What better evidence that birds arose from dinosaurian reptiles than the discovery of a fossil with both scales and feathers? Further, the fossil comes from the right time period: after reptiles had already evolved but before we see modern flying birds with fully-developed feathers.
Of course, we already knew that birds are the only living descendants of dinosaurs—some biologists classify them as dinosaurs—but as we go earlier and earlier back into the evolution of dinos, we’re beginning to find that many, perhaps most, had feather-like structures. That is what we call a “preadaptation”—a feature that could be co-opted later for a different useful function: in the case of birds, gliding and then flight. (“Preadaptations,” of course, didn’t evolve because they’d be useful in the future, for natural selection doesn’t anticipate future needs; it produces features that enhance reproduction in the here and now. But those features can be hijacked for other things later, like penguins’ vestigial wings that became modified for swimming.)
The earliest feathers, as we’ll see on the specimen I’ll show shortly, are small, filamentous structures that occur along with scales. They were of no possible use for flying or gliding, but they wouldn’t evolve unless they enhanced the animal’s reproduction (or its proxy, survival). What were they for? The authors of the paper we’re discussing today suggest this (my emphasis):
Here we report a new ornithischian dinosaur, Kulindadromeus zabaikalicus, with diverse epidermal appendages, including grouped filaments that we interpret as avianlike feathers. This suggests that all Dinosauria could have had feathers and that feathers arose for purposes of insulation and signaling and were only later co-opted for flight.
So what is the finding? The researchers found a 150 million-year-old fossil of an ornithischian dinosaur in Siberia. The beast was about 1.5 meters long (4.5 feet), so it wasn’t large. The important thing is that it was an ornithischian dinosaur rather than a theropod dinosaur, and (I’m going from memory here) all of the decently-preserved feathered dinosaurs that were found previously were theropods. Although there were earlier suggestions that some ornithischians had feather-like structures, the preservation was not nearly as good as that in the new fossil.
The finding is important because ornithischians are in a completely different evolutionary group from theropods, which were saurischians. The former were herbivores and had hips like birds. “Ornithischian” means “bird-hipped,” even though, confusingly, modern birds descended from the other group, the theropods, a carnivorous subgroup of the saurischians. (“Saurishian” means “lizard-hipped.”)
Here’s the dinosaur family tree showing the two different groups and their difference in skeletal morphology. Note that birds (“Aves”) are descended from theropods:
Now if both sauriscians and ornithschians were feathered, that means either that both groups evolved feathers independently, or that they inherited feathers (probably rudimentary filaments that later evolved into full plumage) from their common ancestor. The latter possibility is more likely given the probable developmental complexity of feathers. But even if feather evolution was independent in the two groups, it still suggests that most dinosaurs, not just the theropods whose descendants became birds, had feathers. T. rex (a theropod) could have been covered in down!
But let’s back up and see the details. The new report in Science by Pascal Godefroit et al. (reference and link below, no free download) reports the finding of feather and scale impressions on an ornithischian dinosaur they named Kulindadromeus zabaikalicus (there were actually six skulls and many bones). The source of the name and conditions of preservation are given by the lead author in a “news and views”-type piece in National Geographic:
The dinosaur’s name essentially means “Kulinda River running dinosaur.” Zabaikalsky Krai is the region of Siberia where it was discovered (which explains its species name, zabaikalicus).
“There were lakes and there were volcanoes there, lots of volcanoes,” Godefroit says. The plant-eating dinosaurs likely died and fell to the lake bottom, where eruptions soon after covered them with a fine ash. That is what preserved the feather imprints with the fossil bones.
“We don’t know how big this fossil bed is, and it is likely we will find more when we go back,” Godefroit says.
The authors of the paper were working in four countries—Russia, Ireland, Belgium, and the UK—showing once again the international character of science. Since I’d like the readers to be able to read at least parts of scientific papers, I’ll put the paper’s abstract below, which is not too technical:
Middle Jurassic to Early Cretaceous [JAC: the Cretaceous went from 145 million years ago to 66 million years ago] deposits from northeastern China have yielded varied theropod dinosaurs bearing feathers. Filamentous integumentary structures have also been described in ornithischian dinosaurs, but whether these filaments can be regarded as part of the evolutionary lineage toward feathers remains controversial. Here we describe a new basal neornithischian dinosaur from the Jurassic of Siberia [JAC: the Jurassic was earlier, from about 201 to 145 million years ago] with small scales around the distal hindlimb, larger imbricated scales around the tail, monofilaments around the head and the thorax, and more complex featherlike structures around the humerus, the femur, and the tibia.The discovery of these branched integumentary structures outside theropods suggests that featherlike structures coexisted with scales and were potentially widespread among the entire dinosaur clade; feathers may thus have been present in the earliest dinosaurs.
Here’s a figure from the paper showing the reconstruction of the skeleton; the scale lines, which apply to the bones, are 1 cm. (2.54 cm/inch)
The skull, also with a 1 cm scale:
A reconstruction, showing the downy filamentous “feathers,” by the authors:
And a more colorful reconstruction from the National Geographic piece. The colors are, of course, imagined:
Here are impressions of scales on the leg (tibia and tarsus):
Large arched scales on the tail (B and C):
Below are the “feathers” on the arm bones (humerus and part of radius and ulna). B. shows enlargement of the white box in “A”, with the filamentous structures growing out of “compound structures”, and C is an interpretive drawing. The authors note:
These occur as groups of six or seven filaments that converge proximally and arise from the central regions of a basal plate. Individual filaments are 10 to 15 mm long. Those on the humerus are wider (0.2 to 0.4 mm) and straighter than those on the femur (0.1 to 0.2 mm). These groups of filaments. . . resemble the down feathers of some modern chicken breeds, such as the Silkie, which are devoid of barbules.
The fact that feathers appear to be growing out of scale-like features suggests, as biologists have long assumed, that feathers actually evolved from scales, though the authors suggest that the “scales” on birds’ legs and feet are not persistent scales derived from their reptilian ancestors, but evolved back from feathers! Since scales certainly preceded feathers in the fossil record, this shows that truly new structures, certainly involving new genetic information, can evolve (and then be lost, reverting on birds’ feet to scales). That belies the common creationist criticism that new genetic information can’t evolve (we saw that from one commenter earlier today).
Here are some “monofilaments” around the rib cage. These are distributed widely around the head, neck, and thorax:
Enlargement of above (box), showing filaments:
Here’s the money paragraph from the paper:
. . . the integumentary structures in Ornithischia, already described in Psittacosaurus and Tianyulong, could be homologous to the “protofeathers” in non-avian theropods. In any case, it indicates that those protofeather-like structures were probably widespread in Dinosauria, possibly even in the earliest members of the clade. Further, the ability to form simple monofilaments and more complex compound structures is potentially nested within the archosauromorph clade. . .
Here’s the final statement in the National Geographic article:
“This does mean that we can now be very confident that feathers weren’t just an invention of birds and their closest relatives, but evolved much deeper in dinosaur history,” [Godefroit] adds. “I think that the common ancestor of dinosaurs probably had feathers, and that all dinosaurs had some type of feather, just like all mammals have some type of hair.”
Even so, Godefroit suggests that the largest dinosaurs likely had the fewest feathers, as they wouldn’t have needed them for insulation. “Just like elephants in Africa don’t need fur,” he says.
That suggests that feathers evolved in smaller dinosaurs as insulation, and the largest ones simply lost them, just as elephants, which evolved from much smaller animals, lost their hair (although their mammoth relatives in colder climes either did not, or re-evolved hair). I like the idea that feathers conferred insulation on these creatures, though a signalling function (which means that the feathers probably were colorful, and may have had different colors and patterns in different species) is not out of the question.
Godefroit, P., S. M. Sinitsa, D. Dhouailly, Y. L. Bolotsky, A. V. Sizov, M. E. McNamara, M. J. Benton, and P. Spagna. 2014. A Jurassic ornithischian dinosaur from Siberia with both feathers and scales. 2014. Science 345:451-455.