My top 10 palaeontological research picks of the year, and by far the most difficult listing to complete, because there was a ton of good research this year. Because of that, each item here has a different palaeontological theme, so the list is quite varied. Keep in mind that any arthropod palaeontology is in the arthropod listing. The master list has 62 paper. [OA] indicates open access papers.
The picture shows what this paper describes: coprolites, fossilised pieces of shit, from an ~415 Ma (Early Devonian) locality in Wales. While the study of coprolites is done mostly for the comedic and novelty value of holding million year old feces, it also brings a lot of insights into palaeoecology: match the coprolites to their producers, and you have a summary of what they ate, much like what is done with modern fecal analyses. These coprolites contain bits of nematophytes, an enigmatic group of organisms that are nowadays interpreted as fungi. No plant or animal parts were found, meaning these coprolites are the very first evidence we have of primary fungal feeding, and the producers are the first animals known to be exclusive fungal feeders. The most likely culprits, based on the size and structure of the feces, are millipedes, who nowadays are also fungivores.
For some more impressive palaeoecology, check out Surprisingly complex community discovered in the mid-Devonian fossil forest at Gilboa, which shows that the Gilboa forest, one of the earliest exceptionally-preserved forest ecosystems, is actually a highly-complex mixed forest wetland with a lot of disturbance, unlike the original depiction of it being a very simple ecosystem.
Problematic PR aside, Ida has become established as a great fossil with excellent preservation. As the old palaeontological saying goes, every fossil tells a story, and this paper showcases that. Look at the close-up of Ida’s hand above, and notice that the right hand has a giant bump. This isn’t a chemical concretion from its preservation, but actual bone, a callus caused by an obviously large injury – in this case, a broken wrist. In the paper, it all gets explained in a story-like manner. Pretty neat. The tl;dr version is that Ida was mucking around up in the trees, fell and broke her wrist. The injury is obviously very painful for a primate that spends her time in the trees, so she would have been spending an inordinate amount of time in the ground, where one day she inhaled the poisonous gas that was being burped out by the Messel lake, fainted and sank to the bottom where she was preserved along with all the other fauna of Messel. It’s convincing and plausible, it explains why primates are very rare in Messel – they wouldn’t be on the ground to be hit by toxic gas, while Ida was confined to there due to her injury. She has no bite marks, so it wasn’t a predator that got her. Although obviously anyone can come up with another story with the same set of facts.
The above ammonites come from a location in New Jersey directly overlying the K-T event iridium layer. In other words, they show ammonites that survived the K-T event for at least a little while. While the authors note there is still some stratigraphic work that needs to eb done to pinpoint the exact sequence of events, this is still pretty cool, and just goes to show that there is no such thing as an immediate extinction, not even in the geological sense.
The Miocene mammal Necrolestes demonstrates the survival of a Mesozoic nontherian lineage into the late Cenozoic of South America shows a similar situation, again with the K-T event, this time with a Mesozoic mammal – i.e. not a marsupial, placental, or monotreme, the three extant mammal groups – surviving over 40 million years after the extinction event. It’s not the first known, but it is the longest-surviving one.
This paper goes out to all those who think the fossil record is not a reliable source of information on evolution (yes, such scientists do exist, I have seen them). This paper basically compares extinction and speciation rate estimations from models, fossil record-informed models, and Recent organism only-informed models. Surprise, surprise: using the fossil record gives much better estimates. Maybe it has something to do with, you know, data.
Another paper that shows a great interaction between modelling and fossil data is Robust estimates of extinction time in the geological record, which presents a model for estimating extinction times.
Other papers from this year showing the utility of the fossil record for evolutionary biology include The maximum rate of mammal evolution, which uses a mammoth-sized dataset to set the basis for micro- and macroevolutionary studies in mammal body size evolution and factors affecting it; and Biodiversity tracks temperature over time, which shows that there is a positive relationship between temperature and biodiversity, a correlation that deserves macroevolutionary study.
Detractors of the use of the fossil record cite taphonomical or taxonomical biases – only some types of organisms get preserved, sometimes. While it would be silly to deny these biases exist, it would be even sillier to not quantify them so we know the realism of our data, and all palaeontologists know this: we acknowledge the problems with the fidelity of the fossil record. Case in point: Comparative quality and fidelity of deep-sea and land-based nannofossil records shows that the deep-sea nannofossil record really isn’t so reliable. And, as No gap in the Middle Permian record of terrestrial vertebrates shows with Olson’s Gap in Permian vertebrates, these studies also identify when a perceived fossil record gap is actually illusory.
One of the coolest advances in recent palaeontology has been the study of fossilised pigments in the feathers of the “feathered dinosaurs”. These pigments are identical in microstructure to those of modern birds, so by examining them, we can infer the colour of the feathers. In this case, the famous/iconic isolated Archaeopteryx feather is examined and found to have been black. The feather was a primary covert feather, i.e. a feather on the top layer, not the bottom one. This does not mean that Archaeopteryx was all black – this is just an individual feather, and birds are known to have different-coloured feathers, primarily for sexual communication.
The latest strike back in the whole Apex Chert microfossil debate, outlined here. This paper uses Raman spectroscopy and finds that they’re made of kerogen, a strong hint at a biological origin. Expect a riposte next year.
As I stress every time I discuss the Apex Chert, their biogenicity is actually irrelevant – we know that life already existed from biomarkers. Novel molecular fossils of bacteria: Insights into hydrothermal origin of life shows how such biomarkers form using a newly-discovered example.
That said, preservation of the bodies of unicellular organisms does occur, and this year saw several papers describing that: Remarkably preserved prokaryote and eukaryote microfossils within 1 Ga-old lake phosphates of the Torridon Group, NW Scotland; Fossilized bacteria in a Cretaceous pterosaur headcrest; Fossilized fungi in subseafloor Eocene basalts.
Experimental taphonomy of giant sulphur bacteria: implications for the interpretation of the embryo-like Ediacaran Doushantuo fossils shows one way in which we can confirm the biogenicity of an enigmatic fossil: experimental taphonomy, looking at how modern organisms fossilise in the lab and comparing with the rock structure.
Finally, since we’re on the subject of exceptional preservation of tiny organisms, check out Triassic leech cocoon from Antarctica contains fossil bell animal, where a vorticellid is preserved in the cocoon leech.
If you were getting used to Tiktaalik as the superawesome oldest transitional tetrapod, you might want to update to Tinirau clackae, described in this paper from a specimen in the late Middle Devonian of Nevada. It’s more basal than Tiktaalik and predates it by 5+ Ma – although keep in mind that we still need to find more basal tetrapods, since we have earlier trackways. The features of Tinirau also make it clear that there was considerable convergence happening, and also emphasises the mosaic pattern of early tetrapod evolution.
For another significant transitional vertebrate, A transitional snake from the Late Cretaceous period of North America fits the bill.
A New Rhynchocephalian from the Late Jurassic of Germany with a Dentition That Is Unique amongst Tetrapods [OA] and A New Eusuchian Crocodyliform with Novel Cranial Integument and Its Significance for the Origin and Evolution of Crocodylia [OA] are other important vertebrate findings.
The definitive description of Pikaia, one of the early chordates from the Burgess Shale. If there’s anything you want to know about it, from its morphology to its way of life to its position on the tree of life (note: it was not your n(great)-grandfather) to the history of thought on all of those, this is the paper you’re looking for. You can check out my post on Pikaia for the superdigest version.
This year’s been fairly good for the study of the Cambrian Radiation. Mechanism for Burgess Shale-type preservation [OA] describes how the exceptional preservation in the Burgess Shale and allied Cambrian localities occurred.
Significant new descriptions include: Evidence for gill slits and a pharynx in Cambrian vetulicolians: implications for the early evolution of deuterostomes [OA]; A New Stalked Filter-Feeder from the Middle Cambrian Burgess Shale, British Columbia, Canada [OA]; and Mouthparts of the Burgess Shale fossils Odontogriphus and Wiwaxia: implications for the ancestral molluscan radula.
Some advances on the ecological aspect were done. The biodiversity of Cambrian priapulids has been revised in The disparity of priapulid, archaeopriapulid and palaeoscolecid worms in the light of new data, and a new pripaulid assemblage from the Cambrian of China is described in A new priapulid assemblage from the early Cambrian Guanshan fossil Lagerstätte of SW China.
As for the pre-Cambrian history of animals, some advances have also been made on that front. On the one hand, A merciful death for the “earliest bilaterian,” Vernanimalcula shows how this supposed oldest bilaterian is actually nothing more than geological blah; on the other hand, Bilaterian Burrows and Grazing Behavior at >585 Million Years Ago describes decidedly advanced burrows that were likely produced by bilaterians, giving more evidence for the concept of the Cambrian Radiation being illusory.
This paper deals with the rangeomorph Ediacarans (see here) and constructs a standardised scheme under which all rangeomorphs can be studied. This is exactly what’s needed, since it allows direct comparisons of the weirdos, and also makes cladistic analyses that much easier to do.
Another significant paper on the Ediacaran period is Distinguishing geology from biology in the Ediacaran Doushantuo biota relaxes constraints on the timing of the origin of bilaterians, which analyses specimens from the famous Doushantuo locality, and identifies how to separate geological muck from actual fossilised remains, something that’s critical in Doushantuo because the potential fossils include embryos and even subcellular details.
Those who know me might be wondering if I got hit by lightning, putting idiot fish over the Cambrian and Ediacaran stuff I base my interests in palaeontology on. The reason why this gets top spot is simple: it’s an excellent example of how to infer behaviour from function, and function from morphology – and these are key goals in palaeontology. In the case of this one: you have this weird fish from the Middle Triassic of China, which you called Potanichthys (refer to (b) above). It has a big lobe at the front. You analyse it closer and realise it’s the pectoral fin that’s been grossly enlarged. Then you notice that the caudal fin (tail) is also pretty large. This is the same type of morphology seen in modern exocoetid fishes, also known as the flying fishes. They use the tail to generate a lot of thrust, and the large pectoral fin as a “wing” to maintain gliding. In other words, Potanichthys is a flying fish – not an exocoetid, this is a case of convergent evolution, and probably evolved for the same reason in both cases: evading predators. This paper gets top spot for being a good analysis from beginning to end, going from raw morphology through to phylogeny and finally to functional morphology and ecological implications.