Nicknamed “Rhamphodactylus” – Is it a Transitional Pterosaur?

Last year Rauhut (2012) published on a new pterosaur, BSPG 2011 I 133, now being nicknamed, “Rhamphodactylus,” in honor of its purported transitional status between rhamphorhynchoids and pterodactyloids.

We learned earlier than neither term is monophyletic.

Rhamphorhychoids, as everyone knows, are simply basal pterosaurs and they “stop” being rhamphorhynchoids when some evolve pterodactyloid traits.

The pterodactyloid grade had four origins, two out of Dorygnathus and two out of Scaphognathus (itself a dorygnathid).

Darwinopterus and kin developed several pterodactyloid traits, but they were a dead end, producing no known descendants in the Cretaceous, according to the results of the large pterosaur tree.

Figure 1. Rhamphodactylus in situ, colors applied to identify bones. See reconstruction. Scale bar is 3 cm. The short tail (closeup in figure 5) is just to the left of the scale bars.

Figure 1. Rhamphodactylus in situ, colors applied to identify bones. See reconstruction. Scale bar is 3 cm. The short tail (closeup in figure 5) is just to the left of the scale bars.

Rauhut (2012) mentions the well known traits of the pterodactyloid grade:

  1. short tail
  2. coalesced naris/antorbital fenestra
  3. longer neck and
  4. longer metacarpal.

He lists Darwinopterus (Middle Jurassic, China) and another South American form based on scraps as pterosaur transitional taxa. To these he adds the new specimen (Figs. 1-5). No phylogenetic analysis was performed for the short paper.

Figure 2. Rhamphodactylus skull. Note the large antorbital fenestra. Maxilla

Figure 2. Rhamphodactylus skull. Note the large antorbital fenestra. Maxilla

It would be certainly tempting
to consider “Rhamphodactylus” a transitional taxon, but we already have four well-established transitional series, all made up of tiny taxa. The fact that traditional pterosaur workers continue to refuse to add tiny pterosaurs to their analyses means they will never know the path or mechanism for pterosaur evolution. “Rhamphodactylus” is on the small side (Fig. 6). So, perhaps it will open the door for other tiny pterosaurs to be studied and recognized as tiny adults.

Despite hopes
The new taxon, it turns out, merely fills the gap between tiny TM 10341 and Beipiaopterus + CM  11426 (Fig. 6), so all three are pterodactyloid-grade pterosaurs. This is a dorygnathid-like skull, but the teeth are reduced, a characteristic of this clade that ultimately produced toothless azhdarchids. Moving “Rhamphodactylus” to the darwinopterids adds 11 to 18 steps. Moving “Rhamphodactylus” one node closer to Dorygnathus adds 4 steps.

Rhamphodactylus manus

Figure 3. Rhamphodactylus manus

Rauhut (2012) notes “Rhamphodactylus” (Upper Jurassic) has a metacarpal length exactly between the statistical cloud of rhamphs and pterodacs. For such details it’s worthwhile to check out accurate reconstructions of its sister taxa (Fig. 6) both of which have the shortest metacarpals of all pterodactyloid-grade pterosaurs. Other transitional taxa all had relatively longer metacarpals.

Figure 4. Rhamphodactylus reconstructed. Yes, there's a possible skull at 1/8 the size of the adult specimen near the tail.

Figure 4. Rhamphodactylus reconstructed. Yes, there’s a possible skull at 1/8 the size of the adult specimen near the tail.

Reconstruction of “Rhamphodactylus.”
The study of roadkill specimens benefits greatly from a reconstruction (Fig. 4), but rarely occurs. “Rhamphodactylus” retains the maxillary notch present in Dorygnathus and TM 10341 and provides clues as to the morphology of the unknown skull of Beipiaopterus. Reconstructing the foot is also highly diagnostic.

Figure 5. Abbreviated tail of "Rhamphodactylus" along with a possible aborted embryo at 1/8 the size of the adult.

Figure 5. Abbreviated tail of “Rhamphodactylus” along with a possible aborted embryo at 1/8 the size of the adult. Since the last caudal retains a chevron, my guess  is the tail continues on in reduced form, curling right (dashed green line) then back toward the base where it terminates in loose strands (upper right). The rest of the tail is either lost or buried or both.

Is BSPG 2011 I 133 a mother?
I would encourage the preparators of “Rhamphorhynchus” to be especially vigilante around the tail as there appears to be a possible embryo skull there, aborted during taphonomy. Then again, those indications could represent preparation marks.

Figure 5. Click to enlarge. Rhamphodactylus and kin.  Dorygnathus SMNS 50164, TM 10341, Rhamphodactylus, Beipiaopterus and CM 11426 to scale

Figure 6. Click to enlarge. Rhamphodactylus and kin. Left to righ: Dorygnathus SMNS 50164, TM 10341, Rhamphodactylus, Beipiaopterus and CM 11426 to scale.

According to the large pterosaur tree, “Rhamphodactylus” nests close to Dorygnathus (SMNS 50164 specimen) between TM 10341 and Bepiaopterus and CM 11426. It is certainly a transitional taxon, as all of these taxa are, but it represents the size increase portion of the lineage.

Pterodactyloid-grade traits were already present in tiny TM 10341, which has been known for decades, but has been largely ignored and considered a juvenile or hatchling. TM 10341 is closer to the transitional point. lt has a shorter neck, shorter metacarpus and shorter skull. This is the lineage (Fig. 6) that ultimately produced flightless waders and giant azhdarchids.

The other dorygnathid lineage emphasized the teeth and produced ctenochasmatids.

The two scaphognathid clades reduced the rake-like teeth and produced cycnorhamphids + ornithocheirids on one branch and pterodactylids + germanodactylids and their larger descendants on the other.

It’s nice to celebrate the finding of new transitional taxa,
but let’s remember the real transitional taxa have been known for decades, if not centuries. Let’s not ignore them any longer. Traditional paleontologists won’t appreciate this news. It exposes their oversights and the discoveries that should have been theirs’ but now have fallen into the hands of amateurs. Discoveries are celebrated. Requests for speaking engagements and IMAX appearances can turn on a good run of discoveries.

On the other hand,
being embarrassed in paleontology by a run of false discoveries often turns into a good ole’ Amish shunning, or “Meidung”, the German word for avoidance. Today the only problem with Meidung in professional paleontology is the purposeful avoidance of good data and more parsimonious results based on larger inclusion sets. Pterosaur authors like Hone, Unwin and Witton who avoid looking at tiny pterosaurs and fenestrasaurs in phylogenetic analyses are running the risk here and I encourage them to take their blinders off.

References
Rauhut OWM 2012. Ein “Rhamphodactylus” aus der Mörnsheim-Formation von Mühlheim. Freunde der Bayerischen Staatssammlung für Paläontologie und Historische Geologie e.V., Jahresbericht und Mitteilungen 01/2012; 40:69-74.  online here.

News story in German

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