Whole Hole Catalogue – How to be a Dino-Skull Sleuth

Last month we had a great question about what was inside a dinosaurs head. Today, we look at a dinosaur skull and answer “What are all those openings in the head for?”  Dino skulls do seem totally, wholly hole-y.

Check out our exploded Archosaurus head. The appearance in life is at the top – we don’t really know the color but this fellow had to hide in the bushes, so we painted him green. Archosaurs is INCREDIBLY important in dino evolution. He’s way ancient – from the latest Permian Period of Russia, about 248 million years ago.

The holes in the Archosaurus head are the clues to how it and its close kin were about to evolve into genuine dinosaurs. There weren’t any true dinosaurs in the Late Permian – that would come later, in the Late Triassic, about 220 million years ago. But the basic proto-dino head architecture had been fixed in Archosaurus.

Some holes are easy – the nostril is at the front. The eardrum was in a little notch at the back. The eyeball was in the big oval hole, second hole from the rear. Now for the good part…..

….there are two big holes for jaw muscles behind the eye, one low on the side, the other high up on the top. These jaw-muscle holes are temporal fenestrae – they mark a huge clan of critters that include lizards, snakes, crocs and dinosaurs. We mammals have only one hole on each side, low on the skull.

But wait, there’s more: between eye and nostril  in Archosaurus is a big aperture that you WON”T find in a mammal,  a lizard or a snake. It was packed with a special air-chamber connected to the throat and lungs. When Archosaurus breathed, air went around through these chambers, keeping the head cool.

Many Early Triassic creatures, descendants of Archosaurus, carried these holes, and so did early crocodilians. We call the snout-hole group “Ruling Reptiles” which in Latin is “Archosauria.” Archosaurs took over the land ecosystem during the Triassic, monopolizing the roles of large predator and large herbivore. There was something in that head design that gave Archosaurs a competitive edge.

Then came dinosaurs. All early dinos had the same blueprint – two muscle holes behind the head, one big air-chamber twixt nose and eye. Don’t take my word for it. Go to our galleries and find the holes in our T. rex. You’ll find the same layout in stegosaurs and raptors, duck-bills and ostrich dinos.

That’s the end of the first hole lesson. Do your homework. Find photos of dino skulls and label the openings.

Discovery! Mass Burial of Ancient Red Beds Amphibians Uncovered

PhD scientists aren’t the only ones to make spectacular new fossil finds. Case in point: a skilled bulldozer operator digging a cattle tank in Baylor County caught a glimpse of fossils – hundreds of tree trunks, branches, leaves and…skulls! It’s the biggest discovery ever of flat-headed, bottom-living frog-relatives in the famous Clear Fork beds.

Background of Discovery – the “Age of Frog-oids”

The north Texas Red Beds from the Early Permian Period are most famous for the fin-back reptile Dimetrodon, a tiger-sized predator who was close to the direct ancestry of furry mammals, including us. But the Red Beds habitats swarmed with amphibians too, creatures who hatched from frog-like eggs and breathed with gills early in life the way salamanders do today. So common and diverse were Red Beds amphibians that this geological time-zone can be called: “The Age of Frog-oids.”

Some frog-oids were huge and armed with alligator-shaped skulls. Some were tiny and squirmed through the mud like squatty snakes. Others ruled the pond bottoms and stream beds, hugging the mud with low, wide bodies and wide, flat jaws – a design ideal for ambushing crustaceans and fish passing overhead. One of the dominant bottom-huggers was the “Panzer Mudpuppy,” a twenty-pound amphibian with powerful jaws, curved fangs, and big eyes that scanned the water above. Known technically as Trimerorhachis (“Three-Part-Spine”, in honor of the vertebrae, which were composed of three sections), this flat-bodied hunter was an extraordinary geological success. It survived for twenty or thirty million years, a constant companion to the big Dimetrodons who prowled on shore.

The “Panzer” part of the nickname comes from the armored skin. Amphibians today have mostly naked, frog-oid/toad-oid skin. Red Beds amphibians were different. Their bodies usually were completely covered with thin bone scales that worked like the scale-armor suits of medieval warriors. Darwinian theorists have suspected that “Panzer Mudpuppies” were key elements in the Dimetrodon diet. Few land herbivores were available, so the fin-back predators may well have waded into the water to snag amphibians. If the theory is true, then Trimerorohachis played a vital role in the survival of our reptilian ancestors.

Gaps in the geological record

Despite 130 years of intensive study, “Panzer-Mudpuppy” history still had gaps. This amphibian was very common in the earlier Red Beds, like those in Archer County. But then it became rare. In the later Red Beds, the Clear Fork Group, good skulls and bodies are few and far between. What happened? Were there local habitats where “Panzer Mudpuppies” enjoyed reproducing and growing in Clear Fork time? No one knew, until Jimmy Smajstrla and his bulldozer arrived at the Craddock Ranch. Thanks to the generosity of Mr. Bill Whitley, ranch owner, the Houston Museum has been surveying all the fossil sites in the Clear Fork sediments that outcrop in the ranch. Bits and pieces of “Panzer Mudpuppies” were recovered but no specimen had a complete skull or jaws.

The Discovery

Mr. Smajstrla had a ranch job to perform: excavate a new tank to trap water for the cattle. However, he also had a talent for paleontological discovery. When his twenty-year-old Caterpillar, named “YSOB,” was digging down to the ten foot depth, the blade overturned grey clay chock full of fossilized plant parts. Smajstrla salvaged many valuable chunks and led the HMNS party to the spot. Fossil wood is rare in the Clear Fork, so the discovery was exciting.

Then came what no digger had dared to hope for. Even deeper went the ‘dozer. Fossil parts were in the bed below the plants. Not botanical remains this time, but what thrills the heart of every paleontologist: skulls and jaws, dozens and dozens of them, many perfect. For the very first time, science had a beautiful sample of later “Panzer Mudpuppies.” Some of the heads were larger than any previous discoveries. The official name of the skull-bed is “The Judy Site,” in honor of Mrs. Judy Whitley. What will the “Judy Site” tell us? Lots. We’ll know much more about the habitat choice of the “Panzer Mudpuppies.” And we’ll be able to detect micro-evolutionary changes. Investigations have just begun.

We look forward to sharing updates on our investigations as well as new finds with you. Stay tuned!

100 Years – 100 Objects: Brachiopod

The Houston Museum of Natural Science was founded in 1909 - meaning that the curators of the Houston Museum of Natural Science have been collecting and preserving natural and cultural treasures for a hundred years now. For this yearlong series, our current curators have chosen one hundred exceptional objects from the Museum’s immense storehouse of specimens and artifacts—one for each year of our history. Check back here frequently to learn more about this diverse selection of behind-the-scenes curiosities—we will post the image and description of a new object every few days.

This description is from David Temple, the museum’s curator of paleontology. He’s chosen a selection of objects that represent the most fascinating fossils in the Museum’s collections, that we’ll be sharing here – and at 100.hmns.org/ – throughout the year.

Brachiopod, Grandaurispina kingorum
(Permian, Willis Ranch Member, World Formation, Brewster County, Texas)

CHI_7629The Glass Mountains are famous for silicified fossils of Permian age, such as this Brachiopod. Unique build-ups of fossil shells, both wave-generated accumulations of dead shells and massive brachiopod-dominated reefs, produced by the complex interactive growth of millions of marine invertebrates that occur in the Glass Mountains.

Fossils from the Glass Mountains are of special interest because of their level of detail. Blocks of limestone from the Glass Mountains can be treated with weak acids to dissolve the limestone from the acid-resistant silicified fossils. This process often leaves unharmed the delicate spines and ornamentation found on some brachiopods and bivalves.

Wander among prehistoric beasts in the Paleontology Hall, a permanent exhibition at the Houston Museum of Natural Science.

You can see more images of this fascinating artifact – as well as the others we’ve posted so far this year – in the 100 Objects section at 100.hmns.org.

Live from the Field: The Smoking Gun

Kim Beck, a regular excavator with the
HMNS team, looks for fossils eroding out
at the surface.

Our paleontology team – led by Dr. Robert Bakker – is back in Seymour, TX this week, digging for Dimetrodon at a site they’ve now been working for several years. (You can read more of what’s been found already in our daily blog from the field in 2007).

Listen to the podcast below to hear David Temple – our associate curator of paleontology and a one of our BEYONDbones bloggers – fill us in on the progress from yesterday - including the discovery of “The Smoking Gun,” and evidence of cannibal Dimetrodon – as well as the history of the site the team is digging on, which is so rich that scientists have been pulling Dimetrodon and other Permian-era species out of the ground there since 1877.

If you’re a paleo expert, you can skip this paragraph and head straight to the update – but David mentions a few things that not everyone is familiar with: “matrix” is a term paleontologists use to describe the material that surrounds fossils. “Wet screening” is the process of putting matrix on a small-weave screen and running water through it to find any tiny fossils that might have been missed. And, Dimetrodon grandis is the very largest species of Dimetrodon ever found – making it the biggest, baddest predator of the Permian.


Our field team will be updating us on progress at the site every day this week – so check out yesterday’s update from Kat Havens, another of our excavators – and come back tomorrow for more from the fossil field!