More Amazing Fossils in China Raise Questions
There was the Jehol biota (Cretaceous), with its “feathered dinosaurs,” but now the “prequel” Daohugou biota (Jurassic) is opening eyes wide again.
It’s being called Daohugou: the prequel to the exciting Jehol fossil beds in China – only in this case, the prequel “outshines the original,” Science Daily says. A new open-access paper in the Journal of Vertebrate Paleontology brings together the latest findings for paleontologists around the world to wow at. Here’s what one of them said:
Dr. Paul Barrett, dinosaur researcher at the Natural History Museum, London, who was not involved with the study, commented, “Daohugou is proving to be one of the key sites for understanding the evolution of feathered dinosaurs, early mammals, and flying reptiles, due largely to the fantastic levels of preservation. Many of the fossils are stunning and offer vast amounts of information. There are only a handful of similar sites elsewhere in the world and this article represents the first comprehensive attempt to draw all of the relevant information together into a single benchmark paper.”
The formations in Inner Mongolia are said to be 160 million years old, 30 million years older than the Jehol strata (just across the border of the western Liaoning Province) where exceptionally-preserved fossils of dinosaurs, birds and other creatures have been unearthed over the past two decades. Named after a village in the area, the Daohugou formation contains beautifully-preserved fossils of amphibians, mammals, and reptiles. Science Daily begins with a fossil amphibian replete with soft-tissue impressions of the skin.
The Daohugou Biota makes an immense contribution to our understanding of vertebrate evolution during this period, with such notable creatures as the oldest known gliding mammal, another early mammal that may have swum with a beaver-like tail, the oldest dinosaurs preserved with feathers, and a pterosaur that represents an important transitional form between two major groups. As described by Dr. Corwin Sullivan, lead author of the study, “The Daohugou Biota gives us a look at a rarely glimpsed side of the Middle to Late Jurassic — not a parade of galumphing giants, but an assemblage of quirky little creatures like feathered dinosaurs, pterosaurs with ‘advanced’ heads on ‘primitive’ bodies, and the Mesozoic equivalent of a flying squirrel.”
Dinosaurs or Birds: The alleged “feathered dinosaur” is named Epidexipteryx (see critique of “feathered dinosaur” claim for this fossil, 10/22/08). Live Science speaks of “feathered dinosaurs” (plural), and shows artwork of a landscape with feathered dinosaurs, but did not mention any species by name. Instead, Tanya Lewis’s headline reads authoritatively, “Chinese Jurassic Park Yields Incredible Feathered Dino Find.” Further down, this statement is made:
The fossil trove dates from the Middle-Upper Jurassic, a period when birds are thought to have evolved from feathered dinosaurs. The team found feathered dinosaurs that were extremely birdlike, thought not any actual birds.
At the moment when birds and dinosaurs split from each other, as expected, “you can barely tell them apart,” [David] Hone [Queen Mary College of London, a co-author of the paper] said.
Does the paper mention additional “feathered dinosaurs” beyond Epidexipteryx? “At present, 30 vertebrate taxa (five salamanders, one anuran, two lizards, 13 pterosaurs, five dinosaurs, and four mammals) are known from the Daohugou Biota,” the abstract states, adding, “In general, the vertebrate fauna of the Daohugou Biota is strikingly different from that of the Jehol Biota, although paravian dinosaurs, anurognathid pterosaurs, and salamanders with cryptobranchid and hynobiid affinities occur in both.” What do they mean by feathers, incidentally? The paper explains, “the term ‘feather’ is used to refer to any filamentous or ribbon-like integumentary structure in a theropod, because the homology of such structures with the feathers of modern birds is well established (Prum and Brush, 2002) – well established, that is, among evolutionists who believe birds evolved from theropod dinosaurs. Later in the paper, they refute Feduccia’s critique of bird evolution, but in all fairness he should be allowed a response.
Their list of “feathered dinosaurs” does not include any new species. Instead, they include Anchiornis huxleyii (see 10/01/09), Xiaotingia zhengi (one fossil, bought from a dealer—see 7/28/11), Epidendrosaurus (no feathers, but thought to be similar to Epidexipteryx), Epidexipteryx hui (one specimen, mentioned earlier), and Pedopenna (one specimen, feathered on the feet, 10/01/09). In short: nothing new. The paper just catalogs earlier finds from the Daohugou area, most of which are known by one specimen, some of doubtful provenance. Four are notable for feathers on the feet, not on the forelimbs. The authors cannot establish that any of them were flyers; one or more might have been gliders, but that is not clear. They also are not certain whether the feathers (or integumentary structures) were used for display, thermoregulation, or transportation. Also of interest, the authors mention integumentary structures in some pterosaurs and some ornithischian dinosaurs, not believed to be ancestral to birds. The authors speculate that “the presence of feathers was the primitive condition in Ornithodira,” the presumed ancestor of all three groups. Their spotty appearance seems to demand convergent evolution or divergent loss:
However, the integumentary filaments of ornithischians, pterosaurs, and theropods are not uniform in detailed structure. Those currently known in ornithischians are particularly stiff and very long, whereas the pycnofibers of pterosaurs are distinctive in tending to be wavy (X.-L. Wang et al., 2002). Furthermore, the only theropods known to have feathers fall within the clade Tetanurae (Rauhut et al., 2012), and tetanurans, pterosaurs, heterodontosaurids, and ceratopsians are all remote from one another phylogenetically. Although it is possible that integumentary filaments are indeed primitive for Ornithodira (Rauhut et al., 2012), the phylogenetic distance and differences in detailed filament morphology that exist among the various ‘feathered’ ornithodiran taxa suggest that acceptance of this hypothesis is currently premature.
Mammals: An artist’s rendition of the “flying squirrel” is shown as #5 in Live Science‘s photo gallery, and the swimmer, looking like an otter with a beaver’s tail, is #6. Surprisingly, the caption says that “Mammals may have soared before birds.” Four mammals are mentioned in the paper, all known by single partial skeletons: the beaver-like swimmer Castorocauda; the flying mammal Volaticotherium remarkable for skin and hair impressions; Pseudotribos, an example of convergent tooth evolution(see 10/31/07); and the oldest-known placental mammal Juramaia: “Remarkably for a Jurassic mammal, Juramaia has many features that identify it as a eutherian, a member of the stem-based clade that includes modern placentals but not marsupials.” Volaticotherium “extends the earliest record of gliding flight for mammals to at least 70 million years earlier in geological history” – a “conservative estimate,” the authors note, probably as much as 108 million years before the next occurrence in the fossil record.
Dating
On the basis of index fossils, the authors claim that the Daohugou formation is separated by 30 million years from the Jehol, but it “occupied the same geographic region and was preserved in fine-grained lacustrine deposits similar to those seen at typical Jehol localities.” It seems a stretch to make that distinction on the basis of 30 specimens. If Jehol-type fossils are discovered in the Daohugou, it would falsify the distinction. The authors’ claim for radiometric support seems ambiguous, if not contradictory:
The village of Daohugou contains fossil-bearing clastic strata (Fig. 3A, B) that directly overlie the Precambrian basement (X.-L. Wang et al., 2005a; Y.-Q. Liu et al., 2006:fig. 2I-II; Y.-X. Liu et al., 2006:fig. 1I-II) and are thought to be of lacustrine origin (H.-Y. He et al., 2004; Gao and Ren, 2006). In turn, they appear to be directly overlain by volcanic rocks belonging to the Tiaojishan Formation (X.-L. Wang et al., 2005a; Y.-Q. Liu et al., 2006, Y.-X. Liu et al., 2006). However, some authors (H.-Y. He et al., 2004; X.-L. Wang et al., 2005a) have suggested that the stratigraphic sequence at the Daohugou locality is inverted in such a way that the volcanic layer is older than the Daohugou strata. The point is significant partly because it determines whether radiometric dates that have been obtained from the volcanic layer should be regarded as an upper or lower bound on the age of the Daohugou Biota (at least as represented at the Daohugou locality itself).
This raises questions about why there should be a gap of hundreds of millions of years above the Precambrian, how the stratigraphic sequence could have become inverted, and how delicate fossils were preserved for tens of millions of years in a volcanic region. It also casts doubt on the validity of the assumed age of the fossil-bearing strata, since radiometric dating can only be done on igneous rocks, e.g., the lava. When they cannot tell if it is an upper bound or a lower bound, all bets are off. Later in the paper, it is apparent they picked radiometric dates they considered valid, ignored others, and had to interpret the dates they kept, because results from different teams conflicted. “Although radiometric dating helps to establish the numerical age of the Daohugou strata, the potential of this technique to indicate their correlative relationships on a regional scale is limited by the dating studies that have been carried out for other rock units,” they say.
Puzzles
One puzzle is why such exquisite preservation would persist in this region for tens of millions of years. Since this quality of Lagerstätte is rare in the world, why would conditions in this location ensue for so long, especially with volcanoes around? It would seem that only rare circumstances would preserve skin and feather impressions so well, but the authors say, “lacustrine [lake] shale layers in both rock units are capable of preserving vertebrate specimens with great fidelity, so that it is often possible to recover articulated skeletons retaining significant traces of soft tissue.” Why would lake conditions allow this in Inner Mongolia for at least 30 million years? Why would delicate impressions last for 160 million years?
Another puzzle is the “early occurences of taxa.” Animals appear much earlier than thought. For instance, “all five of the Daohugou Biota salamanders fall within Urodela, the salamander crown group,” yet they are clearly salamanders, not primitive pre-salamanders. Similarly, all the pterosaurs are already flyers, even though they are probably the earliest ever found. In regard to the mammals, their ecological diversity has overturned previous evolutionary beliefs. “Mesozoic mammaliaforms were long regarded as uniformly small and insectivorous, but recent discoveries such as that of the meter-long carnivorous eutriconodontan Repenomamus giganticus from the Yixian Formation (Y.-M. Hu et al., 2005) have done much to change this picture.” In the Daohugou as well as at Jehol, “Late Jurassic mammaliaform faunas also displayed considerable ecological diversity.” This diversity was global. Digging mammals are known from Wyoming, and a platypus-like mammal from Portugal in strata from this period.
Additional puzzles are discussed in the paper, such as how best to organize formations into a time sequence, whether separate formations are part of the same formation, why certain animals appear in some places and not others, and more. A few more species are described in a “note added in proof,” including a tadpole that was reclassified as a cicada-like insect, but some are awaiting confirmation and subsequent “phylogenetic analyses.”
Since the paper is open for public access, other readers may wish to analyze it in more detail. What appears clear is that the popular media have made much more out of the data than is warranted, sensationalizing the “feathered dinosaurs” beyond all justification, trusting the dates uncritically, and minimizing the problems for evolution (like early appearance of taxa and instant diversity). A picture emerges of evolutionary ideologues forcing their data into an evolutionary scenario whether or not it fits, and whether or not it makes logical sense (20 million years of a placid lake bed where various animals drown without decaying, bookended by volcanoes? Instant pterosaurs, flying mammals and placentals?) A more conservative approach would be to recognize that our world is impoverished of many interesting animals that once existed simultaneously. For some of these, the partial preservation of features from single specimens might lead to excessive taxonomical splitting. (If they can’t tell the difference between a tadpole and a cicada, then how can we trust the hair-splitting in mammals and feather-splitting in dinosaurs?) The data require heavy doses of interpretation to prevent Charlie from getting another stomach ache.
Overall, there doesn’t appear to be any good reason to place the Daohugou and Jehol formations (and other nearby formations) into an evolutionary sequence. There also doesn’t appear any justification for millions of years. If you take off the Darwin-colored glasses and look at the data without the storytellers telling you what to see, much of the evolutionary “scenario” collapses, imaginary feathers on dinosaurs disappear, and the picture becomes one of instant appearance of varied and complex creatures by intelligent design, buried suddenly in a watery catastrophe with volcanoes going off.