SYSTEMATIC PALEONTOLOGY

Ophidia Brongniart, 1800
Alethinophidia Nopcsa, 1923
Pythoninae Boulenger, 1890
Python Daudin, 1803
Species indeterminate
Figure 2

Referred specimens. H-GSP 13959, 13961-3, 13965, 13968, 14633, 17631, 17720, 19707, 19799, 21005, 21031, 21914, 22078, 22304, 22306, 22309, 23295, 23345, 23723, 24154, 24229, 24350, 24363, 24364, 26723, 27098, 27252, 27719, 27806, 31166, 31318, 31320, 32557, 40204, 40701, 40906, 41161, 41288, 41632, 42267, 46054, 46102, 46184, 46185, 46228, 46420, 46796, 47282, 47381, 47580, 49895-7, 49899, 50044, 50149, 50295, 50425, 50429, 50517, 51109, 51123, 53114, 53115, 53125, 53126, 53178, 53297, 53298, isolated precloacal vertebrae.

Localities and ages. Y-802 (16.80 Ma), Y-642 (15.20 Ma), Y-478 (14 Ma), Y-650 (13.05 Ma), Y-882 (13 Ma), Y-698 (12.94 Ma), Y-849 (12.81 Ma), Y-750 (12.7), Y-496 (12.30 Ma), Y-634 (12.20 Ma), Y-883 (11.98 Ma), Y-499 (11.95 Ma), Y-515 (11.95 Ma), Y-498 (11.55 Ma), Y-504 (11.52 Ma), Y-061 (11.46 Ma), Y-809 (11.40 Ma), Y-773 (11.34 Ma), Y-076 (11.31 Ma), Y- 311 (10.00 Ma), Y-262 (9.49 Ma), Y-633 (9.27 Ma), Y-1001 (9.25 Ma), Y-327 (9.18 Ma), Y-401 (8.89 Ma), Y-024 (8.14 Ma), Y-547 (7.93 Ma), Y-946 (7.76 Ma), Y-457 (7.30 Ma), Y-856 (7.28 Ma), Y-921 (7.24 Ma), Y-370 (7.13 Ma), Y-910 (6.98 Ma), Y-908 (6.78 Ma).

Description. Vertebrae assigned to Python are large and block-shaped, and include elements from all recognizable regions of the precloacal vertebrate column. In anterior view (Figure 2A.1), the cotyle has a strongly subequal ventral margin that is continuous with the haemal keel, resulting in a slightly pointed cotylar ventral apex. There is no indication of paracotylar foramina on any recovered specimens assigned to Python. Dorsal to the cotyle, the neural canal is triangular and capped by a prominent zygosphene. The zygosphene is tall, with large, high-angled articular facets. Medially, a pronounced, rounded tuberosity is present on the anterior face of the zygosphene along the dorsal margin of the neural canal. Lateral to the cotyle, the prezygapophyses are low-slung and dorsoventrally thin.

In dorsal view (Figure 2A.2), the interzygapophyseal ridge possesses a straight lateral margin that is posteromedially angled between the pre- and postzygapophyses. The posterior median notch of the neural arch is deep with straight margins, exposing the posteromedial margins of the zygantral articular facets in dorsal view. The prezygapophyseal articular facets are ovate, with straight, transversely oriented anterior margins. Small, pointed accessory processes are visible at the anterolateral margins of the prezygapophyses.

In ventral view (Figure 2A.3), the centrum is wide with a thin, poorly defined haemal keel in all specimens. In vertebrae from the anterior section of the vertebral column, the hypapophysis originates just anterior to the cotyle. Hypapophyses are robust and ovoid in cross section. The synapophyses are moderately developed, with robust, laterally oriented parapophyses and smaller, posteromedially oriented diapophyses. In vertebrae from the posterior region of the precloacal column, the paralymphatic channels and subcentral paralymphatic fossae are well developed and deeply excavated into the ventral surface (Figure 2B.2).

In lateral view (Figure 2A.4), the interzygapophyseal ridge possesses swollen lateral margins, and is elevated between the pre- and postzygapophyses. In posterior view (Figure 2A.5), the lateral margins of the neural arch are strongly sigmoid in outline. The posterior surface of the arch at the level of the zygantrum is rugose and pitted for attachment of intervertebral ligaments. The zygantrum is deep, with a prominent medial ridge.

Discussion. The following character combination diagnoses referred specimens to Pythoninae: zygapophyseal bridge straight and posteromedially angled; triangular neural canal; presence of a zygosphenal tuberosity; absence of paracotylar foramina. Individually, none of these characters are unique to pythonines (see discussions in Kluge 1988; Szyndlar and Rage 2003), but their combined presence is unique to the lineage. Hoffstetter (1964) recognized Python from the Siwalik Group based on a single specimen. Generic assignment was based on overall similarity with extant Python, and Hoffstetter (1964) recognized a specific-level distinction based on the following characters: relatively elongate centrum (compared to neural arch width and vertebral height), longitudinal ridge along the haemal keel, and thick zygosphenal base. There is no indication that a separate longitudinal ridge can be differentiated from the haemal keel in the Siwalik specimens, and the morphology of the keel is indistinguishable from that of other pythonines. A thick zygosphenal base is present in the majority of other pythonines. The relative length of the centrum varies in the column of all snakes, including pythonines (Hoffstetter and Gasc 1969; Polly et al. 2001), and is not considered diagnostic. Hoffstetter did not name his specimen as a new species due to limited sample size and the incomplete nature of the specimen. Based on the generic-level taxonomy of Kluge (1993b) and large sizes of specimens, this study also assigns all pythonine specimens to the genus Python. Because the characters used by Hoffstetter (1964) to recognize the Siwalik Python as a new taxon are present in extant taxa, or are variable throughout the vertebral column, I do not make a species-level assignment.

The Neogene pythonine fossil record includes occurrences in the early Miocene of Africa, Arabia, Asia, Australoasia, and Europe (Hoffstetter 1964; Rage 1976, 2003; Thomas et al. 1981; Underwood and Stimson 1990; Ivanov 2000). Geographic distributions do not exceed the current zoogeography of pythonines (Underwood and Stimson 1990), with the exceptions of a questionable taxon from the Miocene of Sardinia (Portis 1901), P. euboicus from the early Miocene of Greece (Szyndlar and Rage 2003), and Python europaeus from the middle Miocene of France (Ivanov 2000; Szyndlar and Rage 2003). The earliest occurrences of Python in the Siwalik section are from localities in the Kamlial Formation dated at approximately 18 Ma. This record is approximately coeval with the oldest African and European records, minimally constraining the timing of pythonine dispersal into mainland Asia and Africa (Kluge 1993b) to no younger than earliest Neogene.