Hello everyone! The modern human species, who have been able to record history, or leave marks of their existence, in some form or other, have been around for a relatively short time on Earth. However, this means that a significant proportion of life on Earth remains unrecorded, or lost in the sands of the earth. Only fossils remain. Bones, footprint trails, etc. are (partially) kept preserved, hidden in the ground. What the true nature of animals and organisms were, prehistory, in terms of their movement, activities etc., is lost to us. But is it really? Here, we’ll look at different ways that the behaviour of creatures (particularly those which are extinct) might be uncovered from the traces they have left behind.
Inspired by images from sauriangame.squarespace.com
Let’s examine how fossils can paint a better picture of the behaviour of paleofauna. But what are fossils? More deeply, what is behaviour?
Definition Time
Fossilisation: a variety of often complex processes that enable the preservation of organic remains within the geological record (from http://www.discoveringfossils.co.uk/what-is-a-fossil/)
But fossils are not limited to skeletons of creatures. Trace fossils (e.g. footprint tracks, burrows, nests) also indicate the presence of prehistoric organisms. Minibeasts caught in resin (like in my favourite film, JP) also count as fossils. There are even chemical fossils, based on the fact that paleoorganisms would have a chemical footprint. Point being, there’s a wide range of prehistoric artefacts that can give us information about ancient organisms. Alright, but what is behaviour?
Behaviour can be considered the result of all the external and internal influences on an animal. In practical terms, this results in how animals learn about, understand and navigate their environment, interact permissively or aggressively with another and seek its survival. All of these add up to animal behaviour. Sensory neuronal input can involve the brain for a conscious decision or lead to innate or reflex actions, - either way producing motor-neuron-effected behaviour. In humans, this is extended to a large variety of higher order cognitive functions, which psychology, sociology and anthropology try to grapple with. But for our purposes, let’s stick to the basics (movement, diet, etc.).
Movement
Although fossils are themselves static, knowledge cumulatively gained from body fossils and trace fossils, computational modelling and modern-day extant analogues can lead to reliable and sensible predictions of the movement of paleofauna. For instance, the maximum speeds of non-avian dinosaurs can be predicted from trends in surviving animals, given the measured hip length and the stride length of the animal. Moreover, computational modelling of the response of the interior bone structure to different forces can reveal habitual walking motion (and osteogenic bone responses) in hominids. A similar method has been applied to whole T. rex skulls, to deduce the cranial mechanics of a T. rex during feeding (shown below).
From this, one can infer a preferred jaw movement of T. rex (an ideal jaw motion will minimise the sum of compressive, tensile and shear forces on the individual skull bones). Also, by using complete, uncrushed skeletal remains, well-preserved wing membranes and pterosaur tracks, while comparing the pterosaur to closely related reptiles, the gait of pterosaurs can be confirmed as quadrupedal.
Social Interaction
Collective motion of a group of extinct fish (Erismatopterus levatus) was captured in a fossil. The structure of this collection resembles shoals of extant fish (shown below). Behaviour governed by repulsion from close neighbours and attraction towards fish at a distance along with a hierarchical group structure led to an oblong shape of this shoal.
Fossilised remains of both eumelanosomes and phaeomelanosomes in dinosaurs and birds provides information about colours and patterns in the species. The specific colour pattern might denote the social requirement of display, and therefore seeking attention, which is crucial for finding mates, territorial display or finding prey. Parental care of paleofauna can be witnessed in a body and trace fossil, which reveals one adult and two juvenile Oryctodromeus cubicularis skeletons. “Association of adult and young within a terminal chamber provides definitive evidence of extensive parental care in the Dinosauria.”
Feeding Habit
The diet and/or predatory instinct of extinct herbivores and carnivores alike can be inferred from a range of sources, including bone analysis, dental microwear, whole body fossils and coprolites. The dental microwear found on an Edmontosaurus reveals both the jaw mechanics and diet of the hadrosaurid, but also that Edmontosaurus was accustomed to grazing rather than browsing for specific herbs. Here is the image below:
Additionally, a prehistoric specimen of Sanajeh indicus (a prehistoric snake) found at Dholi Dungri, India was seen to partially girdle around 3 titanosaur eggs and a hatchling as well [9]. This explicitly demonstrates a direct prey-predator link in a prehistoric food web.
Moreover, the bone density of Spinosaurus skeletons (after being compared to modern reptiles) reveal that Spinosaurus was likely an aquatic hunter. Finally, an enormous coprolite specimen, which was geographically, temporally and biologically identified to be that of a T. rex, revealed juvenile ornithischians to form part of T. rex’s diet.
Large, bone-bearing theropod coprolite with some of the broken pieces that had eroded downslope. This specimen was found in Chamberry Coulee in the Frenchman River Valley, roughly 11.5 m below the Cretaceous/Tertiary boundary. Scale bar, 10 cm.
The extent of bone digestion also can be indicative of gut-residence time, and so might be indicative of the feeding frequency of T. rex (more bone digestion would indicate less frequent feeding).
Learning and Adaptation
The responses of paleofauna to a changing environment can be seen in ichnogenera (groups of organisms classified according to footprints) and the burrowing behaviour of terrestrial species. For the former, the Oldhamia ichnogenera is shown to reveal the migration of Cambrian undermat miners from the Iapetus Ocean to other waters in response to intense bioturbation during the Cambrian Agronomic Revolution. For the latter, “Complex, large-diameter burrows” in the Salt Wash Member (Upper Jurassic Morrison Formation, southern Utah) were revealed to be created by fossorial mammals, and may have indicated the “subsocial behaviour of fossorial mammals, where the burrow was used for raising young, storage and disposal of food and wastes, and coping with episodic water inundation”.
Now it’s our turn!
We have thought about what existing fossils of ancient species can tell us about the species themselves. But our inferences are only as complete as the fossil record itself. It is a miracle to find even one new fossil, given the number of conditions that must be met.
Now imagine that in the future, Homo sapiens sapiens leave this planet in the search of a better world (or for the pessimists, go extinct!). What would a future intelligent species on Earth conclude about our species?
Well, for one thing, some of the largest structures that humanity has built (e.g. the Great Pyramids of Giza) may take a very long time to fade away, and so these could serve as a marker to show our endeavour as a species. Not to mention another, more permanent trace fossil – our footsteps on the Moon!
Our lunar footprints would last for an estimated 100 million years. Given that there was only 65 million years between us and the non-avian dinosaurs, a future dominant species could see our mark on the lunar surface, realising the range of our exploration.
But what about our bone fossils? Well, using the analysis of our internal bone matrices, they could deduce our bipedalism (walking on two feet leads to a different weight distribution across the limbs than crawling on four limbs).
However, these future species could be very confused about our evolutionary development. Our own attempts to discover more about our own archaeology (which would become the new species’ prehistory) involved us digging up our ancestors’ skeletons, trace fossils etc. If we do not put them back to their initial location before our departure, future species could think that Neanderthals walked alongside Homo sapiens sapiens or some other spurious conclusion, since the fossils would be in the same geological strata. Then again, geological strata formation is relatively slow (avg. speed = one layer in several million years), and the timescale of human evolution might be too quick to be reliably mapped out. There could be massive uncertainty in the future species’ prediction of the age of our fossils.
After seeing skeletons ordered in grids (remains of cemeteries), a future species could think that either we coordinated burial plans (true) or that we progressed in orderly formations (wrong in this case, but true elsewhere). Both cases would demonstrate a higher order of communication and planning compared to other species.
When we consider our own case, we start to see the complexity and difficulty of inferring behaviour from fossil evidences. We cannot any make firm conclusion, but have plenty to fuel our imagination and make some intelligent guesses.
Fossils, ya dig?
That was a lot to take in, but I hope it's a "thinkstarter".
I have frankly never considered my own fossil before! I hope this post serves as a reminder that life is ephemeral, but memory of life is never actually fully lost.
Anyway, I hope to talk about more lively topics in future posts! See you soon!
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