Nothronychus.

We now have the feathered cousin of the T-Rex, the so called Nothronychus. If indeed this animal is or was a (true) dinosaur it was about ten feet tall and weighted almost a ton. It was unearthed in the south west, in what was swamp land 90 million years ago. My question is this at what point (if any) do we stop calling them dinosaurs ? If you believe the theory that some of them did not die out but rather they evolved into something else ! I find it very hard to believe that the dinosaurs all died out at the same time and in the same manner.

'Cousin of T-Rex' is how the media says 'theropod'. (As I've noted before, BTW, the proper abbreviation is _T. rex_.) It was not really all that close to _Tyrannosaurus_. It was a therizinosaur, which are probably related to oviraptorosaurs and, more distantly, troodontids, deinonychosaurs (''raptors', and avians (birds). (Although tyrannosauroids are not too terribly distant from these.)

Feathers were not actually found with _Nothronychus_, but it is reasonable to presume it had them, since its Chinese relative _Beipiaosaurus_ did. Integument is very rarely preserved.

There is no reason to think it was not. Although there has been debate as to the position of therizinosaurs within _Dinosauria_ (and that debate has pretty much closed with them being coelurosaurian theropods), there has never been any question, that I know of, about them belonging to a dinosaurian group.

Under phylogenetic (or cladistic) taxonomy, all taxa must consist of an ancestor plus ALL of its descendants. Thus, if you consider birds to have descended from the ancestral dinosaur (and most, but not all, researchers do), then birds would be considered a type of dinosaur under this school of taxonomy.

_Dinosauria_ may be cladistically defined as 'the most recent common ancestor of _Iguanodon_ and _Megalosaurus_, plus all of its descendants'. By most researchers' proposed phylogenies, this includes _Aves_.

Not all of them did. Remember, over 160 million years span the distance between the first dinosaur and the K/T (Cretaceous-Tertiary) boundary. Many lineages went extinct long before the K/T (stegosaurs, carnosaurs, coelophysoids, etc.), and at least one lineage (neornithean birds plus their close relatives, the lithornithiforms) did survive the K/T extinction. Still, it is true that a great number of dinosaurian lineages did end at the K/T boundary.

Or alternatively, the therizinosaurs are in fact not theropods, which in turn are not terribly closely related to the theropods. Both the birds and the theropods may have descended from pseudosuchian 'thecodonts' but most likely from different groups of pseudosuchians.

'More importantly, therizinosaurs are almost certainly not related to coelurosaurs, and their teeth are very distinctive, with circular roots, basal constriction, and lanceolate crowns. They closely resemble those of basal sauropodomorphs and some ornithischians and are totally unlike the teeth of theropod dinosaurs' (Feduccia 1999:382).

As Feduccia (ibid.) further states: 'This [Zhao and Xu 1998] research, rather than adding support to a dinosaur-bird nexus, vividly illustrates the dearth of our knowledge of theropod phylogenetics.'

Since no one has ever demonstrated that anything other than Longisquama and birds has anything remotely resembling feathers with calamus-base, hollow rachis, pulp caps and follicular origin, it would be a leap to claim that Beipiaosaurus has feathers. It is therefore an even bigger leap to suggest that Nothronychus has feathers on the basis of phylogenetic inference, considering how poorly known theropod phylogenetics is.

Of course, it is also a huge leap to assume that the poorly preserved impressions on the only extant Longisquama fossil are feathers of any kind. Most examiners of the fossil have not seen the finely detailed structures that you seem to believe, based upon one mans short observation of the fossil, to be feathers. Of course you also seem to believe that the evolution of bipedalism occured in the arboreal descendents of Longisquama so as to allow for the emergence of Archaeopterix. Assuming you are correct that Longisquama was an arboreal glider what is the evolutionary benefit to bipedalism? Being tall makes maneuvering amongst tree limbs more difficult.

Ken Shaw

Ken,

I'd like to point out that the one shortsighted man you mentioned is often credited with being the first to prove that Archaeopteryx could fly. But regardless, have you read:

Terry D. Jones, John A. Ruben, Larry D. Martin, Evgeny N. Kurochkin, Alan Feduccia, Paul F. A. Maderson, Willem J. Hillenius, Nicholas R. Geist, and Vladimir Alifanov . Non Avian feathers in a late Triassic Archosaur. Science 2000 June 23; 288: 2202-2205. ?

This makes nine important examiners right here. The online version of this article has a number of very good pictures, which I have prints of in my right hand, and for what its worth, I'll be glad to weigh in as examiner number ten.

Six fossils of the appendages were found at the sight. Quotes from photos:

From Figure 2: 'Note the proximal tapering as well as the distinct, transversely subdivided, hollow core (indicated by the arrows of each tubular base). The morphology of these bases strongly implies that development of Longisquama's elongate integumentary appendages took place within a follicle.'

From Figures 4 and 5: 'At their distal extremeties, the shafts were vanelike and consisted of distinct makedly elongate pinnae that branched regularly from the central axis.'

These feathers are adequately compared to many bird feathers. The only thing missing from normal flight feathers is the barbules branching off of the barbs. However, this is the first feature to be lost in the feathers of secondarily flightless birds, perhaps because they can create drag in the bushes.

This article starts out by saying that Longisquama is a gliding archosaur. I have noticed that it is often in top running on lists of potential ancestors for pterosaurs! Perhaps this is because of it's shoulder joint. They don't prove here that it is a glider, but its possession of aerodynamic foils with hollow shafts could be somewhat indicative that their original design was to aid in that purpose!

I haven't read or contemplated that theory yet. In this case the arms became tied up with maneuvering the flight feathers.

Thanks, Evan Robinson

Considering the size and shape of the feathers, they would definitely have to be follicular in order to exist at all. Imagine erecting a flag pole without anchoring it below the surface of the ground, such a flag pole would be about as secure as Longisquama feathers without follicular support.

I think the evolutionary explanation for the loss of the interlocking mechanisms of the feathers of flightless birds is that their flight feathers are no longer subject to natural selection. A flightless bird with non-functional flight feathers would not fall to its death, unlike a volant bird, and therefore such a bird would not be weeded out by natural selection simply because it lost its hooklets. But that is perhaps only half the picture. Perhaps the loss of the hooklets creates a more hairlike body cover, more effectively insulating the animal. Perhaps the loss of the hooklets makes it possible to evolve more feathers per square inch of body surface, as is the case in the ostrich, the embryos of which still retain the narrow feather tracts typical of volant birds (Feduccia 1996:128).

That was also Sharov's original interpretation of what he considered the feather-like scales of Longisquama.

The alternative explanation of 'display' is unconvincing because such a small animal has no need for such a disproportionally large and potentially maladaptive 'display.' If it is for display, then perhaps a single feather would have sufficed. There is no need to have that many of them on the back, which is wasteful of resources. Time and time again, evolutionary history has shown us that the rigors of biological competition requires lean and mean living machines, not frivolous displays.

Lemurs are capable of bipedal locomotion on the ground. They are also arboreal animals. Larry Martin (Martin and Czerkas 2000, Amer. Zool.) has pointed out that the bipedal stance of Archaeopteryx may have evolved as an adaptation for vertical clinging (to tree trunks) and leaping, similar to how it evolved in the lemur.

Feduccia was well known as an opponent of the bird-dinosaur theory before this.

Looking at same figures from Science I'm not even sure these impressions are part of the animal. For all I can tell they could be fern imprints.

No animal known to glide does it with a few stiff feathers. Gliders uniformly do it by developing a flap of skin between arms and legs. I am not Aeronautical engineer but I know that an animal with no flying/gliding adaptations, ie hollow long bones and extreme light weight for size, would need a great deal of lift to do anything except plummet like a rock.

After some searching on the net I found a good detail of the tip of one 'feather' at: http://www.ento.vt.edu/%7Esharov/reptiles/longisq.html

It seems clear from this tip that this feather had some sort of edge or border. looks a lot more like a scale or skin flap than a feather to me.

Ken Shaw

It has become increasingly obvious to me that they are not scales, and they are not feathers

Reisz and Sues have a talk at SVP (next week!) entitled, simply, 'LONGISQUAMA DOES NOT HAVE FEATHERS'. I will definitely be attending that

These authors have already published a paper arguing the same. And there is nothing in that paper to suggest that Longisquama does not have feathers. Let's see if they can come up with a better argument this time instead of recycling their old argument.

Scute is a type of scale. Feathers are not scales. Feathers are an evolutionary novelty made of a new, uniquely avian protein. Longisquama's feathers have all of the unique anatomical features of avian feathers; they are not scales or scutes.

Hmm, perhaps they used their feathers as some sort of fan to keep themselves cool. Honey bees are known to beat their wings to increase air circulation to keep their hives cool when the weather is hot. Perhaps Longisquama can do the same, but it is doubtful that this is the only or even the primary reason they evolved feathers. Besides, it is doubtful that they can beat their feathers as rapidly as insects can beat their wings. Personally I think gliding is a more likely function for these feathers, as Sharov originally suggested in the 1970's.

Fake tail? How is that anti-predatory? The eyespot theory is intriguing. But how many eye spots does one need to startle predators? As many eyespots as Longisquama had feathers?