Episode 33 – Ontogeny

Listen to Episode 33 at PodBean, iTunes, or a podcast provider near you!

In this episode we discuss the process through which organisms develop throughout their lives, otherwise known as ontogeny. We’ll examine what ontogeny is, what it teaches us, and how we deal with it in the fossil record.

In the news
Ancient “metallic moths” left clues to their wing colors in fossils.
In England: a jaw fragment of a truly enormous ichthyosaur.
A detailed study asks the question: what’s up with Neanderthal faces?
DNA evidence that sea turtles are using magnetic fields to return home.

Ontogeny

Ontogeny is the process of an organism’s development from fertilization to maturity, the changes an organism experiences during an individual lifetime.

Frog metamorphosis is a famous and intense example of ontogeny. Image by LadyofHats from Wikimedia Commons.

There are many areas of science that study ontogeny. Embryology specifically studies the development of an embryo from fertilization to birth. Developmental biology studies the changes an animal goes through typically after birth. Evolutionary developmental biology (Evo-Devo) looks at what these changes can tell us about how traits originate  and evolve over time.

One of the most peculiar trends in ontogeny is known as neoteny. This is the retention of juvenile traits into adulthood. Axolotls, for example, retain external gills throughout their lifetime, a trait normally lost as salamanders grow up and leave the water. For the axolotl, holding onto this feature allows them to stay in the water as adults.

Axolotls aren’t the only one with these gills. External gills can also be seen in other salamanders as adults. Image by Orizatriz from Wikimedia Commons.

A very common trend in ontogeny is allometry: proportional change through growth. This occurs is basically all animals, including ourselves.

The fact that babies do not represent an adult when scaled up is due to allometric ontogeny. Image by Ephert from Wikimedia Commons.

An ontogenetic growth series of Protoceratops. Image by Harry Nguyen from Wikimedia Commons.

Another ceratopsian, this Triceratops horridus growth series beautifully shows how the horns and frill transition as the animal grows up. Image by Tim Evanson from Wikimedia Commons.

Finally we can see that even Tyrannosaurus rex wasn’t spared experiencing the “awkward years“. Image from Flickr by Tim Evanson.

Different Ages or Species?

Growth series like these and the changes we can see in them show that dinosaurs, like other animals, can go through some extreme changes during their lifetime. This has led some paleontologists to wonder if certain dinosaurs are not their own species, but a growth stage of another already-named species. Some famous examples include Torosaurus, Stygimoloch, and Nanotyrannus. This can be very difficult to study due to lack of young specimens or the difficulty of determining ages in fossils. In many cases, these claims can be pretty contentious among paleontologists and dino-fans! The discussion continues.

Links

If you’d like to learn more about ontogeny and fossil examples, feel free to follow the links below.

In addition to the dinosaurs named above (check out those links, too!), here are some others that have experienced some ontogenetic confusion.
Raptorex might be a young Tarbosaurus
Anatotitan could be a mature Edmontosaurus
Nedoceratops might be a young Triceratops

Other ontogeny studies
Ontogenetic changes in dental form and tooth pressures facilitate developmental niche shifts in American alligators – Great research on alligator bite pressures and how it affects their diet as they grow.
Ontogenesis in the Cranium of Alligator mississippiensis Based on Disarticulated Cranial Elements – Will’s own thesis research on the subject.

 

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