| Vulcanodon | |
|---|---|
 | |
| Skeletal diagram showing the known remains | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Clade: | †Gravisauria |
| Family: | †Vulcanodontidae |
| Genus: | †Vulcanodon Raath,1972 |
| Type species | |
| †Vulcanodon karibaensis Raath, 1972 | |
Vulcanodon (meaning "volcanotooth") is anextinctgenus ofsauropoddinosaur from theEarly Jurassic uppermostForest Sandstone of southernAfrica.[1] The only known species isV. karibaensis. Discovered in 1969 inZimbabwe, it was regarded as the earliest known sauropod for decades, and is still one of the mostprimitive genera that has been discovered.
As aquadrupedal,ground-dwellingherbivore,Vulcanodon already showed the typical sauropod body plan with column-like legs and a long neck and tail. It was smaller than most other sauropods, measuring approximately 11 metres (36 ft) in length.Vulcanodon is known from a fragmentary skeleton including much of thepelvic girdle, hindlimbs, forearms, and tail, but lacking the trunk and neckvertebrae as well as theskull. Originally, this genus was believed to be a "prosauropod" because of the knife-shaped teeth found near itsfossils, which fit in with the idea that they wereomnivorous. Scientists now know that the teeth belonged to an unidentifiedtheropod that may have scavenged on theVulcanodoncarcass, which is now known to be a true sauropod. Upon the discovery of the relatedTazoudasaurus, both animals were unified in the familyVulcanodontidae, although this has not been universally accepted.
Vulcanodon was initially thought have been a small sauropod. In 2010,Gregory S. Paul estimated its length at 11 metres (36.1 ft), its weight at 3.5 tonnes (3.9 short tons).[2] Some books mention lower estimates of approximately 6.5 m (21 ft).[3][4] However, in 2018, researchers have estimated a greater body mass of 10.3 metric tons (11.4 short tons).[5] The thighbone was 110 centimetres (43 in) long.[6]
As one of the earliest and basalmost sauropods, it is important for understanding the early evolution of this group. Sauropods descend from basalsauropodomorphs (informally called "prosauropods"), which were primitivelybipedal (two-legged).[7] WhileVulcanodon already was fullyquadrupedal (four-legged), its limb proportions were intermediate between those of its prosauropod ancestors and those of later, more derived sauropods.[7] Its forelimbs were much more similar to later sauropods than basal sauropodomorphs because they are straight, much more gracile, and the proximal end of the ulna is v-shaped.[8] Unfortunately, no skull or neck ofVulcanodon is known, although it is otherwise very well known.[9]
Vulcanodon's limbs were sturdy and column-like,[10] and its forelimbs were already proportionally long, reaching 76% of hindlimb length.[11] Its lower leg,metatarsus, and toes were shortened in comparison to its bipedal ancestors, but still not as short as in later sauropods.[7] Thesacrum was made out of four fused sacral vertebrae; "prosauropods" possessed only three sacrals. The tail vertebrabodies already showed an incipient excavation of their lateral sides, saving weight and giving them a waisted appearance when viewed from below. In later sauropods, this excavations were enlarged to form extensive perforated pockets calledpleurocoels.[6] Contrasting the many sauropod-like features of the skeleton, thepelvis was relatively primitive, reminiscent of its "prosauropod" ancestors.[7][8] One such feature is that the brevis shelf of the ilium has a fossa, which is not found in any more derived sauropods.[12]
Thehallux (the first toe of the foot) showed a large claw that was flattened laterally, as seen in "prosauropods".[6] However, the claws of the second and third toe were unusual in being nail-like and broader than deep.[10][13] This feature was also found in the probably closely relatedTazoudasaurus, but is absent in all other sauropods.[14] The feet ofVulcanodon weresemiplantigrade as in later sauropods (where both the digits and part of the metatarsals contact the ground[7]), a derived feature not found in more basal sauropods likeIsanosaurus. However, they also retained primitive features, like the fact that thephalanges were not reduced.[12]
Many of the features found in sauropods that basal sauropodomorphs lack are related to the change in body size. The greatest regions affected by this are the hind limbs and pelvis. For example, an elongating of theilium, size reduction of the lesser trochanter shelf, and semiplantigrade posture are some features that indicate the amount and positioning of leg muscles being modified.Vulcanodon possessed these features, the latter of which is seen earliest in it. However,Vulcanodon does not have reduced distal phalanges, which are seen inShunosaurus and all more derived sauropods. This means that while the muscle positioning of its legs were changing, they had not yet reduced in the distal region of the limb.[12]
Vulcanodon is known only from a single locality on an island inLake Kariba, the largestartificial lake in the world, in northernZimbabwe (formerlyRhodesia).[15] The island, located west ofBumi Hills,[6] is called "Island 126/127", after early, unpublished lake charts, but has no formal name. The first bone was found by B. A. Gibson of the town ofKariba in July 1969, and an excavation team collected the specimen in October 1969, March 1970 and May 1970. In the later half of 1970, the new find was presented at a scientificsymposium inCape Town and a brief note was published. The find was formally named and described in July 1972 by paleontologist Michael Raath.[10] The nameVulcanodon (lat.Vulcanus – Roman god of fire;gr.odon – "tooth")[16] points to the fact that the skeleton was found insandstone, that was at the time misinterpreted to be part of theBatoka Formation but is actually part of theForest Sandstone lays a few metres below thelava flows of the Batoka Formation, and emphasizes the peculiar knife-shaped teeth that are now known to belong to a theropod.[10] Thespecific name,karibaensis, refers to the place of discovery on a small island in Lake Kariba.[10] It was one of the first dinosaurs found in Zimbabwe.[17]
The skeleton (catalogue number QG24) has been found weathering out of a hill slope and was partially eroded by surface exponation and plant roots, erroneously documented as sandwiched between two basalt layers.[1] It includes the pelvis and sacrum, most of the left hind limb and foot, a right thigh bone, and twelve anterior tail vertebrae. These remains pertain to a single individual as they were all found articulated (still connected together). Additionally, several disarticulated bones were found, including the right forearm and somemetacarpalia andphalanges from both the right and left forefeet, probably also pertaining to this individual.[10] Later, the site was revisited by the scientists Geoffrey Bond and Michael Cooper, who were able to collect additional remains including ascapula (specimen QG152, a shoulder blade) and a fragment of a neck vertebra.[6] These remains show that more than one individual was present, and it is possible that they do not pertain toVulcanodon at all.[18] Today, theVulcanodon remains are stored in theNatural History Museum of Zimbabwe inBulawayo.[6]
Raath (1972) noted the discovery of nine fragmentary carnivorous teeth near the pelvic region of the skeleton. He argued that theVulcanodon carcass might have been embedded with the head and neck bended backwards above the pelvis, a posture calleddeath pose that is frequently seen in dinosaur skeletons. The teeth would have been the only preserved elements of the skull.[10] However, as shown by Cooper (1984), these teeth do not pertain toVulcanodon but to a theropod dinosaur that may have scavenged on theVulcanodon carcass.[6]
Originally, Michael Raath (1972) describedVulcanodon not as a sauropod but as anadvanced, specialized prosauropod, possibly of the familyMelanorosauridae.[10][6] According to Raath, the sauropod-like limb proportions inVulcanodon evolved independently from those of true sauropods (throughconvergent evolution). He argued that primitive features of the pelvis as well as the knife-shaped teeth preclude a classification within the Sauropoda.[10] The teeth, however, are now known to belong to a theropod.Arthur Cruickshank (1975) was the first to show thatVulcanodon was indeed a sauropod, arguing that the fifth metatarsal bone was equally long as the remaining metatarsals, a condition seen in other sauropods but not in prosauropods.[19] Today,Vulcanodon is universally accepted to be one of the most basal (primitive) members of Sauropoda.[13][18]
Michael Cooper (1984) erected a newfamily, theVulcanodontidae, which he regarded as the "rootstock" for later sauropod families.[6] Originally, the Vulcanodontidae includedVulcanodon and theIndianBarapasaurus, but subsequent studies attributed a number of other, much more fragmentary early sauropod genera to this family, includingOhmdenosaurus andZizhongosaurus.[20]Paul Upchurch (1995) showed thatBarapasaurus was more closely related to later, more advanced sauropods than toVulcanodon, rendering the Vulcanodontidaepolyphyletic and therefore invalid.[11]
The exact relationships with other basal sauropod genera remain unclear. Ronan Allain and colleagues (2004, 2008) found thatVulcanodon is most closely related toTazoudasaurus, a newly discovered sauropod genus fromMorocco. These researchers suggested reintroducing the name Vulcanodontidae to name theclade containingVulcanodon andTazoudasaurus.[14][21] However, thissibling relationship betweenTazoudasaurus andVulcanodon could not be confirmed by other analyses.[22][23]
Adam Yates (2004) described a single sauropod tail vertebra from theUpper Elliot Formation ofSouth Africa that may belong to a genus closely related toVulcanodon. The Upper Elliot Formation is famous for its abundant fossils of the prosauropodMassospondylus.[24]
Vulcanodon in a cladogram after Nairet al., 2012:[25]
During the later part of the Lower Jurassic, southern Africa was the scene of massivevolcanism, resulting in extensive lava flows (so calledflood basalts) that covered much of southern Africa andAntarctica. These basalt formations are known as theKaroo-Ferrar large igneous province.Vulcanodon comes from the "Vulcanodon beds", a fossil-bearing sediment unit within theBatoka Formation, which is composed primarily of flood basalts.[26] The skeleton was found near the top of a 30-metre-thick (98 ft)bedded layer ofsand- andsiltstone that is over- and underlain by flood basalts.[10]
It was long assumed thatVulcanodon lived during the lowermost (earliest) part of the Jurassic (theHettangianstage) or at theTriassic–Jurassic boundary, approximately 200 million years ago.[11][18][20] Therefore, it was regarded as the earliest sauropod known, until the discovery of the even olderLate TriassicIsanosaurus was announced in2000.[27] Adam Yates (2004) has recently shown thatVulcanodon is actually much younger than previously thought, dating to the uppermost (latest) part of the Lower Jurassic during theToarcian stage, approximately 175–183 million years ago.[24][28] Thus, it is contemporary to the closely relatedTazoudasaurus.[21] As was assumed that the locality ofVulcanodon itself cannot bedated radiometrically because of weathering of the lavas, it would roughly be a contemporary to Karoo lavas from other localities, as the entire sequence of volcanic eruptions was finished within one million years.[24] In 2018 was revelated that as in 2016 Lake Kariba hosted record-low water levels the unit were accessible to be studied and confirmed that the holotype came from the uppermost Forest Sandstone, being as old as the Rhaetian or as young as the Pliensbachian, with a Sinemurian-Pliensbachian Midpoint.[1]
Vulcanodon is the only named dinosaur from the Vulcanodon beds.[26] Cooper (1984) noted that the habitat was desert-like, as indicated byaeolian (wind-blown) sands of theForest Sandstone Formation, which underlies the "Vulcanodon beds". The sediments in whichVulcanodon was found may represent distalalluvial fan deposits which levelled off into a desert landscape, which may have contained lakes during the wet season. The individual may have roamed the shores ofwadis that cut into the alluvial fan deposits, unless the carcass was transported to the locality it was found by flooding.[6]
Initially, sauropods were thought to be mainly aquatic, inhabiting lush peat swamps and being captive to the buoyancy of water to support their giant body weights.[29] In 1984, Cooper pointed out thatVulcanodon, the most primitive sauropod known at that time, lived in a desert like environment and therefore must have been terrestrial. This indicated that the large body size of sauropods, as already seen inVulcanodon, had not evolved as an adaptation to an aquatic life style.[6]
