Imagine that you are walking through a rocky landscape. You spot a sign that this is promising critter habitat. Next thing, you have conjured up an amazing beast, never before seen.
Sound familiar? Well, this is not Pokémon Go, but serious science, as practiced by paleontologists. Ichnologists, to be precise.
Ichnologists travel the world in search of ichnofossils. Also known as trace fossils, ichnofossils are the remains of the work of animals. They are the animal equivalent of stone tools. Dinosaur footprints are examples of ichnofossils.
The theropods of Otjihaenamaperero
In southern Africa, there is a place with the magical name of Otjihaenamaperero. It lies in Namibia. Somewhere around 200 million years ago, dinosaurs roamed this area. Their footprints remain, criss-crossing the Etjo Formation.
A recent study concluded that the prints represent five different dinosaur species. Alexander Wagensommer and colleagues identified all these as theropods. Think Tyrannosaurus rex to picture a typical theropod. It was not present at Otjihaenamaperero, but smaller theropods were abundant.
To quantify: smaller means smaller than Tyrannosaurus rex, yet larger than a modern rhino. Some of the fossil prints measure 35 centimeters. The theropod dinosaurs that made them are Kayentapus damerensis and Eubrontes giganteus. They are ichnofauna. We only know that they existed because of the tracks they left.
Real theropods still roam Namibia today in the shape of the ostrich. Ostriches weigh around 100 kilograms and their tracks measure less than 20 centimeters. They are the biggest living descendants of the theropod dinosaurs. Bones of the largest extinct theropods suggest that they were rather bigger than ostriches — reaching a mass of 20 tonnes.
Coprolites, urolites and ostriches
Ichnofossils include many things other than tracks. You may have heard of coprolites, or fossilized feces. Coprolites can exceed 60 centimeters in length. In Victorian times, mining of coprolites was an industry in parts of England. As you might expect, the fossilized manure was used as fertilizer.
Coprolites should not be confused with the other type of ancient dropping, paleofeces. Paleofeces are to coprolites what artifacts are to ichnofossils. In other words, made by humans.
Urolites are the fossilized pattern left by a stream of urine hitting the ground. A 2004 paper by Marcelo Fernandes and coworkers describes urolites from Brazil. Their arguments for the cause of these fossils include experimental evidence. In case you wondered, they recreated the patterns using water, not real urine.
The researchers also studied urination in the ostrich, that useful living dinosaur. A sequence of photos of an ostrich urinating graces their paper.
Most trace fossils are the work of invertebrates. Like the dinosaurs, they leave footprints and coprolites, as well as tubes and burrows. Invertebrates have no bones so they don’t fossilize well. Many have left only their works and will remain forever ichnofauna.
It’s remarkable how much scientists can infer from ichnofossils. For example, a row of tracks provides the key to the height and speed of a dinosaur. Coprolites tell a story about who was eating who in the Jurassic. Where most people may only see a barren landscape, the paleontologist conceives a zoo of ancient beasts.
Paleontologists don’t need to play Pokémon Go. They have ichnofauna to hunt.
Fernandes MA, Fernandes LBdosR, Souto, PRdeF. 2004. Occurrence of urolites related to dinosaurs in the Lower Cretaceous of the Botucatu Formation, Paraná Basin, São Paulo State, Brazil. Revista Brasileira de Paleontologia 7(2) pp263-268.
Wagensommer A, Latiano M, Mocke HB, Porchetti Sd’O. 2016. Dinosaur diversity in an Early Jurassic African desert: the significance of the Etjo Sandstone ichnofauna at the Otjihaenamaparero locality (Namibia). Neues Jahrbuch für Geologie und Paläontologie 281(2) pp155-182.
Dinosaur footprint by Greg Willis courtesy of Wikimedia.