We report the first record of a snake from the Cretaceous of northern South America. The remains come from the La Luna Formation (La Aguada Member, Cenomanian of Venezuela) and consist of several vertebrae, which belong to the precloacal region of the vertebral column. Comparisons to extant and extinct snakes show that the remains represent a new taxon,
Until recently, the oldest record of snakes has been from the Albian of Algeria (
Using a combination of traditional node-based dating and novel fossil tip-dating methods,
In South America, the oldest snakes are known from the Mesozoic of Brazil and Argentina. The Brazilian taxa consist of the putative four-limbed snake
The specimen was found in strata of the La Luna Formation (La Aguada Member), exposed in a cement quarry (Cementos Andinos Company) in the Andes of Venezuela, east of Lake Maracaibo, 10 km northeast of Monay in the Candelaria Municipality of Trujillo State (
The Upper Cretaceous La Luna Formation is the most prolific petroleum source rock in western Venezuela and part of eastern Colombia (
(A) Cretaceous lithostratigraphic units of the Chejendé region, near Monay city, Trujillo State (modified after
The outcrops of the Aguada Member in the Cementos Andinos quarry (
(A) Fossiliferous strata; (B) Strata with calcareous concretions; (C), (D). Discoidal calcareous concretions.
The studied specimen (MNCN-1827) is deposited in the Museo de Ciencias Naturales de Caracas, Venezuela. The fossil (
MNCN-1827-A, isolated precloacal vertebra. Anterior (A), left lateral (B), dorsal (C), and ventral (D) views.
(A–B), MNCN-1827-B; (C–D), MNCN-1827-C; (E–F), MNCN-1827-D; (G–H), MNCN-1827-E. Dorsal (A, C, E, G), and ventral (B, D, F, H) views.
MNCN-1827-F, articulated precloacal vertebrae. Dorsal (A) and ventral (B) views.
Following the criteria of
The specimen was scanned using micro-computed tomography (
Phylogenetic relationships of fossil and Recent snakes proposed by
The electronic version of this article in Portable Document Format (PDF) will represent a published work according to the International Commission on Zoological Nomenclature (ICZN), and hence the new names contained in the electronic version are effectively published under that Code from the electronic edition alone. This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix http://zoobank.org/. The LSID for this publication is: urn:lsid:zoobank.org:pub:918B6879-8908-488F-876B-EA741DFF627B. The online version of this work is archived and available from the following digital repositories: PeerJ, PubMed Central and CLOCKSS.
Squamata |
Serpentes |
MNCN-1827-A, isolated precloacal vertebra. Anterior (A), posterior (B), dorsal (C), ventral (D), right lateral (E), left lateral (F), dorsoposterior (G), and posterolateral (H) views; co, condyle; ct, cotyle; hk, haemal keel; izr, interzygapophyseal ridge; na, neural arch; pd, paradiapophysis; plf, paralymphatic fossa; po, postzygapophysis; pr, prezygapophysis; sbr, subcentral ridge; zg, zygosphene.
MNCN-1827-B, isolated precloacal vertebra. Dorsal (A), ventral (B), left lateral (C), and right lateral (D) views; co, condyle; hk, haemal keel; na, neural arch; ns, neural spine; pd, paradiapophysis; plf, paralymphatic fossa; po, postzygapophysis; pr, prezygapophysis; sbr, subcentral ridge; zg, zygosphene.
(A–D) MNCN-1827-C, isolated precloacal vertebra; (E–H) MNCN-1827-D, isolated precloacal vertebra; (I–L), MNCN-1827-E, isolated anterior vertebra. Dorsal (A, E, I), ventral (B, F, J), left lateral (C, G, K), and right lateral (D, H, L) views; co, condyle; na, neural arch; ns, neural spine; pd, paradiapophysis; po, postzygapophysis; pr, prezygapophysis; sbr, subcentral ridge.
Measures (in mm) | MNCN-1827-A | MNCN-1827-B | MNCN-1827-C | MNCN-1827-D |
---|---|---|---|---|
cl | 8.44 | 8.00 | 7.62 | – |
cow | 3.00 | 2.86 | 3.00 | – |
cth | – | 2.82 | 3.00 | 2.58 |
ctw | – | 3.10 | 3.18 | 3.00 |
H | 6.34 | 5.70 | 7.16 | – |
naw | 6.44 | 6.18 | 6.34 | 6.84 |
nal | 10.16 | 9.22 | – | – |
po-po | – | 9.62 | – | – |
prl | 3.56 | 3.34 | 3.50 | 3.26 |
prw | 2.56 | 2.76 | 2.40 | 2.84 |
pr-po | 9.52 | – | 9.20 | 9.14 |
pr-pr | 10.00 | – | – | 10.94 |
zgh | – | 0.40 | – | – |
zgw | 3.66 | 3.60 | – | – |
centrum length condyle wide cotyle high cotyle wide high of the vertebra neural arch wide neural arch length distance between postzygapophyses prezygapophyses length prezygapophysis wide distance between pre- and postzygapophyses of the same side distance between prezygapophyses zygosphene high zygosphene wide
In anterior view, the zygosphene is well-developed and slightly wider than the cotyle (zgw > ctw); it is thin in the middle and its dorsal edge is almost flat. The articular facets are relatively large and anteriorly oriented. The neural canal is small, with a round outline. The prezygapophyses are robust, inflated and large; they are borne at the ventral base of the neural canal and slant above the horizontal plane, but do not reach the level of the zygosphenal roof. There are no prezygapophyseal processes. The cotyle is large, nearly circular, and delimited by a well-marked rim. It is partially filled by sediment. There are strong depressions on both sides of the cotyle but the paracotylar foramen is visible only on the right side of vertebra MNCN-1827-A. In specimen MNCN-1827-B there is not a visible paracotylar foramen on the right side and it is broken on the left. The paradiapophyses are positioned ventral to the cotyle, distant from the prezygapophyseal surfaces and close to each other; they project ventrally with a short and constricted process separating them from the vertebral centrum. The articular surfaces are small, with clearly distinctive parapophyses and diapophyses facing ventrally and strongly projecting beyond the ventral rim of the cotyle.
In posterior view, the neural arch is depressed and forms a protruded bulge above the postzygapophysis as a strong, inflated convexity, especially on vertebra MNCN-1827-B on both sides and on vertebra MNCN-1827-A on the left. These swollen paired posterior portions of the neural arch platform are interpreted as pachyostosis. The zygantra filled by sediment, which also extends over the dorsal condyle. The roof of the neural arch of vertebra MNCN-1827-B is proportionally less depressed than in specimen MNCN-1827-A, and the zygantra are larger. Vertebra MNCN-1827-A has the left postzygapophysis distally broken whereas in vertebra MNCN-1827-B the fracture is on the right. The postzygapophyseal surfaces are large and slightly inclined above the horizontal. There are no parazygantral foramina. The condyle is large and more or less round. The posterior end of a wide hemal keel is slightly visible ventral to the condyle.
In dorsal view, the neural arch is long and wide, with the posterior edge convex in vertebra MNCN-1827-A and almost straight in vertebra MNCN-1827-B. None of the condyle is visible in this view. The interzygapophyseal constriction is concave but not especially deep. The interzygapophyseal ridges are strongly developed and protrude laterally beyond the level of the lateral walls and subcentral ridges. They connect the pre- and postzygapophysis of the same side. The articular surfaces of the prezygapophyses are large, oval, longer than wide, and anterolaterally oriented. The zygosphene is well-developed and concave in the middle. It is partially broken on the left side of specimen MNCN-1827-A whereas it is complete on vertebra MNCN-1827-B. Vertebra MNCN-1827-A does not have neural spine; only a minor crest restricted to the anteriormost part of the neural arch. It is limited by narrow and short depressions at each side. Posteriorly to it, the surface of the arch is smooth. In contrast, a well-defined but very low neural spine is developed, but partially broken in the middle, along most of the roof of the neural arch in vertebra MNCN-1827-B. Longitudinal and marked ridges are extended anteroposteriorly on either side of the neural spine; they are laterally flanked at both sides by deep grooves. These crests and grooves are prominent especially in the posterior half, reaching the posterior border of the neural arch. Distally, over each postzygapophysis, the neural arch forms protruded, swollen bulges representing pachyostosis. The bulging is not developed on the right side of vertebra MNCN-1827-A producing asymmetry.
In ventral view, the vertebral centrum is long (cl > naw) and narrow, slightly wider anteriorly than posteriorly, but not markedly triangular in section. The subcentral ridges are well defined and prominent (
In lateral view, the vertebrae are long, with significantly depressed neural arch roofs. Anteriorly, the neural arch extends beyond the level of the cotyle due to the anterior projection of the zygosphene. Posteriorly, the neural arch is longer than the vertebral centrum (nal > cl), extending beyond the level of the condyle. The neural arch in the vertebra MNCN-1827-B is slightly shorter than in specimen MNCN-1827-A. The neural spine is partially broken in vertebra MNCN-1827-B but it would have been long and low, as a thin crest developed from the base of the zygosphene and almost until the posterior end of the neural arch. The zygosphenal surfaces are prominent, oval, longer than wide, and more anteriorly than dorsally oriented. Posteriorly, on either side, the roof of the neural arch are inflated forming the mentioned hemispheric bulge above the postzygapohysis. As a result, the outline of the neural arch is concave in lateral view. The absence of a neural spine in vertebra MNCN-1827-A produces a more deeply concave arch in lateral view than in vertebra MNCN-1827-B. The prezygapophyses are large, swollen, and anterolaterally oriented. The interzygapophyseal crest is well marked, laterally projected, and strongly separates the roof from the lateral walls of the neural arch. The distance between the interzygapophyseal crests (naw) is much higher than the distance between the lateral walls of the neural arch where they contact with the roof. This is because the lateral walls are borne near the saggittal axis of the vertebra. They diverge dorsoventrally from this point to the subcentral ridges. This structure produces a prominent shelf-like arch roof of the neural arch on each side between the pre- and postzygapophysis (
Vertebra MNCN-1827-C (
Vertebra MNCN-1827-D (
Specimen MNCN-1827-E is a poorly preserved vertebra (
Specimen MNCN-1827-F includes five tightly articulated vertebrae (
(A–D), MNCN-1827-F, articulated precloacal vertebrae; (E–H), MNCN-1827-G, scarcely preserved vertebral fragment. Dorsal (A, E,), ventral (B, F), right lateral (C, G), and left lateral (D, H) views; hk, haemal keel; na, neural arch; ns, neural spine; pd, paradiapophysis; po, postzygapophysis; pr, prezygapophyis.
Following the atlas and axis, the vertebral column of snakes is conventionally divided into precloacal (trunk), cloacal and caudal regions (
Abbreviations: tcb, thickened cortical bone; nc, neural canal.
The overall morphology of the vertebrae in
In the last few years, efforts to understand the origins and evolution of snakes have resulted in several phylogenetic analyses that include extinct species. Crown snakes are split into two major extant clades: scolecophidians, which includes blind snakes and thread snakes, and alethinophidians, which comprises all other snakes. Nevertheless, recent analyses indicate that the unambiguously terrestrial fossil snakes
The vertebrae of
In comparison to other Cenomanian snakes,
The vertebrae of
In conclusion, the vertebrae described here constitute a distinctive taxon that displays features that distinguish it from other known extinct and extant snakes. Outstanding characters of this snake are the walls of the neural arch arising from the midline of the vertebrae and diverging to the subcentral ridges, the pachyostosis on the prezygapophyses and posterior neural arch, the depressed and laterally expanded roof of the neural arch with strong development of the interzygapophyseal ridges, the extension of the arch beyond the level of the condyle and forming a convex posterior edge, the long and narrow centrum with strong lateral development of the subcentral crests, the low placed and closely spaced paradiapophyses with small articular surfaces facing ventrally and projected beyond the ventral rim of the cotyle with a short process, and the substantial changes of the neural spines along the precloacal region from well-developed as a tubular process to an absolutely lacking spine. Although some features available on vertebrae of
The holotype of
The authors wish to especially thank Lilia Vierma (†), Carlos Torres and Cemento Andino Ca., for their valuable assistance in the field; to Alfredo Carlini for his substantial assistance in making this collaborative work possible; to Marcelo Sánchez Villagra, Torsten M. Scheyer, Christian Kolb and members of the Evolutionary Morphology and Palaeobiology group at the Palaeontological Institute and Museum, University of Zurich, Switzerland, for generous and significant counseling and collaboration; Alexandra Wegmann for conducting the scanning; and to the Instituo del Patrimonio Cultural de Venezuela for the authorization and collecting permission. The Academic Editor Hans-Dieter Sues, and the reviewers Alexandra Houssaye and Michael Caldwell, are thanked for providing helpful comments that improved the manuscript.
The authors declare there are no competing interests.
The following information was supplied regarding data availability:
All illustrations and 3D models deposited at Morphobank: doi:
The following information was supplied regarding the registration of a newly described species:
Lunaophis gen. nov. LSID: http://zoobank.org/NomenclaturalActs/D269D7FA-1B3A-431B-85AF-B081E1434049;
Publication LSID: urn:lsid:zoobank.org:pub:918B6879-8908-488F-876B -EA741DFF627B.