Archaeopteryx: Eichstaett and Thermopolis Specimens

The following GIF animation
(Fig. 1) includes the plate and counter-plate of the Eichstaett specimen of Archaeopteryx. The counter-plate was flipped and un-distorted in Photoshop to match the plate (slightly different camera angles introduced the original keystoning). Together the elements better present data identified in the specimen, including feathers, a sternum and furcula (fused clavicles).

Figure 1. GIF animation of the Eichstaett specimen of Archaeopteryx. Six  frames reveal the plate, counter plate, skeleton and feathers at 5 second intervals. The two final plates identify,  Click to enlarge.

Figure 1. GIF animation of the Eichstaett specimen of Archaeopteryx. Eight frames reveal the plate, counter plate, skeleton and feathers at 5 second intervals. The two final plates identify,  Click to enlarge.

The furcula
is difficult to see, even when traced (Fig. 2). It is merely an impression on the counter-plate and was likely better preserved on the lost portion of the plate. Likewise the clavicles and scapula are difficult to trace.

Figure 2. Pectoral girdle of the Eichstaett specimen of Archaeopteryx.

Figure 2. Pectoral girdle of the Eichstaett specimen of Archaeopteryx. Six frames change every 5 seconds.

There is a broken forearm on this specimen
and perhaps that led to its demise in life.

For some unknown reason, the skull
of this specimen has been difficult to figure. Paul (2002) showed several variations illustrated by several paleontologists. We looked at those here. All but one of these were illustrated with three fenestrae in the maxillary fossa, as shown here (Fig. 3 from Rauhut 2013). Only Heilmann (1926) illustrated a single antorbital fenestra without a fossa.

  1. aof – antorbital fenestra
  2. mf – maxillary fenestra
  3. pro – premaxillary foramen
Figure 3. Archaeopteryx as reconstructed by Rauhut 2013 with three fenestra within the antorbital fossa area. This interpretation is not supported in figure 4. Figure 3. Archaeopteryx as reconstructed by Rauhut 2013 with three fenestra within the antorbital fossa area. This interpretation is not supported in figure 4.

Figure 3. Archaeopteryx as reconstructed by Rauhut 2013 with three fenestra within the antorbital fossa area. This interpretation agrees with the Thermopolis and London specimens, but not the Eichstaett specimen. This is an example of why one should not attempt composites of distinct specimens.

I agree with Heilmann (with regard to the Eichstaett specimen) 
I identify only palatal elements and the inside of the other side of the skull on that specimen. See if you agree (Fig. 4).

Although the skull appears to have a concave upper jaw matching a convex mandible, this may be a taphonomic aftereffect. There is a crack in the anterior surangular at the point of greatest stress and no sister taxa share this morphology.

Figure 4. The Eichstaett specimen of Archaeopteryx as a GIF animated movie of seven frames, each five seconds in length. Note the lack of an antorbital fossa and those two other fenestra. Instead you see the inside of the lower maxilla and mandible along with palatal elements.

Figure 4. The Eichstaett specimen of Archaeopteryx as a GIF animated movie of seven frames, each five seconds in length. Note the lack of an antorbital fossa and those two other fenestra. Instead you see the inside of the lower maxilla and mandible along with palatal elements. A broken vomer may have created the illusion seen by others. Click to enlarge.

As usual
I have not seen the specimen first hand, but have relied on photographs to make these identifications. I have championed the use of digitized photographs and Photoshop to glean data from flattened fossils. Here is one more example of their usefulness.

Figure 5. GIF animation of the maxilla with fossa and accessory fenestra in the Thermopolis specimen of Archaeopteryx not present in the Eichstaett specimen.

Figure 5. GIF animation of the maxilla with fossa and accessory fenestra in the Thermopolis specimen of Archaeopteryx not present in the Eichstaett specimen.

Indeed the Thermopolis and London specimens
do have the antorbital fossa with accessory fenestra illustrated by Rauhut, Paul and others (Fig. 5), but then the Thermopolis specimen nests basal relative to the other two Archaeopteryx specimens (Fig. 6), sharing several easily overlooked traits with the proximal outgroup taxon, Xiaotingia. to the exclusion of the other two Archaeopteryx.

Figure 3. Subset of the large reptile tree (595 taxa) with the addition of the Thermopolis specimen of Archaeopteryx.

Figure 6. Subset of the large reptile tree (595 taxa) with the addition of the Thermopolis specimen of Archaeopteryx.

Comparing these three Archaeopteryx specimens
shows they are indeed sister taxa, but also distinct sister taxa. The high Bootstrap numbers indicates that several characters are not shared by these three taxa.

Figure 1. The six tested Solnhofen birds currently named Archaeopteryx, Jurapteryx and Wellnhoferia.

Figure 7. The six tested Solnhofen birds currently named Archaeopteryx, Jurapteryx and Wellnhoferia.

Paleontologists:
Please use individual specimens as taxa whenever possible. Don’t blindly combine specimens until you are sure they are conspecific. By taking the short cut and blending two distinct taxa you throw away any chance of identifying subtle interrelationship changes. And you’re letting amateurs, like me, make discoveries that should be yours to make.

References
Heilmann G 1926. The origin of birds. HFG Witherby, London.
Paul G 2002. Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Johns Hopkins University Press, Baltimore. 406 pp.
Rauhut OWM 2013. New observations on the skull of Archaeopteryx. Paläontologische Zeitschrift 88(2)211-221.

 

 

 

 

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