Mounted specimen on display at Dinosaur Kingdom, in Nakasato, Japan
Reconstruction by Andrey Atuchin
When: Late Cretaceous (~83 to 70 million years ago)
What: Saichania was an armored plant eating dinosaur that roamed the deserts of Mongolia in the late Cretaceous. It was about 22 ft (~6 meters) long and heavily built. It was more fearsome looking than most armored dinosaurs as it did not just have flat armor plates on its body, but rather was covered with spikes. These dinosaurs were armored all over, there is even evidence of armored eyelids! This suit of armor would have protected Saichania from predators in the late Mesozoic mongolian desert. Fossils are typically found in deserts and badlands worldwide, but typically these areas were very different environments when the species represented by the fossils were alive. The ancient Gobi Desert was much closer to the harsh modern environment than most. Saichania was well adapted for desert life, with its stocky body and teeth designed for grinding the toughest of the desert plants.
Saichania falls within Ankylosauridae, a group of armored dinosaurs found almost worldwide. It is one of the last and most derived of the ankylosaurids. One good way to differentiate the deserved ankylosaurids from their armored close relatives is the presence of a tail club. Saichania did not have the most massive club known, but it was still a significant feature. Ankylosaurids were one of the dinosaur groups that made it right up to the end of the Cretaceous period, vanishing with the rest of the non-avian dinosaurs.
Pakasuchus - the cat-like crocodile
When: Middle Cretaceous ~ 105 million years ago
Where: Tanzania, Africa
What: A Notosuchia Crocodylomorpha. Crocodiles today are all aquatic, sprawling, and fairly large (the smallest is about 5ft/1.5 meters long). However, fossil crocodiles occupied many niches and had a wide range of body types not seen in living species. A great example is Pakasuchus. This small and agile croc was completely terrestrial and only about the size of a house cat! Its dentition was also very different from modern crocs. Living crocodiles are all homodont, all of their teeth are fairly similar cones, but Pakasuchus was heterodont like mammals. Its had not only cone like teeth, but also some teeth well suited for shearing and others for crushing and grinding.
Pakasuchus and the rest of the notosuchians, most of which are cool enough they will be individual highlighted in future posts, are excellent examples of how the fossil record can show us lost diversity within clades that today are fairly homogenous. Crocodile line archosaurs (the clade containing crocs and dinos) were hit hard by the end Cretaceous extinction, with only modern forms surviving. Its probable Pakasuchus or animals much like it survived to the end of the Cretaceous, even though we only have a handful of fossils from the mid-Cretaceous. Careful inspection of fossil material for distinctive Pakasuchus teeth needs to happen, and will hopefully increase it’s temporal and geographic range.