Ammonites basking under the Late Cretaceous sun.>
Artwork by Callum Pursall (@cpursall on X)
Yet more evidence incidentally refuting creationism was published two days ago in the journal Nature Communications. That wasn't the intention of the palaeobiologists who presented them, of course, but the facts they presented simply did that by being entirely inconsistent with creationism and at variance with what the facts would be if creationism had any merit.
The paper, by a research team led by palaeontologists at the University of Bristol, concerns the extinction of the ammonites, apparently very suddenly on a geological time-scale. It had previously been thought that their decline had been a slow, gradual process but the evidence found by the researchers is that it was as sudden as that of the non-avian dinosaurs and caused by the same random astronomical event - a meteor strike, 66 million years ago.
The resulting climate change caused a mass extinction at the end of the Cretaceous and the start of the Palaeogene - the so-called K-Pg boundary. (K for Kreidezeit - German).
The ammonites were cephalopod molluscs related to octopuses, squids and the nautiluses and were a major predator in Cretaceous seas. Judging by the abundance of their fossils which I have picked up in fields in Buckinghamshire, they were common and widespread. On holiday some years ago on the north coast of Somerset, my children and I once spent several hours on the beach at Watchet, breaking open pieces of slate to discover ammonites inside them. My children were excited to think they were the first humans to look at each ammonite as we exposed them for the first time in maybe 100 million years.
However, when it comes to assessing the abundance and diversity of extinct orders such as ammonites, local abundance or rarity can be misleading, because it can lead to sampling bias where a local collection of fossils can be mistaken for a general abundance and a local absence can be wrongly extrapolated to indicate a general scarcity. The authors used techniques to minimise this bias in their reassessment of the rate of extinction of ammonites.
Now tell me all about Ammonites and their eventual extinction, please. Ammonites were marine mollusks that lived in the seas from the Devonian period (around 400 million years ago) to the end of the Cretaceous period (about 66 million years ago). They are closely related to modern-day cephalopods like squids, octopuses, and cuttlefish. Here are the key aspects of ammonites and their eventual extinction:The research is the subject of a University of Bristol press release:
Physical Characteristics
- Shell: Ammonites had coiled, spiral shells divided into chambers. The shell structure varied among different species, with some having smooth shells while others had intricate ridges and spines.
- Siphuncle: This was a tube running through the shell’s chambers, used to regulate buoyancy by controlling the gas and liquid within the chambers.
- Tentacles: Like modern cephalopods, ammonites had tentacles used for feeding and locomotion.
Habitat and Lifestyle
- Marine Environment: Ammonites inhabited various marine environments, from shallow reefs to deeper ocean waters.
- Diet: They were likely carnivorous, feeding on small fish, crustaceans, and other marine organisms.
- Locomotion: They moved by jet propulsion, expelling water through a funnel-like structure to navigate through the water.
Evolution and Diversity
- Rapid Evolution: Ammonites were known for their rapid evolution and high species diversity, which makes them important index fossils for dating geological formations.
- Morphological Variation: Their shell shapes and sizes varied significantly, from small, tightly coiled forms to large, loosely coiled or straight shells.
Extinction
- Cretaceous-Paleogene (K-Pg) Event: Ammonites went extinct around 66 million years ago during the mass extinction event at the end of the Cretaceous period, the same event that led to the demise of the non-avian dinosaurs.
- Causes:
- Asteroid Impact: The leading cause of the K-Pg extinction is believed to be a massive asteroid impact, creating the Chicxulub crater in present-day Mexico. This impact would have caused immediate and long-term environmental changes, including wildfires, tsunamis, and a "nuclear winter" effect due to debris blocking sunlight.
- Volcanic Activity: Extensive volcanic activity, particularly in the Deccan Traps in India, released massive amounts of volcanic gases (including sulfur dioxide and carbon dioxide), contributing to severe climate change and ocean acidification.
- Environmental Stress: These events led to drastic changes in the marine environment, such as temperature fluctuations, acidification, and reduced sunlight, which would have severely affected marine life, including ammonites.
Legacy and Significance
- Fossil Record: Ammonites are among the most common and well-preserved fossils, found in sedimentary rocks worldwide. Their widespread presence and rapid evolutionary changes make them valuable for biostratigraphy.
- Cultural Impact: Ammonite fossils have been collected and admired for centuries, often used in jewelry and as ornamental objects. Their spiral shapes have also influenced various cultural symbols and artworks.
Summary
Ammonites were a highly successful and diverse group of marine cephalopods that thrived for hundreds of millions of years. Their eventual extinction, tied to the cataclysmic events of the K-Pg boundary, marked the end of an era for these remarkable creatures. Their well-preserved fossils continue to provide important insights into the history of life on Earth and the dynamics of past ecosystems.
Ammonites’ fate sealed by meteor strike that wiped out dinosaurs
Ammonites were not in decline before their extinction, scientists have found.
The marine molluscs with coiled shells and one of palaeontology’s great icons flourished in Earth’s oceans for more than 350 million years until they died out during the same chance event that wiped out the dinosaurs 66 million years ago.
Some palaeontologists have argued that their demise was inevitable, and that ammonite diversity was decreasing long before they went extinct at the end of the Cretaceous.
However new research, published today in Nature Communications and led by palaeontologists at the University of Bristol, shows that their fate was not set in stone. Instead, the final chapter in ammonite evolutionary history is more complex.
Understanding how and why biodiversity has changed through time is very challenging. The fossil record tells us some of the story, but it is often an unreliable narrator. Patterns of diversity can just reflect patterns of sampling, essentially where and when we have found new fossil species, rather than actual biological history.
Analysing the existing Late Cretaceous ammonite fossil record as though it were the complete, global story is probably why previous researchers have thought they were in long-term ecological decline.
Dr Joseph Flannery-Sutherland, lead author
School of Geography, Earth and Environmental Science
University of Birmingham, Birmingham, UK.
To overcome this issue, the team assembled a new database of Late Cretaceous ammonite fossils to help fill in the sampling gaps in their record.
We drew on museum collections to provide new sources of specimens rather than just relying on what had already been published. This way we could be sure that we were getting a more accurate picture of their biodiversity prior to their total extinction.
Cameron D. Crossan, co-author
Palaeobiology Research Group
School of Earth Sciences
University of Bristol, Bristol, UK
Using their database, the team then analysed how ammonite speciation and extinction rates varied in different parts of the globe. If ammonites were in decline through the Late Cretaceous, then their extinction rates would have been generally higher than their speciation rates wherever the team looked. What the team instead found was that the balance of speciation and extinction changed both through geological time and between different geographic regions.
These differences in ammonoid diversification around the world is a crucial part of why their Late Cretaceous story has been misunderstood. Their fossil record in parts of North America is very well sampled, but if you looked at this alone then you might think that they were struggling, while they were actually flourishing in other regions. Their extinction really was a chance event and not an inevitable outcome.
Dr James D. Witts, senior author
Palaeobiology Research Group
School of Earth Sciences
University of Bristol, Bristol, UK.
And Department of Earth Sciences
Natural History Museum, London, UK.
To find out what was responsible for the continued success of ammonites through the Late Cretaceous, the team looked at potential factors [that] might have caused their diversity to change through time. They were particularly interested in whether their speciation and extinction rates were driven mainly by environmental conditions like ocean temperature and sea level (the Court Jester Hypothesis), or by biological processes like pressure from predators and competition between ammonites themselves (the Red Queen Hypothesis).
What we found was that the causes of ammonite speciation and extinction were as geographically varied as the rates themselves. You couldn’t just look at their total fossil record and say that their diversity was driven entirely by changing temperature, for example. It was more complex than that and depended on where in the world they were living.
Dr Corinne E. Myers , co-author
Department of Earth and Planetary Sciences
University of New Mexico, Albuquerque, NM, USA.
Palaeontologists are frequently fans of silver bullet narratives for what drove changes in a group’s fossil diversity, but our work shows that things are not always so straightforward. We can’t necessarily trust global fossil datasets and need to analyse them at regional scales. This way we can capture a much more nuanced picture of how diversity changed across space and through time, which also shows how variation in the balance of Red Queen versus Court Jester effects shaped these changes.
Dr Joseph Flannery-Sutherland.
The paper:
‘Late Cretaceous ammonoids show that drivers of diversification are regionally heterogeneous’ by Joseph Flannery-Sutherland, Cameron Crossan, Corinne Myers, Austin Hendy, Neil Landman and James Witts in Nature Communications.
AbstractThe conclusion is that ammonites evolution and diversity was driven by local environmental changes such as changes in sea levels, global temperature fluctuations and plate tectonics, and by external influence such as the meteor strike that finally exterminated them, but there was no evidence of a general decline, only local fluctuations, prior to that catastrophe.
Palaeontologists have long sought to explain the diversification of individual clades to whole biotas at global scales. Advances in our understanding of the spatial distribution of the fossil record through geological time, however, has demonstrated that global trends in biodiversity were a mosaic of regionally heterogeneous diversification processes. Drivers of diversification must presumably have also displayed regional variation to produce the spatial disparities observed in past taxonomic richness. Here, we analyse the fossil record of ammonoids, pelagic shelled cephalopods, through the Late Cretaceous, characterised by some palaeontologists as an interval of biotic decline prior to their total extinction at the Cretaceous-Paleogene boundary. We regionally subdivide this record to eliminate the impacts of spatial sampling biases and infer regional origination and extinction rates corrected for temporal sampling biases using Bayesian methods. We then model these rates using biotic and abiotic drivers commonly inferred to influence diversification. Ammonoid diversification dynamics and responses to this common set of diversity drivers were regionally heterogeneous, do not support ecological decline, and demonstrate that their global diversification signal is influenced by spatial disparities in sampling effort. These results call into question the feasibility of seeking drivers of diversity at global scales in the fossil record.
Introduction
Inference of patterns and processes of diversification in the fossil record has a long history of palaeobiological interest1,2,3,4. Ever larger compilations of fossil occurrence data and improved chronostratigraphic constraints have enabled precise quantification of the magnitude and timing of interspersed mass extinctions and evolutionary radiations5,6,7. In turn, this has permitted investigation of the drivers of diversification, broadly divided into intrinsic regulation of taxonomic richness by diversity-dependent mechanisms (the Red Queen Hypothesis)8,9,10,11,12 versus extrinsic, abiotic forcings imposed by the Earth-Solar system (the Court Jester Hypothesis)4,13,14. The influence of the Red Queen remains contentious due to the difficulty of establishing whether biodiversity has ever truly entered a curtailed, diversity-dependent regime15,16,17,18,19,20, with the additional observation that interactions between life and the Earth-Solar system through geological time have dynamically altered Earth’s carrying capacity21,22. By contrast, a series of Court Jester mechanisms are repeatedly hypothesised to have driven patterns of diversification in individual clades to entire biotas, for example, the linked effects of atmospheric CO2 concentration and temperature, the configuration of the continents, or eustatic sea-level variations19,23,24,25,26,27,28,29.
It is also widely recognised that diversity patterns in the fossil record are skewed by geological and anthropogenic biases1,6,30,31,32,33, fuelling development of increasingly sophisticated methods for quantifying diversification dynamics from incomplete, biased fossil occurrence data. In the last decade, Bayesian approaches, which couple birth-death and preservation processes have enabled estimation of sampling-corrected origination and extinction rates from fossil occurrences34,35,36,37, avoiding the problems of inferring these fundamental rates from extant phylogenies38,39,40,41,42. In turn, lineage birth and death rates can be modelled as functions of their potential drivers43,44,45, permitting separate consideration of the factors that promoted origination or drove extinction. These models have enjoyed widespread uptake by the palaeontological community46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61 but the paradigm of global biodiversity analysis, whether of individual clades or entire biotas, is challenged by the observation that the spatial distribution and extent of the fossil record varies through geological time31,32,62. This spatial variation induces geographic sampling biases that distort our view of taxonomic richness and diversification rates even after correction for geological sampling biases31. Not only is it inadvisable to treat the fossil record as a representative sample of varying global diversity, with some workers questioning whether global patterns are biologically informative in the first place63, but this also overlooks its well-established biogeographic nuances, necessitating spatially sensitive approaches31,32,64,65,66,67.
Given that diversity shows spatial heterogeneity, it is reasonable to also expect this of its drivers and such variation is evident in the present-day biosphere, for example latitudinally structured co-variation in irradiance, climate and species richness68,69,70. Some palaeontologists, however, have continued to compare ‘global’ fossil records to potential drivers without considering regional heterogeneity in diversification processes64,71,72. Here we investigate diversification dynamics of Late Cretaceous ammonoids in a regionalised framework (Fig. 1) to determine whether the drivers of diversity show this expected variation. Ammonoids were an iconic clade of pelagic shelled cephalopods, which originated in the Devonian and survived multiple mass extinction events up until their demise at the Cretaceous-Paleogene (K-Pg) boundary73,74. Late Cretaceous ammonoids provide an ideal study system for our investigation as their fossil record is taxonomically mature and extremely well-sampled compared to many other fossil clades75. Ammonoids additionally present an intriguing controversy regarding whether they were in ecological decline prior to their definitive extinction at the end of the Cretaceous73,76,77, with previous authors highlighting the importance of combining global and regional analyses to tackle this problem78,79,80. Palaeontologists are also rapidly recognising the wealth of ‘dark data’, present in museum collections but unrecorded in published literature, that has the potential to transform the scale and completeness of palaeobiological analyses66,81,82,83,84,85,86. We, therefore, take the opportunity to unite publicly available fossil occurrence data with ‘dark’ datasets to address this emerging gap in both knowledge and practice.Here we show that a regionally heterogeneous interplay of Red Queen versus Court Jester processes underpinned spatial variation in ammonoid diversification in the Late Cretaceous. These results highlight the challenges that face confident inference of the drivers of diversity in the geographically biased fossil record and call for more nuanced consideration of spatiotemporal complexity of the processes that jointly underlie past biodiversity and its present-day geological remnants.Fig. 1: Stage-level ammonoid sampling regions in the Late Cretaceous.Chosen regions corresponding to biogeographically distinct ammonoid provinces with sufficient data to derive spatially standardised subsamples for reliable estimation of diversification dynamics. The global dataset encompasses the grey points in addition to all coloured regional points. Source data is available in the electronic supplement accompanying this paper.
' For creationism, of course, there is the little problem of all this happening in that very long pre-'Creation Week' history of life on Earth when Darwinian evolution was proceeding, driven by local environmental changes then as it does now.
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