Albertosaurus sarcophagus

Osborn 1905

Evidence: Well over two dozen partial skulls and skeletons.

Campanian to Maastrichtian

Horseshoe Canyon, Judith River, and Lance Formations

Alberta; Canada: Montana, Wyoming; USA

Biology: 10 meters long – 3 tonnes

Albertosaurus were apparently found in large groups for at least part of their lives. A quarry at Dry Island, Alberta has produced more than two-dozen skeletons of a great variety of ages (Erickson et al.2006). Because all the individuals in the bone bed are over two years old, Erickson et al. hypothesized that there was an extremely high mortality rate before they reached that age. The range of growth stages at Dry Island has enabled a detailed comparison of juveniles with adults. It seems that, among tyrannosaurids, Albertosaurus sarcophagus was one of the more slow-growing species with only a slightly greater growth spurt during adolescence than Gorgosaurus libratus (Erickson et al. 2004). Although it is evident that all the individuals in the quarry belong to the same species, there is an immense amount of variation, especially in the teeth (Buckley et al. 2010). Currie (1998) believed that this aggregation represented social behaviour in Albertosaurusbut other authors have suggested that the presence of their impending doom, such as a flood, was the primary reason so many animals are found together (Roach et Brinkman 2007). It was probably a combination of both factors. Albertosaurus sarcophagus lived a relatively active life that involved interspecific fighting. Some Albertosaurus may have suffered infection from biting one another (Wolff et al. 2009) while most had bone abrasions and breaks as well as tendon pathologies (Bell 2010). These battle scars are evidence that albertosaurs were very social, albeit, not very amiable. The presence of a single very large individual at Dry Island may represent an alpha or senior member of a pack. It is the oldest Albertosaurus known to date at 28 years and 10 meters (Erickson et al. 2006). Because tyrannosaurids grow throughout their lives, giants like this one are possible. The average size of an adult Albertosaurus is closer to 8 meters and 2.5 tonnes (Paul 2010).

Interestingly, the Horseshoe Canyon Formation, were Albertosaurus sarcophagus are primarily found, is also home to Daspletosaurus, another large tyrannosaurid. There has been a lot of speculation over the relationship between these two apex predators since each must have assumed a unique ecological niche. Perhaps the more gracile Albertosaurus pursued faster hadrosaurs and the heavier Daspletosaurus preyed primarily on ceratopsians. In any case, Daspletosaurus ate young hadrosaurs at least some of the time (Varricchio 2001). In all likelihood, both animals probably hunted similar prey and competed violently with one another, just as leopards and lions do in Africa today. The Horseshoe Canyon is unique in its encompassment of Campanian and Maastrichtian fauna. While lambeosaurines are more common in Campanian strata and edmontosaurines in the Maastritchtian, both are present in the Horseshoe Canyon. Perhaps this explains, in part, the coexistence of Daspletosaurus and Albertosaurus in the same ecosystem.

Evolution

A very well known dinosaur, Albertosaurus sarcophagus is the iconic species of its genus and among the best known in its family, the Tyrannosauridae. There is no debate over its placement although the very similar Gorgosaurus libratus is sometimes included in the genus. Among non-Albertosaurinae tyrannosaurids, Daspletosaurus is most similar to A. sarcophagus, as the most basal member of the Tyrannosaurinae (Fiorillo et Tykoski 2014), though an unnamed species of tyrannosaurine from the Dinosaur Park Formation may be even more basal (Loewen et al. 2013). Gorgosaurus may be slightly more basal than A. sarcophagus in the Albertosaurinae.

References:

Bell, P. R. 2010. “Palaeopathological changes in a population of Albertosaurus sarcophagus from the Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada.” Canadian Journal of Earth Sciences 47: 1263-1268.

Buckley, L. G., D. W. Larson, M. Reichel, et T. Samman. 2010. “Quantifying tooth variation within a single population of Albertosaurus sarcophagus(Theropoda: Tyrannosauridae) and implications for identifying isolated teeth of tyrannosaurids.” Canadian Journal of Earth Sciences 47: 1227-1251.

Currie, P. J. 1998. “Possible evidence of gregarious behavior in tyrannosaurids.” Gaia 15: 271-277.

Erickson, G. M., P. J. Makovicky, P. J. Currie, M. A. Norell, S. A. Yerby, et C. A. Brochu. 2004. “Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs.” Nature 430: 772-775.

Erickson, G. M., P. J. Currie, B. D. Inouye, et A. A. Winn. 2006. “Tyrannosaur Life Tables: An Example of Nonavian Dinosaur Population Biology.” Science 313: 213-217.

Fiorillo, A. R. et R. S. Tykoski. 2014. “A Diminutive New Tyrannosaur from the Top of the World.” PLoS ONE 9(3): e91287.

Loewen, M. A., R. B. Irmis, J. J. W. Sertich, P. J. Currie, et S. D. Sampson. 2013. “Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans.” PLoS ONE 8(11): e79420.

Paul, G. S. 2010. The Princeton Field Guide to Dinosaurs. Princeton, NJ: Princeton University Press.

Roach, B. T., et D. L. Brinkman. 2007. “A Reevaluation of Cooperative Pack Hunting and Gregariousness in Deinonychus antirrhopus and Other Nonavian Theropod Dinosaurs.” Bulletin of the Peabody Museum of Natural History 48(1): 103-138.

Varricchio, D. J. 2001. “Gut contents from a Cretaceous tyrannosaurid: implications for theropod dinosaur digestive tracts.” Journal of Paleontology 75(2): 401-406.

Wolff, E. D. S., S. W. Salisbury, J. R. Horner, D. J. Varricchio. 2009. “Common Avian Infection Plagued the Tyrant Dinosaurs.” PLoS ONE 4(9): e7288.

Stegosaurus stenops

This Dinosaur Has God's Name All Over It!

No other dinosaur displays our Savior's handiwork quite like Stegosaurus.

Remains: Two complete skeletons and many partial and fragmentary skeletons. Both Adults and juveniles (Weishampel et al. 2007).

Size: 6.5 meters (21 feet) long and 3.5 tonnes in weight (Paul 2010).

Location: Lived in the lower Morrison Formation of the Preflood world. Skeletons are now found fossilized in Colorado, Wyoming, and Utah (Weishampel et al. 2007).

Habitat: The Morrison was a semiarid habitat of mixed prairie and damp woodland riddled with rivers.

Ecology: Stegosaurus would have browsed on shrubs and small trees. When full grown, the only predators large enough to face it would have been large theropods like Ceratosaurus nasicornis and Allosaurus fragilis.

Taxonomy: Belongs to the Stegosauridae monobaramin with Tuojiangosaurus, Gigantspinosaurus, and Kentrosaurus. There is at least one other species of Stegosaurus, S. ungulatus. It defers from S. stenops in that it was slightly larger (7 meters and almost 4 tonnes) with narrower, more pointed back plates.

Stegosaurus was the epitome of large theropod disembowelment. Unlike most other dinosaurs, Stegosaurus had no stiffening fibers running the length of its tail. Such fibers would normally function in stiffening the tail to aid in balance but the heavy bodied stegosaur wouldn't have needed them. In addition to this unrestrained feature, the stegosaur had extra space between its caudal (tail) vertebrae allowing for ultimate flexibility (Bakker 1986). This feature alone would have made Stegosaurus the ultimate in self-defense, but the Creator thought better. To increase its range of motion, the stegosaur had special features on its forearms too. Each humerus had an immense deltoid crest for the attachment of the deltoid muscles. This growth on the bone almost seems disproportionate but looking at the muscle attachment regions on the scapula (shoulder bone) indicates a very large deltoid muscle, indeed (Bakker 1986). With extra power, the stegosaur could pivot on its front legs to swing its entire hindquarters into the blow, allowing the dinosaur to deliver a hit to a predator attacking near its head. Such a powerful blow would drive the four spines at the tails end so deep into a theropod's guts it would have killed it certainly.
Despite all these incredible features of self defense, the stegosaur's head was still vulnerable. To compensate, this dinosaur had a tight network of bony rounds under its chin to protect the throat. The back plates too ran up to the back of the head. Considering that the predators of the Morrison were nearly 2 tonnes in weight, the stegosaur's armory wasn't overkill.

Stegosaurus was well equipped with a horny beak
and battery of leaf-shredding teeth.

Of course, Stegosaurus didn't spend much time battling theropods (not many dared risk a confrontation). Its massive gut needed filling. Stegosaurus lived in a habitat crawling with giant sauropods. While their long necks were reaching into the tops of the evergreens, the underbrush was being cropped by smaller hypsilophodonts and dryosaurs. Stegosaurus, on the other hand, was perfectly designed for reaching the vegetation that grew in between. It had a perfect beak and battery of teeth for processing its food, this equipment was carried fairly low to the ground. To gain extra height, the stegosaur could rear an extra few feet into the trees. To do this, Stegosaurus had a system of muscles and ligaments running the length of its tall vertebral spines. It worked just like the cable of a crane, levering the stegosaur's beak up into the leaves (Bakker 1986).

Dorsal view of a Stegosaurus stenops skull.

Stegosaurus plate design and function is still debated. Based on some of the best specimens, it is a general consensus among paleontologists that the plates were arranged in two rows in an alternating fashion (Lessem et Glut 1993). The purpose of the plates, however, is far from settled. Some have postulated that they served as solar panels that exposed a network of blood vessels to the hot sun. Or perhaps those blood vessels served a function in communication, turning the plates bright red as the blood flooded the microgrooves in the bone. Not that Stegosaurus needed more weaponry, but even if the plates did serve one or both of the former functions they most likely worked at defense as well. The plates were not attached to bone and it's probably safe to presume that they didn't just flop around limply (an evolutionist partial to vestigial organs might think so). Rather, they almost certainly had attachments for skin muscles (Bakker 1986). These muscles, lying on the surface of the skeletal muscles, would have provided control of the direction of the plates. As an allosaur charged in at the stegosaur's side, it could orient its plates to face the foot-long jaws.
All said and done, Stegosaurus stenops was the ultimate in mega self-defense. It had incredible armory and perfect design for herbivorous feeding. In the predator/prey balance put in place after God's perfect curse on creation, stegosaurs were the perfect piece. When one thinks of design in creation, Stegosaurus doesn't often come to mind. I hope it does now.

This sketch illustrates Stegosaurus stenops lifting to pluck a choice bit of greenery from a limb.

References:

Bakker, Robert. 1986. The Dinosaur Heresies. William Morrow & Company, Inc. New York.

Lessem, Don and Donald F. Glut. 1993. The Dinosaur Society Dinosaur Encyclopedia. Random House, Inc. New York.

Paul, Gregory. 2010. The Princeton Field Guide to Dinosaurs. Princeton University Press. Princeton, New Jersey.

Weishampel, David B., Peter Dodson, Halska Osmolska. 2007. The Dinosauria. University of California Press. Berkeley.