Your Daily Fossil

Pterodaustro

Slab specimen from the Museo Histórico Nacional in Buenos Aires, Argentina. 

Reconstruction by Mark Witton 

When: Cretaceous (~110 - 100 million years ago) 

Where: Argentina

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. 

Argentavis magnificens 

When: Late Miocene (~6 million years ago)

Where: Argentina

What: Argentavis is the largest flighted bird there ever was. Its wingspan has been estimated at 23 feet (~7 meters), almost double that of the largest flying bird that soars today’s skys, the wandering albatross (Diomedea exulans). All specimens of this avaian have been found in Argentina, hence its name, which means ‘magnificent Argentine bird’. Recent studies looking at the biomechanics of flight in Argentavis have determined that it was a soaring bird, like today’s condors and vultures. It would have easily glided upon the strong thermals above the Argentine pampas, but getting up to those winds was a bit more of a challenge. It was too large to just flap its wings and take off, even when it was standing in a strong headwind. Instead Argentavis would have had to run down a steep hill or jumped from a high perch in order to take to the skies. Once it was up there, however, it is estimated it could have soared for hours, hunting for prey as it rode the late afternoon thermals. 

Meganeura  - The Giant Dragonfly

When: Carboniferous (~305-299 million years ago)

Where: France

What: Meganeura is the largest dragonfly, with a wingspan of 2.5 feet (~75 cm) in some specimens. The largest living dragonfly is a comparatively weensy 7.5 inches (~19 cm) across at the wings. A scientific debate had centred upon why Meganeura was able to become so large. It has been suggested that it was only able to reach such a great size due to the relatively higher levels of oxygen in the Carboniferous air. This is based partly upon the way most modern insects respire, they do not truly breathe, but instead simply diffusion oxygen throughout their small bodies. However, more recent studies show that larger insects do breathe via compression and expansion of their trachea. Additionally insects much larger than those today have been found in later rocks which do not show evidence of elevated oxygen levels. More research needs to be done to determine the impact of oxygen levels upon the maximum size of insects.  

Only a few fossils have been found of Meganeura, but despite this, almost every scene ever of a Carboniferous forest has one of these animals perched upon a giant club moss tree. I do not blame them, I could not resist either.  Other animals in these dense forests with Meganeura were a gaggle of other gigantic insects and arthropods, a great variety of amphibians, and the first reptiles. This was the start of the true colonization of land by vertebrates; it has also been suggested it was the arrival of these predators which limited the size of insects such as Meganeura in later time periods. 

Quetzalcoatlus - the largest pterosaur 

Reconstructions by Mark Witton. 

When: Late Cretaceous (68-65 million years ago)

Where: North America

What: Quetzalcoatlus is a gigantic pterosaur. Just how gigantic it was has been the subject of some debate, as no 100% complete specimen has been found. While the first estimates put its wingspan at up to 50 feet (16 meters) this has been reduced to 36 feet (11 meters) in the latest studies. The reason for this disparity is due to allometry - the physical properties of bones require that as an animal gets larger its skeletal structure is not just that of a smaller animal made larger. Thus the wing bones of Quetzalcoatlus were relatively thicker than that of a smaller species, and while this was taken into account in the first estimates, it took a better understanding of pterosaur evolution in general for a refined estimate to be generated. 

This large size brings with it another debate: could Quetzalcoatlus fly? The answer is yes, this pterosaur sailed over prehistoric Texas. A big mystery was how Quetzalcoatlus could take off, and recent work by functional morphologists has provided a solution to this puzzle. Pterosaurs differed from all other flying vertebrates in that they retained the majority of the digits on their hand outside of the wing itself; this not only allowed these fingers to be used to manipulate their environment, but was critical for terrestrial locomotion. Quetzalcoatlus was quadrupedal on the ground, like all other pterosaurs, but it had a specially developed system of ligaments and tendons in its wrist joint that allowed it to ‘spring’ up and take flight.  This can be seen in this video.  

Another, more minor, debate is what did Quetzalcoatlus eat? Most pterosaurs are closely associated with large bodies of water and have a fish based diet - but all Quetzalcoatlus remains have been found hundres of miles from ancient shorelines. This, combined with morphology of the skull, has lead to the conclusion that these giants instead fed on smaller vertebrate that they would capture with their large beaks, such as the baby sauropod not having a good day in one of the reconstructions above. 

Onychonycteris

When: Eocene (all known fossils from a deposit 52.5 million years old)

Where: Wyoming, USA

What:  Onychonycteris is the most basal bat currently known. It differs from living bats in having claws on all five fingers, whereas living bats have lost them. This form also has relatively shorter arms and fingers, as well as longer legs and tail than any other bat, fossil or extant. Onychonycteris was an extremely important find, as allowed us to answer a long standing question about bat evolution: Which came first, flight or echolocation? This taxon was capable of flight, and detailed examination of the cranium revealed that it could not echolocate.  Thus, bats took to the skies before they developed a system for seeing with their ears. 

This amazing fossil is from the Green River fossil lagerstatten in southwestern Wyoming, and is one of two known complete specimens. This example is not the holotype (the specimen which bears the name) as while it looks absolutely gorgeous, the second specimen was arranged on the rock slab in such a way more of the skull could be studied. Additionally, this specimen was actually in the hands of a private collector, and thus not fully available to science.  That is until the specimen was mailed, unannounced, to Dr. Nancy Simmons at the American Museum of Natural History, New York.  She was working on publishing this taxon at the time, and the private collector had been informed of this, so the family sent the specimen to allow her the best examination possible. That was one awesome package to open, believe me! 

Nemicolopterus - perhaps the smallest of the pterasaurs

When: Early Cretaceous (~120 million years ago)

Where: China 

What: Nemicolopterus is a pterosaur. It is the smallest one known, its wing span was just 10 inches (25 centimeters) from tip to tip. It was well adapted for roosting in trees with its highly curved toes and sharp claws and is thought to have eaten insects. Nemicolopterus was one of the few pterosaurs to live far inland, most of the group were fish eaters living near or on coasts. The validity of Nemicolopterus is debated; there are strong arguments in favor of it actually being a juvenile Sinopterus. The single specimen of this proposed minute pterosaur has a very large skull for its size and has  a simular level of bone fusion as other known hatchling pterosaurs - it is thought the young could fly at a very young age. Sinopterus has a wingspan of 4 feet (~1.2 meters), which is on the small end for pterosaurs. (In the example images for today, the two on the right are of Sinopterus.)

Pterosaurs are archosaurs, members of the group that also includes crocodiles and dinosaurs. Within Archosauria they are more closely related to dinosaurs than to crocodiles. This clade is the first vertebrate lineage to have evolved powered flight, already flying by the late Triassic (~220 million years ago). The pterosaur wing was primarily supported by a hyper-elongated 4th digit, leaving digits I-III free in most taxa. This makes pterosaurs the only flying vertebrate group to have retained free digits, as both birds and bats lost the full use of their fingers in the evolution of their wing mechanisms. Pterosaurs went extinct at the end of the Cretaceous period (~65 million years ago).