Revision of the cranial anatomy and phylogenetic relationships of the Eocene minute boasMesselophis variatusandMesselophis ermannorum(Serpentes, Booidea)
Abstract:We provide a detailed anatomical description of the skull of the fossil minute boas Messelophis variatus Baszio, 2004 and Messelophis ermannorum Schaal &Baszio, 2004 from the Middle Eocene Messel Formation (Germany), as well as a cladistic analysis to infer their phylogenetic relationships. Reanalysis of new and known specimens of both species demonstrates previously unrecognized anatomical characters in the skull of these fossil snakes. Both morphological and combined (morphology plus DNA) analyses place both… Show more
“…The traditional "erycine" group is inferred to be polyphyletic, in line with most recent phylogenies [9,28,35,36]. The recently described small booid Rageryx schmidi, also from Messel [11], forms a distinct, well-supported clade together with North American "erycines" Lichanura and Charina, thus excluding New World "erycines."…”
Section: Phylogenetic Analysis and Biogeographic Implicationssupporting
confidence: 59%
“…According to both MP ( Figure 2) and BI ( Figure S4) Eoconstrictor fischeri is unambiguously deeply nested in a well-supported, monophyletic Booidea, in congruence with almost all recent phylogenies based on molecular and combined data [9,28,35,36]. Booid synapomorphies include a long medial foot process of the prefrontal, the posterior placement of the maxillary process of the palatine and the large size of the right posterior aperture of the Vidian canal.…”
Section: Phylogenetic Analysis and Biogeographic Implicationsmentioning
Our knowledge of early evolution of snakes is improving, but all that we can infer about the evolution of modern clades of snakes such as boas (Booidea) is still based on isolated bones. Here, we resolve the phylogenetic relationships of Eoconstrictor fischeri comb. nov. and other booids from the early-middle Eocene of Messel (Germany), the best-known fossil snake assemblage yet discovered. Our combined analyses demonstrate an affinity of Eoconstrictor with Neotropical boas, thus entailing a South America-to-Europe dispersal event. Other booid species from Messel are related to different New World clades, reinforcing the cosmopolitan nature of the Messel booid fauna. Our analyses indicate that Eoconstrictor was a terrestrial, medium- to large-bodied snake that bore labial pit organs in the upper jaw, the earliest evidence that the visual system in snakes incorporated the infrared spectrum. Evaluation of the known palaeobiology of Eoconstrictor provides no evidence that pit organs played a role in the predator–prey relations of this stem boid. At the same time, the morphological diversity of Messel booids reflects the occupation of several terrestrial macrohabitats, and even in the earliest booid community the relation between pit organs and body size is similar to that seen in booids today.
“…The traditional "erycine" group is inferred to be polyphyletic, in line with most recent phylogenies [9,28,35,36]. The recently described small booid Rageryx schmidi, also from Messel [11], forms a distinct, well-supported clade together with North American "erycines" Lichanura and Charina, thus excluding New World "erycines."…”
Section: Phylogenetic Analysis and Biogeographic Implicationssupporting
confidence: 59%
“…According to both MP ( Figure 2) and BI ( Figure S4) Eoconstrictor fischeri is unambiguously deeply nested in a well-supported, monophyletic Booidea, in congruence with almost all recent phylogenies based on molecular and combined data [9,28,35,36]. Booid synapomorphies include a long medial foot process of the prefrontal, the posterior placement of the maxillary process of the palatine and the large size of the right posterior aperture of the Vidian canal.…”
Section: Phylogenetic Analysis and Biogeographic Implicationsmentioning
Our knowledge of early evolution of snakes is improving, but all that we can infer about the evolution of modern clades of snakes such as boas (Booidea) is still based on isolated bones. Here, we resolve the phylogenetic relationships of Eoconstrictor fischeri comb. nov. and other booids from the early-middle Eocene of Messel (Germany), the best-known fossil snake assemblage yet discovered. Our combined analyses demonstrate an affinity of Eoconstrictor with Neotropical boas, thus entailing a South America-to-Europe dispersal event. Other booid species from Messel are related to different New World clades, reinforcing the cosmopolitan nature of the Messel booid fauna. Our analyses indicate that Eoconstrictor was a terrestrial, medium- to large-bodied snake that bore labial pit organs in the upper jaw, the earliest evidence that the visual system in snakes incorporated the infrared spectrum. Evaluation of the known palaeobiology of Eoconstrictor provides no evidence that pit organs played a role in the predator–prey relations of this stem boid. At the same time, the morphological diversity of Messel booids reflects the occupation of several terrestrial macrohabitats, and even in the earliest booid community the relation between pit organs and body size is similar to that seen in booids today.
“…However, the retention of a well-developed aponeurotic system in the jaw adductor musculature of cryptozoic colubroids and its reduction observed during the postnatal development in terrestrial forms [50] invites consideration of the idea that the evolution of anatomical systems other than the skeleton have been also driven by the alternation of underground--surface macrohabitat occupation. Figure 6.Simplified phylogenetic tree of snakes [45] showing the information discussed in this work about body size, macrohabitat, prey type preferences and osteological requirements for macrostomy. Note the early appearance of crucial osteological requirements for macrostomy and the elongation of the gnathic complex present in non-macrostomatan simoliophiids.…”
Section: Discussionmentioning
confidence: 99%
“…Simplified phylogenetic tree of snakes [45] showing the information discussed in this work about body size, macrohabitat, prey type preferences and osteological requirements for macrostomy. Note the early appearance of crucial osteological requirements for macrostomy and the elongation of the gnathic complex present in non-macrostomatan simoliophiids.…”
Section: Discussionmentioning
confidence: 99%
“…Finally, the growing fossil record of snakes reveals that non-macrostomatan snakes with the capacity to consume large prey have existed [51,52], and that other species of miniaturized macrostomatan snakes have lost the skeletal requirements for macrostomy [45], thus indicating that the diversity of snake feeding anatomy was more complex than previously thought. Further investigations of the postnatal trajectory of other anatomical systems involved in macrostomy and more efforts towards the discovery of fossil snakes surely will shed light on this captivating evolutionary issue.…”
Macrostomy is the anatomical feature present in macrostomatan snakes that permits the ingestion of entire prey with high cross-sectional area. It depends on several anatomical traits in the skeleton and soft tissues, of which the elongation of gnathic complex and backward rotation of the quadrate represent crucial skeletal requirements. Here, the relevance of postnatal development of these skull structures and their relationship with macrohabitat and diet are explored. Contrary to the condition present in lizards and basal snakes that occupy underground macrohabitats, elements of the gnathic complex of most macrostomatan snakes that exploit surface macrohabitats display conspicuous elongation during postnatal growth, relative to the rest of the skull, as well as further backward rotation of the quadrate bone. Remarkably, several clades of small cryptozoic macrostomatans reverse these postnatal transformations and return to a diet based on prey with low cross-sectional area such as annelids, insects or elongated vertebrates, thus resembling the condition present in underground basal snakes. Dietary ontogenetic shift observed in most macrostomatan snakes is directly linked with this ontogenetic trajectory, indicating that this shift is acquired progressively as the gnathic complex elongates and the quadrate rotates backward during postnatal ontogeny. The numerous independent events of reversion in the gnathic complex and prey type choice observed in underground macrostomatans and the presence of skeletal requirements for macrostomy in extinct non-macrostomatan species reinforce the possibility that basal snakes represent underground survivors of clades that had the skeletal requirements for macrostomy. Taken together, the data presented here suggest that macrostomy has been shaped during multiple episodes of occupation of underground and surface macrohabitats throughout the evolution of snakes.
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