Manual digit 5 on Bellubrunnus (= basal Rhamphorhynchus)

In several phylogenetic predecessors of pterosaurs
such as Cosesauru, Sharovipteryx and Longisquama. manual digit 5 is small but clearly present (Fig. 1). Traditional workers report that manual digit 5 is absent in pterosaurs.

pterosaur wings

Figure 1. Click to enlarge. The origin of the pterosaur wing and whatever became of manual digit 5?

In pterosaurs
I have shown here, here and here several examples of a vestigial manual digit 5 on the axially rotated metacarpal 4. Unfortunately, other workers do not yet recognize these hard to see bones. Heck, they don’t recognize these taxa as pterosaur sister taxa, so we know the similar frustration John Ostrom and John Huxley felt when workers did not accept their bird/dinosaur hypothesis reviewed here.

Bellubrunnus-digit5

Figure 2. Click to enlarge. The carpus and manus of Bellubrunnus identifying element including a vestige of manual digit 5. Yes, it’s tiny, but all vestiges are. Look closely, fellow workers, and you will find it for yourself. U = ulna. Ul = ulnare. R = radius. Ra = radiale. Pt = pteroid. PC = preaxial carpal. Numbers = unfused distal carpals and manual digits.

Hone et al. 2012
provided exquisite UV closeups of the tiny specimen, but did not identify vestigial manual digit 5. I do so here (Fig. 2). It’s clear, but tiny, as most vestiges are.

The carpal elements
are unfused because this adult specimen is the result of phylogenetic miniaturization. It’s ancestors among the genus Campylognathoides, were much larger individuals, as shown here. Essentially Bellubrunnus is a precocious adult, sexually mature in an otherwise immature, reduced size body. This can confuse those who work in bone histology and workers who don’t understand lepidosaur fusion patterns. Phylogenetic analysis, as shown here, solves these problems.

References
Hone DWE, Tischlinger H, Frey E and Röper M. 2012. A New Non-Pterodactyloid Pterosaur from the Late Jurassic of Southern Germany. PLoS ONE 7(7): e39312. doi:10.1371/journal.pone.0039312

 

 

Notes on Limusaurus (Dinosauria, Theropoda) and its odd little hand

Added November 20, 2015, a report by Guinard G 2015 supports the present results.

Figure 1. Limusaurus in situ. The associated croc has been painted red here.

Figure 1. Limusaurus in situ. The associated croc has been painted red here. Their marriage was legal in only 16 states.  : )

Limusaurus inextricabilis (Xu et al. 2009; earliest Late Jurassic, Oxfordian; 1.7m in est. length; IVPP V 15923; Figs. 1, 2) is an herbivorous theropod with very tiny arms and hands in the lineage of proto-birds. Coincidentally, Limusaurus was buried next to the skeleton of a tiny Jurassic croc (in red above). Pol and Rauhut (2012) nested Limusaurus with Elaphrosaurus and Spinotropheus. Those taxa have not been added yet to the large reptile tree where Limusaurus nests with the oviraptor  Khaan and Juravenator. Limusaurus shares a ventral pelvis, but not long arms and large hands with these bird-like taxa. Like birds, Limusaurus has a pair of sternae. The coracoids appear to be transitional between disc-like and stem-like.

Figure 2. Limusaurus reconstructed. Both hands are shown and colorized. Digit 1= purple. Digit 2= pink. Digit 3 = Green. Digit 0=pale yellow. Digit 0 goes back to basal tetrapods, like Ichthyostega, and only appear here due to the vestigial nature of the manus in which it matured at an embryologically immature state compared to sister taxa.

Figure 2. Limusaurus reconstructed. Both hands are shown and colorized. Digit 1= purple. Digit 2= pink. Digit 3 = Green. Digit 0=pale yellow. Digit 0 goes back to basal tetrapods, like Ichthyostega, and only appear here due to the vestigial nature of the manus in which it matured at an embryologically immature state compared to sister taxa.

Limusaurus is notable for two main reasons:

  1. It is an herbivorous theropod from the earliest Late Jurassic
  2. It has four fingers when all sister taxa have three. This fact has added credence and confusion to the chick embryo digit identification issue we looked at earlier here

It’s well worth looking at both sides of this extra finger issue:
From the Xu et al. abstract: “Theropods have traditionally been assumed to have lost manual digits from the lateral side inward, which differs from the bilateral reduction pattern seen in other tetrapod groups. This unusual reduction pattern is clearly present in basal theropods, and has also been inferred in non-avian tetanurans based on identification of their three digits as the medial ones of the hand (I-II-III). This contradicts the many developmental studies indicating II-III-IV identities for the three manual digits of the only extant tetanurans, the birds. Here we report a new basal ceratosaur from the Oxfordian stage of the Jurassic period of China (156–161 million years ago), representing the first known Asian ceratosaur and the only known beaked, herbivorous Jurassic theropod. Most significantly, this taxon possesses a strongly reduced manual digit I, documenting a complex pattern of digital reduction within the Theropoda. Comparisons among theropod hands show that the three manual digits of basal tetanurans are similar in many metacarpal features to digits II-III-IV, but in phalangeal features to digits I-II-III, of more basal theropods. Given II-III-IV identities in avians, the simplest interpretation is that these identities were shared by all tetanurans. The transition to tetanurans involved complex changes in the hand including a shift in digit identities, with ceratosaurs displaying an intermediate condition.”

There were a long list of authors (see below) that agreed with the above, some of whom have come to our attention earlier for publishing various errors, along with their otherwise excellent work.

Unfortunately the Xu et al. abstract ignores the fact that basal tetrapods, like Acanthostega, had an additional digit medial to digit #1 (we’ll call this digit #0). Therefore digit #0 is part of the phylogenetic history of all tetrapods, despite the fact that it is almost never expressed in tetrapod adults, only embryos. Digit #0 is expressed in Limusaurus, in which the hand is a small vestige relative to those of sister taxa. Like other vestiges the hand of Limusaurus did not continue to develop normally as a hatchling and into adulthood. Rather the hand retained a shape found at a certain embryological stage, a stage that included digit #0.  That’s why the big metacarpal (in purple) has the morphology of metacarpal 1 in sister taxa (Fig. 3) and metacarpal #0 continues the shape of metacarpal #1 in cross section. In most tetrapods digit #0 is fused to metacarpal #0 or otherwise disappears before birth or hatching.

Figure 3. The manus of several theropods including Limusaurus. Here digit 1 is purple, digit 2 is pink and digit 3 is green. Note the presence of digit 0 in this vestigial hand, a holdover from basal tetrapods that has not been correctly identified by Xu et al. and others.

Figure 3. The manus of several theropods including Limusaurus. Here digit 1 is purple, digit 2 is pink and digit 3 is green. Note the presence of digit 0 in this vestigial hand, a holdover from basal tetrapods that has not been correctly identified by Xu et al. and others. Click to enlarge.

That’s why otherwise you only see digit #0 in embryos. Thus there is no “phase shift” of digit identity. There is only loss, fusion or absorption of digit #0, a factor missed by earlier workers.

Supportive work (2015) by Guinard G 2015.
reports the following: “There is controversy between paleontological and developmental data regarding manual digit identities of birds and their tetanuran ancestors (I, II and III vs. II, III and IV). Limusaurus should not be used as a reference concerning the identity of avian manuals digits. Evolutionary teratology supports identities I, II and III of the tetanuran manus via a frame-shift that did not occur in the Ceratosauria lineage.”

References
Guinard G 2015. Limusaurus inextricabilis (Theropoda: Ceratosauria) gives a hand toevolutionary teratology: a complementary view on avian manual digits identities. Zoological Journal of the Linnean Society (advance online publication) DOI: 10.1111/zoj.12329
Xu X, Clark JM. Mo J, Choiniere J, Forster CA, Erickson GM, Hone DWE, Sullivan C, Eberth DA, Nesbitt S, Zhao Q, Hernandez R, Jia C-K, Han F-L. and Guo Y 2009. A Jurassic ceratosaur from China helps clarify avian digital homologies. Nature, 459(18): 940–944.

Darwinopterus carpus and another 5th manual digit

I appreciate it when authors provide close-ups of the pterosaur carpus. It gives me a chance to once again document the near universal presence of a vestigial manual digit 5 and other ptero traits missed by other workers.

Figure 1. The carpus of Darwinopterus linglongtaenis. Vesitigial digit 5 is scattered on metatarsal 4. The pteroid articulates in the saddle of the radiale. The preaxial carpal articulates on the first distal carpal now fused to the other distal carpals in a syncopal.

Figure 1. Click to enlarge. The carpus of Darwinopterus linglongtaenis. Vesitigial digit 5 is scattered on metatarsal 4. The pteroid articulates in the saddle of the radiale. The preaxial carpal articulates on the first distal carpal now fused to the other distal carpals in a syncopal.

Here digit 5 is scattered, but all the elements are there. In red: distal carpal 5. In green: metacarpal 5. In blue: two proximal phalanges. In amber: a sharp ungual. This matches the pattern seen in basal fenestrasaurs in which manual digit 5 is not a vestige.

Note the pteroid is located in the saddle of the radiale (Peters 2009) and disconnected from the preaxial carpal (both former centralia, having migrated to the medial wrist, convergent with the mammalian prepollex).

References
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Wang X, Kellner AWA, Jiang S-X, Cheng X, Meng Xi and Rodrigues T 2010
. New long-tailed pterosaurs (Wukongopteridae) from western Liaoning, China. Anais da Academia Brasileira de Ciências 82 (4): 1045–1062. pdf online

wiki/Kunpengopterus

A Perfect Pterosaur: Pterodactylus scolopaciceps (n21) – part 1

Most pterosaur fossils are incomplete, crushed and disarticulated. By contrast, Pterodactylus scolopaciceps  BSP 1937 I 18 (Broili 1938, P. kochi n21 of Wellnhofer 1970, 1991, Fig. 1) is just the opposite, complete, uncrushed and articulated. (This specimen is commonly considered P. kochi, but the holotype of P. kochi lies outside the Pterodactylus clade and is also basal to the Germanodactylus clade.)

Figure 1. Pterodactylus scolopaciceps  BSP 1937 I 18 (Broili 1938, P. kochi No. 21 of Wellnhofer 1970, 1991) complete, articulated and including soft tissue.

Figure 1. Pterodactylus scolopaciceps BSP 1937 I 18 (Broili 1938, P. kochi No. 21 of Wellnhofer 1970, 1991) complete, articulated and including soft tissue.

That elusive and some would say mythical manual digit 5
So, if pterosaurs had five manual digits, as shown on many other specimens, this specimen should show them complete, uncrushed and articulated.

And it does! Can you see them (Fig. 2)?

Metacarpi of n21. Can you see the vestiges of digit 5 on these images? If not, see figure 3.

Figure 2. Metacarpi of n21. Can you see the vestiges of digit 5 on these images? If not, see figure 3. Note the position of the preaxial carpal, leaning distally while flexed. Extension of the elbow would pull this bone medially by way of extensor tendons.

If you can’t see the vestiges of manual digit 5, please see the next image (Fig. 3) in which the elements are colorized. The posterodorsal position of this digit documents the axial rotation of metacarpal 4, which enables the pterosaur wing to fold in the plane of the wing. This disproves Bennett’s (2008) ghastly hypothesis that the forelimb pronated then finger 4 hyperhyperhyperextended to enable folding against the posterior (former dorsal) side of the hand. Ouch!!

Colorized digit 5 elements including ungual, two other phalanges, metacarpal and carpal 5.

Figure 3. Colorized digit 5 elements including ungual, two other phalanges, metacarpal and carpal 5. Manual digit 5 is present on both metacarpals. All the elements match one another. On the lower image (the right one) digit 5 (or at least the ungual) is rotated axially about 180 degrees, perhaps due to disarticulation.

And here’s a closeup. Note the presence of carpal 5 (pink), metacarpal 5 (green), and three phalanges including the ungual, as in Cosesaurus and other tritosaurs.

Even in primitive snakes some sort of vestige of hind limbs is preserved. So, while digit 5 was shrinking from Cosesaurus to pterosaurs, it remained a vestige in many, if not all pterosaurs, just sitting there, like a human appendix.

Pterodactylus manual digit 5 vestige.

Figure 4. Pterodactylus manual digit 5 vestige. Sorry for the over enlargement. Someday someone should take a sharper image of this.

Tomorrow we’ll take another look at n21, a perfect Pterodactylus and find the wingtip unguals.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E Buffetaut and DWE Hone eds., Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Broili F 1938. Beobachtungen an Pterodactylus. Sitz-Bayerischen Akademie der Wissenschaten, zu München, Mathematischen-naturalischenAbteilung: 139–154.
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.

wiki/Pterodactylus