Did dinosaurs impact how today’s mammals age?

New research proposes a hypothesis that suggests dinosaurs played an important role in shaping the aging rate of present-day mammals.

Aging, the gradual and progressive decline in physiological functions necessary for survival and fertility, affects all organisms of a species [1]. The evolution of aging can be explained by the aging-related fading force of natural selection, the evolutionary process through which the population of living organisms adapt and change [2].

Previous research indicated natural selection causes the deterioration of all phenotypic traits simultaneously. However, recent studies on aging rates indicate natural selection favors asynchronous aging [3]. Natural selection has been observed to favor alleles that promote survival at a younger age and reproductive fitness as compared with those that promote survival at later ages – this suggests that species living in different environments develop different life history strategies.

Longevity.Technology: Demographic rate of aging, which is defined as the rate at which mortality increases with age can be useful for species comparisons. For example, many species of reptiles and amphibians have been reported to show very slow demographic aging as well as negligible senescence. However, this is the opposite in mammals where there is an exponential increase in mortality with age.

A new study in BioEssays by João Pedro de Magalhães aims to determine the cause behind such differences in demographic aging rates and senescence between mammals and reptiles.

The longevity bottleneck hypothesis

One hypothesis suggests that the evolutionary history of mammals during the time of dinosaurs played a key role in shaping the present-day mammalian aging phenotypes. Along with slow aging rates in reptiles and amphibians, other feature traits that are absent among mammals include oocyte regeneration, cancer resistance, continuous tooth replacement and limb regeneration.

Fast aging can be observed in several species such as reptiles, amphibians, birds and mammals. However, mammals have been observed to be absent among the slowest aging and negligible senescence species. The rates of demographic aging have been observed to be lower in some species of reptiles as compared with any mammal [4].

Mammals are known to have evolved from synapsids, which are reptile-like animals that included predators like the Dimetrodon about 250 to 300 million years ago. Dinosaurs are known to have first appeared during the Triassic period and became the dominant terrestrial vertebrates during the Jurassic period (200 million years ago). They eventually started becoming extinct during the Cretaceous–Paleogene boundary about 66 million years ago. When the first mammals appeared is still debatable but it is believed that early large mammals were preyed upon by dinosaurs and therefore the early ancestors of mammals spent more than 100 million years as small, short-lived animals.

As per the hypothesis of João Pedro de Magalhães, the evolutionary pressure on early mammals for fast life history and rapid reproduction led to the loss or inactivation of genes and processes associated with repair and regenerative mechanisms. The ‘longevity bottleneck hypothesis’ was inspired by the ‘nocturnal bottleneck hypothesis’ which states that the early evolution of mammals during the dinosaur era had permanent impacts on the anatomy and physiology of present-day mammals [4].

Although several in vitro studies on the role of reprogramming on rejuvenation exists, the number of in vivo studies is quite limited. Now writing in Trends in Biotechnology
Professor João Pedro de Magalhães

Following the extinction of dinosaurs, mammals became the dominant terrestrial vertebrates, filling up many ecological niches and growing in size. The diversification of mammals led to a huge variety of species with both fast and slow life histories. Extinct and extant mammals are known to have evolved amazing traits and adaptations such as tumor suppression mechanisms and longevity which may also be due to constraints from the time of the dinosaurs (we’re looking at you, naked mole rat!). Similarly, certain aging phenotypes of modern mammals such as tooth erosion, reproductive senescence and negligible senescence may also be due to the biological constraints from the dinosaur era.

Limitations and prospects

Along with the longevity bottleneck hypothesis, other contributors may help to explain the differences in aging between mammals and other taxa. Two such contributing factors may be higher body temperature and cancer incidence among mammals. Moreover, development has been observed to be more plastic in reptiles and amphibians as compared with mammals. Further studies on longevity, aging, age-related diseases and regeneration will help to shed additional light on the evolution of aging and its impact on present-day species – including humans.

Longevity unbottled

The longevity bottleneck hypothesis is significant since it explains several aging traits such as tooth erosion, the absence of very slow demographic aging and reproductive senescence. However, further studies are required to confirm whether other defence, repair, or regeneration systems were lost or inactivated in mammals due to other predation or ecological constraints.

[1] https://www.ncbi.nlm.nih.gov/books/NBK10041/
[2] https://education.nationalgeographic.org/resource/natural-selection/
[3] https://www.journals.uchicago.edu/doi/abs/10.1086/718589?journalCode=an
[4] https://onlinelibrary.wiley.com/doi/full/10.1002/bies.202300098