Falseryx, 2008

Szyndlar, Zbigniew, Smith, Richard & Rage, Jean-Claude, 2008, A new dwarf boa (Serpentes, Booidea, ‘ Tropidophiidae’) from the Early Oligocene of Belgium: a case of the isolation of Western European snake faunas, Zoological Journal of the Linnean Society 152 (2), pp. 393-406 : 395-399

publication ID

https://doi.org/ 10.1111/j.1096-3642.2007.00357.x



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Holotype: IRSNB R 240 , one trunk vertebra.

Referred material: IRSNB R 237-239, 241 (four trunk vertebrae), unnumbered 78 trunk vertebrae, collection R. Smith; IRSNB R 233 (one cloacal vertebrae); IRSNB R 234-236 (three caudal vertebrae), unnumbered 16 caudal vertebrae, collection R. Smith.

Type locality: Boutersem TGV ( Belgium).

Type horizon: Earliest Oligocene ( MP 21).

Etymology: After the name Neervelp, a hamlet from Boutersem quite near the Boutersem TGV site.

Diagnosis: Differs from Falseryx petersbuchi by having trunk vertebrae provided with longer centra, shallower interzygapophyseal constriction, deeper posterior notch of the neural arch, lower and more thickened dorsally neural spine, underdeveloped or absent central lobe of the zygosphene, distinctly larger tubercles developed from the prezygapophyseal buttresses, smaller and less extended dorsoventral paradiapophyses; larger vertebral foramina; by having cloacal and anterior caudal vertebrae provided with shorter hypapophyses.



The holotype ( IRSNB R 240; Fig. 1 View Figure 1 ) is a completely preserved vertebra, coming from the middle trunk portion of the column. The centrum length (= ‘CL’ sensu Auffenberg, 1963; the distance between the cotyle lip and the end of the condyle) is 4.1 mm, the centrum width (= ‘NAW’; the width of the interzygapophyseal constriction) is 3.4 mm.

In lateral view, the vertebra is longer than high. The neural spine is distinctly reduced in height, occupying one-third the length of the neural arch, and beginning far behind the posterior border of the zygosphenal articular facets. The dorsal portion of the spine, in particular of its anterior half, is strongly thickened. The lateral foramina are clearly visible. The paradiapophyses are stout, somewhat higher than long, weakly divided into para- and diapophyseal portions. The prezygapophyseal buttresses (between the paradiapophyses and prezygapophyseal processes) are developed into prominent, anteriorly facing tubercles. The subcentral ridges are indistinct. The ventral margin of the haemal keel is straight.

In dorsal view, the vertebra is somewhat longer than wide. The posterior notch of the neural arch is moderately concave. The interzygapophyseal constriction is moderately deep. The neural spine is broad, uniform in width throughout its length. The zygosphene has two well-developed lateral lobes; the central lobe is reduced. The prezygapophyseal articular facets are relatively large, rhomboid in shape, and elongate in anterolateral direction. The prezygapohyseal processes are very short but clearly visible.

In ventral view, the centrum is somewhat longer than wide. The haemal keel is constricted in the middle and distinctly broadened anteriorly and posteriorly; its posterior part is flattened. The subcentral grooves are rather shallow. The subcentral foramina are distinct (the left foramen has an enormous diameter). The postzygapophyseal articular facets are teardrop-shaped.

In anterior view, the vertebra is strongly flattened dorso-ventrally. The zygosphenal roof is concave; it is wider than the circular cotyle. The neural spine is ‘T’-shaped. The prezygapophyses are located clearly above the floor of the neural canal and are slightly inclined. The paradiapophyses do not project downwards beyond the cotyle lip. The paracotylar foramina are absent.

In posterior view, the neural arch is strongly depressed; its posterodorsal borders are slightly convex. The neural spine is extremely low and thick. The zygantrum is distinctly wider than the suborbicular condyle. Tiny doubled parazygantral foramina are located on both sides of the zygantrum.


The only significant differences between the anterior trunk vertebra ( Fig. 2A–C View Figure 2 ) and those from the middle trunk portion of the column are, as typical of most snakes, the presence of a hypapophysis instead of haemal keel and higher neural spine. The parapophyses of the anterior trunk vertebra project downwards far beyond the cotyle lip; they are devoid of parapophyseal processes.

Middle trunk vertebrae ( Fig. 2D–F View Figure 2 ), by their morphology and size, are very similar to the holotype. Slight differences can be observed in the shape of the zygosphene in dorsal view. The most common condition is a three-lobed zygosphenal roof: the lateral lobes are distinct, while the central lobe is usually weakly developed (as in the holotype). In a few cases the central lobe is entirely underdeveloped: the anterior edge of the zygosphene is straight or concave in dorsal view; this must result from intracolumnar variation.


Posterior trunk vertebrae ( Fig. 2G–K View Figure 2 ) are relatively longer and more depressed than those from the middle portion of the column. They possess distinct subcentral ridges, deeper subcentral grooves and a prominent haemal keel. The keel is broad, strongly depressed and roughly uniform in width throughout its length.

Another vertebra ( Fig. 2L–P View Figure 2 ) probably represented the posteriormost trunk portion of the column. This vertebra is somewhat shorter than the preceding posterior trunk vertebrae, especially in dorsal or ventral aspect. However, it cannot be interpreted as the last trunk vertebra because it is relatively distinctly longer than the cloacal vertebra (see below). The haemal keel, rounded in cross-section and posteroventrally developing into an obtuse tip, can be interpreted rather as a short hypapophysis (as typical of the end of the trunk portion of the column in booids and various other snakes).


One cloacal vertebrae ( Fig. 3A–C View Figure 3 ), as typical of this portion of the column, is provided with (partly broken) lymphapophyses. The vertebral body is distinctly shortened. In having a low and posteriorly located neural spine, it resembles the preceding vertebrae from the trunk portion of the column. The hypapophysis is reduced to a distinct though small bulge. Based on its similarities to the anterior caudal vertebrae (see below) rather than to those from the posterior trunk region as well as on the reduction of the hypapophysis, the vertebra is interpreted as originating from the posterior rather than anterior cloacal portion of the column.


Nineteen vertebrae represent clearly three main regions of the caudal portion of the column: anterior, middle and posterior. In general, more anterior caudal vertebrae can be easily differentiated from those located more posteriorly by having larger absolute dimensions, relatively shorter centra, anteroposteriorly shorter neural spines, and laterally (or latero-posteriorly) directed pleurapophyses (directed latero-anteriorly in posterior caudals).

The basic difference between caudal and cloacal vertebrae is the presence of lymphapophyses in the latter instead of pleurapophyses characteristic of the former. Apart from this difference, however, the anterior caudals closely resemble the cloacal vertebra, among others in having a short and posteriorly located neural spine. The spines of the caudal vertebrae are, however, relatively higher than those of the trunk vertebrae and devoid of ‘T’-like thickening on their dorsal edges.

The most peculiar feature of the caudal portion of the column in F. neervelpensis is a changing sequence of subcentral structures observed in succeeding vertebrae. The anterior caudals are provided with a very short hypapophysis, flattened (plate-like) in posterior or ventral view and pointed distally in lateral view ( Fig. 3D–H View Figure 3 ).

In middle caudals, the hypapophysis is replaced by paired haemapophyses ( Fig. 3I, J View Figure 3 ). Both structures have the same shape, when seen in lateral aspect. Another vertebra carries an ‘intermediate’ subcentral structure, namely a hypapophysis slightly forked distally; this vertebra is interpreted as coming from the transition between anterior and middle regions of the caudal portion of the column.

In posterior caudals ( Fig. 3K, L View Figure 3 ), the haemapophyses are reduced to a small haemal keel. Some of these vertebrae, however, retain a trace of the haemapophyses in the form of medially located grooves or a pits.


Institut Royal des Sciences Naturelles de Belgique


Departamento de Geologia, Universidad de Chile


Mohonk Preserve, Inc.