Did Tiny Algae Doom Mighty Dinosaurs?


Seventy million years ago, they all came to drink in the rapidly drying river: long-necked sauropods, fierce theropods, crocodiles, lizards, and raven-sized birds. They never left. (Science)

How are animal remains fossilized?

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Majungasaurus was the top predator of the Maevarano Formation, a Cretaceous rock formation in northwestern Madagascar.
Photograph by Kumiko, courtesy Wikimedia. CC-BY-SA-2.0


Discussion Ideas

Illustration courtesy NOAA
  • An intriguing new theory suggests that a series of harmful algal blooms (HABs) may have killed thousands of animals—including dinosaurs, early birds, reptiles, and a spectacular giant frog named Beelzebufo—during the Cretaceous period in what is now northwestern Madagascar. What is a harmful algal bloom?
    • A harmful algal bloom describes the rapid growth of algae or bacteria that can threaten an aquatic environment by reducing the amount of oxygen in the water, blocking sunlight, or releasing toxic chemicals.
      • HABs occur naturally in both seawater and freshwater, and can appear seasonally, developing in the same place at the same time every year.
      • HABs can contaminate plankton, shellfish, and marine or aquatic animals that consume these creatures. In the late 1980s, for example, “14 humpback whales mysteriously washed up on the shores of Cape Cod. Testing found that the whales died from sudden asphyxiation after feasting on Atlantic mackerel loaded with saxitoxin, a neurotoxin found in dinoflagellates [plankton].”
      • How do HABs impact water quality? Use our activity to find out.
      • Forecasting and mitigating the impact of HABs is a key focus of NOAA and other environmental and commercial fishing organizations. Learn more about HABs here.


  • How do researchers think HABs might have killed so many critters in the Cretaceous community in Madagascar?
    • Much like the whales in Cape Cod, scientists think the animals were quickly suffocated due to toxins present in harmful algal blooms.
      • Although the individual animals died quickly, the Maevarano Formation “bone bed” may be the result of years of HABs that appeared regularly in a river that was a key source of freshwater for the community.


  • What clues do researchers have that HABs may have been responsible for the Maevarano Formation bone bed?
    • Scientists think the animals died quickly because the fossils include early birds that were “dropped in their tracks” and marine and terrestrial animals found with an arched-back posture, suggesting neck convulsions and perhaps an inability to breathe. This is consistent with the presence of a neurotoxin.
    • The rock in which the fossils were found includes a carbonate layer similar to those left by algae.


  • What clue might best support the HAB theory for the Maevarano Formation bone bed?


This 3.5-billion-year-old Precambrian fossil shows growth patterns of algae and sand.
Photograph by O. Louis Mazzatenta, National Geographic



Science: Did tiny algae fell mighty dinosaurs?

Nat Geo: What is a fossil? reference resource

Nat Geo: Water Quality Degradation in the Ocean activity

NOAA: Harmful Algal Blooms

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