Messelopython freyi, Zaher & Smith, 2020

Zaher, Hussam & Smith, Krister T., 2020, Pythons in the Eocene of Europe reveal a much older divergence of the group in sympatry with boas, Biology Letters 16 (12), pp. 1-6 : 2-4

Messelopython freyi gen. et sp. nov.

urn:lsid:zoobank.org:act:E8C2F2DA-1434-4580-8D30A5EDA71A2CAC

urn:lsid:zoobank.org:act:84AF3F8E-1B68-4807-A5A331D95A9ADE84

Holotype: SMNK-PAL 461 , nearly complete skeleton with partial skull ( figure 1 a–c )

Paratypes: SMF-ME 710 , nearly complete skeleton with a badly crushed skull ( figure 1 f ); SMF-ME 2784 , a nearly complete skeleton with a skull ( figure 1 d,e,g ); HLMD-Be 165 , a nearly complete skeleton with a partial skull ( figure 1 h,i ).

Referred specimen: HLMD-Me 10583

Diagnosis: Medium-sized pythonoid (electronic supplementary material, S6) sharing with Pythonidae the following synapomorphies: a toothed premaxilla with no midline diastema; palatine foramen present in palatine; and mid-sagittal crests on parietal and basisphenoid. Autapomorphies: 6 premaxillary teeth; sigmoid lateral margin of maxilla; large, crescentic supraorbital bone nearly equal in length to the frontal; ectopterygoid overlap of pterygoid reduced.

Type locality and horizon: Messel Pit, Germany; Middle Messel Formation, latest early to earliest middle Eocene [ 35].

Etymology: ‘Messel’, after the type locality [ 25], and ‘python’, after its close living relatives. The specific epithet honours Eberhard ‘Dino’ Frey, for his detailed studies of fossil and extant reptiles.

4. Results

The premaxilla of M. freyi ( figure 1 ) possesses a short nasal and a pair of long vomerine processes. It is toothed, with six tooth positions, and lacks a median tooth or midline diastema. The long, paired nasals taper anteriorly. The prefrontals lack a lateral foot-process but possess an ascending lamina; these laminae do not meet on the midline. The paired frontals are long and have a concave lateral margin, corresponding to the supraorbital bone, for which an articulation facet is developed (see explanation on homologies of circumorbital bones in electronic supplementary material, characters 73, 74, 77 and 170). The orbital margins of the frontals are upturned. They articulate with the parietal on an anteriorly concave suture. The postfrontal has a bifurcated dorsal articulation on the parietal corner, and it does not reach the frontal. It possesses a long articulation with the supraorbital, which extends some distance ventrally. The large size and crescentric shape of the supraorbital distinguishes M. freyi from all extant Pythonoidea (electronic supplementary material, figure S1 ).

The elongate parietal possesses a low, mid-sagittal crest over nearly three-quarters of its length. It is somewhat inflated anteriorly. The posterior margin of the parietal contacts the small, oval supraoccipital in an anteriorly directed V-shaped suture, as in most pythonids. The ophidiosphenoid is broad and the foramen for the maxillary branch of the trigeminal nerve is open anteriorly in the prootic. A low, mid-sagittal crest is present on the parabasisphenoid.

The supratemporal extends beyond the posterior end of the braincase. The quadrate has a triangular, plate-like dorsal portion, whereby the cephalic condyle is at an oblique angle to the mandibular condyle.

The maxilla has a weakly sigmoid lateral margin and a single labial foramen. As in most pythons [ 18], it retains an anterior foramen located just on the medial side of the bone, and two dorsal foramina on the palatine process for the superior alveolar nerve. The palatine process is broad and rounded, rather than posteriorly directed and club-like as in Booidea. The ectopterygoid expands in width anteriorly, where its distal tip is bifurcated. Posteriorly, it possesses a short articulation on the pterygoid, but no pronounced posterior process as in Pythonidae . The toothed palatine is pierced by the palatine nerve. Details of the articulation with the pterygoid are unknown. Both palatine and pterygoid were toothed, although an exact tooth count cannot be given. The pterygoid terminates posteriorly just short of the mandible.

The dentary has one mental foramen on the right side of SMF-ME 2784 and two on the left. The surangular notch is not particularly deep. The splenial has a posteroventral knob, which would have inserted into a concavity on the angular. The compound bone possesses a weak but distinct ventrolateral crest. The surangular crest rises relatively straight and gradually, whereas the prearticular crest is strongly convex. The anterior surangular foramen is small.

The maxilla possesses approximately 18 tooth spaces. The teeth are long and needle-shaped, diminishing from front to back, but anterior teeth are not notably enlarged.

There appear to be somewhere between 205 and 210 trunk vertebrae in the holotype. HLMD-Be 165 has approximately 209 trunk vertebrae followed by at least two visible cloacals. SMF-ME 2784b preserves the tail, with at least two cloacal vertebrae with bifurcated lymphapophyses followed by approximately 67 vertebrae and tail tip. This yields an approximate total vertebral count of 275. The trunk vertebrae are short and high. Hypapophyses are present only on anterior trunk vertebrae. Mid-trunk vertebrae have an anteroposteriorly long neural spine whose base extends onto the zygosphenal tectum (electronic supplementary material, figure S2 ). Short accessory processes are present. Broadly rounded zygantral mounds (see [36,37]) are present even in the posterior trunk. Haemapophyses are present in the tail.

Our phylogenetic analysis strongly supports the position of Messelopython freyi on the stem of Pythonidae (figure 2 a; electronic supplementary material).

Excluding Messelopython freyi , BioGeoBEARS results support a Gondwanan origin of Alethinophidia and dispersal of stem pythonids over Antarctica to Australia and Asia. Including M. freyi , both DEC and DEC + J support a Laurasian, and more specifically European, origin of Pythonoidea and Pythonidae (electronic supplementary material, figures S4–S9), with the dispersal of the total clade of Pythonidae to Africa and Oceania ( figure 2 b ); analyses assuming an African range for our Python terminal do not alter this conclusion.

Figures

Figure 1. Hypodigm of Messelopython freyi gen. et sp. nov. (a) and (b) Photograph and drawing of skull of holotype, SMNK-PAL 461a. (c) Photograph of holotype. (d) and (e) Photograph and drawing of skull of paratype, SMF-ME 2784a. (f) Drawing of left splenial and angular in medial view in counterpart of paratype. (g) Drawing of right ectopterygoid in dorsal view in main part of paratype. (h) and (i) Photograph and drawing of skull of paratype, HLMD-Be 165. Abbreviations: an, angular; boc, basioccipital; bpt-pr, basipterygoid process; bs, basisphenoid; d, dentary; ec, ectopterygoid; fr, frontal; mx, maxilla; n, nasal; ot, otooccipital; pa, parietal; par, prearticular part of compound bone; pl, palatine; pf, postfrontal; prf, prefrontal; pro, prootic; pt, pterygoid; q, quadrate; sa, surangular part of compound bone; smx, septomaxilla; so, supraorbital; soc, supraoccipital; spl, splenial; st, supratemporal.

Figure 2. (a) Phylogenetic relationships of Messelopython freyi gen. et sp. nov. Support values for nodes are Jackknife/Bremer, values of 100% (Jackknife) or greater than 20 (Bremer) are indicated with an asterisk. (b) Palaeogeographic map of continental distributions at 48 Mya based on Gplates model [38] with location (palaeocoordinates for 48 Mya) of Palaeogene records of the total clades of Boidae, Loxocemidae and Pythonidae. Large arrows indicate hypothesized dispersal directions for the total clade of Pythonidae.