Tiny TM13104 – ancestor to cynorhamphids AND ornithocheirds AND germanodactylids AND pterodactylids

This is a key taxon, long ignored.
While Darwinopterus gathered all the headlines as the “missing link” between long-tailed primitive pterosaurs and short-tailed derived pterosaurs (ahem, total rubbish), this specimen is the real long-sought transitional taxon. And it doesn’t rely on made-up fantasies like “modular evolution.” Ironically it’s been known for 140 years, but relegated to the phylogenetically discarded pile of putative “juvenile” pterosaurs simply because of its diminutive size. As it happens, phylogenetically, size meant survival of the lineage. Without shrinking, pterosaurs might have gone extinct much earlier than they ultimately did (at the end of the Cretaceous).

Figure 1. Tiny TM13104 nests as the ancestor to both the cycnorhamphids and ornithocheirids and germanodactylids.

Figure 1. Tiny TM13104 nests as the ancestor to cycnorhamphids and ornithocheirids and germanodactylids. It’s a little scaphognathid, but distinct in its metacarpal length and tiny size, This specimen was only half the size of the smallest Scaphognathus species (see figure 2), continuing a clear size reduction trend from the twice as tall Scaphognathus holotype.

Pterodactylus? micronyx? TM 13104 (Winkler 1870, No. 34 in the Wellnhoger 1970 catalog) ~2.5 cm skull length, was considered a juvenile Pterodactylus, but it is not closely related, according to the results of the large pterosaur family tree. No. 34 was derived from a sister to the Maxberg specimen of Scaphognathus (Fig. 2) and phylogenetically preceded other tiny pterosaurs including Gmu-10157 (basal to cycnorhamphids like, BSP 1968 XV 132 and the basal ornithocheirid, Yixianopterus). Moreover, TM 13104 was also basal to the lineage of pterodactylids and germanodactylids and their kin (that encompasses all the derived short-tailed pterosaurs in this branch of the large pterosaur tree) via some of the tiniest of all pterosaurs like Ornithocephalus and No. 6 (B St 1967 I 2760 (Fig. 2).

The only derived (short-tailed, long-snouted) pterosaurs TM 13104 was NOT ancestral to were the azhdarchids and ctenochasmatids, both of which find their ancestors more directly in various species of Dorygnathus.

Evolution
Overall smaller and distinct from the Maxberg specimen of Scaphognathus (Fig. 2), the skull of No. 34 had a shorter, more pointed rostrum. The skull and mandible were more gracile with smaller teeth. The naris was smaller. This is how the naris was reduced in this line of derived pterosaurs.

The entire vertebral spine was shorter and more gracile, including the tail.

The sternal complex was anteroposteriorly shorter but retained distinct lateral processes. The metacarpus was longer, subequal to the ulna. The fingers were smaller. The proximal phalanges were longer.

The ischium was broad and its rims approach both the pubis and ilium. Metatarsal 5 and digit 5 were shorter. The metatarsals were not appressed.

Just imagine how tiny the hatchlings were
One centimeter tall hatchlings of TM 13104 might not have been volant due to their high surface-to-volume ratios. Instead they may have been restricted to humid leaf litter or risk desiccation as in modern very tiny lizards (Hedges and Thomas 2001).

TM 13104 and kin. These tiny pterosaurs nest at the bases of several clades of much larger and later pterosaurs.

Figure 2. TM 13104 and kin. These tiny pterosaurs nest at the bases of several clades of much larger and later pterosaurs. The longer snouts are beginning to become apparent on these tiny pterosaurs, but not Ornithocephalus, which does not have any known descendants. These are not juveniles. None are identical to larger putative adult pterosaurs. If anyone has access to images of the rest of SMNS 81775, let me know.

The Family Tree
See the pterosaur family tree here. Note the positions of these tiny pterosaurs at the bases of major clades of larger forms. These are the real transitional taxa. Darwinopterus, you’ll note, is an interesting footnote that ultimately did not lead to any higher clades.

The Rio Pterosaur Symposium 2013 featured this talk 
“The basal monofenestratan Darwinopterus and its implications for the origin and basal radiation of pterodactyloid pterosaurs.” by David M. Unwin and Junchang Lü. So these two are unfortunately still promoting this falsified hypothesis.

Darren Naish in Tetrapod Zoology
happily bought into the Darwinopterus transitional taxon fable and the wonders of “modular evolution,” which doesn’t happen anywhere else in the animal family tree. He wrote lavishly about it here. You’ll remember that he’s the one who warned his blog readers against ReptileEvolution.com.

Well…
At least in this instance, it’s not my words and images you have to watch out for, but his (I won’t try to tarnish all of Naish’s works as he did mine, because otherwise he does a damn good job in that blog, and I’m not out for blood). Sadly, in this case, Naish did not put on his scientist cap and test the Darwinopterus hypothesis. He merely accepted the report as a journalist would on the authority of its authors.  Among them was Dr. David Unwin, who has been behind some of the biggest bungles in pterosaur studies including, most famously, the Sordes deep-chord wing membrane myth along with the myth of pterosaur egg burial and others.

So long as pterosaur workers continue to refuse to include tiny pterosaurs in their analyses they’ll have about as much success in resolving their family trees as they have had in the past. I’m here to suggest more inclusive alternatives that work.

References
Hedges SB and Thomas R 2001. At the Lower Size Limit in Amniote Vertebrates: A New Diminutive Lizard from the West Indies. Caribbean Journal of Science 37:168–173.
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.
Winkler TC 1870. Description d’un nouvel exemplaire de Pterodactylus micronyx du musee Teyler. Archives des Musee Teyler 3: 84-99.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.