grew toward the tail. The osteoderms, were actually embedded in the skin, and formed much
Johnson 9 like the way crocodiles form their armor in current times, which is ossification of the cartilage nodules. They also possessed a unique tail club, which didn t form until over halfway in life. The tail club was formed from modified, tightly interlocking distal caudal vertebrae (the handle) and enlarged osteoderms that envelop the terminus of the tail (the knob). The handle vertebrae were different from any other club-bearing tetrapods because of elongated and robust prezygapophyses, neural spines/postzygapophyses, and haemal arches (Arbour and Currie, 2015). Moreover, since they belonged to ankylosaurids, they possessed those characteristics as well, such as the triangular shape of the skull, and the shape of the teeth, which were worn, and ill-suited for tearing through flesh. They also had bad eyesight and a bad sense of smell, inferred from cranial casts. Also due to the largeness of the pituitary gland, the brain size is about half the size in comparable forms. The ankylosaurs themselves were believed to have originated in Europe, and spread through North America, Asia, South America, and Antarctica, before the end of the Cretaceous. They also evolved through the progressive widening of the hindgut, as seen through the widening of the pelvis. This is the result of the changing diet, and the need for longer fermentation time. Pinacosaurus remains an important species of dinosaur, due to the abundance of fossils, which can give more detailed information of the surrounding climates, and the other dinosaurs of their times.
Johnson 10 Works Cited Arbour, Victoria M., and Philip J. Currie. "Ankylosaurid Dinosaur Tail Clubs Evolved through Stepwise Acquisition of Key Features." Journal of Anatomy 227.4 (2015): 514-23. Web. <http://onlinelibrary.wiley.com.proxy.lib.fsu.edu/doi/10.1111/joa.12363/full> Farlow, James Orville, and M. K. Brett-Surman. The Complete Dinosaur. 2nd ed. Bloomington: Indiana University Press, 1997; 2012; Print. Hill, RV, LM Witmer, and MA Norell. "A New Specimen of Pinacosaurus Grangeri (Dinosauria: Ornithischia) from the Late Cretaceous of Mongolia: Ontogeny and Phylogeny of Ankylosaurs." American Museum Novitates. New York NY.3395 (2003): 1-29. Web. <http://ha6lk3ly9z.search.serialssolutions.com/?ctx_ver=z39.88-2004&ctx_enc=info%3aofi%2fenc%3autf- 8&rfr_id=info:sid/summon.serialssolutions.com&rft_val_fmt=info:ofi/fmt:kev:mtx:journ al&rft.genre=article&rft.atitle=a+new+specimen+of+pinacosaurus+grangeri+%28dinos auria%2c+ornithischia%29+from+the+late+cretaceous+of+mongolia+%3a+ontogeny+ and+phylogeny+of+ankylosaurs&rft.jtitle=american+museum+novitates&rft.au=hill%2 C+Robert+V&rft.au=Witmer%2C+Lawrence+M&rft.au=Norell%2C+Mark&rft.au=Mon golyn+shinzhl%c4%97kh+ukhaany+akademi&rft.date=2003&rft.pub=american+mus eum+of+natural+history&rft.issn=0003-0082&rft.eissn=1937-352x&rft.spage=20&rft.externaldbid=rmh&rft.externaldocid=oai_digitallibrary_am nh_org_2246_2821¶mdict=en-us> "New Dinosaur Fossils Discovered in Inner Mongolia." Xinhua News Agency 2012. Web. <http://bi.galegroup.com.proxy.lib.fsu.edu/essentials/article/gale%7ca286420008?u=t all85761&sid=summon&usergroup=tall85761>
Johnson 11 Paul, Gregory S., and Inc ebrary. The Princeton Field Guide to Dinosaurs. Princeton: Princeton University Press, 2010. Web. <http://site.ebrary.com.proxy.lib.fsu.edu/lib/fsulibrary/detail.action?docid=10404084> Weishampel, David B., et al. The Dinosauria. 2nd;2; ed. Berkeley: University of California Press, 2004. Web. <http://site.ebrary.com.proxy.lib.fsu.edu/lib/fsulibrary/detail.action?docid=10595414>