Gastonia (Gastonia burgei)
Size
Gastonia was approximately 6m long, although half of this length was its tail.
Behaviour
There is some evidence for Gastonia having a mobile braincase: this may have acted as a shock absorber during head-butting behaviour. The head-butting hypothesis is also supported by the very thick and slightly domed skull of Gastonia, and the fact that its eyes point forward: a feature seen in head-butting dinosaurs, but uncommon among herbivores generally. Gastonia's mobile braincase has been refuted by some palaeontologists.
Gastonia had very short legs. It would have moved slowly and was not adapted to running. Gastonia also had lateral tail spines, and may have swung its tail from side to side during defensive behaviour.
By studying fossilized brain cases, scientists have determined that the Polacanthid ankylosaurs (the group of armored, bony, plant-eating dinosaurs to which Gastonia belonged) were the most intelligent ankylosaurs, and would have been most aware of their surroundings.
Position in Food Chain
Gastonia was a herbivore and would have grazed on low plants.
Gastonia is the most common dinosaur in the particular fossil layer in which it is found - the Yellow Cat member of the Cedar Mountain formation in Utah. The most common large predator found in this location is Utahraptor: this suggests Gastonia may have been preyed upon by Utahraptor.
Habitat
The Cedar Mountain formation where Gastonia is found represents sediment deposits on the floodplain of a system of linked streams, called a braid-plain. This suggests Gastonia was living in a reasonably arid braid-plain.
Reconstruction
Gastonia is known from several hundred bones including a skull, but lacks the lower jaws. The lower jaw of the closely related Animantarx was used as a substitute in this case.
Recreating Gastonia for Earthsim
Sounds
The nasal cavities are large, and it has been suggested that they were used as resonating chambers, for making sounds. As a reasonably large heavy animal, probably gruff rumbling sounds! It’s also not unreasonable to perceive Gastonia snuffling, whilst browsing on low-lying plants.
Range of movement and dynamics
Generally limited, most limited of all the dinosaurs in the ecosystem:
Gastonia could look up to about a 30 degree angle, look down to place the beak on the floor, and sideways to about 45 degrees each way. Gastonia had little flexibility of the back, although the long spikes would sway slightly (alternating left and right) as the animal walked.
Visual Reconstruction
As mentioned above, Gastonia is known from “several hundred bones” including a skull, but lacks the lower jaws. The lower jaw of the closely related Animantarx can be used as a substitute.
General Dimensions
6m long, but half this length was tail. Gastonia had very short legs, a short neck and a long tail, which would have approached but not touched the floor. The body was wide and rounded, roughly an egg-shape, with a large stomach. As in other ankylosaurs, the dorsal (back) and lateral (sides) were studded with a distinctive arrangement and number of bony projections embedded in the skin. These are not strictly part of the skeleton. The head was small.
Skull
The skull can be thought of as a rough box, it is rectangular when looked at from the front/back, with the top gently arching in side view, from the back of the skull to the tip of the snout. It is triangular when looked at from above, almost as wide across the rear of the skull as it is long, with four short blunt horns projecting from the back of the skull; one on each side at the top/back pointing backwards/sidewards, and one on each side below the orbit (eye), projecting straight down. The eyes were widely spaced, each on opposite sides of the skull, facing sideways-forwards. They could not be seen from above, but could both be seen from the front. The nostrils were also on the sides, and were barely visible from above. A rounded toothless beak (not pointed) is the only part of the skull not covered in armour. This would have been smooth with vague fine ridges and furrows running along its length. A thick rough boney texture covers most of the skull, this is especially thick on the top of the skull between the horns and eyes. The pattern of this skull armour, is indistinct, in contrast with other ankylosaurs where there are clear patterns. 15-16 small denticle-like teeth were in each upper jaw tooth row (total teeth in upper jaw = 32). The lower jaw has been recreated based on Animantarx. The jaw is shallow, and in side view the lower margin is flat. It too, was tipped with a (smaller) beak, which was slightly over-bitten by the beak of the upper jaw. The teeth of the skull are inset, and in life would have been obscured by thin cheeks (see below).
Facial features
As noted above, a cheek covered the sides of the face – this would have been thin (not fleshy) and would have reached forwards to just behind the beak. A thick strong muscular tongue would be used for pushing vegetation around the mouth. Closely related ankylosaurs are known to have shutter-like armoured eyelids, Gastonia was probably no exception. The orbit is circular, the rim of which would have been slightly visible as a depression around the actual eye. The bony (upper) eyelid would have been elongate oval shaped, and covered about 2 thirds of the orbit when closed. The nostrils (nares) appear large in the skull, but these would have had a fleshy covering and the actual nostrils would have been small and positioned at the front of the nares (and widely spaced). The rest of the skull surface would appear in life, almost identical to the condition seen in the fossil skull described above, however, the four spikes at the rear of the skull would be slightly more pronounced in life, being covered by a keratin sheath. Underneath the jaws and running along the bottom of the neck was the soft flesh of the throat. A conservative reconstruction would keep these tight and restricted, but it is very possible that loose floppy jowls/dewlap/wattle were present, as in some living animals. This is all the more likely in an animal such as Gastonia, which we already know to have been ornate.
Legs and posture
In Gastonia, the forelimbs are functionally legs – they were used for walking only – it was quadropedal. This contrasts with the condition seen in theropods and some ornithopods, where the forelimbs may act as arms, or have a duel function, used as both legs and arms. The forelimbs were two-thirds the length of the hindlimbs – the highest point of the animal is at the hips, and the spine slopes down towards the pelvic (shoulder girdle). All four legs are short, robust, stocky and well muscled. They were mostly not visible when Gastonia was seen from above, being obscured by the rounded belly, and lateral rows of spikes. The elbows point backwards and slightly sideways, and the position of the hands on the ground is at a level roughly equivalent, to the hind feet. The ‘hands’ each have 5 forward-facing fingers each terminating in a rounded ‘hoof’. These were all roughly the same size but digit 3 (the middle finger) was slightly larger, and digit 1 (the thumb) and 5 (the little finger) was smaller. The hind legs were orientated straight, with the knees bending forwards (not splayed like the fore-limbs). The hind feet were wide with four forward facing toes, larger than the hands, each with a rounded hoof.
Armour
The dermal (outer covering) armour made up of osteoderms (these range from small boney scutes to large spines embedded in the skin,) was quite distinctive, and it is this that will distinguish Gastonia from other ankylosaurs, when seen from a distance. The armour can be divided into three parts for descriptive purposes: the tail, the sacral plate, and the neck-back.
Neck and Back
This region is the most heavily armoured part of the animal, and bears the largest of the spines. There are two major rows of spikes running from the neck (immediately behind the head) to the shield: one double row (7 spines each side) point upwards sideways backwards, and the second and larger row (also 7 each side), points sideways. All of these spikes are recurved backwards and flattened somewhat from top to bottom. Between these two rows is another row of blunter osteoderms (4 on each side). All of the rows are in pairs, thus there is no row running along the middle of the spine. Between these major rows was a patchwork of randomly distributed small polygonal lumps and bumps – small ones filled in the gaps between larger blunt osteoderms.
Sacral shield
The sacral shield is conspicuous in Gastonia. It consists of a number of small indistinct osteoderms, which have fused to each other to form a large flat shield over the hips. Again, this is embedded in the skin. The boundaries of this shield are straight and abrupt. The shield contrast with the rest of the animal’s back and tail in its smoothness, although the smooth surface is punctuated by an irregular scattering of short round osteoderms, and its lateral surfaces are bordered by four flat pointed spikes in line with the lower main spike rows of the body and tail.
Tail
The long tail bears two main rows of spines, roughly in line with those of the body and neck. There is a double row of 17 small elongate spikes pointing upwards, and a double row of 17 large triangular flattened spikes as on the body. These triangular lateral tail spikes were flattened into pointed blade-like structures, not unlike scissors. With sideways movement of the body, and especially the tail, during defensive behaviour, a scissor action would have made an imposing defence. The rest of the upper tail surface is as described above for the body.
Additional notes on the appearance of armoured dinosaurs
Osteoderms and other bony projections represent the inner ‘core’ of the actual spine in life. The bone was in life covered by a keratin sheath, not unlike our fingernails, or the spikey projections on living reptiles. Therefore, the fossil spikes in the fossil represent the bare minimum extension of the armour of the animal. So, at least a few centimetres must always be added onto spikes and spines, and it is not totally unreasonable to add a superfluous covering of keratin sheath, to give the appearance of a prehistoric porcupine. The spines (even if restored conservatively) would also be prone to breakage from attack (predators, fighting for a mate etc.) and it would be common to see some individuals with parts broken off or damaged, just as occurs today e.g. in elephants with a broken tusks and deer with broken antlers.
Skin
The skin of dinosaurs, especially large species, is often portrayed as leathery/ smooth like an elephant, this is wrong. Skin impressions are known for Gastonia, and for the closely related polacanthus. The armour has been described above. The skin over the undersurface and sides (belly, tail, legs) (non-armoured) would have likely been held tight in contrast to the possible dewlap of the neck. The scales are large 1cm – 5cm, and closely packed like a mosaic – not overlapping. The colour of dinosaur skin is unknown and must be restored using logic – but at the end of the day, pretty much anything goes (look at living reptiles and the huge variety of patterns and colours in birds!). However, there is a general trend for animals to be lighter underneath and darker above – ‘countershading’. This is because light from above will shine on the dark surface and make it equivalent to the lighter under-surface, therefore the animal will appear uniform in colour and be better camouflaged (this is especially true in, say, marine animals like sharks and whales, but can be seen in crocodiles and mammals etc.)
Primary references
Carpenter, K., J.I. Kirkland, D.Burge and J.Bird. 1999. Ankylosaurs (Dinosauria: Ornithischia) of the Cedar Mountain Formation, Utah, and their stratigraphic distribution. Pp. 244-251 in D.Gillette (ed). Vertebrate Paleontology in Utah. Utah Geological Survey Miscellaneous Publication 99-1.
Kirkland, J.I. 1998, A polacanthine ankylosaur (Ornithischia: Dinosauria) from the Early Cretaceous (Barremian) of Eastern Utah, Pp. 271-281 in S.G. Lucas, J.I. Kirkland and J.W. Estep (eds.), Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History and Science Bulletin No. 14.
Lee, Y.-N., 1996. A new ankylosaur (Dinosauria: Ornithischia) from the Paw Paw Formation (Late Albian) of Texas. Journal of Vertebrate Paleontology 16:232-245.
Martill, D. M. and Naish, D. 2001. Dinosaurs of the Isle of Wight. The Palaeontological Association.
Weishampel, W. D ., Dodson, P. and Osmólska. H. (eds.), The Dinosauria. Second Edition. University of California Press.