Palæos:		Unit 220:  Lepidosauromorpha
The Vertebrates		820: Tricleidia

Lepidosauromorpha: Cryptocleidoidea: Tricleidia

EUREPTILIA
|--ARCHOSAUROMORPHA
|--Lepidosauromorpha
   |--Sauropterygia
   |  |--Pachypleurosauridae
   |  `--+--Nothosauridae
   |     `--Plesiosauria
   |        |--Pliosauroidea
   |        `--Plesiosauroidea
   |           |--Elasmosauridae
   |           `--Cryptocleidoidea
   |              |--Cryptoclididae 
   |              `--Tricleidia 
   |                 |--Tricleidus  
   |                 `--+--Cimoliasauridae
   |                    |  |--Kimmerosaurus  
   |                    |  `--Cimoliasaurus  
   |                    `--Polycotylidae 
   `--Lepidosauriformes
      |--RHYNCHOCEPHALIA
      `--SQUAMATA                

1. Cimoliasauridae X

2. Cimoliasaurus X

3. Kimmerosaurus X

4. Polycotylidae X

5. Tricleidia X

6. Tricleidus X

Tricleidia:  

Range: Late Jurassic

Phylogeny: Cryptocleidoidea : Cryptoclididae + * : Tricleidus + (Cimoliasauridae + Polycotylidae).  ATW020709.

Tricleidus: T. seeleyi Andrews 1909.  

Range: Late Jurassic (Callovian) of Europe (Peterborough, UK).

Phylogeny: Tricleidia : (Cimoliasauridae + Polycotylidae) + *.

Characters: 2.5-3.0 m; skull 22 cm; rostrum shorter & skull table taller than in Cryptoclidus; parietals form sagittal crest; quadrate overlaps quadrate ramus of pterygoid posteromedially; paroccipital process relatively long and slender; occipital condyle ringed by a groove; occipital condyle formed from basioccipital only; pterygoid with articular process for basisphenoid; teeth with dense longitudinal ridges; dentaries with 17 tooth pairs; premaxillae with 5 teeth each, 1st and 5th small & 2nd to 4th large; anterior most maxillary tooth (6th upper) small and 8th & 9th uppers large; 26+ cervical vertebrae with relatively amphicoelous centra; cervical centra length only slightly exceeds height (but never the width) in most anterior vertebrae; pectoral girdle with "large interclavicle and a pair of well developed elongated clavicles"; clavicles are triangular, well-developed, and visceral to interclavicle which separates them in the midline; the interclavicle is well-developed and plate-like; the coracoids meet the scapulae in midline in 'adults'; width of posterior cornua of the coracoids exceeds interglenoid width in 'adults'; the humerus is not greatly expanded distally, and articulates with four epipodials; probable trap-feeder, but with fewer teeth than Cryptoclidus. 

Note: supposed Tricleidus remains from Wyoming are now believed to be a distinct genus.  See Tate Geological Times. 

Links: Plesiosauria Translation and Pronunciation Guide; The Plesiosaur Site - Species  ATW020709

Cimoliasauridae: originally an unfashionable family based on scrappy materials and a vague definition, to wit: "A family in the Plesiosauroidea with neck relatively shorter than in the Plesiosauridae and the Elasmosauridae. Teeth of the general Plesiosaurian type (crowns high and slender). The height of at least the middle and posterior cervical centra approximately equal to the length, but the breadth of these centra considerably greater than the length; the end faces of the centra flat or slightly concave. Ribs single-headed."  See Plesiosauria Translation and Pronunciation Guide.  It has been resurrected as a clade, but remains an unfashionable family based on scrappy materials and a vague definition.

Range: Late Jurassic to Late Cretaceous of Europe, North America, Australia, & new Zealand

Phylogeny: Tricleidia :: Polycotylidae + * : Kimmerosaurus + Cimoliasaurus.

Links: Plesiosauria Translation and Pronunciation Guide; plesiosarus (Swedish). ATW020709.

Kimmerosaurus:  K. langhami Brown 1981.

Range: Late Jurassic (Kimmeridgian) of Europe (Kimmeridge Clay, UK).  Known from 3 partial skulls & several cervicals.

Phylogeny: Cimoliasauridae : Cimoliasaurus + *.

Characters: skull broad, but very lightly built and more elongated than in Cryptoclidus; no parietal sagittal crest; quadrate overlaps quadrate ramus of the pterygoid anterolaterally; paroccipital process relatively short & massive; occipital condyle is not ringed by a groove, and extends onto pedicles of exoccipitals; tooth ornament absent; teeth highly recurved, thin (laterally compressed), sharply pointed, with 36 dentary pairs & 6 premaxillary pairs.  

Note: Postcranial skeleton is not known.  Possible junior synonym of Colymbosaurus.  

Links: Plesiosauria Translation and Pronunciation Guide; The Plesiosaur Site - Species; FILTER FEEDING REPTILES.  ATW030114.

Cimoliasaurus:  C. maccoyi Etheridge 1904, C. planus, numerous others, all nomina dubia.

Range: Early Cretaceous II (Aptian? Albian?) to Late Cretaceous of Australia, North America, Europe & New Zealand.

Phylogeny: Cimoliasauridae : Kimmerosaurus + *.

Characters: 3-8 m; and long, slender, recurved teeth; teeth conical, with oval cross section at base, becoming more flattened toward tip, somewhat flattened & without carinae; teeth coated with enamel, smooth, with some growth cracks, usually 2-5 cm long; relatively short neck, for holding fish [1]; centra dorsoventrally compressed and constricted in the middle, with oval articular surfaces and two large nutritive foramina; vertebrae morphologically similar, but decreasing in size from mid-dorsal toward sacrum; 

Note: [1] This is odd, because we are also informed that no skull is known.  [2] The Australian species, C. maccoyi, is said to differ from the others in lacking lateral ridges on the cervical centra.  It is likely that this is a garbage taxon without diagnosable characters.  [3] The following portion of a description of the vertebra from Leidy sounds interesting, but I can't quite make out what he means:

The sides of the body of the vertebræ form, together with the sides of the vertebral arch and the upper part of the transverse processes, a nearly uniform slope, broken only by a slight elevation formed by the apparent sutural coossification of the transverse process with the body. The under part of the body between the transverse processes nearly forms a level surface, more or less elevated into a ridge between the venous foramina, and depressed along a line with the position of the latter.

Image: Cimoliasaurus vertebra from the Late Cretaceous of New Jersey.  From D&D Fossils & Meteorites.  

Links: Marine Reptiles (NOT Dinosaurs); Cope - Elasmosaurus2; Cope Additional Note; (these are where Cope explains how he managed to put the head on the wrong end of an elasmosaur!); Plesiosauria Translation and Pronunciation Guide; The Plesiosaur Site - Species; Cimoliasaurus vertebrae $45; Cretaceous Fossils:  Cimoliasaurus magnus Page; Big Brook Plesiosaur Page (are these vertebrae from a plesiosaur?); Exponat mesice - Regionalni Muzeum v Teplicich (Czech); Leidy, 1865 (OOK: portions of Leidy's description.  The OOK treatment is, of course Best on the Web); Plesiosaur History (OOK: the early papers); Big Brook Plesiosaur Page (very nice page with summary of anatomy, other information, and a rough life reconstruction). 

References: Molnar (1991). ATW030708. MAK990821.

Polycotylidae: Ceraumasaurus, Dolichorhynchops, Georgiasaurus, Polycotylus, Trinacromerum. 

Range: K. 

Phylogeny: Plesiosauria ::: Elasmosauridae + *. 

Characters: Short-necked, long-jawed elasmosaurs, up to 9m. Very long, slender premaxilla and maxilla; premaxilla forms dorsal & anterior margin of nares; dorsal process of premaxilla extends posteriorly to separate frontals and meet the parietals between the orbits (!!); replacement teeth grow in pits medially to extant teeth; pineal foramen closed dorsally; thin vomer separates premaxillae with anterior V-shaped slit possibly housing chemosensory vomeronasal (Jacobson's) organ; maxilla also extends posteriorly and forms much of lower rim of orbit; lachrymal absent; frontals form upper orbit and have wing-like process over top of orbit; temporal fenestrae very large, leaving parietal as a sort of tall, central, tent-like crest covering the braincase; large pterygoids, ectopterygoids and palatines cover most of ventral surface, leaving two small vacuities posterior to body of the parasphenoid process, and one small medial vacuity anterior to the parasphenoid; dentaries bear splenials and coronoids; quadrate short, wide & articulates with large squamosal and quadrate process of pterygoid; basioccipital forms ventro-posterior margin of braincase; stapes absent; cervical ribs are single-headed; scapular is separated by clavicular arch; pelvis large, with elongated ischia; distal bones of limbs very short.

Links: Kazmer's Trinacromerum bones; Royal Tyrrell Museum Tour: Bearpaw Sea; TMM - Exhibits - Scratching the Surface - Plesiosaur; The Plesiosaur Site - Species; Marine Reptiles (NOT Dinosaurs); Plesiosauria Translation and Pronunciation Guide; ???????? (Japanese). The Sternberg site at Oceans of Kansas has an exceptional number of good images. ATW020709. MAK990821.

checked ATW040131

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