Paläontologische Zeitschrift

, Volume 87, Issue 4, pp 473–491

The forgotten remains of a leptocleidid plesiosaur (Sauropterygia: Plesiosauroidea) from the Early Cretaceous of Gronau (Münsterland, Westphalia, Germany)

Authors

    • Museum für Naturkunde—Leibniz-Institut für Evolutions- und Biodiversitätsforschung
Research Paper

DOI: 10.1007/s12542-013-0175-3

Cite this article as:
Hampe, O. Paläontol Z (2013) 87: 473. doi:10.1007/s12542-013-0175-3

Abstract

Gronausaurus wegneri n. gen. n. sp. represents a newly discovered leptocleidid sauropterygian based on one individual from the Early Cretaceous (Berriasian) of Gronau in Westphalia, Germany. The holotype and only known specimen consists of a skeleton, which lacks most of the dermal skull bones, a large number of cervical vertebrae and distal limb elements. Gronausaurus wegneri is unique in having distinct cavities, the subdiapophyseal fossae, below the transverse processes of the pectoral and anterior dorsal vertebrae, that probably stabilised the bones against tensile forces of the rotator and levator muscles in the living animal.

Keywords

BerriasianBückeberg FormationGronausaurus wegneriLeptocleididae

Kurzfassung

Gronausaurus wegneri n. gen. n. sp. ist ein neu entdeckter leptocleidider Sauropterygier aus der frühen Kreide (Berriasium) von Gronau in Westfalen, Deutschland. Holotypus und einzig bekanntes Individuum besteht aus einem Skelett, dem die meisten dermalen Cranialelemente, eine größere Anzahl von Cervicalwirbeln sowie distale Extremitätenknochen fehlen. Einzigartig für Gronausaurus wegneri sind die sich unterhalb der Transversalfortsätze der Pectoral- und vorderen Dorsalwirbel befindlichen ausgeprägten Gruben, die Fossae subdiapophysealis, welche wahrscheinlich eine höhere Stabilität gegen Zugkräfte der Mm. rotatores et levatores im lebenden Tier gewährleisteten.

Schlüsselwörter

BerriasiumBückeberg-FormationGronausaurus wegneriLeptocleididae

Introduction

The here-presented skeletal remains were discovered in 1912 in a pit of the former brickworks company Gerdemann & Co. in Gronau (North Rhine-Westphalia, y 2568 760, x 5788 040, Fig. 1). Today, the partial skeleton belongs to the collection of the Geomuseum at the University of Münster (Pferdegasse 3, DE-48143 Münster; abbrev. GMM). The Gerdemann locality has been long known, containing different vertebrate fossils such as fish and reptilian remains.
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Fig. 1

Map of northwest Germany showing the City of Gronau close to the Dutch border

The fish fauna is represented by teeth of hybodont sharks (Hybodus, Egertonodus, Lonchidion, Lissodus) and of actinopterygian genera, such as the amiiform Caturus, the semionodontid Lepidotes, the pycnodontids Coelodus and Sphaerodus and the pholidophoriformes Ionoscopus and Callopterus (Kemper 1976; Nyhuis and Herbig 2009).

Reptiles are documented, among others, by the quite well-preserved chelonid Desmemys bertelsmanni (Wegner 1911), which was formerly grouped into the Thalassemyidae until Brinkman et al. (2000) expressly included Desmemys within the Pleurosternidae. A crocodilian tooth was identified early by the famous palaeontologist Eberhard Fraas (Landois 1904).

The first plesiosaur vertebrae from Gronau became public through notes of Landois (1900, 1902), originally identified as ichthyosaur vertebrae. Other plesiosaur vertebrae from the Gronau locality were subsequently discovered in the private collection of an official of the local public health authority, Dr. Kanzler (Koken 1905). Koken classified these vertebrae as belonging to three already known species (Plesiosaurus degenhardti, P. limnophilus and P. valdensis) and erected in addition a new species (Plesiosaurus kanzleri). Later, Welles (1962) was the first to consider these remains as nomina vana because Plesiosaurus vertebrae do not show taxonomically significant characters. P. valdensis was also considered a nomen vanum by Kear and Barrett (2011). Andrews (1922), Ketchum (2011) and Benson et al. (in press) pointed out unique features and Benson et al. (in press) placed it into a new genus, Hastanectes. Hosius (1893) described a clavicula of the ornithopod dinosaur “Iguanodon” from the Gronau pit. However, this element belongs to the distal propodial part of a large plesiosaurid according to Wegner (1914).

Ultimately, in 1910, the articulated skeleton of an elasmosaurid plesiosaur was unearthed in the clay pit. This specimen has been studied by Wegner (1914) in detail, who introduced therefore the new taxon Brancasaurus brancai. The discovery of a second skeleton was mentioned in the same publication. Wegner (1914: 237) wrote in 1912 that well-preserved plesiosaurid vertebrae and other parts of a skeleton had been found. He assumed that they might belong to another species and noted that the isolated fragments were under preparation. No further remarks or field book notes exist about this second skeleton. Particular circumstances and detailed data on its discovery are unknown. This second skeleton was later classified as belonging to Brancasaurus (Siegfried 1961), although Wegner (1914) recognised differences from Brancasaurus.

Stratigraphic age

At the beginning of the 20th century, the pit of the Gerdemann & Co. brickworks had a depth of 30–40 m that contained Berriasian (“Wealden”) and middle Valanginian shales (Schleicher 1995). The pit was closed in 1917, because of a water ingress (Thiermann 1968). During a period of water shortage in 1959 the pit was later dewatered but subsequently closed again (Kemper 1961).

Wegner (1914) described a profile of the northern part of the mine. His description is less detailed, and a final stratigraphical column was not presented. Previously, Hosius (1893) studied the stratigraphy of the pit, and his results differ clearly from Wegner’s descriptions. Additionally, Hosius’s report reveals several contradictory statements which lower the importance of its use for recent study.

The geological situation of this area is characterised by NNW–SSE striking and NE dipping Wealden deposits that occur through an anticlinal fold in Brook W of Gronau (Wolburg 1953; Thiermann 1968). The stratigraphic results of Kemper (1961) are considered to date to be the most exact ones for the Gronau clay pit (Fig. 2). His studies were undertaken there after the dewatering in 1959 (Hiß, pers. comm.). The α-section (= Berriasian–Valanginian intersection) in Kemper (1961) could probably be correlated with the conglomerate described by Wegner (1914). The skeletal remains of the second plesiosaur described in this paper were found directly below the conglomerate according to Wegner. Therefore, a latest Berriasian age (upper Osterwald Succession, Bückeberg Formation) could be estimated for Gronausaurus wegneri n. gen. n. sp. (Fig. 2). The occurrence of the monotypic myoid clam Corbula indicates a brackish environment of the Osterwald Succession (Kemper 1976).
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Fig. 2

Stratigraphy of the former Gerdemann & Co. brickworks pit in Gronau, Westphalia, Germany (based on Kemper 1961), showing the positions where the plesiosauroids Brancasaurus brancai Wegner 1914 and Gronausaurus wegneri n. gen. n. sp. were discovered

Materials and methods

The partial skeleton of the new leptocleidid plesiosaur was transferred for the recent study temporarily from the Geomuseum in Münster to the Museum für Naturkunde in Berlin. The remains, containing a few isolated teeth, jaw fragments, the braincase, six cervical vertebrae, four pectorals, 16 dorsals, four sacrals, and 22 caudal vertebrae, rib fragments, the left coracoid, pelvic girdle, propodials of fore and hind limbs, and several epipodial and autopodial elements were additionally cleaned, prepared and hardened in Berlin. The bones were measured, drawn and photographed.

For comparative and supplementary studies the collections in Münster (Geomuseum), Gronau (Driland-Museum), Bonn (Goldfuss-Museum, Steinmann-Institut für Geologie, Mineralogie und Paläontologie), Stuttgart (Staatliches Museum für Naturkunde), Holzmaden (Urwelt-Museum Hauff) and London (The Natural History Museum) were visited.

The phylogenetic analysis was performed using WINCLADA 1.00.08 (Nixon 2002) and NONA 2.0 (Goloboff 1999).

Systematic palaeontology

  • Order Sauropterygia Owen 1860

  • Suborder Plesiosauria de Blainville 1835

  • Superfamily Plesiosauroidea Welles 1943

  • Family Leptocleididae White 1940

  • Genus Gronausaurusn. gen.

Type species

Gronausaurus wegneri, n. gen. n. sp.

Etymology

After the name of the Town of Gronau.

Diagnosis

A leptocleidid plesiosaur with the following characters: lateral portions of the parasphenoid ending directly anterior to the basioccipital tubers; elongated cochlear facet on the dorsal side of the braincase; gently procoelous cervical centra; presence of a subdiapophyseal fossa below the transverse processes at the 2nd to 4th pectoral and anterior dorsal vertebrae; (number of pectoral vertebrae probably 4); humeri with facet for supernumerary postaxial epipodial elements; epipodials longer than wide.

Distribution

Early Cretaceous, latest Berriasian, upper Osterwald Succession, Bückeberg Formation of Münsterland, Westphalia, Germany.

Referred species

Only Gronausaurus wegneri n. sp.

Gronausaurus wegnerin. sp. Figs. 3, 4, 5, 6, 7 and 8.
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Fig. 3

Gronausaurus wegneri n. gen. n. sp., GMM-A3B.2. Braincase in a dorsal view, b ventral view, c left aspect, d posterior view

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Fig. 4

Gronausaurus wegneri n. gen. n. sp., GMM-A3B.2. One of three preserved teeth showing the closely arranged longitudinal striations with less or no cristae on the labial side: a, c axial views, b labial view, d lingual view

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Fig. 5

Gronausaurus wegneri n. gen. n. sp., GMM-A3B.2. Preserved bones of the anterior spine: a anterior cervicals in right lateral view, b posterior cervicals, c pectorals and anterior dorsals in left lateral view, d same in a detailed drawing, e detail of the subdiapophyseal fossae of the last pectoral and the two first dorsals, f dorsals 4–13 in left lateral view

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Fig. 6

Gronausaurus wegneri n. gen. n. sp., GMM-A3B.2. Bones of the posterior spine: a posteriormost dorsals and sacral vertebrae in left lateral view, b the first caudals in left lateral view, c drawing of the ilium above, d caudals 6–11, e the end of the tail (caudals 12–22) in roughly ventral (above) and dorsal (below) views

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Fig. 7

Gronausaurus wegneri n. gen. n. sp., GMM-A3B.2. Remains of the girdle elements in dorsal view: a pectoral girdle, b pelvis

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Fig. 8

Gronausaurus wegneri n. gen. n. sp., GMM-A3B.2. Limb bones: a distal part of the left humerus in ventral view, b right humerus in ventral (left) and dorsal (right) views including radius and ulna in dorsal view, c left femur in ventral (left) and dorsal (right) views, d right femur in ventral (left) and dorsal (right) views plus fibula in dorsal view

Holotype

Partial skeleton, GMM-A3B.2.

Etymology

After Thomas Wegner, palaeontologist and discoverer of the skeleton.

Type locality

Former pit of Gerdemann & Co. brickworks, Gronau/Münsterland, Westphalia, Germany.

Type horizon

Bückeburg Formation, Osterwald Succession, Berriasian, Lower Cretaceous.

Distribution and range

Latest Berriasian, Early Cretaceous of W Germany.

Material

Incomplete skeleton containing three isolated teeth, jaw and skull roof fragments, braincase, 6 cervical, 4 pectoral, 16 dorsal, 4 sacral, and 22 caudal vertebrae, rib fragments, pectoral girdle with left coracoid, glenoid ramus of the left scapula, fragments of the right proximal coracoid, pelvic girdle containing both pubes, left ischium and ilium, shaft of right ilium, propodials with right humerus, distal end of left humerus, both femora, several epipodial and autopodial elements.

Diagnosis

As for genus.

Remarks

Remains of the skull are stored in the collection of the Geomuseum in Münster separately from the postcranium, which is regularly on display. These elements are insufficiently labelled but are not determinable to other remains than Gronausaurus.

Description

Cranium. The preserved braincase has a length of 6.4 cm and a maximum width of 3.5 cm between the basioccipital tubers and contains a hemispherical occipital condyle that is formed only by the basioccipital bone (Fig. 3). The condyle is separated from the anterior portion of the basioccipital by a distinct rim followed by a short constricted collum, recognisable best from the ventral aspect (Fig. 3b). The condyle has a notochordal pit situated slightly above its centre (Fig. 3d).

Prominent auricle-shaped processes are developed on each side (basioccipital tubers) that articulate with the pterygoids in a completely arranged skull (Fig. 3a, c). The dorsal surface of the basioccipital bears a pair of proportionally large, shallowly depressed exoccipital facets (Fig. 3a). The facets do not reach the marginal rim of the occipital condyle. A distinctly developed elliptical groove on the dorsal side separates the exoccipital facets. The anteriorly following basisphenoid is separated by a transversally oriented suture. Elongated cochlear fossae are situated on the lateral margin of the braincase at the transition between basioccipital and basisphenoid (Fig. 3a). The most anteriorly preserved portion ends with the optic groove in front of the partially damaged sella turcica.

At the ventral side, the preserved braincase is covered by the parasphenoid, which is characterised by the presence of a median keel (Fig. 3b).

Other remains, a maxillar fragment and skull roof parts (?parietal, ?squamosal) are preserved too poorly to provide a meaningful description.

Dentition. Only three isolated tooth crowns of different lengths are preserved. They have a slender shape, being slightly curved and pointed (Fig. 4a, c). The surfaces are ornamented with numerous parallely arranged longitudinal striations. These fine cristae are most prominently developed at the lingual (concave) side (Fig. 4d). There are less or no cristae on the labial (convex) aspect of the tooth crowns (Fig. 4b).

Vertebral column. The majority of the cervical vertebrae are unknown. With the beginning of the pectorals the rest of the spine is obviously complete. Only a few caudal vertebrae could be lost in the middle part. Generally, all vertebrae are well preserved except minor compressions. Only a few vertebrae lack the neural spines. The size of the centra steadily increases up to about the 14th preserved dorsal. Then it decreases caudally. All undeformed vertebral bodies have the same proportions: width > height > length (Table 1).
Table 1

Measurements of the vertebrae of Gronausaurus wegneri n. gen. n. sp. from the latest Berriasian, Bückeberg Formation of the Western Münsterland area, Germany

Vertebral centrum

Length (mm)

Width (mm)

Height (mm)

Height incl. neural spine (mm)

“C1”

45

54

48

“C2”

46

52

46

132

“C3”

46

53

45

145

“C4”

40

(59)

(49)

“C5”

43

53

48

148

“C6”

43

54

49

(150)

Pc1

42

62

53

170

Pc2

44

53

Pc3

47

Pc4

45

(158)

D1

42

D2

43

D3

44

59

52

D4

43

59

54

156

D5

46

160

D6

41

153

D7

41

158

D8

41

150

D9

43

153

D10

42

D11

43

D12

42

D13

37

58

50

D14

38

58

136

D15

32

133

D16

38

S1

(33)

S2

(33)

S3

(35)

S4

(40)

Cd1

27

49

37

(102)

Cd2

26

39

109

Cd3

28

Cd4

27

Cd5

28

Cd6

24

47

38

Cd7

22

37

Cd8

23

45

Cd9

38

80

Cd10

23

43

39

81

Cd11

24

45

33

Cd12

23

44

33

Cd13

26

43

36

Cd14

24

40

33

80

Cd15

27

79

Cd16

25

Cd17

25

Cd18

26

Cd19

22

39

Cd20

19

33

Cd21

22

35

Cd22

20

17

Cervical vertebrae. There are only six cervicals preserved, which belong to the posterior portion of the cervical column: two isolated ones and four dislocated on a piece of slab (Fig. 5a, b). The anterior articular faces of the centra are gently concave and circular in outline with a slight flattening at the dorsal edge. The centre of the anterior and posterior surfaces possess a small circular notochordal pit surrounded by a broad bulging ring (Fig. 5b). The posterior articular faces are nearly flat, which indicates the procoelous character of the vertebrae. Both anterior and posterior surfaces are surrounded by a distinct rim.

The ventral side of the cervical centra exposes a longitudinal ridge dividing a pair of nutritive foramina. The ridge of the two isolated centra is prominent, and the foramina are situated in a somewhat elongated depression. The ventral ridge of the following four vertebrae becomes weaker and weaker until it nearly disappears at the posteriormost preserved centrum. The foramina decrease in diameter.

Two elliptical foramina are situated on the dorsal side of the vertebral centra. The spinal foramen (neural canal) has a rounded outline.

The neural arch shows prominently developed zygapophyses. The prezygapophyses project only slightly above the level of the articular faces of the centra (Fig. 5a, b). The facets of the prezygapophyses are slightly concave and oriented dorsomedially. A deep groove is located between the zygapophyses extending vertically the proximal quarter of the the anterior edge of the spine. The postzygapophyses project considerably above the level of the posterior end of the centra (Fig. 5a). Their facets are oriented outwards.

The neural spines are high and blade-like compressed. They slightly point posterodorsally. The distal end of the spines is even or slightly rounded (Fig. 5a, b).

The costal facets of the single-headed cervical ribs are situated on the lower posterior quadrant of the vertebral bodies in lateral view (Fig. 5a). Above the costal facets its surface tends to be slightly concave. There are no cervical ribs preserved.

Pectoral vertebrae. Four pectoral vertebrae exist in Gronausaurus. The vertebrae are preserved in their natural sequence followed by the dorsals (Fig. 5c, d). The pectoral vertebrae are transitional between cervicals and dorsals (after definition of Seeley 1874). Cervical ribs articulate at the centrum; body ribs are connected to the transverse processes of the neural arch of the dorsal vertebrae. The pectoral vertebrae reveal a somewhat intermediate position of the rib facets. However, pectorals can only be identified with certainty in juveniles when the neural arches and vertebral bodies are still unfused. Gronausaurus wegneri is an adult specimen which has fused centra and neural arches with no trace of line of fusion. Therefore, the number of pectorals can only be estimated (see also Brown 1981).

The centra of the pectorals are cylindric; the marginal rim of the anterior and posterior surfaces is less developed. The anterior surface seems to be slightly concave, as is the posterior surface. A longitudinal ventral keel is weakly developed; there is still one small foramen placed on each side of the keel. Neural spines and zygapophyses show similar characters to those of the cervicals. However, the prezygapophyses lack an extended vertical groove. Short diapophyses are located at the upper half of the centrum in lateral view, drifting a little upwards from the first to the fourth (Fig. 5c, d). Their articular facets are oval in shape and project back- and downwards.

A distinct character is the presence of a subdiapophyseal fossa below the diapophyses near to the centrum (Fig. 5c). The first subdiapophyseal occurs at the second pectoral. In the following vertebrae these fossae increase in size.

Dorsal vertebrae. There are 16 dorsal vertebrae preserved. The anterior faces of the dorsal vertebrae are not describable, because they are joined close together in an in situ position (Fig. 5f). The ventral keel at the centra disappears and the ventral foramina are tiny. The zygapophyses are of the same shape as those of the preceding cervicals but become slightly smaller posteriorly. The neural spines show the rectangular outline in lateral view. The spines decrease in length caudally, and the distal end becomes a convex margin (Figs. 5f, 6a). There is a deep vertical groove developed on the posterior side of the neural spine, similar to that seen at the cervicals. The groove becomes weaker until it disappears in the last two preserved dorsals. The lateral length of the transverse processes increases along about the first half of the preserved dorsals, then they decrease in size (Fig. 5e).

A subdiapophyseal fossa is also present at the dorsal vertebrae. The most distinctive one is developed at the second dorsal (Fig. 5c, e). Caudally, the fossae become weaker—the last dorsal has only an insignificant subdiapophyseal fossa (Fig. 6a).

Sacral vertebrae. Four vertebrae could be determined to be sacrals. The rib facets are situated at their centrum and have a relatively large and elliptical diameter in dorsoventral extension (Fig. 6a). The neural spines are shorter and become compressed. Their distal end is convex.

Caudal vertebrae. Twenty two caudal vertebrae are preserved in Gronausaurus. The articular faces of the caudal vertebrae are ovally outlined with lateral extension. The anterior surface is slightly concave, the posterior nearly even. The centra do not show a notochordal pit, and the marginal rim is only slightly thickened. There is no ventral longitudinal ridge or keel developed (Fig. 6d). One or two small downward-oriented foramina are situated on the left and right half of the centra. The rib facets are elliptical to somewhat rectangular-rounded and tend to occupy the entire lateral side of the centra of the anterior caudal vertebrae (Fig. 6b). The rib facets decrease posteriorly in size and become more rounded. Chevron bones are preserved to some extent. They are slightly curved backwards, minimally shorter than the corresponding rib and not fused with the centra.

Zygapophyses and neural spines become shorter posteriorly, disappearing from about the 19th preserved caudal vertebra (Fig. 6e).

Ribs. Ribs are only fragmentarily preserved in short pieces. Originally, they were long and narrow, equipped with an enlarged, trumpet-like expanded head and a deep subcostal groove on the posterior side. A few broken and short fragments may belong to the gastral ribs. The caudal ribs also possess a broad proximal base. The ribs become very slender distally in the cranial portion of the preserved tail (Fig. 6d). In the caudal portion, they are quite short, formed like ludo pieces—decreasing distally in diameter and ending with a dilation—not exceeding the diameter of the corresponding vertebral centrum in length (Fig. 6e).

Pectoral girdle. The pectoral girdle is incomplete. Only the left coracoid and the glenoid ramus of the scapula are preserved (Fig. 7a). The glenoid ramus is distally thickened and bears two facets forming a 70° angle to each other (Fig. 7a). The larger facet articulates with the coracoid, and the smaller forms a part of the humeral joint.

The coracoid is a large and broad bone plate, thin posteriorly, and with a relatively thick glenoid process. The anterior part has a mediolaterally thickened belt on the dorsal side between the humeral acetabulum and the symphyseal facet (Fig. 7a). The left coracoid lacks parts of the posterior end and the medial margin. Still, the preserved course of the medial margin indicates the presence of an intercoracoid embayment in Gronausaurus, so that the posterior halves of the coracoids were originally separated posteriorly along the midline. The lower lateral margin of the coracoid has a strong concave course (Fig. 7a). The symphyseal articular face is also thickened.

The measurements are as follows:
  • Left scapula (glenoid ramus):

  • Maximum diameter of coracoid facet: 72 mm

  • Maximum diameter of acetabular facet: 46 mm

  • Left coracoid:

  • Maximum length: 303 mm

  • Maximum width: 158 mm

Pelvic girdle. Both pubes, the right ischium and ilial parts are preserved. The pubes are somewhat rectangular and flat bones, a little wider than long (Fig. 7b). Several cracks run through these thin plates. The medial margin, where the pubes join, is straight and slightly thickened. The anterior margin is convex—the inner posterior margin concave, describing the obturator foramen. The pubes obviously possess an anterolateral directed horn-like projection in the original condition that is unfortunately broken away in both preserved elements (Fig. 7b). The puberal bone is also thickened at the posterior articular facets where ischium (medially) and femur (laterally) join. There is no evidence for the presence of a median pelvic bar (= medial pubis–ischium bone contact).

Generally, the ischium is a triangular bone with a robust, prominent articular process that keeps the ilial and femoral articular facets. Only the left ischium is quite well describable—there exists only a fragment of the right ischium. The left ischium shows an acute caudal end, has a nearly straight symphyseal margin, and a slightly concave lateral margin in its course from the caudal end to the articular process. Anteriorly the ischium is a thin plate—the edge of the obturator foramen is broken here (Fig. 7b).

The better preserved left(?) ilium is a slightly curved, slender but compact bone (Fig. 6c). The ventral extremity, which is broader than the sacral end, bears the ischial facet and a margin of the acetabulum. The right(?) ilium is only partly visible; both extremities are covered by the sacral vertebrae (in situ) or are broken. The ilia cannot clearly be distinguished as to be right or left with certainty, because of the kind of preservation.
  • The measurements are as follows:

  • Right pubis:

  • Maximum length: 150 mm

  • Maximum width: 200 mm

  • Left pubis:

  • Maximum length: 153 mm

  • Maximum width: 192 mm

  • Left ischium:

  • Maximum length: (175 mm)

  • ?Left ilium:

  • Maximum length: 137 mm

  • Diameter of sacral end: (43 mm)

  • Diameter of ventral extremity: 51 mm

  • Width of shaft: 22 mm

Limb bones. The right humerus is slightly sigmoidal curved, seen in dorsal and ventral aspects, and typically dorsoventrally flattened (Fig. 8a, b). The anterior margin is correspondingly wavy, whereas the posterior margin is distinctly concave. The outline of the proximal end is elliptical and divided by a vertical groove into the dorsally oriented humeral head and the distally faced tuberculum. The tuberculum is slightly abraded. The top of the humeral head is flat and not convexly bulged. Five deep, oval grooves are placed on the ventral aspect directly below the rim of the humeral head. An expanded field of strong rugosity follows below these grooves that displays a broad attachment for the M. coracobrachialis (see Robinson 1975). The distal part of the bone is much expanded. Radial and ulnar facets meet one another at an obtuse angle. A postaxial supernumerary facet follows posteriorly (Fig. 8a, b). All facets are not as distinctly developed as, for example, in cryptocleidids, in Tricleidus or in derived elasmosaurs (Andrews 1910; O’Keefe and Street 2009; Welles 1943, 1952, 1962; Sato et al. 2006). The left humerus is documented only by its distal part. Radial and ulnar facets and the third, supernumerary facet can be distinguished—the radial facet is slightly concave.

An isolated radius is damaged with its anterior part broken off. Its distal part is also incompletely preserved. The anterior margin is weakly convex, and the ulnar margin has a concave outline. One ulna had been discovered. The radial margin is concave. The proximal margin is formed slightly convex, and the distal end seems to be nearly straight. In combination, radius and ulna indicate the presence of a large interosseous foramen.

The measurements are as follows:
  • Right humerus:

  • Median length: 266 mm

  • Diameter of the proximal head: 67 mm

  • Maximum distal width: (127 mm)

  • Minimum width of shaft: 60 mm

  • Left humerus:

  • Maximum distal width: 143 mm

  • Minimum width of shaft: (73 mm)

  • Radius:

  • Median length: (88 mm)

  • Median width: (61 mm)

  • Ulna:

  • Maximum median length: 80 mm

  • Maximum median width: (80 mm)

The femora are similar to the humeri in most respects. However, they are a little shorter and less massive (Fig. 8c, d). The femoral head has a convex upper surface and is equipped with two strong longitudinal grooves on the ventral side. The attachment of the M. puboischiofemoralis externus follows below the caput is indicated by a prominent rugosity in the upper third of the femoral length. The great trochanter arises from the dorsal surface as a continuation of the femoral shaft. Trochanter and femoral head are separated from each other by a thin cleft. The shaft is mediolaterally compressed.

The distal extremity is less expanded than that of the humerus. The distal margin is regularly rounded without evidently developed epipodial facets. The anterior margin of the femora is nearly straight—the posterior margin is convex due to the prominent posterior epicondyli.

The proximal margin of the fibula is partly ruptured. The posterior knee is convex. The fibula has two facets on the distal margin, of which the posterodistal is the smaller one. The posterior margin has a convex form, and the tibial margin at the opposite side is concave. There is no tibia distinguishable from the material stored in the Geomuseum at Münster.

The measurements are as follows:
  • Right femur:

  • Median length: 239 mm

  • Diameter of the proximal head: 57 mm

  • Maximum distal width: 128 mm

  • Minimum width of shaft: 47 mm

  • Left femur:

  • Median length: 242 mm

  • Diameter of the proximal head: 63 mm

  • Maximum distal width: 123 mm

  • Minimum width of shaft: 50 mm

  • Fibula:

  • Median length: (69 mm)

  • Median width: 58 mm

Four isolated mesopodial elements, two metapodials, and 12 phalanges are also recorded. The mesopodials are irregularly rounded or elliptic. The phalanges display a characteristic hourglass form. The longest of them measures 45 mm—the shortest 27 mm.

Discussion

The remains of Gronausaurus wegneri n. gen. n. sp. have been known since 1912, but have never been the object of scientific interest. Wegner (1914) supposed that GMM-A3B.2 and Brancasaurus are distinct from one another. However, he does not mention any distinctive criterion, and so the classification remained unclear. According to Schleicher (1995), there are considerable differences between the here-presented skeleton and Brancasaurus. Brancasaurus brancai from the Berriasian of Gronau is documented by a near-complete skeleton (Wegner 1914: Figs. 1–10, pls. V–IX). There are indeed several similarities to Gronausaurus. The teeth of Gronausaurus are most similar to Brancasaurus, but also to Tricleidus seeleyi and Muraenosaurus leedsi. These plesiosauroids have teeth that are ornamented by numerous longitudinal ridges, but there is reduced or no ornamentation on the convex labial side (Wegner 1914: pl. VI, Fig. 10; Brown 1981: 319). The lack of labial ornamentation can also occur in polycotylids, as shown, for example, in Trinacromerum bonneri (Adams 1997: Fig. 2C).

Comparisons of the occipital region imply that Brancasaurus brancai is most similar to Gronausaurus wegneri. Both have an occipital condyle formed only by the basioccipital, and the presence of a median keel on the ventral part of the parasphenoid is common to both. In addition, the basisphenoids are very similar to each other regarding shape and proportions. However, Brancasaurus lacks a constricting groove at the base of the condyle. The notochordal pit, present in Gronausaurus at the posterior aspect of the condyle, is missing in Brancasaurus. The basioccipital tubers of Brancasaurus extend further posterior, so that they partly cover the occipital condyle in lateral view (Wegner 1914: pl. VI, Fig. 8). Also the lateral portions of the parasphenoid extend posteroventrally in Brancasaurus, but end directly anterior to the basioccipital tubers in Gronausaurus. Close similarities to Gronausaurus concerning the braincase are documented with Tricleidus seeleyi (Andrews 1910: Figs. 73, 74). The basioccipital tubers are smaller here than those of Brancasaurus; they do not cover the ventral portion of the condyle in lateral view. The contour of the exoccipital facets correspond nearly exactly with those of Gronausaurus. Different is the form of the cochlear facet, which is oviform in Tricleidus but more oblong in Gronausaurus. The parasphenoid of Tricleidus is not keeled, in contrast to that in Gronausaurus. Parasphenoid keels are also developed in the other leptocleidids Leptocleidus capensis (Cruickshank 1997: Fig. 3), Leptocleidus superstes (Druckenmiller and Russell 2008a: Fig. 5) and Nichollssaura borealis (Druckenmiller and Russell 2008b: text-figs. 5B, 7).

Generally, the definition of the Leptocleididae, to which Gronausaurus belongs, has to be considered in a state of flux. If Gronausaurus is a leptocleidid, this suggests that the diagnosis of Leptocleididae should be modified from that of Druckenmiller and Russell (2008a) because they defined the absence of a constricting groove around the occipital condyle as characteristic for the family. However, Leptocleidus superstes and Gronausaurus wegneri do have a constricting groove. Often, neck length is used as a characteristic feature classifying plesiosaurs (e.g. Bardet et al. 1999; O’Keefe 2001; Gasparini et al. 2003; Ketchum and Benson 2010). It turns out that this is no marker for the classification of the Leptocleididae. The number of cervical vertebrae reveals high variability between the different species: Leptocleidus superstes = 19–20 cervicals (Andrews 1922), Leptocleidus clemai = supposedly 13 cervicals (Cruickshank and Long 1997), Leptocleidus capensis = 22 cervicals (Cruickshank 1997), Brancasaurus brancai = 37 cervicals (Wegner 1914), Umoonasaurus demoscyllus = ca. 19 (see Long 1998: 142/143), Nichollssaura borealis = 24 (Druckenmiller and Russell 2008b).

Very characteristic is the presence of subdiapophyseal fossae below the transverse processes of the pectoral and anterior dorsal vertebrae of Gronausaurus wegneri. This phenomenon is rather unique and could not be detected in many plesiosaurs (e.g. Liopleurodon ferox, “Colymbosaurus manselli”, Macroplata tenuiceps, Tricleidus seeleyi, Muraenosaurus leedsi, Cryptocleidus eurymerus, Leptocleidus superstes in the collection of The Natural History Museum in London). A weak depression ventral to the diapophyses is described by Benson et al. (in press) for Vectocleidus pastorum from the late Berriassian of the Isle of Wight. Other evidence for the presence of subdiapophyseal fossae seems to exist in a few rhomaleosaurids and in Peloneustes philarchus. It is obvious from the functional morphologic point of view that such an anatomical character would stabilise the transverse processes against tensile forces. The transverse processes possess the attachments for the rotator and levator muscles, and increased stabilisation of this part of the trunk with an advantage for turning and swimming cannot categorically be excluded. Whether breathing could have been influenced is speculative at this point.

The axial skeleton of Brancasaurus shows further differences from the elements known from Gronausaurus. Brancasaurus as well as the Early Cretaceous Umoonasaurus demoscyllus from South Australia (Kear et al. 2006: supporting material, Figs. S6b, S7a) show coalesced caudals at the end of the spine (“pygostyle”)—the last preserved caudals of Gronausaurus were obviously separated during life (Fig. 6e). Umoonasaurus is classified to be a leptocleidid by Ketchum and Benson (2010); however, Kear et al. (2006) referred it to Rhomaleosauridae, and Druckenmiller and Russell (2008a) considered it after their analysis as a basal polycotylid.

The pectoral girdle of Gronausaurus is not sufficiently comparable because of the limited preservation. The general morphology of the pubes resemble that of Muraenosaurus and Brancasaurus. However, a distinct anterolateral cornu is also present in Cryptocleidus (Andrews 1896: Fig. 1), polycotylids (Carpenter 1996) and some elasmosaurids (Welles 1943, 1962; Sato 2003).

An elongated ischium is typical for Pliosauridae and Polycotylidae. This tendency is displayed for the Gronausaurus ischium as well. The caudal process of the preserved left ischium is somewhat longer than that of Brancasaurus—overall the ischium of Gronausaurus is about 1/6 longer than the pubis. The short ischia of Brancasaurus look more elasmosaur-like. Other differences from Gronausaurus are the sharply bent ilia and equally sized propodials of Brancasaurus. The pelvic bones are not comparable with other leptocleidids because of lack of information.

The humeri of Gronausaurus show obvious facets for supernumerary epipodials on their distal margin, which are known also from Muraenosaurus leedsi (Andrews 1910: text-fig. 63), Tricleidus seeleyi (Andrews 1910: text-fig. 77, with four epipodials), and the polycotylids Dolichorhynchops osborni (Williston 1903: pl. 20), Trinacromerum bonneri (Adams 1997: Fig. 11) and Polycotylus latipinnis (O’Keefe 2004: Fig. 8). Such facets are not clearly developed in the propodials of Nichollssaura borealis, but this leptocleidid possesses accessory epipodial ossicles (Druckenmiller and Russell 2008b: text-figs. 2, 16). The humerus of Gronausaurus is larger than the femur, which is a characteristic feature for the Cryptoclididae and Elasmosauridae.

Brancasaurus’ femora developed clearly distinguishable epipodial facets at the distal end, whereas Gronausaurus has gently rounded distal margins. The epipodials of Brancasaurus, Muraenosaurus, Hydrotherosaurus, Cryptocleidus and Tricleidus are broader than long, in contrast to Gronausaurus. The more primitive condition having longer epipodials like Gronausaurus is also present in rhomaleosaurids such as Meyerasaurus victor (Fraas 1910: Fig. 9; Smith and Vincent 2010: text-fig. 4D), Rhomaleosaurus zetlandicus (Taylor 1992: Fig. 1B), Bishanopliosaurus yuungi (Dong 1980: Fig. 7) or, generally, in Liassic plesiosaurs. This character is probably supposed to be present also in Leptocleidus capensis. The information of the presence of long epipodials here is only known from the hind limb (Andrews 1911: Fig. 4).

Phylogenetic analysis

To determine the phylogenetic position of Gronausaurus wegneri a cladistic analysis was performed. The Pistosauroidea, known from the Early Triassic of the western Tethys, eastern and western Pacific, and cosmopolitan of the Jurassic and Cretaceous (see Rieppel 2000), was taken as the outgroup for the phylogenetic analysis. For ingroup comparison the following sauropterygian taxa were used (in alphabetical order): Brancasaurus brancai from the Berriasian, Wealden 6 of Gronau, Westphalia, Germany; Callawayasaurus colombiensis from the early Aptian of Loma de la Catalina, Boyacá, Colombia; Cryptocleidus eurymerus from the Callovian, Oxford Clay of Peterborough, England; Gronausaurus wegneri from the latest Berriasian, Bückeburg Formation of Gronau, Westphalia, Germany; Hydrotherosaurus alexandrae from the Maastrichtian, Moreno Formation of Fresno Co., California, USA; Kimmerosaurus langhami from the early Tithonian, Kimmeridge Clay of Dorset, England; Kronosaurus boyacensis from the late Aptian of Municipio de Moniquirá, Boyacá, Colombia; Leptocleidus superstes from the Barrêmian, Weald Clay Formation of Berwick, Sussex, England; Libonectes morgani from the Turonian, Eagle Ford Group of Dallas Co., Texas, USA; Liopleurodon ferox from the late Callovian-Oxfordian of Peterborough, England and Boulogne-sur-Mer, Département Pas-de-Calais, France; Meyerasaurus victor from the early Toarcian, Posidonia Shale of Holzmaden, Germany; Muraenosaurus leedsii from the Callovian, Oxford Clay of Peterborough, England; Peloneustes philarchus from the Callovian, Oxford Clay of Peterborough, England and North Rhine-Westphalia, Germany; Polycotylus latipinnis from the Santonian-Campanian, Niobrara Formation of Logan Co., Kansas, Mooreville Chalk Formation of Greene County, Alabama, USA; Seeleyosaurus guilelmiimperatoris from the early Toarcian, Posidonia Shale of Holzmaden, Germany; Thalassiodracon hawkinsi from the Rhaetian–Hettangian boundary, Blue Lias Formation of Somerset, England; Tricleidus seeleyi from the Callovian, Oxford Clay of Peterborough, England.

The heuristic search was chosen for this parsimony analysis with parameter settings of 1,000 trees to use a tree bisection-reconnection method of branch-swapping including 10 randomised replications. Only characters are used which are comparable with the here newly described taxon Gronausaurus wegneri such as braincase, vertebrae and limb bones. Characters 1–5 cover the braincase, characters 6 and 7 the teeth, characters 8–17 the spine, characters 18–24 the girdle elements and characters 25–33 the pro- and epipodial bones. All characters are treated unweighted in the performed analysis and are based on data collected and verified from Brown (1981), Hampe (1992), O’Keefe (2001), Druckenmiller and Russell (2008a) and Ketchum and Benson (2010) and on personal observations.

The following characters were scored:

1. Parasphenoid in ventral view: the parasphenoid is completely keeled (0), anteriorly keeled (1), flat (2) [K&B 68, D&R 55, O’K 71]

2. Basisphenoid in ventral view: the basisphenoid is exposed (0) or covered by the parasphenoid (1) [K&B 69, D&R 54]

3. Position of the exoccipital facets: dorsal to occipital condyle (0), separated from the occipital condyle by a constricting groove or neck (1) [K&B 79]

4. Notochordal pit on occipital condyle: absent (0), or present (1) [K&B 81, D&R 66]

5. Exoccipital participates in formation of occipital condyle: no (0), yes (1) [D&R 68, O’K 42]

6. Tooth enamel ornamentation: vertical cristae conspicuously coarse (0), fine (1) [D&R 91]

7. Cross-section of teeth in anterior half of tooth row: nearly rounded (0), oval (1) [K&B 109, D&R 92]

8. Articular face of cervical centra in anterior view: uniformly convex (0), ventral notch present (1) [K&B 122, D&R 104]

9. Ventral surface of cervical centra: develops a sharp keel dividing depressions (0), bears a rounded ridge (1), is flat or only slightly convex (2) [K&B 123, D&R 105]

10. Concavity of the articular facet of cervical centra: amphicoelous (0), procoelous (1), acoelous (2) [K&B 124, D&R 106]

11. Rib facets of the cervical vertebrae: two facets broadly separated (0), two co-joined rib facets (1), single rib facet (2), anteroposterior division of rib facet (3) [K&B 125, D&R 107, H 21]

12. Combined width of cervical zygapophyses: broader than the centrum (0), subequal to the centrum (1), distinctly narrower than the centrum (2) [K&B 127, D&R 108]

13. Medial contact of the left and right prezygapophyses: absent (0), present (1) [K&B 128, D&R 109]

14. Height of cervical neural spines in lateral view: lower than their anteroposterior length (0), taller than long (1) [K&B 130, D&R 112]

15. Angle of neural spines in cervical vertebrae: not appreciably angled (0), posteriorly angled (1) [D&R 111]

16. Posterior margin of cervical neural spines: straight (0), grooved (1) [K&B 131, D&R 113]

17. Subdiapophyseal fossa below the transverse process at pectoral and anterior dorsal vertebrae: absent (0), present (1) [new character]

18. Posterior intercoracoid vacuity/embayment: absent (0), or present (1) [K&B 149, D&R 127, O’K 141]

19. Posterolateral margin of coracoid: gently rounded without significant projection (0), forms angled cornu that distinctly extends lateral to the glenoid fossa (1) [K&B 151, D&R 128]

20. Shape of the ilial shaft: straight (0), curved (1) [K&B 167, D&R 142]

21. Sacral end of the ilium: tapers (0), flares equally (1), flares asymmetrically with sacral end that is wider posteriorly (2) [K&B 168]

22. Median pelvic bar: present (0), absent (1) [K&B 171, D&R 145, O’K 146]

23. Anterolateral cornu of the pubis: absent (0); present (1) [K&B 174, D&R 148]

24. Relative length between ischium and pubis: both of subequal length (0), ischium longer (1), pubis longer (2) [O’K 3]

25. Relative length between humerus and femur: both of subequal length (0), humerus longer (1), femur longer (2) [K&B 153, D&R 131, O’K 5, B 32]

26. Humeral robustness. Ratio of maximum proximodistal length over maximum width at the distal end: >1.66 (0), ≤1.66 (1) [K&B 154, D&R 132]

27. Humeral shaft: sigmoidally curved (0), straight (1) [D&R 133]

28. Preaxial margin of humerus in dorsal or ventral view: straight or convex (0), concave or sigmoidal wave (1) [K&B 157]

29. Development of distinguishable epipodial facets at distal end of humerus: no (0), yes (1) [K&B 159, D&R 136, O’K 152]

30. Distinct facet on distal humerus for supernumerary epipodial: absent (0), present (1) [O’K 153]

31. Preaxial margin of radius: concave (0), straight or convex (1) [K&B 163, D&R 139]

32. Postaxial margin of ulna: concave (0), convex (1) [K&B 164]

33. Femoral robustness. Ratio of maximum proximodistal length over maximum width at the distal end: >1.66 (0), ≤1.66 (1) [K&B 175, D&R 149]

It has to be mentioned that characters 1, 9, 14 and 15 show polarity changes in comparison with the outgroup in contrast to the statements of the referred authors.

In the present analysis (Fig. 9), the position of the most basal taxa could not be satisfactorily verified. The position of Thalassiodracon must be considered as still under debate: both Druckenmiller and Russell (2008a) and Ketchum and Benson (2010) previously consider it as a plesiosauroid based on new anatomical data. Ketchum and Benson (2011) consider Thalassiodracon again as a basal pliosaurid (like before, e.g. O’Keefe 2001). In addition, Benson et al. (2011) redescribed the skull of Thalassiodracon and observed several previously unrecognised pliosaurid features. In the here-presented analysis, Thalassiodracon is nested between the rhomaleosaurid Meyerasaurus and the basal plesiosauroid Seeleyosaurus. With the use of a limited number of taxa, Großmann (2007) came to a similar result, documenting Seeleyosaurus as sister group to all other derived sauropterygians in her analysis.
https://static-content.springer.com/image/art%3A10.1007%2Fs12542-013-0175-3/MediaObjects/12542_2013_175_Fig9_HTML.gif
Fig. 9

Phylogenetic relationships of Gronausaurus wegneri n. gen. n. sp. among a selection of Neoplesiosauria. The cladogram shows the strict consensus of three trees, heuristic search setting, default optimization (unambiguous changes only), tree length = 95, consistency index (CI) = 0.43, retension index (RI) = 0.54; the Pistosauroidea have been chosen for outgroup comparison (further explanations, see text) (black squares = apomorphic characters)

The basal position of Meyerasaurus is confusing. The Rhomaleosauridae are commonly considered to be the sister group of the Pliosauridae. Although Druckenmiller and Russell (2008a) came to the result that Rhomaleosaurus is paraphyletic having no clear diagnosis and Meyerasaurus victor is no longer included in Rhomaleosaurus (Smith and Vincent 2010), Meyerasaurus should be the adelphotaxon to the pliosaurids. In addition, the Pliosauridae could not be mapped correctly within the Neoplesiosauria in the recent analysis. A reason is actually the low number of taxa and the selection of characters taken here.

However, Rhomaleosauridae and Pliosauridae are not relevant to explain the relationship of the newly described Gronausaurus. In any case, the clade of the Pliosauridae is described here by unambiguous character states in which character state 21 is apomorphic: the presence of coarse vertical cristae on the tooth crown (6), a posteriorly wide sacral end of the ilium that flares asymmetrically (21) and a femur that is longer than the humerus (25). A close relationship between Rhomaleosaurus and Leptocleidus as argued by Cruickshank (1997), Cruickshank and Long (1997) and Cruickshank et al. (1999) cannot be confirmed with the analysis presented here. The most parsimonious trees of Druckenmiller and Russell (2008a), Smith and Dyke (2008), Ketchum and Benson (2010) and Schwermann and Sander (2011) also disagree with that concept.

The following node contains the most basal taxa Tricleidus and Muraenosaurus of the Cryptocleidia (rank-free taxon of Ketchum and Benson 2010 not confirmed here), which are nested in polytomy with the Polycotylidae and the sister-group clades Leptocleididae, Cryptocleidus plus Kimmerosaurus, and the Elasmosauridae. They all share exoccipital facets separated from the occipital condyle by a constricting groove or neck (3), coracoids with posterolateral margins that form angled cornua which distinctly extend lateral to the glenoid fossa (19) and the presence of an anterolateral cornu of the pubis (23) as synapomorphic characters, and cervicals with single rib facets (11), and curved ilial shafts (20) as homoplastic characters.

The Leptocleididae, including Gronausaurus wegneri, are characterised by two homoplastic features: the posteriorly angled neural spines of the cervical vertebrae (15) and the gently rounded posterolateral margins of the coracoids (19). Brancasaurus has with Gronausaurus the covered basisphenoid (by the parasphenoid) (2), the sharp keel on the ventral surface of cervical centra (9) and the sigmoidally curved humeral diaphysis (27) in common.

The derived Elasmosauridae (Callawayasaurus, Hydrotherosaurus, Libonectes) are significantly grouped in this analysis by eight homoplasies. With the sister group Cryptocleidus and Kimmerosaurus they share three apomorphic characters: an oval cross-section of anterior teeth (7), and robust propodials (26, 33).

The here-presented analysis conforms to the extensive PAUP*- and PAUPRat-based analysis generated by Ketchum and Benson (2010: Figs. 5, 6) regarding the position and composition of the clade Leptocleididae. Ketchum and Benson already affirmed the close relationship of Brancasaurus brancai to be a sister taxon of Leptocleidus. Their Templeton’s test attested the unlikelihood that Brancasaurus is an elasmosaurid. The distance between Brancasaurus and Gronausaurus to the Elasmosauridae is confirmed here, too—and this by a higher consistency index here (0.43) than that obtained by Ketchum and Benson (0.33). The polycotylids, represented by Polycotylus latipinnis, have a close relationship to the Leptocleididae, as was shown already by Druckenmiller and Russell (2008a: Fig. 15) and Ketchum and Benson (2010), who found the Polycotylidae to be a derived sister group of the Leptocleididae. Unfortunately, Druckenmiller and Russell (2008a) did not incorporate Brancasaurus in their analysis, although they focussed in their paper on the leptocleidids. However, nobody knew Brancasaurus was a leptocleidid until that time. It had previously only been considered as an elasmosaurid (see discussion in Benson et al., in press).

O’Keefe (2001) defines the Cryptocleididae containing Muraenosaurus and Cryptocleidus as a sister group to the Tricleidia (including Tricleidus, Kimmerosaurus and Polycotylidae of the taxa considered in this paper) under the clade Cryptocleidoidea that excludes leptocleidid forms, which is also in contradiction to the analysis of Ketchum and Benson (2010). Brancasaurus, which is supported within the Leptocleididae, is still positioned after O’Keefe’s results in the Elasmosauridae branch, where it was grouped traditionally (e.g. Wegner 1914; Welles 1962; Brown 1981; Carpenter 1999). Leptocleidus is the sister taxon of Simolestes within the Rhomaleosauridae in the cladistic analysis of O’Keefe (2001).

Großmann (2007) as well came to different results than the analysis performed here, but she used a different selection of taxa. Cryptocleidus and Kimmerosaurus are corroborated as sister groups, but Brancasaurus is linked with the elasmosaur Libonectes.

Schwermann and Sander (2011: Fig. 26) confirm the leptocleidid nature of Brancasaurus and the close relationship of the Leptocleididae to the Polycotylidae on one hand and the Cryptocleididae on the other hand but complain about the weak CI (= 0.345) in their analysis. In the most recent investigation, Kubo et al. (2012) come likewise to the result that Leptocleidus and Brancasaurus are in a sister-group relationship but close to the more primitive Plesiosaurus dolichodeirus and Occitanosaurus tournemirensis. They form the sister clade basal to the Elasmosauridae and its sister group containing Cryptocleidus plus Kimmerosaurus forming a clade, and the basally positioned taxa Tricleidus, Muraenosaurus and polycotylids.

Character matrix

Taxon (alphabetically)

Character #

 

1

2

3

4

5

6

7

8

9

10

 

11

12

13

14

15

16

17

18

19

20

 

21

22

23

24

25

26

27

28

29

30

 

31

32

33

       

Pistosauroidea (outgroup)

          
 

0

0

0

0

0

0

0

0

0

0

 

0

0

0

0

0

0

0

0

0

0

 

0

0

0

0

0

0

0

0

0

0

 

0

0

0

       

Brancasaurus brancai

          
 

1

1

1

0

0

0

?

0

0

0

 

2

1

0

1

1

0

0

?

0

1

 

1

0

1

2

0

0

0

1

1

0

 

?

?

0

       

Callawayasaurus colombiensis

          
 

0

?

1

0

0

1

1

0

?

2

 

2

2

?

0

0,1

1

0

1

0

?

 

?

1

0

2

1

1

0

1

1

0

 

1

?

1

       

Cryptocleidus eurymerus

          
 

2

0

0

0

1

1

0,1

0

2

0

 

2

1

0

1

0

0

0

0

1

1

 

1

1

1

0

1

1

1

1

1

0

 

1

0

1

       

Gronausaurus wegneri

          
 

1

1

1

1

0

1

0

0

0

1

 

2

1

0

1

1

0

1

1

0

1

 

1

0

1

1

1

0

0

1

1

1

 

0

0

0

       

Hydrotherosaurus alexandrae

          
 

?

?

?

?

?

1

1

1

1,2

2

 

2

2

1

0

0,1

1

0

1

1

1

 

?

0

0

2

1

1

1

1

1

0

 

1

?

1

       

Kimmerosaurus langhami

          
 

2

0

0

?

1

?

1

0

1

0

 

?

1

0

1

?

0

?

?

?

?

 

?

?

?

?

?

?

?

?

?

?

 

?

?

?

       

Kronosaurus boyacensis

          
 

?

?

?

0

?

0

0

0

?

?

 

2,3

?

?

1

?

?

0

?

?

0

 

2

?

0

?

2

0

1

1

0

0

 

1

1

0

       

Leptocleidus superstes

          
 

0,1

0

?

0

0

?

?

0

1

0

 

2

1

0

1

1

?

0

0

0

?

 

?

?

?

?

?

?

1

1

1

0

 

?

?

?

       

Libonectes morgani

          
 

0

1

1

0

0

1

0

1

1,2

?

 

2

?

?

?

0

1

?

1

?

?

 

?

?

?

?

?

?

?

?

1

?

 

?

?

?

       

Liopleurodon ferox

          
 

1

1

0

1

0

0

0

0

2

2

 

1

1

0

1

0

1

0

0

0

0

 

2

1

0

1

2

0

1

1

1

0

 

1

1

0

       

Meyerasaurus victor

          
 

0

0

?

1

?

1

0

0

0,1

?

 

1

?

?

?

?

?

?

0

0

1

 

?

0

0

0

0

0

0

0

0

0

 

0

1

0

       

Muraenosaurus leedsii

          
 

2

0

1

1

0

1

0

0

2

0,2

 

1,2

2

0,1

1

0

1

0

0

1

1

 

1

?

?

0

2

0

1

1

1

1

 

0

1

0

       

Peloneustes philarchus

          
 

1

0

0

1

0,1

0

0

0

0,1

0,2

 

1

1

0

1

0,1

0

1

0

0

0

 

2

1

0

1

2

0

1

1

0

0

 

1

1

0

       

Polycotylus latipinnis

          
 

?

?

?

?

?

1

?

0

?

0

 

2

1

0

1

0

0

?

0

1

1

 

0

1

1

1

0

0

1

?

1

1

 

1

?

?

       

Seeleyosaurus guilelmiimperatoris

          
 

?

0

0

1

?

1

0

0

2

?

 

1

1

0

1

0

0

0

0

0

0

 

1

1

?

?

1

0

1

0

1

0

 

0

1

0

       

Thalassiodracon hawkinsi

          
 

0

0

0

1

0

1

0

0

0,1

0

 

1

1

0

1

1

?

?

0

0

0

 

?

0

0

0

0

0

0,1

0

1

0

 

0

1

?

       

Tricleidus seeleyi

          
 

2

1

1

?

0

1

0

0

0

0

 

2

1

1

1

0

0

0

0

1

?

 

?

?

?

?

0

0

1

1

1

0

 

1

1

0

       

Conclusions

  1. 1.

    A new leptocleidid plesiosaur, Gronausaurus wegneri, n. gen. n. sp., is described here from the latest Berriasian of the Münsterland in Westphalia, Germany. The skeleton was discovered in 1912 but never the subject of scientific research.

     
  2. 2.

    The performed phylogenetic analysis confirms also Brancasaurus brancai as a member of the Leptocleididae, following the concept of the latest analyses of Ketchum and Benson (2010, 2011), Kubo et al. (2012) and Benson et al. (in press).

     
  3. 3.

    Gronausaurus wegneri developed subdiapophyseal fossae below the transverse processes at the pectoral and anterior dorsal vertebrae which probably gave more stabilisation to the trunk against tensile forces of the rotator muscles. Whether this was an advantage for certain styles of swimming and manoeuvring cannot be reconstructed at this stage.

     
  4. 4.

    Certainly, leptocleidid plesiosaurs were a widely distributed group of the Early Cretaceous with Brancasaurus brancai (Berriasian of Münsterland, Germany), Gronausaurus wegneri (latest Berriasian of Münsterland, Germany), Leptocleidus superstes (Berriasian of Sussex, England), Vectocleidus pastorum (late Barrêmian of the Isle of Wight), Nichollssaura borealis (early Albian of Alberta, Canada), Leptocleidus capensis (uppermost Valaginian of Cape Province, South Africa), Leptocleidus clemai (Hauterivian-Barrêmian of Western Australia) and Umoonasaurus demoscyllus (Aptian-Albian of South Australia). However, future investigations and finds have to affirm definition and monophyly of the Leptocleididae.

     

Acknowledgments

First of all I would like to thank Markus Bertling, Münster, who kindly supported all activities concerning the scientific review including the loan of parts of the Gronausaurus skeleton to Berlin. I am indebted to Markus Brinkmann, Berlin, for additional preparation and stabilisation and to Sandra Golze, Berlin, for taking detailed measurements of the specimen and some parts of the description. Lennart Schleicher, Gronau, provided additional information around the Gronausaurus finds and Martin Hiß, Krefeld, the local stratigraphy. Jan Müller-Edzards, Berlin, produced the drawings of the fossil remains except the teeth and Elke Siebert, Berlin, cordially redrew the cladogram. I am also grateful to Sandra Chapman, London, Rolf-Bernhard Hauff, Holzmaden, Georg Heumann, Bonn, and Dennis Nieweg, Enschede, for giving access to relevant collections. Finally, I am thankful to Gerhard Maier, Calgary, for improving the English and to Roger Benson, Oxford, and an anonymous reviewer who helped to enhance the manuscript with valuable suggestions.

Copyright information

© Springer-Verlag Berlin Heidelberg 2013