Creationism in Crisis - Our Placental Ancestors Briefly Lived With Dinosaurs and Survived the Mass Extinction

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June: Humans’ ancestors survived asteroid impact that killed the dinosaurs | News and features | University of Bristol

The beginning of the end for larger dinosaurs. The beginning of the age of placental mammals for us.

According to a new study by palaeontologists from the University of Bristol and the University of Fribourg, placental mammals had evolved in the Cretaceous and were living alongside dinosaurs when the asteroid struck and precipitated the mass extinction that wiped out the larger fauna, leaving smaller feathered dinosaurs to evolve into birds and the early placental mammals to diversify quickly into all today's placental mammals and occupy niches vacated by the larger dinosaurs.

This event is known as the Cretaceous-Paleogene (K-Pg) boundary, marked in the geological column by a thin layer of iridium, believed to be of asteroid origin, the asteroid having vapourized on impact.
The question the team set out to answer was when exactly the placental mammals evolved relative to the mass extinction. The fossil evidence, which has only been found in rocks younger than 66 million years, suggested they evolved after the K-Pg boundary, but molecular data suggested an earlier origin.

The research, which is published, open access, in the journal Current Biology, is described in Bristol University press release:

A Cretaceous origin for placental mammals, the group that includes humans, dogs and bats, has been revealed by in-depth analysis of the fossil record, showing they co-existed with dinosaurs for a short time before the dinosaurs went extinct.

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The catastrophic destruction triggered by the asteroid hitting the Earth resulted in the death of all non-avian dinosaurs in an event termed the Cretaceous-Paleogene (K-Pg) mass extinction. Debate has long raged among researchers over whether placental mammals were present alongside the dinosaurs before the mass extinction, or whether they only evolved after the dinosaurs were done away with. Fossils of placental mammals are only found in rocks younger than 66 million years old, which is when the asteroid hit Earth, suggesting that the group evolved after the mass extinction. However, molecular data has long suggested an older age for placental mammals.

In a new paper published in the journal Current Biology, a team of palaeobiologists from the University of Bristol and the University of Fribourg used statistical analysis of the fossil record to determine that placental mammals originated before the mass extinction, meaning they co-existed with dinosaurs for a short time. However, it was only after the asteroid impact that modern lineages of placental mammals began to evolve, suggesting that they were better able to diversify once the dinosaurs were gone.

The researchers collected extensive fossil data from placental mammal groups extending all the way back to the mass extinction 66 million years ago.

We pulled together thousands of fossils of placental mammals and were able to see the patterns of origination and extinction of the different groups. Based on this, we could estimate when placental mammals evolved.

Emily Carlisle, lead author
Bristol Palaeobiology Group,
School of Earth Sciences
University of Bristol, Bristol, UK.

The model we used estimates origination ages based on when lineages first appear in the fossil record and the pattern of species diversity through time for the lineage. It can also estimate extinction ages based on last appearances when the group is extinct.

Daniele Silvestro, co-author Department of Biology,
University of Fribourg, Fribourg, Switzerland.

By examining both origins and extinctions, we can more clearly see the impact of events such as the K-Pg mass extinction or the Paleocene-Eocene Thermal Maximum (PETM).

Professor Philip C.J. Donoghue, co-author
Bristol Palaeobiology Group,
School of Earth Sciences,
University of Bristol, Bristol, UK.

Primates, the group that includes the human lineage, as well as Lagomorpha (rabbits and hares) and Carnivora (dogs and cats) were shown to have evolved just before the K-Pg mass extinction, which means our ancestors were mingling with dinosaurs. After they survived the asteroid impact, placental mammals rapidly diversified, perhaps spurred on by the loss of competition from the dinosaurs.

The team's open access paper is published in Current Biology:

Figure 1. Patterns of placental mammal diversification

Thick purple lines are crown orders, green lines are stem orders, and black lines are stem placental families.

(A) Explosive model: all placental mammal diversification and origination occurred just after the K-Pg boundary.

(B) Soft explosive model: placental mammals originated just before the K-Pg boundary, but intraordinal diversification only occurred after the boundary.

(C) Trans-KPg model: both interordinal and intraordinal diversification occurred around the K-Pg boundary.

(D) Long fuse model: placental mammals originated in the middle of Late Cretaceous, but intraordinal diversification did not begin until after the K-Pg boundary.

(E) Short fuse model: placental origination and crown order diversification occurred during the Cretaceous.

Figure 3. Clade age and extinction time estimates for placental mammal families

Each line represents a family (arranged by order and clade but without further phylogenetic information), with 95% credible intervals in colors at the root estimates and extinction estimates (where applicable). Gray lines fill in the lineage. 93 families have credible intervals extending into the Cretaceous, but many originated after the K-Pg boundary. For stem and crown order classifications for each family, see Data S1.

Carlisle, Emily, et al. (2023)

Highlights

• The Bayesian Brownian bridge model estimates clade ages based on the fossil record
• The model shows that placental mammals originated in the Cretaceous
• Diversification of placental orders occurred after the K-Pg mass extinction
• Clade age estimates can be obtained without molecular data or phylogenetic models

Summary

The timing of the placental mammal radiation has been the focus of debate over the efficacy of competing methods for establishing evolutionary timescales. Molecular clock analyses estimate that placental mammals originated before the Cretaceous-Paleogene (K-Pg) mass extinction, anywhere from the Late Cretaceous to the Jurassic. However, the absence of definitive fossils of placentals before the K-Pg boundary is compatible with a post-Cretaceous origin. Nevertheless, lineage divergence must occur before it can be manifest phenotypically in descendent lineages. This, combined with the non-uniformity of the rock and fossil records, requires the fossil record to be interpreted rather than read literally. To achieve this, we introduce an extended Bayesian Brownian bridge model that estimates the age of origination and, where applicable, extinction through a probabilistic interpretation of the fossil record. The model estimates the origination of placentals in the Late Cretaceous, with ordinal crown groups originating at or after the K-Pg boundary. The results reduce the plausible interval for placental mammal origination to the younger range of molecular clock estimates. Our findings support both the Long Fuse and Soft Explosive models of placental mammal diversification, indicating that the placentals originated shortly prior to the K-Pg mass extinction. The origination of many modern mammal lineages overlapped with and followed the K-Pg mass extinction.

Carlisle, Emily; Janis, Christine M.; Pisani, Davide; Donoghue, Philip C.J.; Silvestro, Daniele
A timescale for placental mammal diversification based on Bayesian modeling of the fossil record
Current Biology (2023). DOI: 10.1016/j.cub.2023.06.016

Once again, as we've come to expect, there is not a hint of doubt that the Theory of Evolution is the only theory capable of explaining the observations and making sense of the data. Nowhere is there even a hint that these are better explained by magic or the intervention of an unproven supernatural entity making chemistry and physics do things they wouldn't do anyway.

In other words, yet another example of science refuting counter-factual creationism without even trying, simply by discovering the facts.

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