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.
Saurodon - a sword eel
Mounted reconstruction on display at the Rocky Mountain Dinosaur Resource Center, Woodland Park, Colorado
Reconstruction by Charles Bonner
When: Cretaceous (~ 89 - 83 million years ago)
Where: North America
What: Saurodon is one of the large fish which swam though the Cretaceous Seaway, the marine waters that covered much of North America during the late Mesozoic. This particular species was ‘only’ about 8.5 feet (~2.6 meters) long, with a relatively skinny body and large pointed lower jaw. These features are what gives the family Saurodontidae the nick-name ‘sword eels’. The Saurodontidae fall into the later group Ichthyodectidae, a completely extinct clade that contains some of the largest fish on record. Today the living relatives of these gigantic fishes are in the clade Osteoglossomorpha and are some of the largest bony fish that swim though today’s waters.
This was not a very specious group - there are only three described species - but they have been known to science for almost two-hundred years. The first Saurodontidaewas named in 1824 by Richard Harlan (the discover of Harlan’s ground sloth) - but was misidentified as the jaw of an extinct marine reptile. This was corrected only six years later when the first Saurodon specimen was found, and it was clear that the fragmentary specimen which was previously named belonged to a large fish, not a marine reptile. The use of the long lower jaw in Saurodon and its kin is not well understood, but it has been hypothesized that perhaps these predatory fish dug prey out from the deep muds at the bottom of the seaway.
When: Cretaceous (~100 million years ago)
What: Melittosphex is a fossil bee. It is the oldest bee fossil ever found, and this tiny tiny (only 3 millimeters long!) specimen, beautifully preserved in amber, can tell us much about the evolution of this amazing group of social insects. The closest relatives to living bees are the wasps, and some wasps are more closely related to bees than they are to other groups of wasps. The crabronid wasps (the digger-wasps) are the wasps most closely related to bees. These wasps are solitary and while the adults feed on nectar, the young larva feed on a spider or insect that mom-wasp procures for them.
Melittosphex is assuredly more closely related to bees than any wasp, with a great deal of anatomical features found only in bees today, such as the morphology of its hindlimbs and the presence of intricately branching hairs on body. Melittosphex also has features reminiscent of its wasp ancestry that are not seen in any living bee species today; specific spurs on its middle pair of legs and a very slender rear most ‘foot’. This combination of features shows that Melittosphex is an excellent example of a transitional fossil, falling between the crabronid wasps and all living species of bees.
Knowledge of Melittosphex and its kin is critically important for determining how the solitary carnivorous (as larva) wasps gave rise to the eusocial herbivorous bees. But that is not all! These ancient bees also help inform us to how the modern plant biota was established. Today’s flora is dominated by angiosperms - the flowering plants, but this is a relatively recent state of things. The earliest known fossils of angiosperms date to only the Jurassic period, and it is not until the early Cretaceous that body fossils are known. It is at about 100 million years ago that the great angiosperm radiation can be seen, and shortly after this the flowering plants begin to dominate. The one specimen of Melittosphex known preserves minute pollen grains between the branching hairs on its body, showing that even 100 million years ago bees were involved in pollination of these flowing plants. It has long been thought that bees and angiosperms evolved in tandem, that each group depends on the other for its success, and little Melittosphex offers more support for this view.
Reconstruction by Nobu Tamura
When: Cretaceous (~122 million years ago)
What: Shanweiniao is a mesozoic bird. It retains many features that are not found in modern birds, including a toothy beak. It was capable of powered flight, and its tail was used to help it fly. This is seen in modern birds, but it is unknown exactly when the bird lineage developed this trait. It is clear that it was present in Shanweiniao as four flight feathers were preserved on the slab, giving the fossil bird its name. Shanweiniao means fan-tailed bird in chinese.
Shanweiniao falls after the spilt of the bird lineage from the rest of theropods, but it is still very far removed from the living avians. The first birds are called enantiornithes. All of these birds were capable of powered flight to some extent, but retained toothed beaks and claws on their wings. It is debated if the enantiornithes are a monophyletic group that has left no descendants, or if this ‘group’ is instead paraphyletic with some members more closely related to living birds than others.
Slab specimen from the Museo Histórico Nacional in Buenos Aires, Argentina.
Reconstruction by Mark Witton
When: Cretaceous (~110 - 100 million years ago)
What: Pterodaustro is a pterosaur. It is a great example of the tremendous amount of diversity present within the clade in its heyday. Look at those crazy things in its mouth, coming out of its lower jaw. They are so long that when the mouth was closed they extended past the top jaw. They are not baleen, but extremely elongated teeth. They are about 3cm long on average and just a couple of millimeters wide. This extreme height width difference would have allowed the structures to be somewhat flexible. Pterodaustro had over 1000 of these teeth, and they were not in individual sockets, but instead tightly packed into a pair of parallel grooves on each jawbone. The top teeth were small and flat, and also in grooves instead of separate sockets. Pterodaustro would use these elongated teeth to filter feed on small aquatic animals, like the living flamingos do. But even better, because it would not have had to turn its head upside down to feed. Take that dinos!!! Due to this shared ecology some reconstructions have made Pterodaustro colored bright pink… I do not really buy this. Many animals filter feed and are not bright pink.
Many many specimens of Pterodaustro have been recovered, we are approaching 1000 collected specimens. The ages of these individuals range from unhatched juveniles to fully grown adults, which had wing spans of over 8 feet (~2.5 meters). Studies of the growth series of Pterodaustro have revealed that the pterosaur grew rapidly for the first two years of its life, and then grew much more slowly for the next three to four years. It is likely it reached sexual maturity shortly after the onset of the slow growth period. This means that Pterodaustro had more of a determinant growth ( a set adult size) pattern as seen in modern birds rather than indeterminate growth (growing forever) seen in many ‘reptiles’ such as crocodiles and lizards.
Mounted skeletons from the Melbourne Museum of Natural History
Reconstruction on display at the Carnegie Museum of Natural History
When: Early Cretaceous (~130 to 100 million years ago)
What: Psittacosaurus is a ceratopsian. Yes, a ceratopsian like Tricerotops or Styracosaurus, even though it has no horns or even a neck frill. You have to start somewhere! Psittacosaurus is an extremely basal ceratopsian, with some studies finding this animal in the first group to branch off from the clade. Italso was most likely bipedal (quick remake all the reconstructions!), as its forelimbs were much shorter than its hind-limbs, and it possibly could not even rotate its hands enough to put its palms flat towards the ground. This isn’t really surprising, as despite the large number of quadrupedal dinosaurs, the last common ancestor of all dinosaurs has been reconstructed to be bipedal. Psittacosaurus was a plant eater, but it did not have the grinding cheek teeth of later ceratopsians, so it swallowed stones to help it grind its food. It is also possible that it fed on nuts, as its beak has been reconstructed to function very well as a nut-cracker.
There are hundreds upon hundreds of fossil specimens known for Psittacosaurus, making it one of the most well understood of all dinosaurs. There are over 10 species known, with the best known Psittacosaurus mongoliensis, reaching about 6.5 feet (~2 meters) long at its extreme maximum. This includes an amazing slab specimen that was preserved in soft mud that shows this little ceratopsian had bristles on the top of its tail. It is thought these were used for communication between individuals, and it is debated if these are homologous (same evolutionary origin)to the feathers of theropod dinosaurs or not. There is almost a full ontogenetic (growth) series of specimens, with oodles and oodles of hatchings to subadults. The close association of many hatchlings and adults shows that these ceratopsians, like many dinosaurs, had a good amount of parental care of the young dinosaurs.
One benefit of so many specimens is that destructive sampling can be used - this is where the original specimen is damaged, or even destroyed, to provide some information about the animal. Cutting long bones and examining the resulting cross-sections has lead to the determination that Psittacosaurus lived to about 10 to 11 years old.
Remember Repenomamus from a couple of days ago? The juvenile dinosaur found inside was a Psittacosaurus.
Repenomamus - the mammal that ate dinosaurs
When: Cretaceous (~138-129 million years ago)
What: Repenomamus is the largest known genus of mesozoic mammal. Two species are known, R. robustus and R. giganticus. Repenomamus robustus was about the size of a living North American Opossum, and R. giganticus was about 50% as big as this, coming in at about 3 feet (~1 meter) long. This is not very big by today’s standards, but as most mesozoic mammals were rat sized or smaller, this was very large indeed for its time! Repenomamus falls within the group Triconodonta, an extinct clade of mammals that falls between the monotremes and the therians (placentals + marsupials). Their name comes from the three cusps, typically in a row, found on their upper and lower cheek teeth. Fossils of triconodonts are found from the late Triassic to the end of the Cretaceous. Though the end Cretaceous extinction is commonly thought of as the extinction of non-avian dinosaurs, some mammal groups were lost here as well, or at least their numbers drastically redued.
Speaking of dinosaurs, the skeleton of Repenomamus robustus was found with bones belonging to a juvenile Psittacosaurus (a ceratopsian) clearly inside its ribs. Proof that this mammal snacked on some baby dinos! The diet of the larget mesozoic mammals has long been controversial, but here is undeniable evidence that at least some of these taxa were carnivorous and ate other vertebrates. On a more personal note, this specimen was described by Yaoming Hu, who tragically died from cancer at a relatively young age, just three years after publishing the specimen.
When: Late Cretaceous (~80 - 71 million years ago [the beds are poorly dated])
Where: Gobi Desert, Mongolia
What: Nemegtbaatar is a multituberculate. Multituberculata is an extinct group of mammals, but even though they did not make it to the modern day, they are one of the longest lived clades of mammals. Ranging from the early Jurassic (~160 million years ago) to the Oligocene (just about 35 million years ago). The evolutionary history of multituberculates is fairly well known, as there are a multitude of almost complete skeletons known from these 125 million years. One of them is Nemegtbaatar, a fairly typical example of this clade.
Nemegtbaatar was about 6 inches long (~15 cm), not counting its tail. It is reminiscent of a rodent in its appearance, primarily due to its enlarged incisors and the gap between these teeth and its cheek teeth. But a closer look at its denition shows it is very different from rodents, and all other living mammals. Its lower 4th premolar is a blade, and most of the rest of its premolars and all of its molars are elongated anterior to posterior with multiple parallel rows of many cusps. These molars are what gives the clade its name; Multituberculata means ‘lots of cusps’ to use a loose translation. Nemegtbaatar, like most of the other 80 genera of multituberculates, lived in a niche analogous to living rodents such as rats. At the bottom of the food chain, eating whatever it could get its teeth on, with the ability to quickly scurry away if need be. Despite their 125 million years of exsistance, multis always remained fairly evolutionary conservative, they found a niche that worked and stuck with it. Not to say there isn’t diversity here, but Nemegtbaatar is a good ‘default’ multituberculate.
The phylogenetic position of multis within Mammalia is unclear. There are two proposed placements, with good arguments for both possibilities. Multituberculates either fall between the monotremes and the therians (placentals and marsupial mammals), or they are outside all living mammals.
Drawing by Mick Ellison of the American Museum of Natural History, NYC.
When: Early Cretaceous (~125 million years)
Where: Liaoning, China
What: Mei is a paravian dinosaur. Paraves is the clade comprised of birds and two families of non-avian dinsaurs; Troodontidae and Dromaeosauridae. As Mei is a fairly basal member of the troodontids, it is not very far removed from the common ancestor of all paravians. Its bird-like heritage can be easily seen in this extraordinary articulated fossil shown above. This specimen was found in a sleeping pose, which is very much like the resting posture of many modern birds, with the legs folded underneath the body and the head folded back and resting on the shoulder. It is this pose that gives the taxon its full name: Mei long, which translates to ‘sleeping dragon’. This animal is a sub-adult, determined via the ends of its bones not yet being fused, and would be roughly 21 inches (~53 cm) long, if it was not curled up as it is.
The find of a basal troodontid in this pose gives us far more information than just when the sleeping posture was adapted by this clade. It has been determined that modern birds commonly sleep like this to preserve their body heat, covering up the areas that are most prone to radiating heat. If Mei long and its kin were not ‘warm blooded’ than there would be no benefit to sleeping in this pose. Thus, this provides another compelling bit of evidence that the ‘warm bloodedness’ of modern birds was present in their mesozoic non-avian relatives.
First mounted specimen is at the American Museum of Natural History, NYC.
Reconstruction by Todd S. Marshall.
When: Cretaceous (~80 million years ago)
Where: Widespread in Cretaceous seas
What: Elasmosaurus is a plesiosaur. It has the longest neck of any known plesiosaur, made up of over 70 cervical vertebrae. In total it was 46 feet (~14 meters) long, with roughly half of this length made up of the neck. Elasmosaurus was named by Cope in the mid 1800s, and in this paper he made a rather famous blunder. He reconstructed the head of Elasmosaurus attached to what we now know is its tail. I say ‘now know’ but almost immediately upon publication of the specimen, the scientific community pointed out Cope’s blunder. To be as fair as possible to Cope, he was a self educated man and at the time was much more familiar with lizards, especially the giant mosasaurs, which do have spectacularly long tails. Additionally the first plesiosaurs with exceptionally long necks were just being discovered in Europe at this time. Still though, it is a good example of how you should be very careful not to let any preconceived notions you may have distort what is right in front of you.
Despite a number of artistic reconstructions, Elasmosaurus could not lift its body, or even most of its neck, out of the water. All it could do is breach the surface of the water with its head for air. As the animal could not survive out of the water, let along drag itself around with its highly compressed paddles, Elasmosaurus must have given birth to live young. While we have no direct evidence of vivipary in this particular plesiosaur there are amazing fossils of closely related forms showing live birth. Elasmosaurus also was not capable of coiling its neck in a ‘snake like’ manner. Its long neck was used to allow it to move its head close to schools of fish, while its body would remain far behind. It would swim beneath its prey and then lift its head up, creating far less disturbances in the water than its large body would, and allowing it to quickly snack on unsuspecting fish.