SVP 21 – a new largely complete istiodactylid pterosaur with a tail!

Rodrigues et al. 2015
describe a new istiodactylid pterosaur (not this one, Fig. 1) with a tail. I have not seen it.

Istiodactylus

Figure 1. This is the Istiodactylus holotype preserved without a tail. I have not seen the pterosaur described in the Rodrigues et al abstract.

From the abstract
“The Istiodactylidae is a clade of Early Cretaceous pterosaurs which possess very distinct teeth, with crowns triangular in shape and strongly compressed labiolingually. A new specimen from this unit is here reported and comprises the most complete istiodactylid found so far. It is an almost complete skeleton of a young animal, with skull, mandible, most of the vertebral column, pectoral and pelvic girdles, most forelimbs and part of the hind limbs. It presents the first information on the tail of the Istiodactylidae and gives a minimum length of 15 caudals. All caudal centra have an elongated cylindrical shape and show no pneumatic foramina. The vertebrae get gradually thinner. The last nine vertebrae show a gradual reduction in length as well. The last caudal is longer than the preceding one but it is the thinnest, with a posterior end a mere 0.3 mm wide. The istiodactylid tail, as expected from pterodactyloids, is short, but it differs from the tail of Pteranodon, which has duplex centra and ends in a caudal rod.”

Actually
that should be paired and parallel caudal rods in Pteranodon and only two specimens preserve a tail. YPM 2462 is represented only by 6 discontinuous caudals and rods. UALVP 24238 (Fig. 2) includes most of the rest of the Pteranodon and the more complete caudals 2-10 of the tail.

Figure 3. The UALVP specimen of Pteranodon. Note the lack of taper in the rostrum along with the small size of the orbit.

Figure 2. The UALVP specimen of Pteranodon. Note the lack of taper in the rostrum along with the small size of the orbit.

Tails in ornithocheirids
The last caudal of the new istiodactylid, at one-third of a millimeter in width, is remarkable in a pterosaur the size of an istiodactylid. By comparison, the more basal ornithocheirid, Zhenyuanopterus (Fig. 3) has a rather extensive tail of at least 40 caudals terminating in a series of extremely thin bones less than a millimeter in length. The tail is longer than the femur + half the tibia.

In Haopterus, an even more basal ornithocheirid, the tail is about as long as its tibia. Boreopterus has a tail almost as long as its hind limb. JZMP embryo has a tail at least as long as its femur. Yixianopterus has a tibia-length tail. The Anhanguera tail is almost a femur in preserved length. Barbosania preserves just a few continuous causals.

Some of these tail lengths
are much longer than expected in ‘pterodactyloid’-grade pterosaurs. Much of that has to deal with the four origins for ‘pterodactyloid’-grade pterosaurs and the traditional biases that expect certain traits under false assumptions of phylogeny that nest short-tailed Pterodactylus close to the origin of all ‘pterodactyloid’-grade pterosaurs.

Zhenyuanopterus

Figure 3. The orinithocheirid Zhenyuanopterus. Note the tail length.

The large pterosaur tree nests Pteranodon (Fig. 2) far from ornithocheirids (Fig. 3). They share few traits other than a warped deltopectoral crest of distinctive designs. Pteranodon is a giant germanodactylid. Ornithocheirids are giant scaphognathids with cycnorhampids as sister taxa. So comparisons to the tail of Pteranodon are illogical in this abstract.

Finally, 
few ornithocheirids fuse their bones. So the new istiodactylid may not be immature, based on prior studies that consider lack of fusion an ontogenetic character. Phylogenetic studies show that pterosaur bone fusion is largely phylogenetic, following patterns established in lepidosaurs (Maisano 2004), not archosaurs.

References
Rodrigues T et al. 2015.
An almost complete istiodactylid (Pterosauria, Pterodactyloiidea) from the Cretaceous of China provides the first information on the tail of this clade.

 

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