Hairy Museum of Natural History

Deep in southern New Mexico, not far from the city of Las Cruces, lie the Robledo Mountains. Tectonic activity along the Rio Grande Rift pushed up the Robledos during the past 30 million years, but the rocks that make up the mountains are about ten times older. In fact, just about 290 million years ago the most famous rocks of the Robledos were being created as layers of fine-grained mud collected near the shores of an Early Permian sea.

This Permian mud was of a perfect consistency to preserve the imprint of anything that touched its surface—the sharp-clawed tracks of a passing Dimetrodon, ropelike branches fallen from Walchia conifers, impact craters from raindrops—even the footfalls of tiny insects left their marks in the surface. As the mud was buried and hardened into rock, the imprints were preserved within the sandstones and siltstones that today make up the Robledo Mountains. The abundance, diversity, and quality of tracks provide a unique look into an Early Permian ecosystem. And the scientific importance of the site has inspired a grassroots movement campaigning for a Prehistoric Trackways National Monument in the Robledos.

A paper in the latest issue of Palaeontology is a great example of the sort of information coming out of the Robledo Mountains. Nicholas Minter and Simon Braddy describe walking and jumping trackways made by an extinct group of insects and compare their locomotor reportoire to those of their living relatives.

The holotype and paratypes of Tonganoxichnus robledoensis.
Photograph and interpretive line drawing of the trackways.
Scale bar=10mm. This and all subsequent figures from Minter and Braddy 2006.
© Copyright The Palaeontological Association. Reproduced with permission.

The photo and diagram above show the type specimens of the ichnospecies Tonganoxichnus robledoensis. It preserves the imprints made by two small insects as they jumped across the mud, one on the left and one on the right. The trackmakers were travelling from bottom to top in this view, with imprints of legs towards the front and a long abdomen and “tail” trailing behind.

The Paleozoic monuran Dasyleptus.
scale=1mm. From Minter and Braddy 2006.
© The Palaeontological Association

The shape of the tracks is suggests that the trackmaker belonged to a group of insects known as the Archaeognatha, which have simple legs ending in points, long abdomens, and long terminal filaments (“tails”). There are jumping archaeognathans living today called “bristletails” because they possess lateral cerci that give their “tail” a three-pronged appearance. But the Tonganoxichnus tracks show no signs of a bristly tail, and were probably made by an extinct group of archaeognathans called monurans (“one tail”) for what I suspect is an obvious reason.

Trackway of a monuran walking,
then jumping, then walking again.
From Minter and Braddy 2006.
© The Palaeontological Association

Minter and Braddy examined 23 sets of Tonganoxichnus robledoensis trackways and found that the Robledo monurans could travel by means of successive, forward-facing jumps several times their body length. Subtle details in the tracks showed that some of the monurans were pushing off more with their legs, while in others a flexing of the abdomen provided the main propulsive force. There were even a few tracks that suggested the jumper was using both its legs and abdomen to propel itself forward.

A living archaognathan, the bristletail Petrobius brevistylis, has a similar proclivity for jumping, but with a few distinct differences. Petrobius normally progresses by successive, leg-propelled hops about one body-length in distance. But when confronted with a predator, Petrobius switches to a series of confusing, abdomen-propelled jumps that carry it much further, but in an essentially random direction (none of the Tonganoxichnus robledoensis trackways showed any evidence of random jumping).

Petrobius occasionally walks, but only when travelling on the underside of rocks where hopping is problematic. Trackway evidence indicates that the Robledo monurans walked somewhat more regularly. Minter and Braddy note that five specimens of insect-walking trackways (referred to the ichnospecies Stiaria intermedia) either end in a Tonganoxichnus-style jumping trace or begin with a similar landing imprint. One specimen (shown here, travelling from bottom to top) shows where a monuran was walking, jumped a few body-lengths forward, landed on its abdomen, then resumed its stroll. The authors note that similar walking trackways (uninterrupted by jumping traces) are relatively common elements of the Robledo tracksites, suggesting that walking played a greater role in monuran locomotion than it does in their distant, modern relatives.

Minter, N. J. and Braddy, S. J. 2006. Walking and jumping with Paleozoic apterygote insects. Palaeontology 49: 4, 827–835.

Thanks to the Palaeontological Association for granting permission to reproduce figures from the article, and to Nicholas Minter for bringing greater attention to these nifty little tracks. Tip of the toupee to Allan Lerner for sending a copy of the paper my way.

—Matt Celeskey.

File under: Permian, Recent Discoveries.

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or, Stratigraphic Tales from the Gadsden Purchase
Well, its been a couple of weeks since anything new has popped up at the old HMNH, and I figure its about time I did something to rectify that. A fair amount of stuff has been happened through the month of March, and I’m hoping to get a few posts out in the next week or so to review it all.

First on the list was a little field trip that I took during the middle of the month. For five days I was out poking about some Pennsylvanian strata in the southwestern corner of New Mexico (in what state residents call “the bootheel”) tagging along with a stratigraphic research team led by NMMNH&S curator Dr. Spencer Lucas.

Here’s where we were working, a nice 1500-foot pile of more-or-less neatly stacked Late Paleozoic strata called New Well Peak. This photo was taken from our campsite at the “new” well, which had long since run dry. But the layers of limestone that made up the peak told a tale of when this now-arid parcel of the Gadsden Purchase lay at the bottom of the sea.

Climbing through the strata we came across bits of crinoids, brachiopods, coral, and sponges. We looked for rocks bearing fusilinids, protozoans that lived on the ancient sea bottoms whose fossils are helpful in determining the age of the rocks. The largest of these looked like petrified grains of rice; the smallest were barely visible. This photo shows some of the larger ones we found:

Two members of the team were looking for conodonts as well, or to be more accurate, were looking for rocks that they might be able to find conodont fossils in. Conodonts are known almost exclusively from microscopic teeth, which make them difficult to find in the field. So they collected bags of rocks from outcrops that looked promising, which will go back to laboratories where the fossils could be chemically teased from the rocks and identified under high-powered microscopes. Although it seems like a lot of work for tiny fossils, conodont tooth morphology changed over time, which makes them useful as markers for different time periods. And when enlarged, they are beautiful little sculptures in their own right.

So, between rock samples, conodont samples, and fusilinids, we each carried a heavy load of rocks off the mountain each day. It was an awfully quick way to realize just how out of shape I’ve gotten since my last field outing, but the fresh air, conversation, and stunning scenery made the stiff shoulders and sore feet well worth it.

By the end of the last day, the excellent meal prepared by Chet, the camp cook, is far more interesting than another typical New Mexico sunset.

I didn’t sketch too much on this trip, but I did get one little watercolor of New Well Peak done:

—Matt Celeskey.

File under: Carboniferous, Permian, The Day Job.

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The New Mexico Museum of Natural History & Science has just released several additions to its scientific bulletin series, including two that were assembled for the Nonmarine Permian Symposium. Bulletin 30 (The Nonmarine Permian) is the symposium volume, chock full of papers from paleontologists, paleobotanists, geologists, and other researchers from around the world.

But I really want to promote Bulletin 31, The Permian of Central New Mexico. As you might guess, this is a smaller, more focused collection of papers, and it reviews the current state of research in New Mexico Permian localities that are still producing fossils after a century of exploration and collecting. Several of the pen-and-ink drawings displayed in our Dispatch from the Permocarboniferous posts are published in this volume, including a nice toothy Eryops on the front cover (the skull that inspired the image is described inside).

The bulletins can be purchased online here. Longtime HMNH visitors might recognize the artwork on the covers of Bulletins 29 and 30.

—Matt Celeskey.

File under: Permian, The Day Job.

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Still digesting all the info presented over the past week at the Nonmarine Permian Symposium hosted by the New Mexico Museum of Natural History and Science. Luckily, I was able to take a few days away from my regular work in the museum’s Exhibits Department to attend talks by a cosmopolitan collection of researchers and join in the field trips to some of the gorgeous Permian red beds exposed around New Mexico.

All told, it painted a dynamic picture of the world between 300 and 250 million years ago, when the continents were coalescing into the supercontinent of Pangea, when the coal forests of the earlier Carboniferous period were losing ground to conifers and other plants more tolerant of drier climates, and when vertebrates began fine-tuning their adaptations to terrestrial life, diversifying into a riot of forms and leaving bones, footprints, and other traces in red rocks around the world.

Many of the illustrations shown in the HMNH’s Dispatch from the Permocarboniferous series were published in a symposium volume on “The Permian of Central New Mexico,” and all participants got a stylish, Permian Blue Bustin’ up Sphenacodonts T-shirt in honor of the occasion.

This weekend’s Albuquerque Tribune has a good article on the Symposium with additional background (and this illustration in the print version).

—Matt Celeskey.

File under: Permian, The Day Job.

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A Paleozoic moon rises, hanging full and swollen on the horizon. Three hundred-million years ago the moon is closer, and its pull is stronger. At some distant ocean’s shore the tides rise high and horsehoe crabs clamber up onto the beach to spawn, drawn by the moon into a dance that they will continue, year after year, to the present day.

Farther inland, the moon climbs above a tropical forest of tree-sized horsetails and a different dance commences. Antennae probe the thick, humid air and the moonlight glints across multi-faceted eyes. Rivers of roughened cuticle eight feet long flow up from the frond litter and across the forest floor, and the air is filled with rustling as they snake around the gritty trunks of the horsetail jungle.

One by one, giant centipede-like forms emerge from the forest along the edge of an ancient lake. Their pace slows as they crawl across the lakeshore mud, but their stride never falters. Dozens of stout, spiny legs undulate in absolute precision, propelling the animals across the beach towards moonlit rendezvous. Their dance, unlike that of the horseshoe crabs, will falter after a few million years. The world will change, and their unparalleled invertebrate stature will prove impossible to maintain.

Year after year, the number of Arthropleura on the beach will diminish. None will remain at the close of the Carboniferous, but in certain places, the footsteps of their dance will be preserved.

—Matt Celeskey.

File under: Carboniferous, Permian.

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