The Family Tree of the Pterosauria 18 – The Ornithocheiridae part 2 of 3

In part 1 of the Ornithocheiridae we looked at the base of this large clade of long-winged soaring pterosaurs. Here in part 2 we’ll look at ColoborhynchusIstiodactylus and their kin. These taxa form a clade of their own, a little off to the side. In part 3 we will start again where we ended in part 1 and examine more derived taxa such as Anhanguera and Liaoningopterus.

The Ornithocheiridae.

Figure 1. The Ornithocheiridae. Click to enlarge and expand.

We’ll Continue with Coloborhynchus
Coloborhynchus spielbergi (Owen 1874, = Ornithocheirus clavirostris; C. spielbergi Veldmeijer 2003) RGM 401 880, Early Cretaceous was originally lumped with Ornithocheirus and much later was considered congeneric with Anhanguera by several workers (Kellner 2006). Distinct from Haopterus, the skull of Coloborhynchus had an anterior crest both above the snout and below the chin. The pre-antorbital fenestra region was longer. The orbit was narrower and raised higher over the antorbital fenestra. The neural spines were taller. A notarium was formed by several fused dorsals into which the scapula was articulated. The sacrals were interlocked if not fused. The sternal complex was rather deep. The scapulocoracoid was fused. The humerus was much more gracile. The ulna and radius were also thinner, but the distal ends were expanded. The pelvis was more robust with a more ossified ischium and a raised posterior ilium.

Criorhynchus 
Criorhynchus mesembrinus (Owen 1874, = Ornithocheirus clavirostris; = Tropeognathus mesembrinus, Fastnacht 2001) BSp 1987 I 46 from the Early Cretaceous was a sister to Coloborhynchus and may be congeneric with it. Distinct from Coloborhynchus, the skull of Criorhynchus was longer, lower and wider. The palatal elements were more robust. The ischium was narrower.

Nurhachius, a Basal Istiodactylid
Nurhachius ignaciobritoi (Wang, Kellner, Zhou & Campos 2005) IVPP V-13288, Early Cretaceous, skull length ~30 cm, ~2.5 m wingspan. Distinct from Criorhynchus the skull of Nurhachius further extended the rostrum and increased the size of the antorbital fenestra. If predecessors had a crest, it was greatly reduced or underdeveloped in Nurhachius. The orbit was very narrow and posteriorly slanted with a tiny sclerotic ring at the top. The upper temporal fenestra was completely above the orbit. Distinct from Coloborhynchus, the sternal keel was very deep (if that is the keel). The humerus was shorter. Fingers 1-3 were smaller. The femur was shorter. The metatarsals were robust and the pedal digits were slender, as in Zhenyuanopterus.

The largest ornithocheirid

Figure 2. Click to enlarge. The unnamed largest ornithocheirid, SMNK PAL 1136

One of the Biggest Ornithocheirids Still Has No Name
SMNK PAL 1136 (not yet described, figured by Frey and Marill 1994) ~80 cm skull length, Aptian, Early Cretaceous ~130 mya, was originally considered an Anhanguera sp. Larger and distinct from Istiodactylus, the skull of SMNK PAL 1136 had the antorbital fenestra extend into the anterior rostrum just posterior to the premaxillary crest. The orbit was high and small. It was located just aft of the mandibular articulation. The jugal + lacrimal were reduced to slender rods oriented dorsoposteriorly. The sternal complex had a large keel and a reduced sternal plate. The scapulocoracoid was gracile. The gracile humerus expanded distally. Manual 4.1 extended to the elbow when folded. The pelvis was relatively smaller than in Coloborhynchus and the prepubis is tiny. The femur was considerably shorter than the tibia.

Istiodactylus latidens
Istiodactylus latidens BMNH R 3877 (Hooley 1913, Ornithodemus” latidens; Howse, Milner and Martill 2001) ~56 cm skull length, Aptian, Early Cretaceous ~130 mya was an unusual ornithocheirid known from a partial skeleton. Distinct from SMNK PAL 1136, the skull of Istiodactylus was a quarter smaller than SMNK 1136 PAL and similar in size to Coloborhynchus. The long gracile skull was dominated by an antorbital fenestra comprising 63 per cent of its estimated length. The anterior margin of the antorbital fenestra was posterior to all teeth, which fill only the anterior fourth of the jaws. Both narial openings (per side) were dorsal to the teeth. The long quadrates were so inclined that the orbit was positioned even further posteriorly than in PAL 1136. The teeth were lancet-shaped, closely spaced, and interlocked like a bear trap. A central dentary tooth filled the gap left by the medial premaxilla teeth, which were diminutive. The teeth increased in size posterolaterally. Two posterior dentary teeth fit into slots in the premaxilla. The dorsal vertebral transverse processes were nearly vertical. A notarium of six vertebrae was present. Asymmetrical coracoidal articulations on the anterior edge of the deep sternal complex keel continued on the lateral surface. The reconstructed wing/torso ratio was estimated at ~9:1. The deltopectoral crest was warped into a spiral. The ulna had a ridge that supported the radius. The antebrachium was relatively longer than in PAL 1136. What Hooley (1913) identfied as an ischium is identified here as the pubis and ischium.

Istiodactylus

Figure 3. Click to enlarge. Istiodactylus

Istiodactylus sinensis
Istiodactylus sinensis 
NGMC 99-07-011 (Andres and Ji 2006) Aptian, Early Cretaceous ~125 mya, ~35 cm skull length, appears to be more primitive in that the deltopectoral crest was not so curved and the skull was not as gracile. As in Nurhachius, when the wing was folded the elbow was closest to the middle of m4.2. The three free fingers each had only one phalanx, probably via fusion because there is no dimunition of the finger lengths. The resulting proximal phalanges are all subequal, approaching the configuration in Coloborhynchus, which had no phalanx fusion. Only pedal digit I and IV are known and they follow the pattern of larger medial digits seen in sister taxa.

In summary
This clade originated with a big crest on the rostrum tip and a small antorbital fenestra. As taxa evolved the crest slowly disappeared while the antorbital fenestra elongated anteriorly and pushed the orbit higher and smaller posteriorly.

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
Andres B and Ji Q 2006. A new species of Istiodactylus (Pterosauria, Pterodactyloidea) from the Lower Cretaceous of Liaoning, China. Journal of Vertebrate Paleontology, 26: 70-78.
Bowerbank JS 1846. On a new species of pterodactyl found in the Upper Chalk of Kent P. giganteus). Quarterly Journal of the Geological Society 2: 7–9.
Bowerbank JS 1851. On the pterodactyles of the Chalk Formation. Proceedings of the Zoological Society, London, pp. 14–20 and Annals of the Magazine of Natural History (2) 10: 372–378.
Bowerbank JS 1852. On the pterodactyles of the Chalk Formation. Reports from the British Association for the Advancement of Science (1851): 55.
Fastnacht M 2001. First record of Coloborhynchus (Pterosauria) from the Santana Formation (Lower Cretaceous) of the Chapada do Araripe, Brazil. – Palaontologische Zeitschrift 75(1): 23-36.
Frey E and Martill DM 1994. A new Pterosaur from the Crato Formation (Lower Cretaceous, Aptian) of Brazil. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 194: 379–412.
Hooley RW 1913. On the skeleton of Ornithodesmus latidens. An ornithosaur from the Wealden shales of Atherfield (Isle of Wight)”, Quarterly Journal of the Geological Society, 69: 372-421
Howse SCB, Milner AR and Martill DM 2001. Pterosaurs. Pp. 324-335 in: Martill, D. M. and Naish, D., eds. Dinosaurs of the Isle of Wight, The Palaeontological Association
Owen R 1861. Monograph on the fossil Reptilia of the Cretaceous Formations. Supplement III. Pterosauria (Pterodactylus). The Palaeontographical Society, London. (volume for 1858; pp. 1–19 & pls 1–4)
Owen R 1874. A Monograph on the Fossil Reptilia of the Mesozoic Formations. 1. Pterosauria. The Palaeontographical Society, London. pp. 1–14 & pls 1–2.
Wang X, Kellner AWA, Zhou Z and Campos DA 2005. Pterosaur diversity and faunal turnover in Cretaceous terrestrial ecosystems in China. Nature 437 (7060): 875–879. doi:10.1038/nature03982. PMID 16208369.

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