Teleosauroids were a successful group of semi-aquatic crocodylomorphs that were an integral part of coastal marine/lagoonal faunas during the Jurassic. Their fossil record suggests that the group declined in diversity and abundance in deep water deposits during the Late Jurassic. One of the few known teleosauroid species from the deeper water horizons of the well-known Kimmeridge Clay Formation is ‘
Teleosauroids (one of the subgroups of Thalattosuchia) were a successful group of semi-aquatic Jurassic crocodylomorphs. They were abundant in marine/lagoonal faunas for most of the Jurassic of Europe, Asia and Africa (
The teleosauroid fossil record is particularly sparse in the Late Jurassic Kimmeridge Clay Formation (KCF; Kimmeridgian-Tithonian, ∼157–148 Ma) of the UK (
Here we review the two previously identified specimens of
The holotype of
A skull from near Quercy (France) was referred to ‘
The validity problem of ‘
Only one phylogenetic analysis (
Both NHMUK PV OR 43086 and DORCM G.05067i-v were found at the same general locality: Kimmeridge Bay (Dorset, UK), the type locality of the Kimmeridge Clay Formation (
The Upper Kimmeridgian strata of the Franculès (Quercy) area where the LPP specimen was found consist of argillaceous limestones intercalated with marls (
CROCODYLOMORPHA |
THALATTOSUCHIA |
TELEOSAUROIDEA |
ZooBank Life Science Identifier (LSID) for genus urn:lsid:zoobank.org: act:5D902DD6-AE09-466D-8C40-C729F8481636 |
The electronic version of this article in Portable Document Format (PDF) will represent a published work according to the International Commission on Zoological Nomenclature (ICZN), and hence the new names contained in the electronic version are effectively published under that Code from the electronic edition alone. This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix
Map modified from Ron Blakey ©(
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A, G, middle and anterior rostrum in dorsal view. B, H, rostrum in left lateral view. C, I, rostrum in ventral view. D, J, rostrum in right lateral ventral view. E, K, maxillae in posterior view. F, L, premaxilla in anterior view. Wave pattern represents parts of the specimen that have been reconstructed during preparation/conservation. Scale bar equals 30 cm. ©The Trustees of the Natural History Museum, London.
A, F, anterior maxillae and premaxillae in left dorsal view. B, G, anterior maxillae and premaxillae in left lateral view. C, H, anterior maxillae and premaxillae in ventral view. D, I, anterior maxillae and premaxillae in in right lateral view. E, J, premaxilla in anterior view. Scale bar equals 10 cm.
Another specimen from Francoulès, Quercy area, France (
A, E, anterior maxillae and premaxillae in dorsal view. B, F, anterior maxillae and premaxillae in left lateral view. C, G, anterior maxillae and premaxillae in ventral view. D, H, anterior maxillae and premaxillae in right lateral view. Scale bar equals 10 cm.
A, F, skull in dorsal view. B, G, skull in right lateral view. C, H, skull in ventral view. D, I, skull in right lateral view. E, J, skull in posterior view. Scale bar equals 10 cm.
A, C, mandible in dorsal view. B, D, mandible in left lateral view. Scale bar equals 10 cm.
A, tooth in labial view. B, tooth medial-mesial view. C, tooth in lingual view. D, tooth in mesial-medial view. Scale bar equals 3 cm.
A, Dorsal-sacral osteoderm DORCM G.05067ii in dorsal view. B, dorsal-sacral osteoderm DORCM G.05067ii in ventral view. C, caudal osteoderm DORCM G.05067iv in dorsal view. D, caudal osteoderm DORCM G.05067iv in ventral view. E, ventral osteoderm DORCM G.05067iii in view. F, ventral osteoderm DORCM G.05067iv in dorsal view. Scale bar equals 3 cm.
The premaxillae of
The external nares are well preserved in both NHMUK PV OR 43086 and DORCM G.05067i, but less so in the LPP specimen, where only the anterior portion is partially exposed from the matrix that fills the narial cavity. The anteromedial and posteromedial margins of the external nares are exceptionally bulbous, and project anteriorly and dorsally, respectively (
The left side of each diagram depicts the dorsal view, the right side the palatal view. Scale bar equals 5 cm.
A, complete skeleton in dorsal view. B, dorsal region in dorsal view with details of the left forelimb and left hindlimb. C, details of the right forelimb. Scale bar in C equals 5 cm.
The premaxillae in both Dorset specimens (NHMUK PV OR 43086 and DORCM G.05067i) are laterally expanded (such that they extend considerably more laterally than the anterior maxilla lateral margins) in line with the P3-P4 alveoli, and are also strongly ventrally deflected (
As reported by
A,
As well as NHMUK PV OR 43086 and DORCM G.05067i, the LPP specimen shows the combination of characteristic premaxillary and maxillary features of
The maxillae are partially preserved in both NHMUK PV OR 43086 and DORCM G.05067i (although they are slightly more complete in NHMUK PV OR 43086), but their sutures with adjacent posterior elements cannot be assessed (
With reference to the LPP specimen (
Given the incomplete preservation of these specimens, it is impossible to provide a precise tooth count for
The maxillae of the LPP specimen are anteroposteriorly elongated with sub-parallel lateral margins as in other teleosauroids (e.g.,
The nasals are elongated and triangularly shaped as in other thalattosuchians (
The parietal is large, fused and unornamented (
In occipital view (
The LPP mandible is preserved up to the D28 alveolar pair (
No teeth are preserved in the type specimen, with DORCM G.05067v having one loose tooth crown that is well preserved enough to allow description (
There is one tooth (P4) preserved
No osteoderm was found associated with the holotype or LPP specimen, but three osteoderms (two dorsal-sacral and one ventral) are preserved in DORCM G.05067i-iv (
Finally, an osteoderm NHMUK PV OR 40105 of similar shape, preservation and ornamentation to DORCM G.05067ii was found associated with the matrix of
We conducted a phylogenetic analysis to test the evolutionary relationships of
The current dataset consists of 140 crocodylomorph OTUs (70 of which are thalattosuchians, including 18 teleosauroids, seven basal metriorhynchoids and 42 metriorhynchids) scored for 456 characters. Of these 456 characters, 25 characters representing morphoclines were treated as ordered (see
The protocol used to analyse the dataset is the same adopted by
The phylogenetic analysis produced 85 most parsimonious trees (MPTs) with 1,494 steps (ensemble consistency index (CI) = 0.414; ensemble retention index (RI) = 0.841; rescaled consistency index (RCI) = 0.348; ensemble homoplasy index (HI) = 0.586) (
Simplified strict consensus trees of the 85 most parsimonious cladograms of Teleosauroidea within Crocodylomorpha.
The overall picture of crocodylomorph interrelationships are similar to those found in previous iterations of this merged dataset (
Within ‘clade T’,
Note that our dataset does not include the recently catalogued new available materials of
The anterolateral margins of the premaxillae are strongly anteroventrally deflected (
The anterior external nares face anteriorly (or anterodorsally) (
The premaxilla is laterally expanded, in line with the P3-P4 alveoli.
In other teleosauroids (e.g.,
The teeth of
The premaxillary and maxillary dorsal and lateral surfaces of
The shape and arrangement of osteoderm pits are similar in
The ornamentation of the dorsal-sacral osteoderms of
The shift from highly ornamented dermal bone to low levels of ornamentation (or no ornamentation) is characteristic of the shift from amphibious to pelagic forms in Crocodylomorpha (
There is further evidence for a more pelagic lifestyle in the post-cranium of
A, humerus length vs femur length scatterplot, and B, known ranges of humerus:femur ratio in thalattosuchian and extant crocodylomorphs. C, Tibia length vs femur length scatterplot, and D, known ranges of Tibia:femur ratio in thalattosuchian and extant crocodylomorphs. The humerus:femur and tibia:femur ratios of
The first intriguing feature is that the H:F and T:F linear equations of teleosauroids, metriorhynchids and extant species noticeably differ. This further highlights that the body-plans of these three groups where distinctly different, as the linear equations of basicranial length-total body length and femoral length-total body length are already known to have noticeably differed between them (see
When we examine the H:F ratio,
For the T:F ratio,
Interestingly, these temporal trends independently occurred in the two subclades of Teleosauroidea. The basal Toarcian teleosauroid
Overall three independent lines of evidence—reduction of ornamentation, modification of the appendicular skeleton, and their recovery in deeper-water sediments—hint that by the Late Jurassic, some teleosauroids were beginning to evolve a more pelagic lifestyle. All three lines of evidence are present in
Interestingly, this pattern may be a response to the deepening of waters in the Late Jurassic.
Nevertheless, to the extent of our knowledge, teleosauroids never became fully pelagic completing the land-to-sea transition, unlike their relatives the metriorhynchoids. The latter are a textbook example of a secondary adaptation to an aquatic lifestyle, as witnessed by the numerous osteological (e.g., enlarged skull relative to body length, hypocercal tail, modified limb proportions, paddle-like forelimbs, streamlined bodies, complete loss of osteoderms), and soft tissue adaptations (e.g., enlarged nasal exocrine glands, hypertrophied cranial venous systems, simplified and reduced endocranial sinuses) (e.g.,
Here, we describe a new specimen of ‘
Taxon/character matrix
Humerus, femur and tibia measurements of extant crocodylians and Thalattosuchians
basioccipital
nth dentary alveolus
dentary
external nares
exoccipital
frontal
?jugal
lacrimal
nth maxillary alveolus
mandibular spatula
maxilla
nasal
orbitotemproal foramen
occipital condyle
orbit
parietal
postorbital
paraoccipital process
nth premaxillary alveolus
premaxillary projection
premaxilla
?prefrotnal
prootic
pterygoid
quadrate
supraoccipital
splenial
squamosal
supratemporal fossa
cranial nerve twelve
Musée-sur-Mer Boulogne, France (closed over a decade ago)
Bristol Museum and Art Gallery, Bristol, England, UK
Sedgwick Museum, Cambridge, England, UK
Dorset County Museum, Dorchester, England, UK
Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China
Institut de paléoprimatologie, paléontologie, humaine évolution et paléoenvironnements Université de Poitiers, Poitiers, France
Museum of Jurassic Marine Life—the Steve Etches Collection, Kimmeridge, England, UK
Muséum national d’Histoire naturelle, Paris, France
Muséum national d’Histoire naturelle Luxembourg, Luxembourg City, Luxembourg
vertebrate palaeontology collection of the Natural History Museum, London, UK (OR, old register; R, reptiles)
Naturhistorisches Museum Wien, Vienna, Austria
Oxford University Museum of Natural History, Oxford, England, UK
Staatliches Museum für Naturkunde, Stuttgart, Baden-Württemberg, Germany
DF, MMJ and MTY should be considered equal first co-authors of this project, because they contributed equally in research time, specimen examination, and writing. We thank the Photography Department of Natural History Museum (NHMUK) for providing quality photos of NHMUK PV OR 43086. Thanks to Paul Tomlinson and Heather Middleton for help during DF’s visit at Dorset County Museum (DORCM). Thanks to M Riley (CAMSM), X Xu and L Zhang (IVPP), G Garcia and F Guy (LPP), R Allain (MNHN), B Thuy and R Weis (MNHNL), U Göhlich (NHMW), S Maidment (NHMUK) and R Schoch and E Maxwell (SMNS) for MMJ’s access to collections. We would like to thank Stéphane Jouve, Eric Wilberg, Attila Ösi, and the Editor Hans-Dieter Sues for their detailed reviews and comments that greatly improved the quality of this manuscript.
Mark T. Young is an Academic Editor for PeerJ.
The following information was supplied regarding data availability:
The measurements and phylogenetic dataset, including the description of the characters, taxa and scores used in the analyses, are available in the
The following information was supplied regarding the registration of a newly described species:
Publication LSID: urn:lsid:zoobank.org:pub:BA30BB3C-9D18-48ED-A79B-AA660450E54B