Pectinodon: Beast of the Week

Today we will be checking out a the bird-like dinosaur, Pectinodon bakkeri!  Pectinodon lived in what is now Wyoming, USA, during the latest Cretaceous period, about 66 million years ago.  Pectinodon is only known from highly fragmentary remains (mostly teeth) but is roughly estimated to have measured about six feet long from snout to tail when alive.  It would have eaten meat and possibly some plant material when it was alive.  Its genus name translates to "Comb Tooth" because of the deep serrations on the anterior edges of its teeth.  The species name is in honor of paleontologist, Dr. Robert Bakker.

My watercolor life restoration of Pectinodon bakkeri.  This animal was likely hunting smaller prey when it was alive, so cretaceous snakes could have been on the menu.

You may recognize Pectinodon by a different genus name, Troodon.  This is because Pectinodon was renamed Troodon during the 1980s.  Then in 2011, after further study, it was split back into its own taxa again.  In fact, the Troodon genus was split up into multiple taxa based on differences in morphology as well as the fact that all these fossils spanned an extremely long amount of time for only one genus of animal to have been living.  The "Troodon" dinosaur that lived during latest Cretaceous in the North American community, called the Hell Creek Formation, was Pectinodon.  The original name is still used to describe the family that all these smaller bird-like dinosaurs came from, Troodontidae.

Even though we don't have too much fossil material from Pectinodon, itself, we can make educated inferences about it based on its closest family members that we have more material from.  The teeth, which we do have, are sharp and possess deep serrations, but only on the edges that faced the back of the mouth.  The teeth are proportionally smaller than those of dromeosaurids, like Velociraptor or Acheroraptor.  Other troodontids are known to have had proportionally large, forward-facing eye sockets, suggesting they had good vision and may have even been able to see well in the dark.  It is this combination of features that lead many to believe troodontids, like Pectinodon, specialized in hunting small prey, like mammals, and small reptiles.

Photograph of one of Pectinodon's teeth.  Note how the anterior has deep serrations.

Pectinodon was likely covered in feathers when alive and probably would have looked like a bird to most of us at first glance if we encountered it today.  Its legs were probably long and slender, which would have allowed it to have run swiftly if it needed to.  This was probably a helpful trait since it would have been pursuing prey as well as avoiding potential predators, like the similarly sized, but more heavily armed, Acheroraptor, and even Tyrannosaurus rex (which was much faster and more agile as a subadult)   Being most active at night is also another way to avoid predation and is a tactic used by many animals today.  

Many animals evolve to be nocturnal to avoid predation.  During the Mesozoic most of the mammals were small and nocturnal to avoid the dinosaurs.  Naturally there will always be some predators that will evolve the same way.  The troodontids likely filled that niche.

Like dromaeosaurids ("raptor" dinosaurs, like Velociraptor, and Deinonychus) troodontids, like Pectinodon also had a retractable "killer claw" on each of their second toes, but theirs weren't as proportionally large as those of dromeosaurids.  This, combined with the traits already mentioned, further point to them specializing in taking much smaller prey.  I imagine troodontids stalking small mammals and reptiles in the thick brush at dusk or at night, using their senses of sight and hearing to zero in, and their long legs to clear tall foliage, then kicking and pinning  their target with their special claws when the time was right, and finally dismembering their meal with their serrated teeth.  Many modern predatory birds execute similar hunting behavior today in various ways.
 
References

Currie, P. (1987). "Theropods of the Judith River Formation". Occasional Paper of the Tyrrell Museum of Palaeontology 3: 52–60.

Holtz, Thomas R., Brinkman, Daniel L., Chandler, Chistine L. (1998) Denticle Morphometrics and a Possibly Omnivorous Feeding Habit for the Theropod Dinosaur Troodon. Gaia number 15. December 1998. pp. 159-166.

Larsson, H.C.E. 2001. Endocranial anatomy of Carcharodontosaurus saharicus (Theropoda: Allosauroidea) and its implications for theropod brain evolution. pp. 19-33. In: Mesozioc Vertebrate Life. Ed.s Tanke, D. H., Carpenter, K., Skrepnick, M. W. Indiana University Press.

Larson D.W., Currie P.J., 2013, "Multivariate Analyses of Small Theropod Dinosaur Teeth and Implications for Paleoecological Turnover through Time", PLoS ONE 8(1): e54329. 

Nigersaurus: Beast of the Week

Nigersaurus taqueti was a sauropod dinosaur that lived in what is now Niger, Africa, during the Cretaceous Period, about 118 to 110 million years ago.  It measured only about thirty feet long which for a sauropod (largest kind of land animal of all time) is actually on the small side.

My reconstruction of Nigersaurus as it unknowingly disrupts a nesting Kaprosuchus. (or something very similar since these two taxa were actually separated by a few million years.)

Nigersaurus had a unique skull in that its mouth was wide and flat.  The skull actually resembles a vacuum cleaner head to be honest (if you google image search "vacuum cleaner head" and scroll down a bit, a picture of Nigersaurus actually will be one of the results.  No joke go try it).  Inside the mouth were six hundred tiny chisel-shaped teeth, the most teeth in any known sauropod, all lining the front of the mouth.  This arrangement was perfect for clipping low-lying vegetation, like a lawn mower.  Like any dinosaur, whenever one of Nigersaurus' teeth broke off or got worn down, a new one was right underneath ready to take its place.   

Nigersaurus taqueti skeletal mount reconstructed by Tyler Keillor and Stephen Godfrey.  This skeletal mount was unveiled at the National Geographic headquarters in 2007, when Nigersaurus made its public debut.

Nigersaurus had a relatively short neck for a sauropod.  Because of this, combined with the fact that its skull would have been naturally held facing the ground according to how its bones fit together, suggests it specialized in eating low growing plants rather than foliage off trees like some of its longer-necked relatives.  It's also worth noting, that Nigersaurus had eye sockets that were proportionally large and were positioned at the highest point of its skull, when it was in a neutral pose.  When alive you can see that it would have been able to see almost entirely around it at once, and would only need to move its head the slightest bit to either side, in order to see directly behind it or in front of it.  This may be an adaptation to keep lookout for predators without having to stop eating.  Since sauropods weren't particularly fast runners, Nigersaurus may have used its long tail as a weapon, or perhaps lived in herds for protection

Close up of Tyler Keillor's Nigersaurus skull.  You can really get a idea of how unique and specialized this dinosaur truly was!

Special thanks to paleo-artist, Tyler Keillor for allowing me to use images of his awesome skeletal reconstructions.  As always if you have a dinosaur or other prehistoric creature you would like to see covered comment below or let me know on twitter or facebook!

References

Sereno PC, Wilson JA, Witmer LM, Whitlock JA, Maga A, et al. (2007) Structural Extremes in a Cretaceous Dinosaur. PLoS ONE 2(11): e1230. [1] doi:10.1371/journal.pone.0001230.

Wilson, J. A. and Sereno, P. C. (2005). "Structure and Evolution of a Sauropod Tooth Battery". In Curry Rogers, K., and Wilson, J.A. (eds.), The Sauropods: Evolution and Paleobiology, University of California Press, Berkeley, ISBN 0-520-24623-3.

Anodontosaurus: Beast of the Week

This week we will be looking at a heavily-armored dinosaur.  Check out Anodontosaurus!

Anodontosaurus was an armored dinosaur in the ankylosaurid family that lived in what is now Western Canada, between 74 and 67 million years ago.  From snout to tail it measured about 20 feet long, and would have eaten plants when alive.  The genus name translates to "Toothless Lizard/Reptile" because it was originally thought to have been toothless. (but it wasn't). There are two named species within the genus.  The first discovered of the two was Anodontosaurus lambei, which lived later, while earlier-living species by a few million years was named Anodontosaurus inceptus. 

My life reconstruction of Anodontosaurus lambei in watercolors.  

Anodontosaurus, like most ankylosaurids was covered on the top side of its body with bony armor, called osteoderms.  These chunks of bone grew out from the skin, and many were keeled, and slightly triangular in shape.  Over its hips it possessed a sacral shield, a sheet of bone studded with osteoderms, growing over its hips.  Its skull was adorned with short broad horns above the eyes and lining the back of the head, as well as longer, broader horns growing out from under its eyes.  It had a wide beak at the front of the mouth and its jaws were lined with small teeth ideal for processing plants.  At the time of its discovery, however, because the skull as crushed in such a way after the animal's death, causing the teeth to fall out, scientists initially believed it was toothless in life.

After its initial discovery and naming Anodontosaurus was later lumped into the genus with another ankylosaurid relative, Euoplocephalus, thus losing its genus name.  However, in 2010, it was re-examined more closely and once again deemed different enough for its own genus, in a study led by paleontologist, Victoria Arbour.  The main reasons why the genus was split was because Anodontosaurus' horn arrangement, neck armor, and tail club were different from those of Euoplocephalus, and a few other ankylosaurids, which were also given their own genus from the study.  Anodontosaurus' tail club was unique in that it was elongated and pointed on either end, while Eouplocephalus' club is a smoother oval shape.

Cast of Anodontosaurus tail club on display at the American Museum of Natural History in New York.

Like all ankylosaurids, Anodontosaurus would have relied on its armor and tail club, which could be swung from side to side very powerfully, for defense against predators, like tyrannosaurids.  It is also very possible that ankylosaurids engaged in combat within the species, possibly smashing each other with their clubs, as well.  Anodontosaurus' tail club looks particularly wicked, since it comes to a point on either side, concentrating all the force onto a smaller surface when swung.  I'd imagine getting hit by Anodontosaurus would be more like being pummeled with a hammer than a club.  Ouch.

References

Arbour, Victoria (2010). "A Cretaceous armoury: Multiple ankylosaurid taxa in the Late Cretaceous of Alberta, Canada and Montana, USA". Journal of Vertebrate Paleontology. 30(Supplement 2): 55A.

Arbour, V. M.; Currie, P. J. (2015). "Systematics, phylogeny and palaeobiogeography of the ankylosaurid dinosaurs". Journal of Systematic Palaeontology. 14 (5): 1–60.

C. M. Sternberg (1929) "A toothless armoured dinosaur from the Upper Cretaceous of Alberta." Canada Department of Mines Geological Survey Bulletin (Geological Series)54(49):28-33

Coombs, W.P., Jr. (1986, June). A Juvenile ankylosaur referable to the genus euoplocephalus (reptilia, ornithischia). Journal of Vertebrate Paleontology, 6(2), 162-173.

Penkalski, P. (2013). "A new ankylosaurid from the late Cretaceous Two Medicine Formation of Montana, USA". Acta Palaeontologica Polonica.