The Mysterious Fenestrated Pteromimus

Pteromimus

Figure 1. Pteromimus. Left: as originally reconstructed (Antanassov 2001). Right. New reconstruction further extending the missing frontal and jugal. Far right, cervical vertebra in two views. Note resemblance of all elements to Langobardisaurus (Fig. 2) and Tanytrachelos (Fig. 3)

Pteromimus longicollis (Atanassov 2001, 2002, Fig. 1) was described as a sister to pterosaurs and Scleromochlus (unfortunately while ignoring Cosesaurus and the fenestrasaurs). More unfortunately langobardisaurs (Langobardisaurus and Tanytrachelos) were not compared. Here Pteromimus shares more traits with langobardisaurs, notably in the shape of the skull elements and the elongated cervical vertebrae. Pteromimus was probably more primitive than Langobardisaurus based on the unspecialized premaxillary teeth. The skull of Pteromimus is incomplete (gray areas are restored). Atanassov (2001) reconstructed the skull with an antorbital fenestra, which was not reported in Langobardisaurus (Renesto 1994, Muscio 1997), but one or two appear to be present (Figs. 2, 3), nevertheless.

The skull of Langobardisaurus tonneloi.

Figure 3. The skull of Langobardisaurus tonneloi. Above: restored. Below: In situ. Note that the portion of the jugal (warm gray) over the red quadrate is broken and displaced over the suborbital portion of the jugal. The premaxillary ascending process (yellow) is broken. The maxilla appears to have two antorbital fenestrae, similar to the multiple situation in Cosesaurus. Is this one fenestra divided by the descending nasal? Could be. Distinct from Pteromimus, the jugal/lacrimal suture extends ventral to the entire lacrimal here, but is reduced to a stem in Pteromimus -- if correctly identified.

Langobardisaurus
Langobardisaurus pandolfii (Renesto 1994a) Norian, Late Triassic ~ 210mya, ~15 cm in length was a longer-necked, smaller sister to CosesaurusMacrocnemus, Jesairosaurus and Huehuecuetzpalli. Distinct from a primitive Macrocnemus, the skull of Langobardisaurus was shorter and dominated by a huge orbit. The upper temporal bar bisected the orbit and the posterior cranium was depressed. The procumbent premaxillary teeth were transformed into a narrow rake-like configuration. The posterior teeth were broader and multi-cusped, as in the smaller Tanystropheus.

The cervical series was longer and more gracile, but still composed of eight vertebrae. The number of dorsals was reduced. Eleven caudals bore transverse processes. The tail tip is unknown, but rapid dimunition suggests a short caudal series.

The scapula and coracoid were relatively smaller. The scapula was strap-like. The manus was relatively smaller with shorter digits.

The ilium was elongated both anteriorly and posteriorly. The ischium was narrow proximally. The pedal digits were shorter. Digits II-IV were the same length. Pedal 5.1 was greatly elongated and extended nearly to the distal end of metacarpal IV. Pedal 5.4 extended as far as p3.4.

With a cropping muzzle, grinding, slicing teeth, a high coronoid and the ability to rise on their hind legs and reach high places with their long necks, it appears possible that the langobardisaurs plucked insects from high locations, possibly after dark. Occasional biepdal locomotion appears possible (Renesto, Dalla Vecchia & Peters 2002).

Langobardisaurus tonneloi was similar overall, but the orbit was not so large. The premaxillary dentition was smaller. The posteriormost teeth had elongated cutting/grinding surfaces. The coronoid process was larger than in any sister taxon. Only four anterior caudals bore elongated transverse processes. The hind limbs were longer. No pedal digit tips were aligned and digit III was the longest.

Langobardisaurus tonneloi

Figure 2. Langobardisaurus tonneloi. A short rostrum, a large orbit, an elongated and posteriorly displaced naris, an antorbital fenestra and an elongated cervical ally this taxon with Pteromimus.

Tanytrachelos
Distinct from LangobardisaurusTanytrachelos has twelve cervicals. The posterior cervical ribs had large “heads” that kept the cervical ribs far from each centrum. So-called “heterotopic” bones were present. These appear to be elongated proximal chevrons.

The sternum was wider and longer. The humerus was slightly bowed anteriorly. Metacarpal 1 was half the length of mc 2. Metatarsal 3 was the longest as in Tanystropheus.

Tanytrachelos

Figure 4. Tanytrachelos - a little closer to Tanystropheus, but tiny with a distinct skull.

Gwyneddichnium
Gwyneddichnium is an ichnotaxon (footprint) described by Bock (1952) that appears to be the correct size and proportions to match Tanytrachelos, which is found nearby (online pdf). If so, the tracks indicate that Tanytrachelos walked in a digitigrade fashion, not permitting its heels to touch the substrate, and all toes faced anteriorly, unlike Cosesaurus
online story
.

An Antorbital Fenestra?
Apparently yes. One is visible in Pteromimus, Langobardisaurus and Tanytrachelos. That means in the descendant taxon, Tanystropheus, the antorbital fenestra would have been secondarily closed. Interesting! Even the smaller Tanystropheus specimens have no trace of an antorbital fenestra, other than a deep depression at the junction of the lacrimal, prefrontal and maxilla.

The presence of an antorbital fenestra, even a tentative one, should bring langobardisaurs and their descendants closer to the Fenestrasauria, perhaps modifying Peters (2000). Although controversial an antorbital fenestra also appears to be present in Jesairosaurus and the drepanosaurids.

The Tritosauria

Figure 3. This tree represents updates and corrections to the large reptile tree. It shifts Langobardisaurus, Tanytrachelos and Tanystropheus closer to Cosesaurus. This solves the little fifth toe problem of Macrocnemus, which now nests alone with Dinocephalosaurus.

Earlier Mistake Rectified
Earlier I was puzzled about the unlikely re-elongation of pedal digit 5 when the large pterosaur tree nested Tanystropheus, Tanytrachelos and Langobardisaurus with short-toed Macrocnemus. Further investigation uncovered certain errors. When corrected the new nesting of Langobardisaurus moved closer to Cosesaurus and further from Macrocnemus. That solved the problem and the red flag came down.

Insight into Tanystropheus?
Re-establishing the ancestral sisters of Tanystropheus provides certain insights into the morphology and behaviors of this, the strangest and largest of the Triassic tritosaurs.  Paleontologists have long wondered how Tanystropheus got around, preferring a marine niche for it and a plesiosaur-like attack method, despite the fact that it had no obvious marine adaptations.  Here, descending from likely bipeds, a terrestrial niche is preferred in which Tanystropheus attacked tree-dwellers with its elevated neck while its feet were planted on the ground (whether hard turf or muddy, sandy shallows).

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
Atanassov M 2001. Two new archosauromorphs from the Late Triassic of Texas. – Journal of Vertebrate Paleontology Abstracts 21(3): 30A.
Atanassov M 2002. Two new archosauromorphs from the Late Triassic of Texas. Dissertation.online abstract | pdf
Muscio G 1997. Preliminary note on a specimen of Prolacertiformes (Reptilia) from the Norian (Late Triassic) of Preone (Udine, north-eastern Italy). Gortania – Atti del Museo Friulano di Storia Naturale 18:33-40.
Peters D 2000. A redescription of four prolacertiform genera and implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293-336
Renesto S 1994. A new prolacertiform reptile from the Late Triassic of Northern Italy. Rivista di Paleontologia e Stratigrafia 100(2): 285-306.
Renesto S and Dalla Vecchia FM 2000. The unusual dentition and feeding habits of the Prolacertiform reptile Langobardisaurus (Late Triassic, Northern Italy). Journal of Vertebrate Paleontology 20: 3. 622-627.
Renesto S and Dalla Vecchia FM 2007. A revision of Langobardisaurus rossii Bizzarini and Muscio, 1995 from the Late Triassic of Friuli (Italy)*. Rivista di Paleontologia e Stratigrafia 113(2): 191-201. online pdf
Renesto S, Dalla Vecchia FM and Peters D 2002. Morphological evidence for bipedalism in the Late Triassic Prolacertiform reptile Langobardisaurus. Senckembergiana Lethaea 82(1): 95-106.
uninisubria/Langobardisaurus
wiki/Langobardisaurus

1 thought on “The Mysterious Fenestrated Pteromimus

  1. The antorbital fenestrae of Langobardisaurus have such irregular shapes and strange positions that I wonder if they’re just damage from splitting the slab. And are you sure that the “spur” that lies dorsal to the caudal fenestra and is yellow in the in-situ tracing but green in the restoration hasn’t broken off the lacrimal (light purple)?

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