Fossil and model both on display at the American Museum of Natural History, NYC
Model created by Louis Ferraglio
When: Early Devonian (~410 to 392 million years ago)
What: Gemuendina is an odd little placoderm fish. It is known only from the early Devonian of Germany, from deposits that have been reconstructed to represent areas with anoxic bottom waters. Anoxic means ‘lack of oxygen’, so there was no oxygen in the sediments where the dead or dying fish fell, and thus scavengers and decomposing organisms could not disturb the remains. Specimens of Gemuendina have only been preserved in such conditions because their armor was not a solid shield, as seen in some other placoderms, but rather a series of unfused relatively thin bony plates. This placoderm bears a close resemblance to a ray, with its flat body and series of horizontal fins. This is another excellent example of convergent evolution. Unlike rays, however, the eyes of Gemuendina were on the top of its head, not the side, and its nostrils were on top as well, not on its ventral (under) surface.
Within Placodermi Gemuendina falls into the clade Rhenanida. This group shares the characters of a ray-like body and the lose series of unfused plates that covered their flat bodies. While the ray-like body is a shared derived feature that unites the group, the seires of individual plates is likely a retained primitive feature that was also found in the first placoderms, which gave rise to all of the rest, including massive forms such as Dunkleosteus. Gemuendina is one of the earliest well-known members of the clade, but isolated plates from tens of millions of years earlier in the Silurian period may represent the true first rhenanids. Though the fossils are rare and fragmentary, rhenanids swam throughout the Devonian waters all over the world.
Reconstruction by Gerhard Boeggemann
When: Jurassic (~ 156 - 151 million years ago)
What: Europasaurus is the smallest sauropod known. Now remember I said smallest SAUROPOD known, so we are still looking at an animal that was about 20 feet (~6 meters) long. Keep in mind though, this includes the long neck and tail - taking those out of the picture and the animal’s body length was about 6.5 feet (~ 2 meters). This length, coupled with the shoulder height of Europasaurus ( about 5 feet [~1.5 meters]), gives us a sauropod with a body that was about the size of a modern elephant. There are a number of proposed tiny sauropods out there, but I have selected Europasaurus as it is known from several almost complete skeletons, from juveniles to adults, so we can be sure this is not just a baby sauropod that would have grown much larger. Above I have included a diagram from the original description of Europasaurus rather than a reconstructed mounted skeleton to show you just how much of the skeleton is known. Why is Europasaurus so small? Its our good friend Island Dwarfism back again! The specimens have been found in Germany, on what would have been one of many islands in the area during the late Jurassic, owing to the higher sea levels.
This smallest of all sauropods is in the clade Macranaria within the sauropod family tree. This group actually contains some of the biggest sauropods (and thus dinosuars) ever known! Talk about some size diversity within a group! An adult Europasaurus could have easily walked between the legs of some of its larger cousins. The great range of ages in the recovered specimens of Europasaurus have allowed for detailed study of the microstructure of the bones, revealing how these animals grew. From this study it has been proposed that Europasaurus managed to stay small on its restricted island habitat by not stopping its growth exceptionally earlier than its relatives, but instead by dramatically slowing down its growth rate.
I hope this cute little sauropod makes up for ruining all of those childhoods with the reality (or should I say unreality) of Brontosaurus a few posts ago. ;)
When: Eocene (~48-40 million years ago)
Where: Found at the Messel fossil site in Germany
What: Leptictidium is one of the more common mammals found in the Messel fossil pit in Germany. The adults ranged from about two (~60 cm) to three (~90 cm) feet in length, with most of this length being in the long tail. Leptictidium had extremely short forelimbs relative to the length of its legs, and has been reconstructed as the first bipedal mammal. There is debate as to its precise mode of locomotion, with some researchers proposing that the animal was a fast runner and others suggesting it was saltatorial (hopping). More recent studies have supported a hopping and leaping mode of locomotion. Thanks to the extraordinary preservation of fossils from Messel, we know the tail was bald for much of its length, that Leptictidium had a short ‘trunk’, like the elephant shrews of the modern day, and that this animal ate insects and small vertebrates. Contemporaries of Leptictidium include the tiny horse Propalaeotheirum and the predatory giant flightless bird Gastornis.
Leptictida is the larger clade that includes Leptictidium and its kin. The first members of this group appear in the latest Cretaceous of western North America and the order quickly spreads throughout the northern continents, lasting until the early Oligocene about 30 million years ago, when the forests worldwide started to give way to grasslands. Previously leptictids were thought to be related to either the living lipotyphla (hedgehogs, shrews, and moles) or elephant shrews, but recent studies of the relationships of mammals have placed them outside of placental mammals entirely, making them stem eutherians and not members of Placentalia.
When: Early Triassic (~210 million years ago)
Where: Germany and Thailand
What: Proganochelys is the oldest known terrestrial turtle. It shows that even in the early Mesozoic turtles already had a very modern body plan, with a fully formed shell. In fact, Proganochelys had a bit more armor than modern turtles. This is because it could not retract it limbs or head into its shell for protection. The way that this ancient turtle protected its head was a series of spikes on the top of its neck. It also had a heavily spiked tail, which ended in a club. Beyond these features, and a slightly larger shell in general, Proganochelys is remarkably simular to a modern turtle.
Proganochelys and other early Mesozoic turtles are so simular to living forms that for many years they were thought to be closely related to these extant species. Modern turtles are divided into two groups, the Cryptodira and Pleurodira. The major difference between these two forms is how the neck is retracted into the shell, with the former pulling the head straight back and the latter curving the neck into an S-shape. Recent cladistic studies now place Proganochelys and many other early Mesozoic turtles outside either of these two groupings, as stem turtles.
Propalaeotheirum - a tiny tiny horse
When: Middle Eocene (~50 to 40 million years ago)
Where: Europe and Asia, the best fossils are from the Messel Pit in Germany
What: Propalaeotheirum is a fossil horse. It is maybe the tiniest horse there ever was, even smaller than the oldest horses. The largest specimens are estimated to have stood just under 2 feet (~60cm) at the shoulder, and the smallest adult specimens known come in at just about 1 foot (~30cm) tall at the shoulder. The average estimated weight of Propalaeotheirum is roughly 22 pounds (~10 kilos). Horses at this time had not yet developed the single hooved toe seen in modern forms; this tiny animal had three small hoved toes on each forefoot and four each on its hindfeet. From the exceptionally preserved Messel fossils we can tell this ancient horse ate leaves and berries. It is most often reconstructed with a striped coat, as this is the coloring of most tiny ungulates which live in forests today.
Propalaeotheirum is thought to be an immigrant into Europe, its lineage migrated from North America, where the oldest horse fossila are found. This tiny European horse lineage indures for a few million years after the last record of Propalaeotheirum, but eventually all members of this sub-clade of horses go extinct. There is no direct connection between this small horse and modern species, it is an excellent example of perhaps the earliest ’side branch’ of equid evolution.
When: Late Cretaceous (~100-65 million years ago)
Where: Northern Hemisphere
What: Parapuzosia is the largest of the ammonites! Like the rest of it’s clade it vanishes from the rock record at the end of the Cretaceous period, in the same extinction event that took out the dinosaurs. Ammonites are molluscs, putting them in the same group as snails, clams, squids, etc. Within Mollusca they are in celphalpoda along with octopuses, squids, cuttlefish, and nautiluses. Though ammonites strongly resemble nautiluses, they are more closley related to the less shelly taxa in this clade. As mentioned before Parapuzosia is HUGE. How huge? The shell measures 8 feet (~2.5 meters) across. And that is just the shell! The body and all its tentacles would have extended from the carapace by almost this much again. This fossil is even not that rare! Its known from thoughout the northern hemisphere, though most of the specimens are fragmentary. The amazing almost complete specimen above was collected in Germany.
Parapozosia, like all ammonites, was carnivorous. It ate fish and anything else it could get its tentacles on. They were pelagic, meaning they freely swam around the ocean. As they were so large each individual probably had a very large geographic range. The clade Ammonoidea had an extremely large temporal range. Fossils are found from the Devonian (~400 million years ago) to the end of the Cretaceous (~65 mya). These fossils are so common and well preserved that we use them today to help date different rock layers. They also have a very long modern scholarly history; there are records of romans writing about ammonites! Here I will shamelessly end with a fact from wikipedia: “Pliny the Elder called fossils of these animals ammonis cornua (“horns of Ammon”) because the Egyptian god Ammon was typically depicted wearing ram’s horns. ”