Haestasaurus | |
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Left humerus of the type specimen | |
Scientific classification![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | †Sauropodomorpha |
Clade: | †Sauropoda |
Clade: | †Neosauropoda |
Clade: | †Macronaria |
Genus: | †Haestasaurus Upchurch, Mannion, & Taylor, 2015 |
Species: | †H. becklesii |
Binomial name | |
†Haestasaurus becklesii (Mantell, 1852) |
Haestasaurus is agenus ofherbivoroussauropoddinosaur, belonging to theMacronaria, that during theEarly Cretaceous lived in the area of present-day England. The onlyspecies isHaestasaurus becklesii.[1]
As a sauropod,Haestasaurus would have been a large quadrupedal long-necked dinosaur. Little information is available about the specifics of its build because only a forelimb is known of the animal.
An indication of the size ofHaestasaurus is given by the length of the forelimb elements. Thehumerus is 599 millimetres long, theulna 421 millimetres and the radius, situated next to the ulna in the lower arm, has a length of 404 millimetres.[1]
A 2015 study found several unique anatomical traits (autapomorphies) distinguishingHaestasaurus from related species. The inner front corner of the humerus is protruding, forming aprocessus entepicondylaris anterior. Between the front condyles of the lower humerus two small vertical ridges are present. The upper surface of the radius has, measured from front to rear, its largest width along the outer rim, which edge is nearly straight instead of strongly convex. The lower front of the radius is lightly concave between outer and inner ridges. A unique combination is present of a robust ulna, its upper surface having a width equalling more than 40% of the shaft length, with a slender radius having an upper width of less than 30% of total length.[1]
A rock associated with the forelimb, NHMUK R1868, was the first specimen known preserving parts of the sauropod skin. These probably are not impressions as the visible surface of the scales is convex, but natural casts. An area of 215 by 195 millimetres has been preserved. It shows non-overlapping hexagonal scales with a diameter of between ten and twenty-five millimetres. The scales gradually decrease in size, perhaps towards the elbow, to provide it greater flexibility. The scales strongly resemble skin impressions of later sauropod finds.[1] In 2022 a study reported the presence of small covering protuberances or papillae on the scales. WithNeosauropoda, these would have served for a better camouflage or thermoregulation.[2] These structures had already been noted byReginald Walter Hooley in 1917,[3] but had incorrectly been identified as representing the underside of theepidermis.
In 1852, the collectorSamuel Husband Beckles obtained a block ofWealden Sandstone that had become visible at low tide off the coast ofEast Sussex nearHastings. The precise location is today unknown. It proved to contain a large forelimb which was studied byGideon Mantell. The same year, Mantell in a lecture named the find as a second species ofPelorosaurus:Pelorosaurus becklesii, thespecific name honouring Beckles.[4]
Pelorosaurus becklesii at first received little attention, perhaps also because the fossils remained in the private collection of Beckles; they were acquired by theBritish Museum (Natural History) in 1891. In 1888,Richard Lydekker described a cast present in the museum, BMNH R28701, but seemed to be unaware of its status as a separate species and misidentified the discovery site as theIsle of Wight.[5] In 1889, the American paleontologistOthniel Charles Marsh coined the new combinationMorosaurus becklesii.[6] However, this was not accepted by Lydekker who in subsequent publications referred the material toCetiosaurus brevis.[7][8][9] In 1932,Friedrich von Huene concluded thatP. becklesii represented a separate genus but provided no name, referring to it as "Gen. (?)becklesii", the question mark indicating an unknown genus that would have been a member of theCamarasaurinae within theBrachiosauridae.[10] In 1990,John Stanton McIntosh confirmed that the species was not co-generic withPelorosaurus conybeari.[11]
In 2015, Paul Upchurch, Philip D. Mannion andMichael P. Taylor, having established thatP. becklesii differed in many traits fromPelorosaurus conybeari and was not itssister species, named the separate genusHaestasaurus. The generic name is derived fromHaesta, the presumed fifth century tribalSaxon chieftain whose existence has been deduced from the original name of Hastings,Haestingas, "the people of Haesta" (Old Englishhǣst ‘violence, violent’), and Greeksauros, "reptile". Thecombinatio nova isHaestasaurus becklesii. Thetype species remainsPelorosaurus becklesii. The name was published in anelectronic journal,PLoS ONE. Such names require aLife Science Identifier which in this case is 9D2E9827-D6D5-444A-A01C-69CAE4FFCA22.[1]Haestasaurus was one of eighteen dinosaur taxa from 2015 to be described in open access or free-to-read journals.[12]
Theholotype,NHMUK R1870, was found in a layer of theHastings Beds dating from theBerriasian-Valanginian, roughly 140 million years old. It consists of a left forelimb containing the associated humerus, ulna and radius. Specimen NHMUK R1868 was part of the original block and consists of a natural cast of a part of the skin, near the elbow. When theBeckles Collection was acquired, ametacarpal was referred toP. becklesii, specimen NHMUK R1869, but its large size precludes its belonging to the holotype.[1]
By the end of the twentieth century, most researchers agreed thatP. becklesii was a member of theTitanosauriformes, possibly specifically within theTitanosauria. In the latter case it would have been one of the oldest known European titanosaurs. The 2015 study performed some detailedcladistic analyses to establish the exact position ofHaestasaurus in the evolutionary tree. Due to the limited material available however, it proved impossible to obtain a single solution to this problem. Two major alternatives presented themselves. One possibility was thatHaestasaurus was indeed a, basal, member of the Titanosauria. Alternatively,Haestasaurus was a basal member of the largerclade of theMacronaria, a close relative ofCamarasaurus,Janenschia orTehuelchesaurus. The authors favoured the last possibility because the traits pointing to a membership of the Titanosauria, such as a robust humerus and a robust ulna, could easily have been developed in a process ofconvergent evolution, as adaptations for weight-bearing.Haestasaurus would then represent a rare late-surviving basal macronarian.[1]