Brancasaurus
| Brancasaurus Temporal range:
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| Holotype specimen | |
Scientific classification
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | †Sauropterygia |
| Order: | †Plesiosauria |
| Genus: | †Brancasaurus Wegner, 1914 |
| Species: | †B. brancai
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| Binomial name | |
| †Brancasaurus brancai Wegner, 1914
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| Synonyms | |
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Brancasaurus(meaning "Branca's lizard" ) is agenusofplesiosaurwhich lived in a freshwater lake in theEarly Cretaceousof what is nowNorth Rhine-Westphalia,Germany.With a long neck possessingvertebraebearing distinctively-shaped "shark fin" -shapedneural spines,and a relatively small and pointed head,Brancasaurusis superficially similar toElasmosaurus,albeit smaller in size at 3.26 metres (10.7 ft) in length as a subadult.
Thetype speciesof this genus isBrancasaurus brancai,first named by Theodor Wegner in1914in honor of GermanpaleontologistWilhelm von Branca.Another plesiosaur named from the same region,Gronausaurus wegneri,most likely represents asynonymof this genus. While traditionally considered as abasalmember of theElasmosauridae,Brancasaurushas more recently been recovered as a member, or close relative, of theLeptocleididae,a group containing many other freshwater plesiosaurs.
Discovery and naming
[edit]
Theholotypespecimen ofBrancasaurus brancaiis GPMM A3.B4, stored at theUniversity of Münster.It originates from a clay pit near the city ofGronau, North Rhine-WestphaliainGermany.The specimen was discovered in July 1910 by workers in the clay pit, who dug it out using pickaxes; in doing so, they damaged the specimen (in particular, thepubishad been broken into 176 pieces), and left behind a number of small fragments that were later personally collected by paleontologist Theodor Wegner, who in 1928 described the specimen in detail. The skeleton is fairly complete, consisting of various parts of the skull, most of the vertebrae, several isolated ribs andgastralia,parts of thepectoralandpelvicgirdles, bothhumeri,onefemur,and various foot bones from the flippers. Over time, a number of parts have been lost, including several pieces of the skull, teeth, gastralia and caudal vertebrae, a second femur, and aradius,tibia,andfibula.A waxendocastof the brain of the type specimen is stored as SMF R4076 in theNaturmuseum Senckenberg.[1]
The clay pit from which the type specimen originates is part of the Isterberg Formation in theBückeberg Group,[2]also known in the past as the "German Wealden facies".[3]The Bückeberg Group, which is divided into six zones,[4]belongs to theBerriasianof theCretaceous,with the boundary between the Berriasian and theValanginianbeing at the top of the group.[5]The parts of the Isterberg Formation exposed at Gronau belong to the zones "Wealden 5" and "Wealden 6", which correspond to the uppermost-Berriasian. A second, more fragmentary subadult individual, GZG.BA.0079, consists of thepubis,ischium,and several vertebral components; it originates from the slightly lower Deister Formation ( "Wealden 3"[4]) in the Bückeberg Group, and can only be referred toBrancasaurus sp.,since it is relatively incomplete and differs in several minor vertebral characteristics from the type ofB. brancai.Other probable but isolatedBrancasauruselements come from outcrops of the Isterberg and Fuhse Formations inLower Saxony;the latter formation is also in the Bückeberg Group.[1]
Synonyms
[edit]
The specimen GPMM A3.B2 consists of teeth, parts of the jaws, thebraincaseand other fragmentary parts of the skull, vertebrae, pieces of ribs, part of the pectoral girdle, the entire pelvic girdle, one complete and one partial humerus, anulna,two femora, a fibula, and various foot bones. While this specimen was originally assigned toBrancasaurus,Hampe (2013) referred it to a new genus and species,Gronausaurus wegneri.[6]It was discovered some 8 metres (26 ft) higher in the stratigraphic column than the type specimen ofBrancasaurus.Later analysis found that this specimen, which was mature, was virtually indistinguishable from the type ofBrancasauruswith the exception of the length of the ischium, the height of the cervicalneural spines,the width of the cervicalcentra,and whether the dorsal neural spines are constricted at their base. These minor differences can probably be attributed to either individual-based or age-based variation, supportingG. wegnerias a junior synonym ofB. brancai.[1]
E. Koken namedPlesiosaurus limnophilusin 1887 based on isolated cervical vertebrae from outcrops of the Bückeberg Group in Lower Saxony. From the same locality, Koken subsequently named two further species ofPlesiosaurus,P. degenhardtiandP. kanzleri,and also referred some material toP. valdensis.All of this material is not particularly diagnostic, and has been partially lost; thus, they have been considerednomina dubia.Sachset al.considered all of these to represent remains ofBrancasaurus,with the exception ofP. degenhardti,which was retained as anomen dubiumon account of lacking the distinctive cervical neural spines ofBrancasaurus.[1]
Description
[edit]Brancasauruswas a medium-sized plesiosaur, with theholotype specimenmeasuring 3.26 metres (10.7 ft) in length; this specimen likely belongs to a subadult, judging by the unfused sutures in the vertebrae as well as the development of processes on the limbs andpubis.[1]
Skull
[edit]
The skull of the holotype, which measures 23.7 centimetres (9.3 in) long, is long and narrow, with a tapered snout that slopes downwards at an angle of 15°. The eye sockets were roughly the same size as the temporal openings immediately behind them. A narrow, rounded ridge along the middle of the top surface of the skull extends from near the front of thepremaxillato the back of the eye sockets. Thefrontal bonesform a rectangular bar that separates the eye sockets down the middle. A ridge running across the bar intersects with the forward-extending ridge to produce a dagger-shaped protrusion. Thejugal bone,which extends from the bottom of the eye socket back to the level of the temporal openings, is entirely bordered on its bottom by themaxilla.Thesquamosal bonesarch around to form the curved back of the skull, and bear a ridge on top for attachment of neck muscles. There is also a ridge at the point where the two bones fuse. A cast of thebraincaseshows impressions of thesemicircular canalsand membranous inner ear, as well as canals of thehypoglossal,accessory,glossopharyngeal,andvagusnerves, which can also be observed on the bony exoccipital-opisthotic of the braincase. On the imperfectly-preserved lower jaw, thecoronoid eminenceseems to be relatively low, judging by the narrow and slightly curved top edge of thesurangular bone.While the teeth have been lost, they were initially described as long, slender, and awl-shaped, with rough ridges on the outer surfaces. Although it has been suggested thatBrancasaurushad very reducedtooth socketsin the premaxilla, as inLeptocleidus,[7]this is impossible to verify because of damage to this portion of the skull.[1]
Vertebral column
[edit]
The entire neck bears 37cervical vertebrae,and is approximately 1.18 metres (3 ft 10 in) long. Thecentraof the vertebrae are wider than they are tall or long. Both ends of each vertebra are slightly concave, meaning that the vertebrae are amphicoelous. The sides of the vertebrae are likewise weakly concave; unlike many other long-necked plesiosaurs, they did not bear a ridge on the side (although this may be affected by age). Theneural spinesof the vertebrae are distinctively shaped like shark fins, being high and triangular. There are three pectoral vertebrae at the neck-body transition, which are weakly concave, taller than they are long, and have rectangular-shaped neural spines that are directed slightly backwards. The cervical and pectoral vertebrae have deep indentations through which thenotochordpassed.[1]
The 19dorsal vertebraeare similar to the pectoral vertebrae, being weakly concave and taller than long, but the neural spines are proportionally taller than the centra. The single-headed dorsal ribs are rounded but slightly flattened in cross-section, and some have a prong-like projection at the top end; theirarticular surfacesare slightly concave. Underneath, there are at least ten pairs ofgastralia,each of which tapers to the sides and has a central groove on the bottom surface. The threesacral vertebraeare similar, but have much smaller, blunter, more oval-shaped ribs. The comparatively smaller first sacral rib is directed further outwards and backwards than the other two ribs. There initially were 25 caudal vertebrae preserved, with 22 still being accounted for. The last several caudal vertebrae are partially fused into apygostyle-like structure. The preserved caudal ribs are flattened, triangular, and taper towards the tip of the tail.[1]
Limbs and limb girdles
[edit]
Theinterclavicleis a large plate with a smooth upper surface and a prominent groove on the bottom surface. It also bears a small, pointed projection at its back end. Thescapulaehave prominent shelves on each side (diagnostic ofleptocleididsandpolycotylids,but not strongly differentiated inelasmosaurids), and theirglenoidsare clearly concave, with roughened attachments for cartilage. The twocoracoidscurve outwards in the middle and contact at their ends, forming a hole in the middle, although the exactmorphologyof this hole is uncertain. The regions where the coracoids contact is vaulted and thickened to form a weak, ridge-like projection, comparable to but probablyconvergentlyacquired from elasmosaurids. Thepubesform a somewhat rectangular dish, with a convex front edge and concave outer edge, while theischiaare flat, triangular, and plate-like. The edges of the pubes where they meet the ischia curve inwards from the midline to each side. The corresponding edges of the ischia are similarly-shaped, with the curved edges of the bones collectively forming two rounded fenestrae that are connected in the center by a small rhombus-shaped opening, as also seen inFutabasaurus.[8]Theiliaare rod-shaped and bent, with blunt projections halfway along their outer rims; at the top end, they are flattened into a fan-like shape.[1]
Thehumeri,which have a length of about 24 centimetres (9.4 in), are oval in cross-section, and about half as wide as they are long at the widest point. Their leading edges are curved in an S-shape, a trait also seen inLeptocleidus,Hastanectes,polycotylids, and the elasmosauridWapuskanectes,but not inNichollssaura.[7][9]The onlyfemurthat is presently available is 21.5 centimetres (8.5 in) long; it is concave on one edge, whereas the other edge is straight near the top but curves sharply near the bottom. The rest of the long bones of the limb have been lost. Allegedly, theradiuswas similar to but smaller and straighter than thetibia,and there was a hole present between the tibia andfibula.The 14 preservedphalanges,which likely include elements from both the forelimbs and the hindlimbs, are long and hourglass-shaped.[1]
Possible soft tissue
[edit]Soft tissue was apparently preserved with the specimen, but was subsequently removed during preparation. Covering the limbs and the rest of the body was a layer of smooth, multilayeredcalcite,which was originally interpreted as preservation of decaying skin. Additionally, an accumulation of sediment in the abdominal region may have represented gut contents, with bothgastrolithsand digested bones. However, since both samples of the alleged soft tissue are no longer available, it is impossible to verify these interpretations.[1]
Classification
[edit]
Initially,Brancasauruswas assigned to theElasmosauridaeby Wegner. He noted, however, that it had a shorter neck and a narrower head, as well as various distinctive morphologies of the skull roof, teeth, and vertebrae (especially the "shark fin" -shapedneural spinesof the cervical vertebrae) compared to other members of the group known at the time. A number of subsequent studies have consideredBrancasaurusas a basal member of the Elasmosauridae,[10][11][12][13]with some even usingBrancasaurusto define theclade.[11]Nevertheless, a number of contrary taxonomic opinions have been expressed; in particular, Theodore E. White created a new family,Brancasauridae,to containBrancasaurus,Seeleyosaurus,and "Thaumatosaurus", a defunct genus with species now belonging toRhomaleosaurusandMeyerasaurus.[14][1]
An alternative phylogenetic hypothesis that has gained substantial traction placesBrancasaurusin the cladeLeptocleididae,[15][7][16]along with other leptocleidids includingLeptocleidusitself,Vectocleidus,Umoonasaurus,Nichollssaura,and also possiblyHastanectes.[16]This result has been recovered by the phylogenies of Bensonet al.,who have also noted a number of morphological traits which allyBrancasauruswith the more generalLeptocleidia.[7][1]
A 2016 phylogenetic analysis conducted by Sachset al.found two equally strong alternative placements ofBrancasaurus(includingGronausaurus): within the Leptocleididae; or as thesister taxonof a clade containing both Leptocleididae andPolycotylidae,with the clade containing all of the aforementioned taxa being the sister taxon of Elasmosauridae. The study concluded that, currently, no phylogenetic dataset is sufficient to resolve the relationships ofBrancasaurus.In addition to the fact that the type specimen is a subadult, this inconsistency in results can be attributed to the mix of leptocleidid, polycotylid, and elasmosaurid characteristics that is seen inBrancasaurus.[16]The cladograms below illustrate the alternate arrangements.[1]
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Topology A:Brancasaurusin the Leptocleididae,based on Bensonet al.(2013)[7]
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Topology B:Brancasaurusoutside Leptocleididae,based on Benson & Druckenmiller (2014)[16] |
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Paleoecology
[edit]
The Bückeberg Group, from whichBrancasaurusoriginates, likely represented a large, continental freshwater lake that the surrounding uplands drained into. In turn, the lake itself was temporarily connected to theBoreal Seavia a passage to the west. During the time at which the layers of "Wealden 5" and "Wealden 6" were deposited, the lake expanded and became more brackish as a result ofmarine transgression.[17]The deposited sediments probably represent the oxygen-poor bottom portion of the lake, with the plesiosaurs of the Bückeberg Group being presumably preserved after they sank through the water column to the bottom.[1]
Asides fromBrancasaurus,other constituents of the Bückeberg Group are benthic invertebrates, including neomiodontidbivalves;[1]hybodont sharks,includingHybodus,Egertonodus,Lonchidion,andLissodus;theactinopterygian fishCaturus,Lepidotes,Coelodus,Sphaerodus,Ionoscopus,andCallopterus,[6]whichBrancasauruswould have preyed on in surface waters;[18]the turtleDesmemys;[6]crocodilians,includingGoniopholis,Pholidosaurus,andTheriosuchus;the theropodAltispinax;themarginocephalianStenopelix;and anankylosaurreferred toHylaeosaurus.[19][20]Other indeterminate remains have been assigned topterosaurs;the crocodilian cladesHylaeochampsidaeandEusuchia;and the dinosaurian cladesDryosauridae,Ankylopollexia,Troodontidae,andMacronaria.[20]
See also
[edit]
References
[edit]- ^abcdefghijklmnopSachs, S.; Hornung, J.J.; Kear, B.P. (2016)."Reappraisal of Europe's most complete Early Cretaceous plesiosaurian:Brancasaurus brancaiWegner, 1914 from the "Wealden facies" of Germany ".PeerJ.4:e2813.doi:10.7717/peerj.2813.PMC5183163.PMID28028478.
- ^Casey, R.; Allen, P.; Dörhöfer, G.; Gramann, F.; Hughes, N. F.; Kemper, E.; Rawson, P. F.; Surlyk, F. (1975). "Stratigraphical subdivision of the Jurassic-Cretaceous boundary beds in NW Germany".Newsletters on Stratigraphy.4(1): 4–5.doi:10.1127/nos/4/1975/4.
- ^Allen, P. (1955)."Age of the Wealden in North-Western Europe".Geological Magazine.92(4): 265–281.Bibcode:1955GeoM...92..265A.doi:10.1017/S0016756800064311.S2CID129186916.
- ^abElstner, F.; Mutterlose, J. (1996). "The Lower Cretaceous (Berriasian and Valanginian) in NW Germany".Cretaceous Research.17(1): 119–133.doi:10.1006/cres.1996.0010.
- ^Mutterlose, J.; Bodin, S.; Fahnrich, L. (2014). "Strontium-isotope stratigraphy of the Early Cretaceous (Valanginian–Barremian): Implications for Boreal–Tethys correlation and paleoclimate".Cretaceous Research.50(4): 252–263.doi:10.1016/j.cretres.2014.03.027.
- ^abcHampe, O. (2013). "The forgotten remains of a leptocleidid plesiosaur (Sauropterygia: Plesiosauroidea) from the Early Cretaceous of Gronau (Münsterland, Westphalia, Germany)".Paläontologische Zeitschrift.78(4): 473–491.doi:10.1007/s12542-013-0175-3.S2CID129834688.
- ^abcdeBenson, R.B.J.; Ketchum, H.F.; Naish, D.; Turner, L.E. (2013). "A new leptocleidid (Sauropterygia, Plesiosauria) from the Vectis Formation (Early Barremian–early Aptian; Early Cretaceous) of the Isle of Wight and the evolution of Leptocleididae, a controversial clade".Journal of Systematic Palaeontology.11(2): 233–250.doi:10.1080/14772019.2011.634444.S2CID18562271.
- ^Sato, Tamaki; Hasegawa, Y.; Manabe, M. (2006)."A new elasmosaurid plesiosaur from the Upper Cretaceous of Fukushima, Japan".Palaeontology.49(3): 467–484.doi:10.1111/j.1475-4983.2006.00554.x.
- ^Albright, L.B.; Gillette, D.D.; Titus, A.L. (2007)."Plesiosaurs from the Upper Cretaceous (Cenomanian–Turonian) Tropic Shale of Southern Utah, part 2: Polycotylidae"(PDF).Journal of Vertebrate Paleontology.27(1): 41–58.doi:10.1671/0272-4634(2007)27[41:pftucc]2.0.co;2.JSTOR4524666.S2CID130268187.
- ^Brown, D.S. (1981)."The English Upper Jurassic Plesiosauroidea (Reptilia) and a review of the phylogeny and classification of the Plesiosauria".Bulletin of the British Museum.35:253–347.
- ^abO'Keefe, F.R. (2001)."A Cladistic Analysis and Taxonomic Revision of the Plesiosauria (Reptilia: Sauropterygia)".Acta Zoologica Fennica.213:1–63.
- ^O'Keefe, F.R. (2004)."Preliminary description and phylogenetic position of a new plesiosaur (Reptilia: Sauropterygia) from the Toarcian of Holzmaden, Germany"(PDF).Journal of Paleontology.78(5): 973–988.doi:10.1666/0022-3360(2004)078<0973:PDAPPO>2.0.CO;2.S2CID53590349.
- ^Großman, F. (2007)."The taxonomic and phylogenetic position of the Plesiosauroidea from the Lower Jurassic Posidonia Shale of south-west Germany".Palaeontology.50(3): 545–564.doi:10.1111/j.1475-4983.2007.00654.x.
- ^White, T.E. (1940). "Holotype ofPlesiosaurus longirostrisBlake and Classification of the Plesiosaurs ".Journal of Paleontology.14(5): 451–467.JSTOR1298550.
- ^Ketchum, H.F.; Benson, R.B.J. (2010). "Global interrelationships of Plesiosauria (Reptilia, Sauropterygia) and the pivotal role of taxon sampling in determining the outcome of phylogenetic analyses".Biological Reviews.85(2): 361–392.doi:10.1111/j.1469-185X.2009.00107.x.PMID20002391.S2CID12193439.
- ^abcdBenson, R.B.J.; Druckenmiller, P.S. (2014). "Faunal turnover of marine tetrapods during the Jurassic–Cretaceous transition".Biological Reviews.89(1): 1–23.doi:10.1111/brv.12038.PMID23581455.S2CID19710180.
- ^Mutterlose, J.; Bornemann, A. (2000). "Distribution and facies patterns of Lower Cretaceous sediments in northern Germany: a review".Cretaceous Research.21(6): 733–759.doi:10.1006/cres.2000.0232.
- ^Halstead, L.B. (1989)."Plesiosaur locomotion".Journal of the Geological Society.146(1): 37–40.Bibcode:1989JGSoc.146...37H.doi:10.1144/gsjgs.146.1.0037.S2CID219541473.
- ^Sachs, S.; Hornung, J.J. (2013)."Ankylosaur Remains from the Early Cretaceous (Valanginian) of Northwestern Germany".PLOS ONE.8(4): e60571.Bibcode:2013PLoSO...860571S.doi:10.1371/journal.pone.0060571.PMC3616133.PMID23560099.
- ^abHornung, J.J. (2013).Contributions to the Palaeobiology of the Archosaurs (Reptilia: Diapsida) from the Bückeberg Formation ('Northwest German Wealden'– Berriasian-Valanginian, Lower Cretaceous) of northern Germany(Dr. rer. nat.).Georg-August University School of Science.pp. 318–351.hdl:11858/00-1735-0000-0001-BACB-5.
External links
[edit]- Brancasaurusin the Plesiosaur Directory
