Episode 4 – Island Evolution

Listen to Episode 4 on PodBean, Spotify, YouTube, or your podcast source of choice!

Pop in your copy of Cast Away, it’s time to talk about islands!

Paleo News
This episode’s news pieces are as follows:
Fossil Oysters & Conservation Paleontology
Studying fossil oysters may have been revealed new and more effective methods for conserving and protecting modern oysters in Chesapeake Bay. [Report]
Laser-Imaged Dinosaur Soft Tissue
A new technique for viewing fossils has revealed a detailed look at some of the soft tissues of a small, bird-like dinosaur known as Anchiornis. [News Report]
Ancient Tropical DNA
DNA of a giant tortoise discovered at the bottom of a blue hole in the Caribbean Islands, a very rare find for such a warm environment. [News Report by David]
Giant Ancient Bobbit Worm
The jaws of a sizable polychaete worm were identified in fossil material from Ontari0, Canada, showing that these worms have been big and intimidating for a long, long time.
[News Report by David]

Why are islands weird?

Evolution on islands yields some very interesting and odd animals when compared to their mainland cousins. This is caused by a few factors that make island ecosystems unique from most others. Limited size and resources, a lack of large mammalian predators, and isolation from other gene pools all lead island wildlife to evolve in strange and new ways. This creates ecosystems and food chains that you wouldn’t expect, with certain animals filling ecological niches outside of the norm.

The Kiwi, a small flightless bird found in New Zealand, fills the role typically filled by small foraging mammals. Image by denisbin on Flickr.

As amazing as these unique micro-worlds can be, they are notoriously fragile and sensitive to change. Because of this, island ecosystems often suffer greatly when humans encounter them. The majority of species extinctions in recent history have been from island faunas.

The Dodo is probably the most famous of the island species driven to extinction by human interference. Here is one of the few remaining stuffed Dodo birds at the Natural History Museum, Berlin. Image modified from Thomas Quine on Flickr.

Allopatric Speciation

The isolation that islands provide ensures that island populations rarely interbreed with members of the same species on the mainland or on other nearby islands. This means that as mutations build up in island populations they become more and more different, eventually driving them to become separate species. This isolation-and-splitting of species is know as allopatric speciation, and it is particular common and rapid on islands.

File:Darwin's finches by Gould.jpg
Darwin’s Finches are a classic example of allopatric speciation. Their evolution is so clear that Peter and Rosemary Grant have spent decades watching first-hand the evolution of these birds. Image by Shyamal on Wikimedia Commons.

Giants and Dwarfs

One of the most notable trends of island evolution is the appearance of much larger or smaller versions of familiar animals. This is known as insular (meaning island) gigantism and dwarfism, and may be caused by a series of factors. Limited resources favor smaller versions of large species, while a lack of predators allows small species to become larger. On top of that, a species may grow or shrink in response to the size of their own predators or prey.

The direct causes of dwarfism and gigantism may vary, but the trend is clear. Dwarfs and giants have evolved among elephants, eagles, sauropod dinosaurs, rabbits, and even early humans. Some species even show both trends at the same time, such as some tiger snakes and rattlesnakes.

File:Brookesia micra on a match head.jpg
Brookesia micra, a tiny species of chameleon found on the island of Madagascar, only reaches a max length of 29 mm (1.1 in.).  Image from Glaw et al 2012 on Wikimedia Commons.

Safe Haven for Odd Animals

As vulnerable as these ecosystems can be, the isolation of an island can also offer protection when extinction strikes mainland ecosystems. In such cases, an island serves as a refugium. On Wrangel Island, for example, woolly mammoths held on for thousands of years even after their continental cousins had all vanished.

Tuataras are the last remaining members of a order of reptiles known as the Rhynchocephalians. Today they are only found on the islands of New Zealand. Image by Bernard Sprag on Flickr.

Other links
How can animals raft to new islands?

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3 thoughts on “Episode 4 – Island Evolution

  1. Taab March 9, 2022 / 7:58 pm

    Hey, something that has been bothering me w the narrative of “animals go extinct when humans show up”
    And by the way you both talk and repeat this narrative it gives the impression you are both white and most certainly not indigenous
    This is an old episode so maybe you already got this crit but maybe you haven’t so I will speak
    This is an eco facist talking point
    Sweeping statement about how humans are the problem ignoring colonialism and capitalism
    two infrastructures that motivate echological violence
    Echological violence doesn’t just effect effect plants and animals and land it effects indigenous people.
    This violence is inflicted and motivated by white people and settlers in general.
    For example in the case of the buffalo
    Driven to near extinction in order to further the genocide of Indigenous people in America by starvation and to colonize further westward.
    Many of the examples you give in this episode
    It’s not indigenous people committing echological violence
    It’s settlers and colonizers
    Not just in Americas
    This is seen on all continents
    Colonial violence isn’t just violence against people it’s violence against the land and all that are connected to it, plants , animals, everything.
    And you saying “until humans showed up” feeds this narrative that no people where there till European colonizers arrived. It offers humanity solely to the colonizers and not to indigenous and colonized people. It puts the narrative that indigenous are animals “part of the wildlife that needs to be tamed” not really people.
    So bottom line
    Colonial narrative
    Paleontology can be an excellent way to demonstrate the violence of colonialism against echo systems (Wich people are a part of not separate from) but you ignore colonial and capitalistic violence that contributes to the extinctions you speak of
    You don’t have a full story and understanding if you don’t acknowledge and make your audience acknowledge these aspects of echological violence
    I am hoping that several years later you have come to this understanding and work to challenge this narrative currently but if not I hope this was educational in some way and leads you to do the work and learning to challenge this narrative
    Your work is very much appreciated paleontology and education is fascinating and amazing it just needs to work on the narratives presented bc perception doesn’t exist in a vaccume
    America is a settler colony
    The world is devastated by colonialism
    And audience perceptions need to be challenged with education
    Not reinforced


    • commondescentpc March 14, 2022 / 11:01 am

      Thank you for sharing this. The importance of recognizing and respecting the perspectives of indigenous people and other underrepresented (or misrepresented) groups is something that comes up quite a bit in discussions of paleontology, and we’ve been learning over the years to be better about it. We hope we’ve improved since these early episodes, but we also know we always have more to learn.


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