Dinosaur eggs 101

[Visitors walk past a display of two dinosaur fossils next to a nest of eggs.]

NARRATOR (voiceover): How did dinosaurs make more baby dinosaurs?

[The logo for the American Museum of Natural History appears on top of footage of model baby dinosaurs.]

KIMBERLEY CHAPELLE (Research Associate, Division of Paleontology): Behaviors in dinosaurs–

[Visitors look at a fossil nest of dinosaurs eggs in the halls of the American Museum of Natural History].

CHAPELLE: –is something that's really hard to infer.

[CHAPELLE appears on screen, speaking to the camera. Text appears: “Kimberley Chapelle, Research Associate, Division of Paleontology.”]

CHAPELLE: We have to rely on the fossil record that we have. And one of the really helpful fossils that we can use, or types of fossils that we can use to look at reproductive behaviors,

[Fossil dinosaur eggs appear, in boxes within a collections space. Hands pick up the fossils.]

CHAPELLE: –are fossil dinosaur eggs and embryos.

NARRATOR: So–did all dinosaurs lay eggs?

[CHAPELLE reappears on screen, speaking to the camera.]

CHAPELLE: Yes. So all dinosaurs that we know of laid eggs.

[The screen shows three images of fossil dinosaur eggs. From left to right, text appears that labels these eggs as ornithischian, sauropodomorph and theropod dinosaur eggs.]

CHAPELLE: We’ve found dinosaur eggs in the three major groups of dinosaurs, so ornithischian, sauropodomorphs, and theropod dinosaurs.

[Side by side, video shows a person holding a huge ostrich egg and a tiny speckled quail egg.]

CHAPELLE: Birds and reptiles today have a wide variety of eggs. They come in different shapes and sizes and textures and colors.

[Video pans over a collection of different bird eggs in a drawer, some blue and some green, some speckled and some plain, some huge and some small.]

CHAPELLE: And dinosaur eggs seem to be doing the same thing.

[Side by side images of two lizards emerging from soft-shelled eggs, and a soft-shelled dinosaur egg fossil.]

CHAPELLE: Some of them have softer shelled eggs, so similar to some snakes and reptiles today.

[An image of a classic oval dinosaur egg with a cracked shell appears next to video of a baby bird emerging from a hard-shelled white egg.]

CHAPELLE: And some of them have hard-shelled eggs like birds have today.

[A picture of an almost perfectly spherical dinosaur egg appears next to a picture of very oblong and oval dinosaur eggs.]

CHAPELLE: Some of them are more circular. Some of them are more oval.

[Footage of model Gigantoraptor eggs appear on screen, with text labelling them. The eggs are oblong and bright green with speckles.]

NARRATOR: Some dinosaur even laid colored eggs, like the pigmented eggs we see in some birds.

[CHAPELLE reappears on screen, speaking to the camera.]

CHAPELLE: Colors in eggs today are based on certain pigments, and those pigments seem to be able to fossilize. Scientists have been able to infer that those types of pigments were still- already present in fossil eggs.

[An illustration of several eggs of different shapes appears. Some are blue or green, some have brown speckles, and some are white.]

CHAPELLE: And so they can look at what color they would have been. Some of them are blue-green eggs. Some of them are speckled eggs. Some of them are white eggs.

[CHAPELLE reappears on screen, speaking to the camera.]

CHAPELLE: So they do vary greatly in, like, all those different types of eggs.

[Footage from above shows a white heron or egret perched on top of a nest made of branches, in the top of a tree. Inside the nest are several eggs.]

NARRATOR: Much like their living relatives today, dinosaurs would have laid their eggs in nests.

[A model of a nest of white eggs with fluffy white baby dinosaurs emerging from them appears. Text appears: “model Citipati nest”.]

NARRATOR: But the nests looked different from one dinosaur group to the next.

[CHAPELLE reappears on screen, speaking to the camera.]

CHAPELLE: As far as I know, we've never found dinosaur nest in trees, but we have found evidence that some dinosaurs laid their eggs in open nests.

[An illustration shows a side view of a dinosaur nest on top of the ground, with eggs out in the open. Next to it, video appears of a bird nesting on the ground with its eggs visible. Text appears: “open nests”.]

CHAPELLE: So they would have just left their eggs in the wide open air.

[The previous images disappear and are replaced with an illustration showing dinosaur eggs buried underground. Next to the illustration, a timelapse of a turtle covering the ground over its eggs appears. Text appears: “buried nests”.]

CHAPELLE: Whereas other evidence seems to point to the fact that they would have had to have buried their eggs, and that's mainly due to–

[A closeup of several soft-shelled turtle eggs half-buried in sand appears.]

CHAPELLE: –the texture of the eggshells. Softer eggshells, lose water much quicker.

[CHAPELLE reappears on screen, speaking to the camera.]

CHAPELLE: And so to stop them from drying out, they have to be buried, and that also helps to protect them.

[An image of a fossil dinosaur with eggs beneath it appears on screen.]

CHAPELLE: One of the most famous dinosaur and dinosaur egg fossils is the Citipati fossil.

[CHAPELLE reappears on screen standing next to a cast of the same Citipati fossil, labelled with onscreen text, and indicating features of it as she speaks.]

CHAPELLE: It was found in Mongolia. And we can see that there’s a skeleton on top, and then underneath here there’s a bunch of eggs.

[Different archival photos appear. First, a photo labelled “Gobi Desert, 1993” shows a person in the Gobi Desert uncovering the Citipati fossil that was previously on screen.]

NARRATOR: Before this Citipati fossil was discovered in the 1990s,

[A nest of fossil eggs in an archival black and white photo appear. Text reads: “Gobi Desert, 1925”.]

NARRATOR: –similar eggs in the Gobi Desert had been described–

[A paleontologist wearing a large hat kneels and holds fossil dinosaur eggs in the Gobi Desert in an archival black and white photo.]

NARRATOR: –as Protoceratops eggs,

[A wall of Protoceratops skulls on display at the American Museum of Natural History in an archival black and white photo.]

NARRATOR: –since Protoceratops is one of the most abundant dinosaur fossils found in Mongolia.

[A fossil oviraptor on display in today’s American Museum of Natural History.]

NARRATOR: Occasionally paleontologists would find a theropod dinosaur near these nests,

[A closeup of the exhibition label reads “oviraptorid, ‘egg robber’”.]

NARRATOR: –and called them “oviraptorosaurs” or “egg thieves”–

[An illustration shows a herd of Protoceratops running, and an oviraptorasaur sneaking towards an exposed nest of eggs.]

NARRATOR: –as it was assumed that they were eating the eggs of Protoceratops. 

[CHAPELLE reappears on screen, with the fossil cast of Citipati.]

CHAPELLE: And then this type of fossil was discovered much later in the ‘90s, and that's when it was realized that, you know, the oviraptorosaur or the, in this case, Citipati was actually lying on top of the eggs. And we can see–here are its legs, and here are its two arms–

[Closeups show the eggs tucked beneath the arms of the fossil Citipati dinosaur.]

CHAPELLE: –and so it sort of has its arms wrapped around the eggs, just like a chicken would do today while it's brooding. And so it wasn't eating the eggs or hunting the eggs, it was actually protecting the eggs and brooding the eggs.

[A model of a Citipati nest pans above it, with a feathered Citipati adult sitting next to it and watching over it.]

NARRATOR: It’s rare that you can find such a clear example of behavior–in this case, parental care–

[An image of another dinosaur fossil lying on top of a nest of eggs.]

NARRATOR: –preserved in the fossil record. But it’s not impossible.

[A fossil nest of dinosaur eggs, arranged in a circle.]

NARRATOR: And every fossil nest has the potential to uncover other dinosaur behaviors.

[CHAPELLE reappears on screen, speaking to the camera.]

CHAPELLE: Some early branching, sauropodomorph dinosaurs that buried their nests, there's evidence in the fossil record that those nests are stacked vertically, but they're also stacked horizontally within the rock. And so that tells us a couple of things.

[An illustration shows a top-down view of the ground, where several different dinosaur nests appear next to each other.]

CHAPELLE: Several dinosaurs seem to be together laying the eggs at the same site.

[Text appears below the illustration: “herd living”]

CHAPELLE: And so there's evidence of herd living.

[A new illustration appears, showing the ground as if sliced through like a cake. There are three layers on top of each other, and in each layer there is a nest of eggs, stacked neatly on top of the nest in the layer below it.]

CHAPELLE: Then the vertical stacking, that’s sort of evidence through time that they're coming back to the same site on a seasonal basis to lay their eggs.

[Text appears below the illustration: “nest fidelity”]

CHAPELLE: And so that's nest fidelity.

[An illustrated nest of eggs appears with increasingly larger, dinosaur-like footprints tracking in circles around it.]

CHAPELLE: There have been some sites where they have found, like, little trackways around the nest. Some people have hypothesized–

[CHAPELLE reappears on screen, speaking to the camera.]

CHAPELLE: –that those trackways were from hatchling dinosaurs, and even sometimes they get a bit bigger. So that would mean that the hatchling dinosaurs and older ones are hanging out around the nest together, which might be evidence of parental care.

[Footage of a fossil dinosaur nest appears.]

NARRATOR: But without further fossil evidence, we may never know for sure.

[Closeup of a fossil dinosaur egg in a collections space.]

NARRATOR: It can also be hard to know exactly which species an egg or nest belongs to,

[Footage of another fossil dinosaur nest in a museum collections drawer, followed by another fossil dinosaur nests.]

NARRATOR: –if an adult dinosaur is not found next to it. A lot of the time, scientists can only narrow it down–

[The camera pans up from a label that says “Dinosaur egg frags” to a reassembled dinosaur egg from broken fragments.]

NARRATOR: –to a possible group of dinosaurs, not a species.

[A dinosaur egg is shown on a pedestal in a museum hall. Text appears: “sauropod eggs”.]

CHAPELLE: Sauropod eggs are slightly larger–

[Another sauropod egg, huge and perfectly spherical, is shown in a museum display.]

CHAPELLE: –or larger than a lot of other eggs.

[A hand holds an oval-shaped egg fossil with a fractured shell. Text appears: “theropod eggs”.]

CHAPELLE: The oval-shaped eggs, like we see in Citipati–

[Two oval-shaped fossil eggs, stacked on top of each other.]

CHAPELLE: –and other oviraptorosaurs, that seems to be quite diagnostic–

[A fossil dinosaur nest behind glass, on display at the Museum. The eggs are also oval-shaped.]

CHAPELLE: –for that part of the dinosaur tree. And again, like–

[CHAPELLE reappears on screen, speaking to the camera.]

CHAPELLE: ­–there’s so much variety in egg types across the clades that it’s actually difficult to be able to say, like, oh, that’s definitely that egg.

[A scientist carries a specimen through a lab and puts it in a large machine, which is a CT scanner.]

NARRATOR: Now, with CT scanning, scientists are able to look–

[A CT-scanned image of a curled up dinosaur fossil, an embryo, appears.]

NARRATOR: –inside dinosaur eggs–

[Another image of a fossil nest with a jumble of tiny bones in one corner.]

NARRATOR: –at the embryos that are sometimes–

[An inset square zooms in on the jumbled tiny bones, which are a fossil dinosaur embryo.]

NARRATOR: –fossilized within, helping to identify what dinosaur they belong to.

[On display at the Museum, a tiny fossil dinosaur embryo sits behind a magnifying glass so visitors can better see it.]

NARRATOR: Looking at fossil embryos can also answer questions about dinosaur development.

[CHAPELLE reappears on screen, speaking to the camera.]

CHAPELLE: It's become much easier to study those embryos and to reconstruct them digitally and to look at features that are usually–

[Footage of the skull of a fossil dinosaur embryo.]

CHAPELLE: –quite difficult to see. Some scientists have looked at–

[Two images of a detailed microscopic image of tiny teeth appear.]

CHAPELLE: –the embryonic teeth. There'll be little lines that grow in those teeth.

[The previous images are replaces with an image of what looks almost like tree rings – an image of concentric lines with a red cast. Green dotted lines start to trace over some of the lines.]

CHAPELLE: And those lines can tell you how long that tooth has been present–

[Text appears next to the dotted lines: “Age of tooth”.]

CHAPELLE: –in the embryo, and it seems that dinosaurs have–

[Text appears at the bottom of the image: “dinosaur egg incubation: ~3-6 months”]

CHAPELLE: –longer incubation periods, between three and six months. And there's a sauropod embryo,

[Two images of a baby duck and a baby chicken appear.]

CHAPELLE: –that seems to preserve something like–

[There is a small white bump present on the tip of the beaks of both the duckling and the chick, and each is circled with a green line. Text appears: “egg tooth”]

CHAPELLE: –an egg tooth. In birds and in crocodiles,

[CHAPELLE reappears on screen, speaking to the camera.]

CHAPELLE: –some of them will get a little point on the end of their snout when they're in the egg,

[Footage of a tiny beak poking its way out of an incubated egg. The bird is mostly not visible.]

CHAPELLE: –and they use that to tap the egg in order to hatch. So that's quite exciting, because again, it tells us that, like,

[CHAPELLE reappears on screen, speaking to the camera.]

CHAPELLE: –dinosaur relatives alive today are doing something very similar to what we see in the- in the dinosaur fossil record.

[Credits roll.]