The destination of this expedition is the Mesozoic, 252 to 66 million years ago. We will gain insights into the living organisms during this period of our earth’s history and get to know a few representatives of the groups of animals alive at that time: Dinosaurs, pterosaurs and marine reptiles. In the end, one question remains: Have all of the dinosaurs really gone extinct?

The Senckenberg Nature Museum Frankfurt ranks among the most important European natural science museums. With its rare and spectacular exhibits, it conveys the current diversity of life as well as the evolution of organisms and thus our earth’s transformation over millions of years. Since the dinosaurs lived more than 66 million years ago, all that remains of them today are fossils. Over millions of years, mineral deposits turned their bones into stone. Fossilized dinosaur bones are not common, and complete skeletons are found very rarely.

Dr. Johann Christian Senckenberg was a physician from Frankfurt. In 1763, he donated his fortune for the construction of a citizens’ hospital that allowed even the poor access to medical care. In his honor, the museum and the Senckenberg Gesellschaft für Naturforschung bear his name.

The Nature Museum in Frankfurt is owned and managed by the Senckenberg Gesellschaft für Naturforschung, which also displays nature’s treasures in two additional museums. But there is much more: it is one of the most important geological and biological research institutions, with worldwide research projects.

Dinosaurs are terrestrial reptiles and populated the earth during the Mesozoic era, approximately 252 - 66 million years ago. But not all of the prehistoric giants occurred at the same time. The Mesozoic is subdivided into three periods, during which different species lived and became extinct: The Triassic (252 - 201 million years ago), the Jurassic (201 - 145 million years ago) and the Cretaceous (145 to 66 million years ago). Besides the terrestrial dinosaurs, pterosaurs and marine reptiles also occurred during the Mesozoic.

Diplodocus longus occurred in the late Jurassic period, 155 to 145 million years ago. It could reach a length of up to 28 meters, but weighed less than 12 tons. As a herbivore, it likely fed on a diet of horsetails, ferns and coniferous trees.

Tyrannosaurus rex is among the largest predators of all times. It lived approximately 70 to 66 million years ago during the late Cretaceous. Its jaws contained teeth of various sizes. As in all dinosaurs, its teeth continued to regrow throughout the animal’s lifetime.

Triceratops horridus occurred during the late Cretaceous period, about 70 to 66 million years ago. It used its curved horny beak to clip off twigs, which it crushed in its mouth with rows of razor- sharp teeth. It is assumed that these animals lived in herds.

While dinosaurs populated the mainland, pterosaurs such as Quetzalcoatlus northropi ruled the airspace. These flying reptiles lived during the late Cretaceous, about 70 million years ago. With a wingspan of approximately 11 meters, Quetzalcoatlus probably glided low over the ocean to hunt fish.

While during the Mesozoic dinosaurs populated the mainland and pterosaurs the air, life under water was ruled by the marine reptiles. Like all reptiles, they also breathed through lungs and had to occasionally come to the surface to breath. In the ocean, there is a higher probability of fossil formation than on land. The dead animals are more quickly covered with sand or mud, and with a lack of oxygen at the ocean floor, even parts of the skin could become fossilized.

The extrication of fossilized marine reptile skeletons, such as this ichthyosaur skeleton, requires an enormous amount of patience. Ichthyosaurs occurred over a very long period of time, from approximately 250 to 93 million years ago, i.e., almost throughout the entire Mesozoic.

This 182-million-year-old ichthyosaur shows an excellent state of preservation. Due to the lack of oxygen and currents at the ocean bottom, the skeleton did not fall apart and we can even recognize the shape of the body: a so-called skin shadow reveals the petrified skin.

The marine reptiles of the Mesozoic constitute the descendants of various reptiles that formerly dwelt on land. Changes in their body shape from generation to generation eventually allowed them to assume an entirely aquatic lifestyle in the ocean. Relatives of these marine reptiles survive until today. For example, the skulls of the mosasaurs are very similar to those of the modern-day monitors.

This placodont is a true sensation: it represents world’s only complete skeleton of a Placodus gigas. The name Placodus (“flat tooth”) is due to its set of teeth that are shaped like paving stones. It lived during the Middle Triassic, approximately 235 million years ago.

This mosasaur, Tylosaurus proriger, lived about 85 million years ago during the late Cretaceous. With its large, pointy teeth it ate ammonites and fishes. Mosasaurs could reach a length of up to 10 meters and moved in a snakelike fashion through the water.

Scientists postulate that today’s living birds are the direct descendants of small, two-legged and carnivorous dinosaurs. This means that, strictly speaking, not all dinosaurs became extinct 66 million years ago but survived in the form of today’s avifauna. Thus, we can regard birds as feathered dinosaurs, and it is safe to assume that all of us have actually seen a real, living dinosaur at one time or another.

Moa were flightless birds of New Zealand, which were presumably hunted to extinction by humans at the beginning of the 14th century. The Giant Moa (Dinornis giganteus) reached a height of up to 3.5 meters, with an estimated weight of up to 270 kilograms.

Sometimes, even in representational art, all is not quite as it appears. Scroll on to pull back the curtain and reveal some of art history's secret codes and hidden messages...

Painted in 1888, Café Terrace at Night is one of Van Gogh’s most famous works. The image shows a street in the French city of Arles. The artificial light from the nearby café illuminates much of the scene, while the background is dotted with windows and the sky lit up by stars. 

Some experts have speculated that this is actually Van Gogh’s version of The Last Supper. The central, Jesus-like figure is surrounded by 12 people, one of whom, like Judas, is slipping off into the shadows. There also appear to be a number of crucifixes dotted around the scene, emphasising the work's religious overtones.

This brings us neatly to The Last Supper itself, painted by Leonardo da Vinci in the late 15th century (shown here in a 1520 copy by Giampietrino). One of the most famous artworks in the world, the painting has long been the subject of speculation and creative interpretation. 

One popular theory is that the layout of the bread and crockery on the table is supposed to represent musical notes. When put together, these create a short 40-second hymn. Having music hidden within the piece definitely helps to bring the work to life and gives us a tantalising glimpse into the creative mind of Da Vinci. 

Painted by Hans Holbein the Younger in 1533, The Ambassadors is one of the most famous works from the Tudor period. Almost every object in the picture is there to symbolize something, making this a favorite for code breakers everywhere. 

The most intriguing secret contained in this painting can be found right at the front of the image – an anamorphic skull that can only be seen clearly when viewed from the correct angle. A stark memento mori, it also shows off Holbein's talent with perspective. 

Netherlandish Proverbs was painted by Pieter Bruegel the Elder in 1559. The busy scene is filled with people and animals, many of which tell the stories of old Dutch proverbs. In fact, the painting is so action packed, you can spot a saying or phrase almost everywhere you look.

Many of these sayings are still in common use. For example, this man here is ‘banging his head against a brick wall’. 

While this figure is ‘swimming against the tide’.

And this man is ‘armed to the teeth’.

Altogether, there are around 126 proverbs and idioms contained within the image, though it’s possible the scene contains more sayings that have since fallen out of use. This makes it one of the most code-packed paintings around. 

Before the advent of instant communication, the best way to reach people was through the mail. Scroll to see correspondence from notable figures around the world!

Frida Kahlo, one of Mexico's most beloved artists, was also a prolific writer of letters. She hand-wrote letters to friends, lovers, and relatives throughout her life, like the one addressed to Leon Trotsky painted here. This 1937 piece resides at NMWA in Washington DC.

Frida wrote this letter to her husband, the painter Diego Rivera, in 1940.

...and sealed it with a kiss.

Frédéric Chopin was a shooting star in the world of music, composing hundreds of pieces for piano in his brief 39 years. Maximilian Fajans created this lithograph in the decade after Chopin's death.

Chopin penned this letter to his pupil Marie de Rozières and said, "country-house life in high society is really very interesting. They have nothing like it on the continent."

Florence Nightingale, a British statistician and activist, laid the foundation for modern nursing. After a spiritual experience, she dedicated her life to helping people--caring for soldiers during the Crimean war, founding the first secular nursing school, and much more.

In this letter to her cousin Marianne Nicholson, she describes the vision which inspired her lifelong quest of service. You can read a transcript of the letter courtesy of Leeds Museums & Galleries.

Vincent van Gogh's storied life is well documented in his numerous letters to friends and relations, though the lion's share of the surviving correspondence is addressed to his brother Theo.