The Big Dinosaur Podcast

In our 37th episode of I Know Dino, we had the pleasure of speaking with paleontologist Jack Horner. Jack Horner is the curator of paleontology at the Museum of the Rockies, the Regent’s professor of paleontology, adjunct curator of the National Museum of Natural History, and he teaches the honors program at Montana State University. He is also the inspiration for the character Dr. Alan Grant in the original Jurassic Park. His first big discovery was in the 1970s of a nesting site for the dinosaur Maiasaura, which means “Good Mother Lizard.” Since then he has named several other dinosaur species, including Orodromeus, and he even has two dinosaurs named after him (Achelousaurus horneri and Anasazisaurus horneri). He has also discovered one of the largest T-rexes known (even larger than the famous T-rex named Sue). His research includes dinosaur evolution and ecology, emphasizing growth and behavior. He has written eight books about dinosaurs, including a children’s book, as well as over 100 professional papers, and numerous articles. And he has also given Ted Talks about dinosaurs.

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In this episode, we discuss:

• The dinosaur of the day: Maiasaura, whose name means “Good Mother Reptile”
• A hadrosaurid (duck-billed) dinosaur that lived in Montana in the late Cretaceous
• First fossils found in 1978, and genus named in 1979
• Marion Brandvold and her son David Trexler found “Egg Mountain” (a nesting site) in Montana
• Marion found the eggs, and Laurie Trexler found the holotype
• Laurie Trexler found a Maiasaura skull, and Jack Horner and Robert Makela described the holotype
• Species is Maiasaura peeblesorum
• Name is based on the nests with eggs, embryos and young dinosaurs that were found, which were evidence that Maiasaura fed the young in the nest (first evidence of a dinosaur doing so)
• Maia was a goddess in Greek mythology; using the feminine form of saurus, saura, to emphasize the motherness
• Most dinosaurs have a male-oriented name (saurus v saura)
• The fossils were found on John and James Peebles’ land, so species type is named after them
• Hundreds of Maiasaura fossils have been found (over 200 specimens, all ages)
• Other dinosaurs that lived in the area at the same time included the troodontid Troodonand, the hypsilophodont Orodromeus, the dromaeosaurid Bambiraptor, the hadrosaurid Hypacrosaurus
• The herd of Maiasaura were buried in volcanic ash
• Herds may have been as large as 10,000 Maiasaura
• Maiasaura is one of the few dinosaurs where there is solid proof of living in herds
• Lived in herds and had muscular tails (only defense)
• Because there was such a large herd, they may have migrated seasonally to find more food
• Area where the eggs were found is now known as “Egg Mountain” in the Two Medicine Formation in Montana
• The nesting site is communal
• Nests were close together, like modern seabirds (23 ft or 7 m in between nests, about the length of adult Maiasaura)
• Eggs were about the size of ostrich eggs, and nests had 30-40 eggs in them (in a circular or spiral pattern)
• Maiasaura was probably too heavy to sit on its nest
• Incubated eggs using rotting vegetation (Maiasaura put the vegetation in the nest instead of sitting on top of the eggs)
• As the vegetation rotted, it emitted heat
• When eggs hatched, the baby Maiasaura did not have fully developed legs and could not walk (but they had partly worn teeth, so adults probably brought food to them)
• In 1996, a new study was published that compared newly hatched birds and crododilians to dinosaur embryos and hatchlings, which found that hip bone development was more important than leg bone development, so the non-developed leg bones of newly hatched Maiasaura did not necessarily indicate a lack of mobility. The study concluded baby Maiasaura was more precocial (advanced) than previously thought and may not have needed as much parental care at first
• However, in 2001 Horner found that growth rates and other developmental differences between Troodon, Orodromeus, and Maiasaura (Troodon and Orodromeus were precocial while Maiasaura was altricial or needing a lot of care)
• Dr. Paul L. Else hypothesized that Maiasaura produced “crop milk”, like how some modern birds (pigeons, flamingos, produce a fatty liquid for their babies)
• Crop milk had antibodies, fat, protein, etc.
• Else wrote an article called “Dinosaur lactation?” about crop milk, based on the relationship between dinosaurs and birds. Maiasaura were probably producers of crop milk because babies may not have been able to break down plants, and also this fortified milk substance may have helped the babies grow quickly
• However, the way birds secrete their crop milk is different (pigeons have a crop organ, but emperor penguins have it come from the lining in their esophagus), and also crocodylians (closest living relatives to dinosaurs, other than birds) do not have this ability, so it’s unlikely Maiasaura could do this
• Jack Horner found that “multiple horizons of nests layered one on top of each other” so the dinosaurs probably went to the same site “over multiple breeding seasons”
• Maiasaura may have been similar to sea birds, where they usually live in smaller groups, but once a year live in the same area to raise its young
• In their first year, the babies grew from 16 in (41 cm) to 58 in (147 cm) and then left the nest (rapid growth may mean they were warm blooded)
• Babies looked very different from adults (larger eyes, shorter snout–much cuter, as seen in animals who need their parents in order to survive when they are young)
• Juveniles (under 4 years) walked on two legs, adults on four legs
• Front legs were much shorter than hind legs, so when Maiasaura ran, probably ran on back legs, using its tail for balance
• In 2001 paleontologist David Dilkes said Maiasaura may have changed its posture as it grew older, based on muscle scars that show young Maiasaura ran on two legs and then walked on four legs when it got bigger
• Jorge Cubo, Holly Woodward, Ewan Wolff, and Jack Horner reported that, after cutting open two bones (one of a one-year old Maiasaura and one of a four-year old), the bone growth shows the one-year-old being similar to bipedal animals, and the four-year-old as similar with quadrupedal animals
• The bones had “rinds of extraneous bone that quickly grew over the outer surfaces”, showing a response to strains. Both dinosaurs probably broke their right fibulae, and extra bone grew in response to the strains on their tibias
• This leads to more speculation on whether or not there are too many different types of named dinosaurs, and whether some of them may actually just be juveniles of others
• Adult Maiasaura was about 30 ft (9 m) long
• About 6-8 ft (2-2.5 m) tall and weighed 3-4 tons
• Had a flat beak, thick nose, spiky crest in front of eyes (males possibly used to fight each other to impress females and attract mates)
• Four fingers on hands and feet had hoof-like claws
• Toothless beak, cheeks to hold in food
• Adult Maiasaura probably ate about 200 pounds of food per day (leaves and seeds)
• Maiasaura coprolites (from Wyoming) show that they ate lots of wood
• Maiasaura is the state fossil of Montana (as of 1985)
• In 1985, astronaut Loren Acton went on an 8-day mission called Spacelab 2, and took with him a piece of Maiasaura bone and eggshell into space (they are now in the Museum of the Rockies in Montana)
• In 2010, there was an animated Japanese film (based on a book) called You Are Umasou, where a Maiasaura raises a baby T-rex
• A hadrosaur, but not the largest hadrosaur
• Maiasaura is most closely related to Brachylophosaurus, which is known as the “dinosaur mummy” because in 2000, a subadult named “Leonardo” was found, and it was a partially mummified skeleton
• Maiasaura is a saurolophine hadrosaur, because the crest on its snout is solid
• Two subfamilies: lambeosaurines (hollow crests) and saurolophines with solid crests (pre-2010 most hadrosaurines classified as saurolophines) (talk more about it on Episode 31: Corythosaurus)
• Maiasaura is part of the subfamily of hadrosaurids, saurolophinae
• Before the group was known as Hardosaurinae (hadrosaurs that for the most part didn’t have crests), but then the genus Hadrosaurus was found to be more primitive so the subfamily was renamed Saurolophinae
• Saurolophinae dinosaurs either have no crests or solid crests (the other subfamily is Lambosaurinae, which have hollow crests)
• Fun Fact: Fossilization requires specimens to be burried quickly (like in a marsh or quicksand), so we may not ever discover dinosaurs that lived on tops of mountains or in other conditions that don’t lend themselves to fossilization

For those who may prefer reading, see below for the full transcript of our interview with Jack Horner:Continue Reading …