Should Scientists Reconsider the Romer’s Gap? Paleontologist Thinks So, After 3D Scanning Reveals Ancient Tetrapod Fossil Inside a Rock

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Professor Jenny Clack

Professor Jenny Clack

Most humans enjoy something that is of great importance to our place in the natural history of the world, but that you likely don’t even think about much, unless you’re trying to pick something up, play the piano, or give someone a celebratory high five. I’m talking, of course, about five fingers on each hand. From an evolutionary standpoint, the fact that most humans are born with ten fully-functioning digits is a big deal. Backbones, hinged jaws, a set of lungs, and four limbs are all important parts of the evolutionary development of tetrapods, which in Greek literally means ‘four-footed.’ Amphibians, reptiles, birds, and mammals are all tetrapods. Jenny Clack, Emeritus Professor at the University of Cambridge and a renowned paleontologist, recently worked on a multi-authored scientific paper about five new tetrapod fossils, one of which was only discovered through 3D scanning and printing.


From the paper: a, Still from a micro-CT scan of the block containing most of the specimen. b, Interpretive drawing of the right side of the skull and palate. c, Stills from a micro-CT scan of the right lower jaw in dorsal view (upper image) and mesial view (lower image). d, Still from a micro-CT scan of the right palate in approximately ventrolateral view. In c and d note the sutures between pterygoid and marginal palatal bones, and the lower jaw bones, are tightly sutured and difficult to see in the scan. e, Still from a micro-CT scan of the entire specimen in the main block. Arrows point to elements in g. f, Enlargement of the ilium in lateral (left image) and medial (right image) views. g, Elements of the hind limb. Scale bars in a–e,g, 10 mm; scale bar in f, 5 mm. Mar Meck fen, margin of Meckelian fenestra; Sym, symphysis; Septomax, septomaxilla.

This fossil, christened “Tiny,” or Aytonerpeton microps, is encased in a chunk of black rock: no one has actually seen the fossil itself. Found in the Scottish borders, Tiny is incredibly rare – she (Guardian writer Elsa Panciroli decided Tiny was female, though scientists don’t actually know) comes from a time in the ‘rock record’ that has traditionally not produced many fossils, called the Romer’s Gap. It was in the Tournaisian period, roughly 345 million years ago, and comes right after the Devonian area, sometimes called the “age of fish.” The paper describes the etymology of Tiny’s name:

“Genus name from Ayton, the parish in the Scottish Borders from which the specimen came, and erpeton (Greek) ‘crawler’ or ‘creeping one’. Species from micro (Greek) ‘small’ and ops (Greek) ‘face’.”

Tetrapod environment, roughly 345 million years ago

Tetrapod environment, roughly 345 million years ago [Image: Mark Witton/National Museums Scotland via The Guardian]

The enigma of the Romer’s Gap “obscures the development of the first animals to live on land.” No one knows what caused the gap – it could have been low oxygen, or mass extinction. But Professor Clack’s discovery of Tiny, and the other Tournaisian fossils, suggests that scientists just may not have been looking hard enough, and that the gap may not exist at all.

“It does appear that if there had been a ‘gap’ it was much smaller than previously thought, and might have affected some groups less severely than others. There was an extinction event for many fish species, but no-one is really sure what caused it,” said Professor Clack.

Early Scottish tetrapod

Early Scottish tetrapod [Photo: Elsa Panciroli/National Museums Scotland via The Guardian]

Professor Clack has spent her life researching tetrapod fossils studying what often referred to as the “fish to tetrapod transition” of the first vertebrates to take to the land. In the 1980s, she recovered some fossils in Greenland, which showed signs of going through this transition of fins to limbs. Limbs allowed our ancient ancestors to push through the swamps they inhabited. Many tetrapods had over five digits on each limb, even up to eight. Professor Clack explained that “as limbs with digits evolved from fins, there must have been experimental forms, and the genetic regulation was less precise, allowing variability.”

national-museum-of-scotland-logoShe is on the research staff of the TW:eed project (Tetrapod World: early evolution and diversification), which includes researchers from the National Museum of Scotland (which has had some of its artifacts 3D scanned), the British Geological Survey, and the Universities of Leicester, Cambridge, and Southampton. They are focused on the rocks found in Southern Scotland, from the Romer’s Gap.

TW:eed researchers have painstakingly bored and logged two cores through hundreds of meters of solid rock from the Tournaisian period. They’ve uncovered evidence in the rock cores that fires burned during the period, which challenges theories that extinctions at the time were caused by low atmospheric oxygen. In addition to Tiny, Professor Clack and her colleagues have officially named five new species.

A chunky 3D printed plastic model of Tiny, which could fit in the palm of your hand, sits on the desk of Dr. Nick Fraser, Keeper of Natural Sciences at the National Museum of Scotland.

Dr. Fraser said, “We didn’t really know it was in the small piece of rock that we collected until it was CT scanned. We were quite surprised to find Tiny hiding in the sediment – we still only know it from the 3D scan and the 3D print and so haven’t had the pleasure of seeing the actual fossil!”


Tiny is encased in the black rock; the white material is the 3D print of Tiny [Photo: Elsa Panciroli/National Museums Scotland via The Guardian]

Micro CT-scanning means that they don’t need to break open the rock to see Tiny, but can instead digitally reconstruct the tiny, toothed fossil. 3D printing allowed scientists to hold a copy of Tiny and get a closer look: the features of the fossil have been enlarged, so you can actually tell what it looks like.

“We estimate that Tiny had a skull that was about five centimetres long. In other words pretty tiny, and certainly so when compared with some of the other tetrapods we’ve been finding,” said Dr. Fraser.

He said that while they “can’t be sure about the number of digits as it is somewhat disarticulated,” what’s left of Tiny’s toes hints that she may indeed have had five digits. Below is a video supplemental to the research paper showing an Aytonerpeton whole specimen:

Without 3D scanning and printing, researchers may never have discovered Tiny. Fossils like Tiny are extremely important – they help us learn about the “diversity of life on Earth over 345 million years ago,” and that the Romer’s Gap might be nothing more than an incorrect theory. Could it be possible that scientists need to change their view of the ancient fossil record? Professor Clack certainly thinks so, and says that Scotland has “by far the richest assemblages of fossil tetrapods from the Tournaisian anywhere in the world,” though researchers should continue to look elsewhere for these fossils as well.

“No-one bothered to look at the right rocks previously,” said Professor Clack. “Because they don’t yield commercially exploitable resources these rocks did not have a history of accidental finds. So because no-one had ever found anything, no-one ever looked, and they were considered barren. It was a vicious cycle.”

christmas-tetrapodI happened upon the TW:eed Project’s blog, Tetrapod World, which explains more in-depth about their tetrapod research. I found this image there of a tetrapod in a Santa hat, and it has nothing to do with anything, except that it makes me laugh, and further reinforces my feelings that fossils truly rock. Discuss in the Tetrapod Fossil forum at 3DPB.com.

[Source/Images: The Guardian]


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