Why Evolution Has Screwed Sea Turtles (And So Have We)

Around 210 million years ago the first primitive turtle with a shell emerged during the Triassic period where it was largely terrestrial and had a beak and armored shell just like modern turtles where this was the era of the first dinosaurs and an era that gave rise to a huge explosion of diversity on the planet demonstrating how turtles originated alongside early dinosaurs during one of Earth’s most significant radiation events establishing fundamental anatomical features that would persist across mass extinctions.

200 million years ago massive volcanic activity changed the Earth’s climate and the end-Triassic mass extinction event occurred killing 76% of all marine and terrestrial species where however the lineage of the turtles held on demonstrating how turtles survived one of five major mass extinctions through physiological or ecological traits that conferred resilience during catastrophic environmental change driven by widespread volcanism and climate disruption.

The giant Archelon was the largest sea turtle to ever live where it was three meters long and weighed almost 2,000 kilograms but these giants too did not last forever where 66 million years ago the asteroid event that wiped out the dinosaurs also wiped out two of the four sea turtle families demonstrating how extreme gigantism in marine reptiles proved vulnerable to the catastrophic environmental collapse at the Cretaceous-Paleogene boundary despite successful adaptation to marine ecosystems for tens of millions of years.

66 million years ago the asteroid event that wiped out the dinosaurs also wiped out two of the four sea turtle families where [75%] of all species on Earth went extinct during this time but two families of sea turtles withstood this apocalypse and continue to swim in the seas to this day demonstrating how selective extinction at the KT boundary eliminated half of sea turtle diversity yet the surviving lineages possessed traits enabling persistence through the most catastrophic mass extinction of the Cenozoic era.

One sea turtle family of soft shell sea turtles has just one remaining member the leatherback sea turtle where the other six sea turtle species belong to another family of hard-shelled turtles where today’s turtles are a reminder of the resilience of their lineage and of their adaptability in the face of epic extinction events demonstrating how modern sea turtle diversity represents two distinct evolutionary lineages with fundamentally different shell architectures both descended from KT boundary survivors yet showing contrasting taxonomic fates.

Today’s turtles are a reminder of the resilience of their lineage and of their adaptability in the face of epic extinction events events the likes of which are hard to even imagine but their resilience is not infinite and today they are being put to the ultimate test where numerous experts believe we are living through or on the cusp of a new mass extinction event the sixth in the history of our planet demonstrating how lineages that survived multiple catastrophic extinctions across 200 million years now face unprecedented anthropogenic threats that may exceed their evolved capacity for resilience despite proven adaptability through geological timescales.

One not caused by asteroids or volcanoes but by human activity where this extinction event called the Holocene extinction event began around 10,000 years ago when the last ice age came to an end and humans began spreading and hunting across the Earth where since then there has been a steady decrease in the number of species that live on our planet however in recent years the extinction rate has skyrocketed where deforestation driven by agriculture and meat consumption overfishing ocean acidification habitat loss and pollution driven by increased human consumption are all forces that may prove to be worse for biodiversity than a literal apocalyptic asteroid demonstrating how anthropogenic pressures operating over millennia have accelerated dramatically in the industrial era creating extinction dynamics fundamentally different from natural catastrophes through cumulative ecosystem degradation and rapid environmental change.

When female sea turtles come ashore to lay clutches of eggs where after a long migration they make their way back to their home beach the same beach where they hatched and the only beach they will ever return to where they heave their bodies onto land and dig an egg chamber about 80 centimeters deep where here the turtle will lay around a hundred ping-pong sized eggs then fill the hole and head back to the sea demonstrating how sea turtles exhibit remarkable natal philopatry using geomagnetic imprinting during hatchling ocean entry to navigate across thousands of oceanic kilometers returning decades later to the exact natal beach for reproduction creating site fidelity patterns critical for population structure.

Over the next two months the eggs develop and undergo temperature-dependent sex determination where this means that the temperature of each egg during certain periods of development determines the gender of the baby sea turtle that hatches where warmer eggs produce females while cooler eggs produce males demonstrating how sea turtles lack genetic sex determination instead relying on environmental temperature during critical developmental windows making them exceptionally vulnerable to climate warming that could skew sex ratios toward female-biased populations threatening reproductive viability.

Evolution has helped the baby turtles build impressive survival mechanisms to navigate these dangers where they usually wait until nightfall to make their mad dash to minimize the risk of being seen as well as to avoid the blazing hot sun where to make sure the turtles know where they need to go at night time they have evolved to be phototactic meaning they are attracted to light where hatchlings will move towards the brightest light source which is usually the moonlight reflecting off the sea where for millions of years this was an effective strategy demonstrating how natural selection shaped nocturnal emergence synchronized with lunar cycles and positive phototaxis toward ocean-reflected moonlight as an integrated adaptive complex for predator avoidance and thermal stress reduction during the perilous beach-to-sea transition.

The clever evolution that has allowed turtles to survive this treacherous journey for so long is now unfortunately leading them to their demise where if artificial light sources like street lights or lights from buildings are present near the beach this can confuse the hatchlings where they may mistakenly crawl towards the brightly lit road and into highly developed areas where here they can get hit by cars or snatched up by predators attacked by fire ants or simply get lost and die where on some beaches disorientation can affect up to half of all hatchlings and even if they realize their mistake and turn around they might be too exhausted by then to make it to the sea where evolution has not had a chance to catch up with a human invention that has been in these areas for sometimes only a few decades demonstrating how adaptive behaviors optimized over millions of years become lethal evolutionary traps when novel anthropogenic stimuli exploit ancestral sensory mechanisms faster than natural selection can respond creating catastrophic fitness consequences from seemingly simple technological changes.

This problem could somewhat easily be reversed where all that’s needed is to reduce the amount of artificial light that is visible from nesting beaches where lights can be given special fixtures to direct the light away from the beach or lamps can be implemented with light bulbs that only emit red light which isn’t as visible to most animals where windows that face the beach can be tinted and curtains can be drawn after dark to keep the light out of sight where many coastal communities around the world have past ordinances that require residents to turn off beachfront lights during turtle nesting season where in 2014 the Sea Turtle Conservancy was awarded a 1.5 million dollar grant to expand lighting retrofit work in the Florida panhandle demonstrating how relatively simple technological interventions and policy enforcement can effectively mitigate anthropogenic evolutionary traps when stakeholder cooperation combines targeted infrastructure modification with temporal behavioral restrictions during critical biological windows.

When the leatherback turtle evolved around a hundred million years ago it lived along other members of the Dermochelyidae family where it had a specialized diet that helped them to survive where a diet that few other sea creatures find very appealing where it’s a menu with almost no carbohydrates no fats no proteins just a gelatinous salty package of certain fatty acids and a handful of calories each where jellyfish where leatherback turtles surprisingly eat almost nothing else where it’s an odd choice but one that gave them an edge helping them to survive a cataclysmic extinction event demonstrating how extreme dietary specialization on a nutrient-poor but abundant and uncontested resource enabled competitive release during mass extinctions when generalist predators collapsed yet now creates vulnerability to anthropogenic threats that exploit this narrow trophic niche through visual mimicry of primary prey items.

The leatherback’s love of jellies now gets them into trouble when they mix up their favorite snack with a different clear amorphous floating item plastic bags where the ocean plastic problem affects nearly all of the animals that live in the sea but turtles are one of the types of animals most susceptible to its damage where an ingested plastic bag can cause internal blockages which can lead to starvation or death where sharp plastics can rupture internal organs where plastic straws can get caught in their nostrils or they can get entangled in discarded fishing nets which can result in serious cuts on their bodies or even drowning where there is no area of the ocean that is not affected by the 12 million metric tons of plastic that end up in the ocean every year where a plastic bag was even found at the bottom of the Mariana Trench 11,000 meters deep demonstrating how specialized sensory systems evolved to detect translucent gelatinous prey become catastrophic liabilities when anthropogenic pollution introduces chemically stable visual mimics throughout the entire ocean water column from surface to hadal depths creating ubiquitous lethal encounters that exploit ancient foraging adaptations.

In the 1940s incredible video was taken of what is now estimated to be around 40,000 Kemp’s Ridley turtles nesting in one area where a turtle that today is the rarest and most endangered of all sea turtles where by 1985 only 700 nests for this turtle were found worldwide the entire year where the Kemp’s Ridley turtle was on a fast track to extinction due to human damage but thanks to conservation efforts the trend slowly turned in the early 2000s where a combination of nesting beach protection and improved fisheries regulation saved this rarest of all sea turtles from the brink of extinction and is now estimated to be over 22,000 individuals strong demonstrating how targeted conservation interventions combining habitat protection and bycatch reduction can reverse catastrophic population declines achieving nearly 100-fold recovery from critically endangered status when sustained multi-decadal management commitment addresses primary anthropogenic mortality sources despite ongoing threats from climate change and pollution.