Mecistotrachelos Temporal range: Late Triassic, | |
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Slabs and CT scans of Mecistotrachelos specimens VMNH 3649 (A-B) and 3650 (C-D) | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Clade: | Archosauromorpha (?) |
Genus: | † Mecistotrachelos Fraser et al., 2007 |
Type species | |
†Mecistotrachelos apeoros Fraser et al., 2007 |
Mecistotrachelos is an extinct genus of gliding reptile from the Late Triassic of Virginia. It is generally interpreted as an archosauromorph, distantly related to crocodylians and dinosaurs. The type and only known species is M. apeoros. This specific name translates to "soaring longest neck", in reference to its gliding habits and long neck. This superficially lizard-like animal was able to spread its lengthened ribs and glide on wing-like membranes. Mecistotrachelos had a much longer neck than other gliding reptiles of the Triassic such as Icarosaurus and Kuehneosaurus . It was probably an arboreal insectivore.
Mecistotrachelos is known from several fossil specimens excavated from the Solite quarry from the Cow Branch Formation on the Virginia-North Carolina border. [1] Only two of these have been formally described in a scientific journal. The first fossil was found in 1994 and the second fossil eight years later by Nick Fraser, a vertebrate paleontologist at the Virginia Museum of Natural History. The first fossil, VMNH 3649, is the holotype of the genus and is preserved completely articulated, although missing the tail, hindlimbs, and most of the pelvic girdle. The second fossil, VMNH 3650, is sometimes considered a paratype and is more complete, only missing part of the tail as well as the left hindlimb. [2]
The Solite quarry was once a large lake and surrounding wetland which formed in a rift basin when Pangaea started to break up during the Late Triassic. The quarry's sediments were initially believed to have formed during the Carnian stage of the Triassic, about 230 million years ago. [3] [2] More recent magnetostratigraphy of the Cow Branch Formation supports a younger age in the middle Norian, closer to 220 million years ago. [4] [5] The ancient lake held abundant populations of insects and the tanystropheid reptile Tanytrachelos . [6] The fossils of the Solite quarry are often preserved as dark grey bones embedded in dark grey mudstone, and are thus usually very difficult to observe and prepare. As a result, the Mecistotrachelos specimens had to be CT scanned to be properly described. This makes Mecistotrachelos one of the first extinct animals to be described based almost entirely on CT scan data. [2]
The skull is lightly built and pointed, and there is some evidence for holes in the back of the head, indicating that the animal was a diapsid reptile. The neck is long, consisting of 8 or 9 cervical vertebrae. These vertebrae are elongated but seemingly lack visible cervical ribs, although it is possible that they were too thin or close to the vertebrae to be preserved as separate structures. 13 or 14 dorsal (back) vertebrae were present, a condition similar to most diapsids. The first few dorsals were short and almost all of the dorsals had bony prongs (transverse processes) sticking out of their sides. The tail is missing or incomplete in the described specimens. Specific details of the pectoral and pelvic girdles cannot be identified in the CT scans. The limbs are long and slender, with the hind limbs slightly longer than the front limbs. The manus (hand) had five fingers while the pes (foot) had short metatarsals and an indeterminate number of toes which seemed to have hooked inwards, at least in VMNH 3650. [2]
The most unusual and characteristic feature of this genus relates to its ribs. While the first dorsal rib was quite short, at least the next 8 (termed 'thoracolumbar ribs') were very long. They had robust attachment points (particularly the first few) and curved backwards slightly before straightening and tapering. This contrasts with the gliding ribs of kuehneosaurids, which were straight before curving backwards and downwards. The longest ribs were attached to the third and fourth vertebrae, after which they started to decrease in size. At their longest point (~70 centimeters or 28 inches in VMNH 3650) they were a bit less than half the total estimated length of the animal. [2]
The long ribs of Mecistotrachelos almost certainly were covered with some form of skin which facilitated gliding habits. In addition, the flexible hind limbs with "hooked" toes preserved in VMNH 3650 indicate that it was well-adapted for an arboreal habitat. However, the long and rigid neck would have hampered gliding abilities. The small teeth of Mecistotrachelos would have been suitable for an insectivorous diet. [2]
Unlike in kuehneosaurids, which had downward-curving "wings", the ribs of Mecistotrachelos were mostly straight, and were not naturally cambered to create an airfoil. Nevertheless, if the front ribs could be flexed independently of the others, it is possible that a Mecistotrachelos would have been able to create a variable airfoil. In this case they would function as a pteroid bone in pterosaurs or an alula in birds, increasing or decreasing drag depending on their position. The robust rib heads of these front ribs also support this hypothesis. [2]
Mecistotrachelos was far from the only rib-gliding reptile in prehistory. In the Permian lived the weigeltisaurids, primitive reptiles with small spiked crests. There are also various different gliding lizards, such as Draco (the flying dragon) of the modern day as well as Xianglong from the early Cretaceous. [7] The only other Triassic rib-gliding reptiles were the kuehneosaurids, which are usually interpreted as lepidosauromorphs distantly related to rhynchocephalians (such as the tuatara) and squamates (such as lizards and snakes). [8]
The skull of VMNH 3649 is comparatively larger than that of VMNH 3650, but the forelimbs are shorter. This may be an example of sexual dimorphism. [2]
Oddly enough, Mecistotrachelos shares few features with other gliding reptiles, apart from its gliding adaptations and general body shape. Instead, the pointed skull and long neck of this genus is more reminiscent of early archosauromorphs, also known as "protorosaurs". Archosauromorpha is the lineage which would eventually lead to crocodilians and dinosaurs (including birds). Early representatives of the group superficially resembled long-necked lizards, despite true lizards being on a different reptilian lineage. However, few skull details can be observed in the CT scans to clarify this classification. [2]
Mecistotrachelos is not the only putative "protorosaur" with gliding adaptations. Sharovipteryx , a genus from Kazakhstan, preserved skin impressions stretching between its long legs and its tail. This form of gliding contrasts with the rib gliding of Mecistotrachelos, and they are probably not particularly closely related even if they are both archosauromorphs. [2]
Dinocephalosaurus is a genus of long necked, aquatic protorosaur that inhabited the Triassic seas of China. The genus contains the type and only known species, D. orientalis, which was named by Chun Li in 2003. Unlike other long-necked protorosaurs, Dinocephalosaurus convergently evolved a long neck not through elongation of individual neck vertebrae, but through the addition of neck vertebrae that each had a moderate length. As indicated by phylogenetic analyses, it belonged in a separate lineage that also included at least its closest relative Pectodens, which was named the Dinocephalosauridae in 2021. Like tanystropheids, however, Dinocephalosaurus probably used its long neck to hunt, utilizing the fang-like teeth of its jaws to ensnare prey; proposals that it employed suction feeding have not been universally accepted. It was probably a marine animal by necessity, as suggested by the poorly-ossified and paddle-like limbs which would have prevented it from going ashore.
Archosauromorpha is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs rather than lepidosaurs. Archosauromorphs first appeared during the late Middle Permian or Late Permian, though they became much more common and diverse during the Triassic period.
Tanystropheus is an extinct genus of archosauromorph reptile which lived during the Triassic Period in Europe, Asia, and North America. It is recognisable by its extremely elongated neck, longer than the torso and tail combined. The neck was composed of 13 vertebrae strengthened by extensive cervical ribs. Tanystropheus is one of the most well-described non-archosauriform archosauromorphs, known from numerous fossils, including nearly complete skeletons. Some species within the genus may have reached a total length of 6 meters (20 ft), making Tanystropheus the longest non-archosauriform archosauromorph as well. Tanystropheus is the namesake of the family Tanystropheidae, a clade collecting many long-necked Triassic archosauromorphs previously described as "protorosaurs" or "prolacertiforms".
Weigeltisaurus is an extinct genus of weigeltisaurid reptile from the Late Permian Kupferschiefer of Germany and Marl Slate of England. It has a single species, originally named as Palaechamaeleo jaekeli in 1930 and later assigned the name Weigeltisaurus jaekeli in 1939, when it was revealed that Palaeochamaeleo was a preoccupied name. A 1987 review by Evans and Haubold later lumped Weigeltisaurus jaekeli under Coelurosauravus as a second species of that genus. A 2015 reassessment of skull morphology study substantiated the validity of Weigeltisaurus and subsequent authors have used this genus. Like other Weigeltisaurids, they possessed long rod-like bones that radiated from the trunk that were likely used to support membranes used for gliding, similar to extant Draco lizards.
Drepanosaurs are a group of extinct reptiles that lived between the Carnian and Rhaetian stages of the late Triassic Period, approximately between 230 and 210 million years ago. The various species of drepanosaurid were characterized by specialized grasping limbs and often prehensile tails, adaptions for arboreal (tree-dwelling) and fossorial (digging) lifestyles, with some having also been suggested to be aquatic. Fossils of drepanosaurs have been found in Arizona, New Mexico, New Jersey, Utah, England, and northern Italy. The name is taken from the family's namesake genus Drepanosaurus, which means "sickle lizard," a reference to their strongly curved claws.
Macrocnemus is an extinct genus of archosauromorph reptile known from the Middle Triassic of Europe and China. Macrocnemus is a member of the Tanystropheidae family and includes three species. Macrocnemus bassanii, the first species to be named and described, is known from the Besano Formation and adjacent paleontological sites in the Italian and Swiss Alps. Macrocnemus fuyuanensis, on the other hand, is known from the Zhuganpo Formation in southern China. A third species, Macrocnemus obristi, is known from the Prosanto Formation of Switzerland and is characterized by gracile limbs. The name Macrocnemus is Greek for "long tibia".
Langobardisaurus is an extinct genus of tanystropheid archosauromorph reptile, with one valid species, L. pandolfii. Its fossils have been found in Italy and Austria, and it lived during the Late Triassic period, roughly 228 to 201 million years ago. Langobardisaurus was initially described in 1994, based on fossils from the Calcare di Zorzino Formation in Northern Italy. Fossils of the genus are also known from the Forni Dolostone of Northern Italy and the Seefeld Formation of Austria.
Cosesaurus is a genus of archosauromorph reptiles likely belonging to the family Tanystropheidae. It is known from fossil imprints of a single small skeleton, MGB V1, which was found in Muschelkalk outcrops near the municipalities of Mont-ral and Alcover in Spain. These outcrops are dated to the Ladinian age of the middle Triassic about 242 to 237 million years ago. The specimen is stored at the Museu Martorell, which is now part of the Museu de Ciències Naturals de Barcelona. The poor preservation and likely juvenile nature of the specimen has led to the anatomy of Cosesaurus being misidentified by several different sources. For example, Paul Ellenberger claimed that it was an ancestor to birds in the 1970s, while David Peters claimed that it was a pterosaur ancestor in 2000. Both of these claims contrast with mainstream scientific theories on the origins of either group, and other paleontologists who study the specimen are unable to find the features which Ellenberger or Peters reported to be present. The Ellenberger and Peters hypotheses are thus considered fringe theories with questionable scientific soundness due to their low reproducibility. Mainstream hypotheses for the relations of Cosesaurus generally agree that it is a "protorosaur", specifically a tanystropheid closely related to long-necked reptiles such as Macrocnemus, Tanytrachelos, Tanystropheus, or Langobardisaurus.
Jesairosaurus is an extinct genus of early archosauromorph reptile known from the Illizi Province of Algeria. It is known from a single species, Jesairosaurus lehmani. Although a potential relative of the long-necked tanystropheids, this lightly-built reptile could instead be characterized by its relatively short neck as well as various skull features.
Prolacerta is a genus of archosauromorph from the lower Triassic of South Africa and Antarctica. The only known species is Prolacerta broomi. The generic name Prolacerta is derived from Latin meaning “before lizard” and its species name broomi is in commemoration of the famous paleontologist Robert Broom, who discovered and studied many of the fossils found in rocks of the Karoo Supergroup. When first discovered, Prolacerta was considered to be ancestral to modern lizards, scientifically known as lacertilians. However, a study by Gow (1975) instead found that it shared more similarities with the lineage that would lead to archosaurs such as crocodilians and dinosaurs. Prolacerta is considered by modern paleontologists to be among the closest relatives of the Archosauriformes.
Jaxtasuchus is an extinct genus of armored doswelliid archosauriform reptile known from the Middle Triassic of the Erfurt Formation in Germany. The type species, Jaxtasuchus salomoni, was named in 2013 on the basis of several incomplete skeletons and other isolated remains. Like other doswelliids, members of the genus were heavily armored, with four longitudinal rows of bony plates called osteoderms covering the body. Jaxtasuchus is the first doswelliid known from Europe and is most closely related to Doswellia from the Late Triassic of the eastern United States. However, it was not as specialized as Doswellia, retaining several generalized archosauriform characteristics and having less armor. Jaxtasuchus fossils have been found in aquatic mudstones alongside fossils of temnospondyl amphibians, crustaceans, and mollusks, suggesting that Jaxtasuchus was semiaquatic like modern crocodilians.
Pamelaria is an extinct genus of allokotosaurian archosauromorph reptile known from a single species, Pamelaria dolichotrachela, from the Middle Triassic of India. Pamelaria has sprawling legs, a long neck, and a pointed skull with nostrils positioned at the very tip of the snout. Among early archosauromorphs, Pamelaria is most similar to Prolacerta from the Early Triassic of South Africa and Antarctica. Both have been placed in the family Prolacertidae. Pamelaria, Prolacerta, and various other Permo-Triassic reptiles such as Protorosaurus and Tanystropheus have often been placed in a group of archosauromorphs called Protorosauria, which was regarded as one of the most basal group of archosauromorphs. However, more recent phylogenetic analyses indicate that Pamelaria and Prolacerta are more closely related to Archosauriformes than are Protorosaurus, Tanystropheus, and other protorosaurs, making Protorosauria a polyphyletic grouping.
Tanystropheidae is an extinct family of archosauromorph reptiles that lived throughout the Triassic Period, often considered to be "protorosaurs". They are characterized by their long, stiff necks formed from elongated cervical vertebrae with very long cervical ribs. Members of the group include both terrestrial and aquatic forms. While some tanystropheids were small lizard-like animals, other tanystropheids such as Tanystropheus were large animals that had necks that were several meters long, longer than the rest of their bodies.
Fuyuansaurus is an extinct genus of "protorosaur" reptiles known from the Middle Triassic Zhuganpo Formation of southern China. Fuyuansaurus was first named by Nicholas C. Fraser, Olivier Rieppel and Li Chun in 2013 and the type species is Fuyuansaurus acutirostris.
Eorasaurus is an extinct genus of archosauromorph reptile known from the middle Late Permian of Tatarstan, European Russia. It contains a single species, Eorasaurus olsoni. When originally described by Sennikov (1997), Eorasaurus was identified as an early archosauromorph and assigned to the family Protorosauridae, Ezcurra et al. (2014) and Ezcurra (2016) later reclassified Eorasaurus and placed it within the group Archosauriformes. Eorasaurus is based solely on scant fossil material from the neck region, and is thus considered an unstable taxon in phylogenetic analyses. If Eorasaurus is an archosauriform, it would be the oldest known member of the group and would pre-date the previous record holder.
Ozimek is a genus of sharovipterygid archosauromorph reptile, known from Late Triassic deposits in Poland and closely related to the Kyrgyzstani Sharovipteryx. It contains one species, O. volans, named in 2016 by Jerzy Dzik and Tomasz Sulej. Like Sharovipteryx, Ozimek had long, slender limbs with the hindlimbs longer than the forelimbs; the hindlimbs likely supported gliding membranes as fossilized in Sharovipteryx. Another unusual characteristic was the shoulder girdle, where the massive coracoids formed a shield-like structure covering the bottom of the shoulder region that would have limited mobility. In other respects, such as its long neck, it was a typical member of the non-natural grouping Protorosauria. Phylogenetic analysis has indicated that it, possibly along with Sharovipteryx, may have been an unusual member of the protorosaur group Tanystropheidae, although further study of its anatomy is needed to resolve its precise relationships.
Shringasaurus is an extinct genus of archosauromorph reptile from the Middle Triassic (Anisian) of India. It is known from the type and only known species, S. indicus. Shringasaurus is known from the Denwa Formation in the state of Madhya Pradesh. Shringasaurus was an allokotosaur, a group of unusual herbivorous reptiles from the Triassic, and is most closely related to the smaller and better known Azendohsaurus in the family Azendohsauridae. Like some ceratopsid dinosaurs, Shringasaurus had two large horns over its eyes that faced up and forwards from its skull. Shringasaurus also bears convergent physical similarities to sauropodomorph dinosaurs, such as its long neck, its shoulders and forelimbs, and the shape of its teeth. Shringasaurus possibly occupied a similar ecological niche as a large browsing herbivore before such dinosaurs had evolved.
Pectodens is an extinct genus of archosauromorph reptile which lived during the Middle Triassic in China. The type and only species of the genus is P. zhenyuensis, named by Chun Li and colleagues in 2017. It was a member of the Archosauromorpha, specifically part of the unnatural grouping Protorosauria. However, an unusual combination of traits similar and dissimilar to other protorosaurs initially led to confusion over its evolutionary relationships. In 2021, it was placed in a newly-established group, Dinocephalosauridae, along with its closest relative Dinocephalosaurus.
Boreopricea is an extinct genus of archosauromorph reptile from the Early Triassic of arctic Russia. It is known from a fairly complete skeleton discovered in a borehole on Kolguyev Island, though damage to the specimen and loss of certain bones has complicated study of the genus. Boreopricea shared many similarities with various other archosauromorphs, making its classification controversial. Various studies have considered it a close relative of Prolacerta, tanystropheids, both, or neither. Boreopricea is unique among early archosauromorphs due to possessing contact between the jugal and squamosal bones at the rear half of the skull.
Aenigmaspina is an extinct genus of enigmatic pseudosuchian (=crurotarsan) archosaur from the Late Triassic of the United Kingdom. Its fossils are known from the Pant-y-ffynnon Quarry in South Wales, of which its type and only known species is named after, A. pantyffynnonensis. Aenigmaspina is characterised by the unusual spines on its vertebrae, which are broad and flat on top with a unique 'Y' shape. Although parts of its skeleton is relatively well known, the affinities of Aenigmaspina to other pseudosuchians are unclear, although it is possibly related to families Ornithosuchidae, Erpetosuchidae or Gracilisuchidae.