Evidence that Epidendrosaurus, an extinct reptile, was indeed a dinosaur

Post of the Month: March 2007

Subject:    | Why Epidendrosaurus is a Dinosaur
Date:       | 26 Mar 2007
Message-ID: | 45kf03hktnjsnuagin0n4ltrbnbvihpr6n@4ax.com

JTEM wrote:
>>> Wait a minute. Let's not mince words here. You're lying and you know you're
>>> lying. I cited the relevant posts. Responding directly to you, after I pointed
>>> out that it may not even be a dinosaur, I demonstrated this fact with URLs.

Augray wrote:
>> No, you didn't.

JTEM then pointed to one of his previous messages at
<http://tinyurl.com/2rwbsw> which included the following:

> http://www.vertpaleo.org/jvp/16-723-741.html
>
> | Dinosauria is diagnosed by 17 apomorphic features,
> | such as: deltopectoral crest distally projected; at
> | least three sacral vertebrae; perforated acetabulum;
> | presence of brevis shelf on ilium; astragalar ascending
> | process inserts beneath the tibia; distal tarsal 4
> | proximodistally depressed.
>
> The above isn't a fluke:
>
> http://www.palaeos.com/Vertebrates/Units/Unit310/100.html#Dinosauria
>
> While you're studying, concentrate on question #8:
>
> http://www.ldeo.columbia.edu/edu/dees/courses/v1001/pracmid03_ans.html
>
> Also: This find seems to have taken the dinosaurs-evolved-from-birds
> arguments that most people are really making.
>
> It's primitive AND bird like, more primitive and more bird like
> than archaeopteryx. Not that there was ever any shortage of
> dinosaurs more bird like than archaeopteryx, but it's the
> "primitive" that has got us here.

Augray wrote:
Christ but you're dense. When are you going to get it through your head that making a claim is not the same as making an argument? To use a definition whose source will instantly be recognized by the regulars here, "An argument is a connected series of statements intended to establish a proposition."

Yes, it is.

But it's something that you have yet to do regarding the non-dinosaurian status of Epidendrosaurus. It's obvious that you need to be shown how it's done, so I'll argue the opposing position, demonstrating that Epidendrosaurus is indeed a dinosaur.

My source for the traits of Epidendrosaurus are Zhang et al. (2002). In addition, I'll refer to the traits of Scansoriopteryx (Czerkas & Yuan 2002) as this is considered a junior synonym of Epidendrosaurus (Harris 2004; Padian 2004).

Novas (1996) lists the following 17 traits of Dinosauria:

Postfrontal absent.
Post-temporal foramen present.
Quadrate head laterally exposed.
Ectopterygoid dorsal to transverse flange of pterygoid.
Temporal musculature extended anteriorly onto skull roof.
Epipophyses on cervical vertebrae.
Deltopectoral crest distally projected.
Manual digit IV with three or fewer phalanges.
At least three sacral vertebrae.
Perforate acetabulum.
Presence of brevis shelf on the lateroventral side of the postacetabular blade of the illium.
Ischium with slender shelf and with ventral "keel" (obturator process) restricted to the proximal third of the bone.
Reduction of the tuberosity that laterally bounds the ligament of the femoral head.
Presence of a proximal anterior (lesser) trochanter on the femur.
Tibia overlaps anteroproximally and posteriorly the ascending process of the astragalus (=ascending process inserts beneath the tibia) and consequently the posterior process of the tibia projects ventrally.
Calcaneum with a concave proximal articular surface, for the reception of the distal fibular end.
Distal tarsal 4 proximodistally depressed and triangular-shaped in proximal view

Of these, the states of traits 1, 2, 4-6, 11, and 13-17 are unknown for Epidendrosaurus, leaving us the following six traits that can be checked:

3- Quadrate head laterally exposed?
Yes (Czerkas & Yuan 2002, Fig.31)

7- Deltopectoral crest distally projected - at least 25% of the length of the humerus?
In Epidendrosaurus, the deltopectoral crest is roughly 30% of the length of the humerus (Czerkas & Yuan 2002, Fig.8).

8- Manual digit IV with three or fewer phalanges?
As Epidendrosaurus completely lacks digit IV, the answer is yes (Zhang et al. 2002; Czerkas & Yuan 2002).

9- At least three sacral vertebrae?
Epidendrosaurus has five (Czerkas & Yuan 2002).

10- Perforate acetabulum?
Much has been made of this trait, and while the pelvis is not present in the holotype, it is in the referred specimen. Czerkas and Yuan write that

A cast of a separated sacral rib covers part of the acetabulum, but the indication from the texture and color extending from the illium suggests that the hip socket was not as widely perforated as in theropods or dinosaurs in general. The inner edge of this reduced perforation in the hip socket can be seen in both acetabula on the counterslab.

But this is irrelevant to Novas, who states that

The opening of the acetabulum is relatively small in the saurischians _Staurikosaurus_ and _Herrerasaurus_, and in the early ornithischians _Lesothosaurus_ and _Pisanosaurus_, but it is larger in other dinosaurs.

In other words, it's the perforation that counts, and not the size. Similarly, the perforation of the acetabulum is reduced in Unenlagia, but no one claims that it's not a dinosaur (Novas & Puerta 1997).

12- Ischium with slender shelf and with ventral "keel" (obturator process) restricted to the proximal third of the bone?
Yes (Czerkas & Yuan 2002, Fig.12)

Of the six known traits of Epidendrosaurus, none of them disqualify it from being a dinosaur. But it's also obvious that it's a derived theropod, as it has a manual phalangeal formula of 2-3-4, and a pedal phalangeal formula of 2-3-4-5. In addition, proximal end of metatarsal I does not contact the ankle, and it possesses a semilunate carpal.

Finally, Zhang et al. (2002) write that

Many of the features of Epidendrosaurus such as the structures of the foot, the hand and the frontal with a deep cerebral fossa clearly show that it is a coelurosaur. Epidendrosaurus has also preserved several characters such as the long forelimb compared to the hindlimb, ulna bowed posteriorly, and pedal digit IV longer than II and closer to III in length, indicating that it probably belongs to the Maniraptora. Phylogenetic analysis has shown that Epidendrosaurus is very close to the transition to birds.

That's how you make an argument. When you claimed that it could be argued that Epidendrosaurus wasn't a dinosaur, you obviously didn't know what you were talking about, as there is no known trait that disqualifies it. Simply pointing to web pages that you don't understand doesn't cut it.

REFERENCES

Czerkas, S. A. & Yuan C.-X. 2002. An Arboreal Maniraptoran from Northeast China. In "Feathered Dinosaurs and the Origin of Flight", edited by S. J. Czerkas, pp. 63-95. Blanding, Utah: The Dinosaur Museum.

Harris, J. D. 2004. 'Published works' in the electronic age: recommended amendments to Articles 8 and 9 of the Code. Bulletin of Zoological Nomenclature 61(3):138-148.

Novas, F. E. 1996. Dinosaur Monophyly. Journal of Vertebrate Paleontology 16(4):723-741.

Novas, F. E. & P. F. Puerta. 1997. New evidence concerning avian origins from the Late Cretaceous of Patagonia. Nature 387:390-392.

Padian, K. 2004. Basal Avialae. In "The Dinosauria", Second Edition, editied by D. B. Weishampel, P. Dodson, and H. Osm¢lska, pp. 210-231. Berkeley: University of California Press.

Zhang F.-C., Zhou Z.-H., Xu X., & Wang X.-L. 2002. A juvenile coelurosaurian theropod from China indicates arboreal habits. Naturwissenschaften 89:394-398.

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