Old Bones - a blog about Vertebrate Paleontology

As an organization committed to advancing the study of fossil vertebrates, promoting education, and to the conservation and preservation of fossil sites, the Society of Vertebrate Paleontology (SVP) is excited to see the abundance of celebratory events taking place across the U.S.  

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Evolution, deep-time history, comparative, multidisciplinarity, anatomy, geology

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Shape, that is morphology, also helps us learn how the animals lived - their ecology, or in the case of fossils, their paleoecology.  

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One of the key phrases to describe how paleontology gets done is, "The present is the key to the past" - by studying animals in the present we can make inferences about extinct life in the past.

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I thought I would try and start having some shorter, more conversational posts, instead of the instructive tomes I've been writing.  This is for a couple reasons: 1) I have the feeling that the longer entries are a bit TOO long, and maybe even a bit dry; 2) it's hard to compose those longer entries - there's research to do, figures to make, etc.  Shorter entries, means more blog posts... hopefully...

So what I thought I'd start doing is talking a bit about "the life of a paleontologist", at least from my point of view, which I think is fairly typical.  I'll talk about myself and other sorts of paleontologists so that hopefully a student, or even a youngster, hoping to get into the field, will know what it takes, and what it will entail.

This week I was actually doing some paleontology, which can sometimes be rare.  Since most of us are academics of a sort (instructors at institutions of higher education), we don't actually put "Paleontologist" on our business cards; often it's "Professor" or "Instructor".  We spend a significant portion of our time teaching, grading, being on committees, advising students, etc. that any academic would do.  Right now I'm teaching a summer school class in Human Dissection Anatomy.  Teaching anatomy is a typical position for a certain class of paleontologists, but the reasons behind that are a story for another time.

As I was saying, this week I was doing some paleo, specifically heading to a museum - the San Diego Natural History Museum (SDNHM).  I'm in Los Angeles, so this was a long day of driving - 2+ hours in the morning, the same in the evening at the end of the day.  Museums are meccas for paleontologists in this way.  The displays the public sees at museums are usually a very small portion of the collections housed there.  The back rooms are filled with banks of drawers filled with more fossils, skins, specimens preserved in alcohol, archeological bits, etc.  For every piece you see on display, there are probably 10's, if not 100's more, in the back.  Most of these aren't "museum quality", meaning that they wouldn't look good on display, and the public wouldn't get much out of them.  But they are precious to the researchers in various fields that flock to see them.  This highlights the dual duties of museums - to inform the public and act as centers for academic research.  Both are equally important.  They help push science forward, while presenting the findings to the public.

This has been one of my favorite parts about being a paleontologist.  Going to museums, opening drawers, not knowing what you'll find.  Often the work is a little dull, comparing specimens, taking measurements, etc.  Every once in a while though you get a gem.  You realize you're looking at a new species, or you notice an interesting feature not documented before.  Really though, for me, it's just opening that drawer and seeing all the knowledge in there, waiting to be discovered.  Every fossil is a data point to help us build the tree of life and reconstruct the grand past of this planet.

A drawer of Eocene (about 40 million years ago) fossils at the San Deigo Natural History Museum

I'll continue next time with what I did while I was at the museum, and about the people that work at the museum.

What is a bird? It sounds like a simple question, because we all have some general idea of what a bird is. You probably make that impression based on characters you associate with birds - birds have feathers, most of them fly, they lay eggs, etc. This kind of definition goes back to what I discussed in my post about turtles - defining groups of animals (taxa) based on collections of characters that they all share. This is all well and good for modern birds, but what happens as we get closer to the ancestral bird, the common ancestor of all birds. There things get tricky, as there were probably a number of taxa around that were 'almost birds'. These taxa may have had some, or even most, of the characters we use to define birds, and you may have even called them a bird on first impression (if you had been around the 150 million years ago when birds first arose), but they weren't birds.

For a long time the archetypal ancestral bird was Archaeopteryx. Even many lay-people have heard of this amazing fossil, mostly because of its exquisite preservation. Found in the mid-1800's in Germany, the fossils of Archaeopteryx come from the Solnhofen limestone. This fine-grained muddy rock is a gold-mine of fossils. Probably deposited in a calm lagoon, which allowed for fairly rapid deposition with relatively little disturbance, the fossils found within its layers are amazingly well preserved. Not only has Archaeopteryx been found there, but so are fossils of small dinosaurs, pterosaurs (winged reptiles that shared the world of the dinosaurs), invertebrates like horseshoe crabs and starfish, and countless plant fossils. There are also tracks of some of the animals, preserved as they walked across the muddy bottom of the lagoon. There's a great German word for a fantastic collection of fossils like this - a Lagerstatten (German for "storage place").

One of the specimens of Archaeopteryx from Solnhofen (image from Wikipedia). Note the impressions of feathers.

The Archaeopteryx fossils from Solnhofen are amazing for their impressions of feathers. The skeletons are pressed between layers of the muddy limestone, and although all the soft tissues, such as the feathers, are gone, they left impressions in the mud before rotting away. The same is true of many of the fossils from these deposits; there are wing-skin impressions from the pterosaurs and body impressions of soft-bodied molluscs.

It was these feather impressions that earned Archaeopteryx the title of the 'earliest bird'. While still retaining some primitive characters from its dinosaurian ancestors, such as teeth and a bony tail, there were enough bird characters, feathers being the biggest one, to call it a bird. Now a new fossilfrom China has knocked Archaeopteryx from its avian pedestal.

Reconstruction of Archaeopteryx by Heinrich Harder - 1916 (from Wikipedia)

Birds have long been known to be related to dinosaurs. Even Charles Darwin remarked on this connection in the 6th edition of his "Origin of Species", and Archaeopteryx was proof of this connection. It was actually thought to be a dinosaur, until someone noticed the feather impressions surrounding the bony fossilized remains. Specifically, birds are thought to be related to theropod (two-legged, meat-eating) dinosaurs, like Velociraptor and Compsognathus made famous in the "Jurassic Park" movies (Note: The famed dinosaur in the first of those movies was actually based on Deinonychus, a species closely related to Velociraptor; Velociraptor is much smaller than the critters shown in the movies, but it has a cooler name than Deinonychus). Technically birds ARE dinosaurs, which is why some paleontologists have taken to calling what the public would normally just call 'dinosaurs', 'non-avian dinosaurs'.

A passage from "Origin of Species" where Darwin talks about Archaeopteryx (from Darwin Online). Even he knew birds were dinosaurs!

This new fossil from China, dubbed Xiaotingia by Xing Xu and the other authors of the study, is closely related to Archaeopteryx. The analysis the authors did found this relationship, but more dramatically, showed that these taxa are closer to the theropod relatives of birds, and not to birds themselves. We know that many of these theropods had feathers, but were not birds (thereby removing one of the seemingly unique features of birds), so Archaeopteryx and Xiaotingia are just another group of feathered dinosaurs. The authors admit that their analysis is somewhat tentative in the robustness of its findings. The findings make some profound implications about the evolution of flight. It's thought that Archaeopteryx was capable of powered (as opposed to gliding) flight, so the new arrangement implies that either flight evolved twice, or was primitive for that theropod group.

Phylogeny showing the relationships of Archaeopteryx and Xiaotingia to birds and "non-avian" dinosaurs.  The dotted lines represent two possibilities for their relationships - one closer to birds, the other closer to small theropod dinosaurs.  The paper by Wu and colleagues suggests the latter.

So the question "What is a bird?" has gotten even more muddied (like the bottom of the Solnhofen lagoon), and only more fossils will tease out the answer.

How do paleontologists, or biologists generally, classify groups? This is a topic that generates a significant amount of research and debate in our field, and one worth discussing.

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Mass extinctions capture the imaginations of layperson and scientist alike.  The most famous mass extinction is the most recent - the K/T extinction.

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The question of the origin of traits that are unique to a group of animals (or taxon) is often a topic of study for paleontologists, and biologists in general.

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Any technology that would allow us to peer inside skulls without damaging them would be a godsend.  Luckily we have that technology - CT scanning.

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