Hairy Museum of Natural History

About a week ago, the Geological Society of America announced the discovery of an unique trace fossil from the Mississippian-age Mauch Chunk Formation in eastern Pennsylvania, which preserved the impressions of three temnospondyl amphibians that laid in this Mississippian mud some 330-million years ago.

Photo credit: Spencer G. Lucas,
New Mexico Museum of Natural History and Science

Spencer G. Lucas (New Mexico Museum of Natural History and Science), David L. Fillmore and Edward L. Simpson (both from Kutztown University in northeastern Pennsylvania) presented this unique fossil at the 2007 GSA Annual Meeting. Spencer asked me to draw up a reconstruction showing the temnospondyls whose imprints were preserved in the fossil, which I took particular pride in, since I, too, happen to be a tetrapod from eastern Pennsylvania. My take on the temnospondyl trio is shown below:

My take on the temnospondyl trio. The impressions in the fossil slab are raised, so when you look at it you are
actually seeing the animals’ imprints from underneath; in this top-down view their positions are flipped horizontally.

This drawing was included in the press release but, due to a miscommunication, it was not initially credited. Oddly enough, I was back in northeast PA visiting family when the release went out, so I didn’t realize it until I returned to New Mexico yesterday. I’m happy to say that the oversight has since been corrected on the GSA page.

But beyond my personal stake in the story, the fossil really is quite spectacular. The imprints seem to show your standard temnospondyl four-fingered hand, and what looks like a crease of skin down the midline of their bellies, with no apparent sign of scales. As Lucas et al. note in their abstract, the fact that the three were preserved together indicates some sort of gregarious activity, and the tastefully phrased “head-to-tail overlap” shown in two of the impressions is reminiscent of the courtship behaviors of some modern amphibians.

—Matt Celeskey.

File under: Carboniferous, Recent Discoveries, Tetrapods.

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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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This stocky fellow is Diadectes (Die-uh-DECK-tees), a solid, six-foot-long sprawler known from 300,000,000+ year-old remains found in North America and Europe. From our modern perspective as highly-refined terrestrial tetrapods, he might look to be little more than a lizard with a weight-control problem. For his time, however, Diadectes was a trailblazer. His distinctive teeth mark him as a plant-eater, and he is in fact the earliest vertebrate known to be a dedicated herbivore. While all of our ancient ancestors were evolving better ways to eat each other, Diadectes discovered the pastoral pleasures of Permo-carboniferous vegetarianism.

Diadectes and its relatives (collectively known as diadectomorphs) have been classed as amphibians, reptiles, or some transitional form between the two. Current studies find the Diadectomorpha to be the sister group of the Amniotes—more closely related to us than to any amphibians, yet falling just outside the group that led to modern reptiles and mammals.

As usual, all manner of animals are on parade at this week’s Friday Ark over at The Modulator.

—Matt Celeskey.

File under: Carboniferous, Tetrapods.

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…according to an impressive fossil trackway reported from the Carboniferous of Scotland.

The ichnofossil, described in the latest issue of Nature, shows the trail left by a 5-foot long eurypterid (your-IP-ter-id) as it hauled its body over a 330,000,000 year-old beach. Eurypterids were aquatic relatives of scorpions that thrived during the Paleozoic Era. Eurypterids were some of the top predators of their time, growing to a length of 6 feet and sporting nightmarish claws, which were the likely end of many of our fishy ancestors. Fossils of eurypterid exoskeletons are known from marine and freshwater deposits, but it has long been uncertain whether they were able to leave the water and crawl ashore.

A menacing eurypterid provides the impetus for lobe-finned fish to crawl onto the nearest beach in this detail of a mural by Margie O’Brien at the New Mexico Museum of Natural History and Science. A trackway reported from Scotland shows that these large aquatic invertebrates were coming ashore around the same time.

Unlike the menacing predator shown here, the trackway was likely made by Hibbertopterus, one of a group of eurypterids that had comb-like paddles instead of pincers. These paddles would have been used as filters to trap small invertebrates and other tiny prey items, so it is doubtful that this particular trackmaker was chasing any early tetrapods ashore.

The 20-foot long trackway preserves traces of six of the animal’s limbs digging into the muck and pulling its heavy tail behind it. The Nature article presents a photo and diagram of the trackway along with a reconstruction of the trackmaker, and a larger photo of the tracksite can be seen at BBC News.

—Matt Celeskey.

File under: Carboniferous, Recent Discoveries.

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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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