Tag Archives: Fossil

Earliest signs of vertebrates’ ancestor?

Studies of DNA among living animals suggest that our own group, the vertebrates of the phylum Chordata, originated from a common ancestor that we share with echinoderms (sea urchins, star fish, sea cucumbers etc) and one of many worm-like phyla. This superphylum comprises the deuterostomes, but it is just one of several that encompass all animals and happens to be one of the smallest in terms of the number of living species that belong to it. We deuterostomes are vastly outnumbered by arthropods, nematodes, other worm-like creatures, molluscs, the rest of the animal kingdom and, of course, single-celled organisms, plants and fungi. Yet the DNA-based Circle of Life reveals that the deuterostome ancestral spoke originated early on in animal evolution.

The ‘Circle of Life’ as compiled by Cody Hinchliffe of the University of Michigan and 21 collaborators from the USA, and partly based on Fischetti, M. 2016. The circle of life. Scientific American, v. 314 (March 2016).

The ‘Circle of Life’ as compiled by Cody Hinchliffe of the University of Michigan and 21 collaborators from the USA, and partly based on Fischetti, M. 2016. The circle of life. Scientific American, v. 314 (March 2016).

The majority of animals of all kinds are blessed with a mouth separate from means of expelling waste products and can be divided into two similar halves, hence their name bilaterians. The earliest fossils judged to be of this kind date to about 580 to 600 Ma ago, in the Doushantuo Formation of southern China, all of them visible only using microscopes. A DNA-based molecular clock hints at around 900-1000 Ma for the emergence of all animal body plans known today. Now another important time marker has turned up, again in sediments showing exquisite fossil preservation from China (Han, J. et al. 2017. Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China). Nature, v. 542, (online); doi: 10.1038/nature21072). The Chinese-British team of palaeontologists has found tiny, bag-like fossils preserved in phosphate, which have a mouth surrounded by folds and conical openings on either side of the body. They lived in limy muds on the sea bed now preserved as limestones at the base of the Cambrian System (541 Ma) and probably had a habit akin to worms in the most general sense. The authors sifted through 3 tonnes of rock to recover the fossils, rather than relying on a lucky hammer stroke.

Reconstruction of Saccorhytus coronarius from the lowest Cambrian of Shaanxi, China. (credit: Han et al 1917)

Reconstruction of Saccorhytus coronarius (diameter about 1 mm) from the lowest Cambrian of Shaanxi, China. (credit: Han et al 1917)

Not especially prepossessing, the fossils are said to show more affinity to deuterostomes than anything else and to be the earliest known fossil examples. Yet the world’s media pounced on them as the ‘earliest known human ancestors’, which is a bit rich as they could equally be the earliest sea urchins or may have led to several odd-looking fossils known only from the later Cambrian. It isn’t possible to say with any certainty that they lie on the path that led to chordates and thus ourselves. Of course, that would not raise headlines in newspapers of record, such as Britain’ Daily Telegraph, on the BBC News website or Fox News.  The authors are much more honest, claiming only that the Saccorhytus coronarius fossils are probably deuterostomes whose affinities and later descendants are obscure. Their most important conclusion is that the cradle of our branch of animals lay in deep water muds laid down around the Precambrian-Cambrian boundary, ideal for subtly varied small, flabby creatures behaving like worms.  Many more varieties are likely remain to be found in similar rocks of the late Precambrian and slightly younger Cambrian when they are studied painstakingly in microscopic detail. A start has been made, that’s all.

For more on early evolution see here and here

Hunting down the Tully Monster

The word ‘monster’ has its origin in the Latin monere ‘to warn’ but has broadened out in its usage.  It has even reverted to its origins as a verb: a highly critical, verbal attack. But I prefer ‘something about which one needs to be warned’, and the Tully Monster encapsulates that meaning. It once lived in Illinois, specifically at just a single location, Mazon Creek, where thousands of them have been seen. But should you be especially fearful of Tullimonstrum gregarium? Well, at first sight, no; it’s only about 10 cm long and apparently has no proper bones and it’s dead. The first was spotted in a coal-mine waste heap by Francis Tully in 1958, a pipefitter with an interest in Carboniferous fossils. Two years after his death in 1987, he and his monster were honoured by a bill that the Illinois State Legislature passed to make it the official State Fossil.

Artist's impression of the Carboniferous Tully Monster (

Artist’s impression of the Carboniferous Tully Monster (Tullimonstrum gregarium) (credit: Sean McMahon, Yale University)

It seems to have become a ‘monster’ by stumping all previous attempts to categorise it; so much so that it long served as a warning to eager palaeontologists not to tangle with its taxonomy. That’s not surprising, because as well as bearing a passing resemblance to Captain Nemo’s submarine in Jules Verne’s 20 000 leagues Under the Sea, it has some truly astonishing features.  Portholes down its sides are not the weirdest – actually they are gill openings. It has a biting apparatus at the end of an absurdly lengthy forward protuberance, that would not be unexpected if it were one of those fish from the Amazon that, you know, men really ought to be warned about. Most of us would not share a bath with it if we had been. And then, there are the eyes on the ends of a dorsal bar which would give Tullimonstrum gregarium superb stereoscopic vision to guide it unerringly to its target, lashing its efficient-looking caudal fin. The fact that it has only a single nostril is merely puzzling by comparison.

Six decades on, Victoria McCoy of Yale University (now at Leicester University, UK) and 15 undeterred colleagues have pored over more than 1200 Tully Monster fossils and seem to have cracked its affinities (McCoy, V.E. et al. 2016. The ‘Tully monster’ is a vertebrate. Nature, v. 532, p. 496-499). In fact, it’s surprising that it has remained an enigma for so long, because McCoy and colleagues have documented almost every aspect of its anatomy, available from a huge number of superbly preserved specimens – teeth, fin, muscle traces, gills, nostril, notochord, gut and so on. As well as being a vertebrate, its dreadful proboscis is very like that of the Cambrian oddity Opabinia from the Burgess Shale. A  separate study by four British palaeontologists and a Texan concentrated on the eyes using electron microscopy and found ‘ultrastructural details’, including pigment cells (Clements, T. et al. 2016. The eyes of Tullimonstrum reveal a vertebrate affinity. Nature, v. 532, p. 500-503) which unequivocally confirm that it is a vertebrate. It has all the hallmarks of being related to lampreys and hagfishs. They devour rotting, drowned corpses.

Hallucigenia gets a head

The Middle Cambrian Burgess Shale of the Canadian Rockies is one of those celebrated sediments that show extraordinary preservation of soft-bodied and easily disarticulated organisms and rich assemblages of fossils. Being one of the earliest known of such lagerstätten, many of the denizens of the ecosystem in which the shale originated were at first regarded as members of hitherto undiscovered and now vanished phyla, the basal branches of the ‘tree of life’. Some certainly looked pretty odd, such as Opabina with a feeding apparatus looking similar to the extension nozzle of a vacuum cleaner; but that is clearly some kind of arthropod. Others turned out to be astonishingly large, once it was realised that parts of their broken bodies had previously been taken to be different organisms, an example being Anomalocaris. But perhaps the oddest, certainly to palaeontologists, was Hallucigenia. However, there are plenty of even more weird and wonderful living creatures, such as the sea pig, although modern creatures are more easily pigeonholed, taxonomically speaking.

Halucigenia as originally reconstruicted (i.e....

Hallucigenia as originally reconstructed; i.e. upside-down. (credit: Wikipedia)

The trouble with Hallucigenia was not so much its complexity – it was a fairly simple-looking beast – but that there were two choices as to which way up it lived; a feature that surprisingly led to a great deal of pondering that ended with the scientist who formally described it in 1977 making the wrong choice. That was eventually resolved fourteen years later, but the creature might also have inspired the Pushmi Pullyu in Hugh Lofting’s Dr Doolittle stories for children. Not that it resembled a unicorn-gazelle cross: far from it, for no-one could decide which its front was and which its backside, and even if it may have lain on its side. But Hallucigenia does demonstrate bilateral symmetry beautifully – it must have a front and back, and a top and bottom, even though which was which remained veiled in mystery – and so belongs to the dominant group of animals, imaginatively known as bilaterians.

The Burgess Shale lagerstätte seemingly was heaving with Hallucigenia so would-be taxonomists have had no shortage of specimens to ponder over in the 38 years since Simon Conway Morris made his dreadful mistake: of course, that was not of such enormity as Einstein’s ‘biggest blunder’ in the form of his cosmological constant, and Conway Morris quickly accepted his error when the beast was turned right-way-up in 1991. The problem is, exquisite as they are, Burgess Shale fossils are flattened and all that remains of mainly soft-bodied animals are delicate carbonaceous films, which need electron microscopy to unravel.

The latest reconstruction of Hallucigenia, by palaeontological illustrator Danielle Dufault (http://www.ddufault.com)

The latest reconstruction of Hallucigenia, by palaeontological illustrator Danielle Dufault

In 2015, Hallucigenia’s front end was definitely found and a great deal more besides by Canadian palaeontologists Martin Smith and Jean-Bernard Caron of the Royal Ontario Museum and the University of Toronto (Smith, M.R. & Caron J.-B. 2015. Hallucigenia’s head and the pharyngeal armature of early ecdysozoans. Nature, v. 523, p. 75-78). It has eyes, albeit rudimentary, and a throat, deep within which it has pointy teeth. Hallucigenia was a lobopod, whose living relatives lie within that large and diverse group the Ecdysozoa, which all have throat teeth and include the wondrous water bear (tardigrade) and the velvet- and penis worms (onychophores and priapulids, respectively) as well as lobsters, flies and woodlice. It may indeed have been close to the last common ancestor of all animals who moult their carapaces.