Amber Fossils Do Not Accurately Record Animal Diversity
A survey of arthropods trapped in tree sap shows that the unlucky ones do not represent an accurate cross section of the community.
Creatures trapped in amber (fossilized tree sap) are among the most spectacular, because people can see all the details of wings, legs, and even microbes in the creatures’ stomachs. But is there an equal likelihood that the living things in an area where tree sap flows will eventually find themselves done in this way? Seven scientists tried to answer this question by studying which spiders and insects became trapped in tree sap on Madagascar. Their results just came out in PNAS, “Arthropods in modern resins reveal if amber accurately recorded forest arthropod communities.”
It is not known whether the fossil content of amber accurately represents the arthropod biodiversity of past forests, and if and how those fossils can be compared with recent fauna for studies and predictions of biodiversity change through time. Our study of arthropods (mainly insects and spiders) living around the resinous angiosperm tree Hymenaea verrucosa Gaertner, 1791 in the lowland coastal forest of Madagascar, and arthropods trapped by the resin produced by this tree species, demonstrates that amber does not record the true past biodiversity of the entire forest. However, our results reveal how taphonomic [fossil-creating] processes, arthropod behaviors, and ecological relationships can influence arthropod death assemblages in resins and play a crucial role in controlling their taxonomic compositions.
Suppose, for instance, there was one insect that had a habit of luring its enemies into tree sap. That’s fictional, but illustrates the problem: an overabundance of one type of insect cannot give a true indication of what was out there in a past forest community. Or suppose that a big wad of sap fell into an ant hill, or a termite mound, entombing a large number of the same kind of insect at one time. If the pieces of that resin subsequently broke up and scattered, a scientist today might think that the unobserved past forest had lots of that species. The results of this new survey show that behaviors, burial processes and habitats of amber fossils can strongly influence our picture of past biodiversity. This is known as “taphonomic bias.”
Many factors might cause taphonomic bias. These include, but are not limited to,
- Which animals live on or near resin-producing trees
- The odor of the sap, whether it attracts or repels creatures
- The ability of a creature to free itself from the resin once caught
- Behavior of the species
- Habitat of the species (tree-dwelling, underground, aquatic)
- Body size
- Which animals eat others before they can be trapped
- Resin chemistry and viscosity
Because “limited research has been done on this topic,” Kraemer et al., compared the number and types of insects caught in resin, in sticky traps, and in “malaise traps” (nets) around Hymenaea, one of the more important resin-producing trees in the area. Some species known to be important in the ecology were not represented or were poorly represented in the resin. Butterflies and moths, for instance, are abundant in the forest but do not show up in the resin, nor do damselflies and some others, even though they show up in the malaise traps.
Our results imply that the fauna recorded in amber or in Anthropocene resin is not a good representation of entire arthropod forest (paleo) communities, but instead is influenced by habitat and ecological biases. The modern resin in our samples mainly recorded biota living on, or having a close relation with, the resin-producing trees and the arthropods living there; thus important groups of arthropods abundant in the forests can be rare in resin assemblages. If the research focus is limited to the knowledge of the ancient resiniferous tree communities of arthropods, then amber contains a suitable fossil record. However, as trees are also protected from attacks by herbivores, those kinds of arthropods can be underrepresented. Nevertheless, the thanatocoenosis, or set of organisms that died together, constituted by faunal inclusions in resin, contains valuable data about the biology and ecology of the arthropods themselves, which is crucial for the reconstruction of paleohabitats and the study of the evolution of specific behaviors. Inclusions in amber and subfossil resin represent a relevant part of the forest biodiversity of the past. However, the entrapment is principally conditioned by some arthropod behaviors, especially scavenging, predation, microbivory, parasitism, and mating rituals that occur in the arboreal habitat, and herbivory.
Some interpretations about biodiversity can be drawn, they indicate, if they are limited in scope to the types of tree-dwelling organisms likely to be caught in resin. These results, however, sound a cautionary tale about interpreting past habitats and diversity from amber alone.
Other Sources of Error in Ecology and Paleontology
Rethinking the umbrella species concept (Phys.org). Some ecologists figure that certain species in a community influence so many others, they can be called “umbrella species.” The fate of the umbrella species influences the fate of the others that depend on it. If so, focusing conservation efforts on the umbrella species should help all the others, right? This article says that such an “appealing shortcut” can backfire:
According to the “umbrella species” concept, preserving and managing habitat for a single high-profile species also benefits a whole suite of other species that share its habitat—but how well does this really work? Not all species that share the same general habitat necessarily have the same specific needs, and a new study from The Condor: Ornithological Applications finds that habitat management to benefit Greater-Sage Grouse in Wyoming can actually harm some of its songbird neighbors.
25 years of fossil collecting yields clearest picture of extinct 12-foot aquatic predator (Phys.org). Could research on one fossil species be forgetting the lessons from amber? “After 25 years of collecting fossils at a Pennsylvania site, scientists at the Academy of Natural Sciences of Drexel University now have a much better picture of an ancient, extinct 12-foot fish and the world in which it lived,” the article boasts, but no complete fossil of Hyneria has been found. The fossil hunters bluff about evolution:
All of the new information gleaned about Hyneria is doubly valuable because it provides more information about the ecosystem – and time period – it lived in. The Devonian was a pivotal time in vertebrate evolution, especially since some of Hyneria‘s fellow lobe-finned fish developed specialized fins that would take them onto land and eventually give rise to all limbed verterbates including reptiles, amphibians and mammals.
“Hyneria lived in a time and place that is of incredible interest to those of us studying the vertebrate fin-to-limb transition,” Downs commented. “Each study like this one contributes more to our understanding of these ecosystems and what may have played a part in the successful transition to land.”
The article seems to forget some important questions that challenge their interpretation. Lobe-finned fish alive today, like the Coelacanth, are living fossils that did not evolve into land animals, nor are their lobed fins used for walking. And is anyone asking how fish fossilized? Usually fish float and are picked apart by scavengers. To have 12-foot fish entombed in rock should say more about taphonomy than evolution. Besides, tetrapods already existed in this fish’s environment:
Due to its sheer size, weaponry, and sensory abilities, Hyneria may have preyed upon anything from ancient placoderms (armored fish), to acanthodians (related to sharks) and sarcopterygians (lobe-finned fish, the group Hyneria belongs to) – including early tetrapods (limbed vertebrates) that are also found at the site.
That seems to be an important question. Why were tetrapods found with ocean fish? Doesn’t that speak of a catastrophic burial and transport?
Fossils do not interpret themselves. Worse than taphonomic bias is Darwinian bias. It colors the interpretation of any observation, forcing it into a world picture of slow, gradual progress. It asks the wrong questions, and provides wrong answers.
Scientists can fool themselves according to their worldview. They can attempt to correct for known sources of bias, like in the amber research, but can never correct for the unknown sources of bias. There could be some hope if the public could bust open the fossilized consensus about evolution and let other qualified research in, unchained from obligatory obeisance to King Charles, free to think and question. It might end the bluffing extrapolation committed by all the downstream propagandists in the media and education. It might lead to more humility in science. Hasten the day.