A few weeks old, but worth noting: World’s oldest flying insect fossil. A beautiful resting trace from a Carboniferous insect that landed with its limbs sprawled out like a mayfly; found in Massachusetts by a geology student at Tufts University.

Moving back in time, Chris Nedin kicks off his new Ediacaran blog with a compelling Cambrian tale of how flexible trilobites avoided unlucky breaks in The Spandrels of San Marco and the Anomalocaris Paradigm.

Speaking of the Cambrian, scientists are furthering their insight into the exceptional preservation of the famous Burgess Shale fossils, according to this article.

And  The Life of Madygen provides a brief introduction to the Triassic titanopterans, an extinct group of insects, related to grasshoppers and crickets, but with wingspans reaching half-a-meter across!

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.

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:

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.

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.

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.

The Dissorophids were more fully committed to a terrestrial lifestyle than most other temnospondyls. They developed a series of overlapping bony plates that covered their spinal column, which added strength to their backbones as they clambered across the Paleozoic landscape, and helped protect them from larger predators. Based on this feature, some workers have informally referred to the group as “armadillo toads.”

Big-headed Cacops is one of the best known dissorophids, but the showiest was undoubtedly Platyhystrix, shown here running from the varanopseid pelycosaur Ruthiromia. Platyhystrix (whose name means “flat porcupine”) had a sail along its back supported by dramatically curved and textured extensions of its vertebrae, and in lieu of bony plates along its back it had roughened bony armor stuck to its ribs. While this might not have been sufficient protection from the largest predators of the Permocarboniferous, it doubtless allowed Platyhystrix to cut quite a profile as it strutted through the swamps.

Dissorophids like Cacops and Platyhystrix went extinct at the end of the Permian, but they may have spawned a legacy more successful than any of their temnospondyl kin. Some researchers think that all modern amphibians—frogs, toads, salamanders, and the wormlike caecilians—can trace their ancestry back to these “armadillo toads.” Other scientists disagree, and conclude that temnospondyls ultimately left no descendants that are alive today. Whatever the case, temnospondyls were a particuarly successful group of early terrestrial vertebrates whose lineage stretched from the Early Carboniferous to at least the Middle Cretaceous—350 million to 100 million years ago. Few other vertebrate groups can claim such longevity or tenacity.

This image was based on two different types of tracks found in Permian sediments in southern New Mexico. A small temnospondyl leaving behind Limnopus tracks confronts a scorpion, who has made a series of Permichnium traces. This specific confrontation is not based on a particular trackway, although some paleoichnologists (scientists who study fossil footprints) have suggested that fine-grained rocks from the Permian of New Mexico show evidence of predatory interactions between vertebrates and invertebrates. The direct evidence for such confrontations is equivocal. But it seems certain that scenarios like this would have taken place along sandy shorelines towards the end of the Paleozoic, whenever two such disparate trackmakers scuffled over a few square feet of beachfront property.

I am, of course, exaggerating. Temnospondyls were subjected to the same forces of modification and selection that shaped every other animal lineage, and throughout their long dynasty they did undertake some noteworthy evolutionary experiments. But they are unusual in that they retained the complex, multi-part vertebrae and intricately folded teeth that most other backboned animals modified shortly after making the transition from surf to turf. And looking at the flat, toothy, textured skull of a temnospondyl, one gets the impression that instead of wasting their time adapting to their environment, they had decided to hunker down and force their environment to deal with them.

Eryops, shown here lunging after a xenacanth shark, exemplifies the niche that temnospondyls returned to time and time again—that of the “crocamander” or “frogodile”. Long before the first alligators swam through any prehistoric bayou, Eryops and its kin were cruising the Carboniferous waterways. One hundred million years later, when dinosaurs first appeared, a group of temnospondyls called metoposaurs were still prowling the swamps, snapping at prey with heads so broad and flat that they resembled sharp-toothed toilet seats. And one hundred million years after that, when true crocodiles had muscled in on their territory in most of the world, the last of the”crocamanders” were still hunting in the relatively isolated waters of Australia.

Eryops is typically pictured as a squat, fat beast with a large, frog-like head and a somewhat insipid grin. This is probably not entirely inaccurate. However, restorations such as these fail to show the dozens of sharp, recurved teeth that line the edges of its mouth, or the extremely nasty-looking fangs that projected from its palate (a trait shared by all tempnospondyls). This portrait of Eryops, inspired by a skull collected from the Permocarboniferous of New Mexico, was drawn with those features in mind.

More temnospondyls to come…

At the dawn of the Carboniferous period, around 350,000,000 years ago, great changes were taking place in the waters of the world. Many once-diverse and successful groups of fish hadn’t made it past the end of the previous period (the Devonian), so a plethora of aquatic opportunities had just become available for the fish that were fortunate enough to survive.

One of these fortunate groups were the sharks and their relatives, collectively known as chondrichthyans or “cartilaginous fish” for their most distinctive feature, a skeleton made largely of cartilage. Chondricthyans exploded into a fantastic diversity of forms during the Carboniferous, many of them odd and bizarre. Some developed tooth-rows like buzzsaw blades or pinking-shears, some grew winglike fins from the sides of their necks, some evolved long, antler-like pincers on their snouts, and some developed large clusters of spines atop their heads and over their dorsal fins. This last group is known as the stethacanthids, or spiny-brush sharks.

Stethacanthus (shown here in purple) is the most-familar of the group, and the most commonly illustrated. Its strange, wedge-shaped dorsal fin topped with dozens of sharp denticles must have cut quite a profile in the Carboniferous seas. Several suggestions have been made about the purpose of this unusual feature. Some have suggested that, from above, the two patches of tooth-like denticles on its fin and head might have appeared to be the gaping maw of a much larger shark. Others have thought that it might have served as a sort of velcro attachment point, allowing Stethacanthus to hitch a ride on larger fish, as remora do with sharks today. Unfortunately for these hypotheses, the spiny-brush of Stethacanthus and the closely-related Akmonistion (at left) were not particularly flexible and probably wouldn’t be of much use in those suggested situations.

One clue comes from the fact that all known stethacanthid specimens that bear the spiny-brush are male (this is easy to tell in most sharks, because males have prominent claspers behind their pelvic fins). Clasper-less (female) stethacanthid specimens are known, but none have been found with the dorsal spiny-brush. Some researchers have classified them as different animals, but it seems just as likely that they are female Stethacanthus or Akmonistion. Fossils of close stethacanthid relatives named Falcatus and Damocles support this idea.

Falcatus (“hook/sickle”) and Damocles (named after the king with a sword hanging over his head) have even more extensively-modified dorsal fins that curve forward over their heads like prongs, with the spiny denticles forming barbs near the tip. A spectacular fossil of two Falcatus from the Bear Gulch Limestones of Montana preserves a prongless, clasperless female was preserved biting the prong of a claspered (and presumably excited) male in what appears to be Paleozoic foreplay. The drawing shown here depicts a Damocles couple in a similar romantic moment.

Because the prongs of Falcatus and Damocles are modified versions of the same spiny-brush that adorns Stethacanthus and Akmonistion, it seems probable that all these sharks used their fins for similar purposes—as distinctive structures that males could use to advertise their prowess, and where females could focus some toothy affection during courtship and mating.

This artwork was used in PowerSharks!, “the Fintastic game for card sharks everywhere” developed by Ray Troll and myself.