Flipper size in Mesozoic Enaliosaurs.

Earlier we looked at three tylosaurs distinguished by their widely varying flipper size. Today we’ll do the same with a few closely related pliosaurs (Fig. 1) and ichthyosaurs (Fig. 2).

Figure 1. Three pliosaurs, Trinacromerum, Brachauchenius and Kronosaurus, to scale, all Late Cretaceous.

Figure 1. Three pliosaurs, Trinacromerum, Brachauchenius and Kronosaurus, to scale, all Late Cretaceous. Variations in flipper size, rib count and girdle size mark the major differences here. The girdles anchored large ventral swimming muscles. Scale bar = 1 meter. How flipper size affected speed and agility is a topic that has not been brought up yet, as far as I know.

Pliosaurs were some of the largest marine reptiles of all time.
They reached an acme in the Late Cretaceous with a variety of morphologies derived from smaller ancestors. Shown here are Trinacromerum, Brachauchenius and Kronosaurus, three taxa rarely shown together to scale. The big difference is in flipper size. It’s also worth noting the size of the girdles anchoring each flipper set. In whales, flipper size also varies greatly and not always for swimming advantage.

Ichthyosaurs,
even closely related ones (Fig. 2), also had widely varying flipper sizes. Here we see ‘Cymbospondylus’ buchseri and the related Guizhouichthyosaurus. Both were probably sinuoous swimmers, rather than tail or flipper swimmers.

Figure 2. Two closely related ichthyosaurs, Guizhouichthyosaurus tangae and "Cymbospondylus" buchseri, one with large flippers, one with small.

Figure 2. Two closely related ichthyosaurs, Guizhouichthyosaurus tangae and “Cymbospondylus” buchseri, one with large flippers, one with small.

References
Carpenter K 1996. A review of short-necked plesiosaurs of the Western Interior, North America. Neues Jahrbuch fur Geologie und Palaontologie, Abhandlungen 201(2):259-287.
Hampe O 2005. Considerations on a Brachauchenius skeleton (Pliosauroidea) from the lower Paja Formation (late Barremian) of Villa de Leyva area (Colombia). Fossil Record – Mitteilungen aus dem Museum für Naturkunde in Berlin 8 (1): 37-51.
Longman HA 1924. A new gigantic marine reptile from the Queensland Cretaceous, Kronosaurus queenslandicus new genus and species. Memoirs of the Queensland Museum 8: 26–28.
O’Keefe FR 2001. A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia). Acta Zoologica Fennica 213:1-63.
Owen R 1840. British Fossil Reptiles. Chapter V Order—Sauropterygia, Owen. Genus—Pliosaurus, Owen. 152-165.
Romer AS and Lewis AD 1959. A mounted skeleton of the giant plesiosaur Kronosaurus. Breviora 112: 1-15.
Williston SW 1903. North American plesiosaurs. Field Columbian Museum, Pub. 73, Geological Series 2 (1):1-79.
Williston SW 1907. The skull of Brachauchenius, with special observations on the relationships of the plesiosaurs. United States National Museum Proceedings 32: 477-489.
Williston SW 1908. North American Plesiosaurs: Trinacromerum. Journal of Geology 16(8): http://www.jstor.org/stable/30068152

wiki/Brachauchenius
wiki/Pliosaurus

wiki/Kronosaurus
wiki/Trinacromerum

Did the frontal migrate to the nasal in pliosaurids? – part 3

Earlier here and here we looked at the possible migration of the frontals to the shape and position of the nasals in pliosaurs, those giant marine relatives of the plesiosaurs.

Figure 1. Although this pliosaur is missing the skull roofing bones, Sassoon et al. 2012 restored the nasals and frontals of BRSMG Cd6172 like so. Color added for clarity.

Figure 1. Although this pliosaur is missing the skull roofing bones, Sassoon et al. 2012 restored the nasals and frontals of BRSMG Cd6172 like so. Color added for clarity. Rather than show the central frontals fused to the parietals, as Sassoon et al. indicates, I have combined them with the lateral frontals (both in white) here. They also show the prefrontals contacting the postfrontals, but other specimens (see earlier posts) show a palpebral portion of the frontals extended laterally beyond them, despite prf/pof contact in some cases.

Sassoon et al. 2012 described the skull of Pliosaurus (BRSMG Cd6172). Although they report the skull roof is missing (Fig. 1) they restored and described the frontals and nasals like so:

“Missing elements. Skull roofing elements (nasals, prefrontals, frontals, lacrimals, postfrontals, postorbitals and epipterygoids) are not preserved in BRSMG Cd6172, and these are reconstructed from other pliosaurian species (Andrews 1897; Taylor and Cruickshank 1993; Fig. 2A–B). The absence of nasals in Plesiosauria was received wisdom for some time (Storrs 1991; Taylor and Cruickshank 1993; Carpenter 1997; see also Ketchum and Benson 2010), and lacrimals were also thought to be missing in Sauropterygia (Storrs 1991; Carpenter 1996; Rieppel 1998). Basal sauropterygians, such as Nothosaurus (Rieppel and Wild 1994, 1996) and Pistosaurus (Sues 1987), have reduced nasals, and it was suggested that these were either lost or fused with the frontals (Romer 1956) in derived sauropterygians. However, two of us (LFN, JS) have observed that BRSMG Cc332 does possess nasals (contra Taylor and Cruickshank 1993), which are also undoubtedly present in the Callovian Liopleurodon (Noe` 2001). Further, lacrimals also appear in both species (Druckenmiller and Russell 2008; Ketchum and Benson 2010). Therefore, the reconstructions of BRSMG Cd6172 (Fig. 2A–C) show both nasals and lacrimals. The presence of nasals and lacrimals, however, should not be surprising as pliosaurids retain a number of plesiomorphic characters  (Ketchum and Benson 2010), also present in BRSMG Cd6172, such as coronoids and suborbital fenestrae; the latter are not present in plesiosauroids or other sauropterygians (Druckenmiller 2002b).”

I did not know about this paper until this yesterday, after I had posted the earlier two blog posts. So, I consider this welcome vindication and confirmation of observation and interpretation.

References
Sassoon J, Noe LF and Benton MJ 2012. Cranial anatomy, Taxonomic implications and Palaeopathology of an Upper Jurassic pliosaur (Reptilia, Sauropterygia) from Westbury, Wiltshire, UK. Palaeontology 55(4):743-773.

Did the frontal migrate to the nasal in pliosaurids? – part 2

Yesterday we broached the subject of pliosaur nasal disappearance, replaced by frontals in their place.This is a standard for pliosaur workers, but it may be a tradition/paradigm that needs to be reexamined. At best the nasals and frontals could be fused, with each bone keeping to its typical position, as shown here (Fig. 1), but I haven’t seen good evidence of that yet. I have seen good evidence of the frontal fused to the parietal (Fig. 2). And I have seen evidence for the nasal fusing to the prefrontal. Both solutions or a third solution could be relevant depending on the taxon or clade.

What you will see here is a variety of interpretations, mine among them.

Figure 1. Rhomaleosaurus skull from Smith and Dyke 2008. Bones and orbits colorized here. Frontals in white.

Figure 1. Rhomaleosaurus skull from Smith and Dyke 2008. Bones and orbits colorized here. Nasals in magenta. Note the premaxillae (yellow) tentatively contact the parietals (brown), probably overlying the frontals (white) as in germanodactylid pterosaurs. Cheek bones (squamosals) are missing here, but color shows where they would be in vivo. Smith and Dyke indicate no suture between the nasals and frontals, but do not acknowledge the fusion, if present. Here the nasals might be fused to the prefrontals, but Smith and Dyke show nasals fused to frontals.

Smith and Dyke (2008) label the frontal the frontal, but they also do not label the nasal anywhere. Sutures appear to be present separating them. Either the nasals and frontals are fused or the prefrontals are fused to the nasals. Closer examination or higher resolution would help here. In either case, the frontals have not migrated.

McHenry (2009) writing about Kronosauurs, reported, “The nasal bone is often considered to be absent in plesiosaurians (Brown 1981, Druckenmiller and Russell 2008, Storrs 1993), but Andrews (1913: p42) mentions that “there is some indication that the posterior and outer borders are formed by a small distinct element, which, if actually present, must be regarded as a nasal”.

Andrews also suggested the nasal bone might be fused to the prefrontal (Fig. 2).

Figure 2. Liopleurodon skull from Andrews 1913. Here either the parietal is broken posterior to the pineal opening or the frontals  include the pineal opening or the frontals are fused to the parietals. In either case the nasals are present and identified.

Figure 2. Liopleurodon skull from Andrews 1913. Color added. Here either the parietal is broken posterior to the pineal opening or the frontals include the pineal opening or the frontals are fused to the parietals. In either case the nasals are present and identified (magenta), distinct from the fronals (white). Prefrontal palpebrals striped amber. Frontal palpebrals in white. Brown dashed line indicates typical extent of parietal, indicating fusion of the frontals and parietals, but not the frontals to each other.

Andrews (1913) described the skull of Liopleurodon including the nasals. Here the pineal opening is in front of a break marking the main body of the parietals, but there is no hint of a suture anterior to the pineal opening. This indicates a likely fusion of the frontals to the parietals, but not the frontals to each other. As mentioned yesterday, both frontals are still present regardless of fusion, no matter what the fused bones are now called. The bones could be called a frontoparietal, but nobody does that. If the frontal were really absent a transitional taxon would show it reducing to a vestige or sliver first. That’s the way it works when a bone actually disappears.

We have seen bones migrate, as in the central wrist bones migrating to the medial rim in pterosaurs and certain mammals. But we haven’t seen the frontal migrate yet.

Then a few problem drawings: Simolestes, case in point (Fig. 3). What are those long bones medial to the naris and orbit (in pink)? Very odd.

Figure 3. Simolestes with bones colorized, including where bones are missing. Here the nasal appears to rim the upper orbit, a very strange organization.

Figure 3. Simolestes with bones colorized, including where bones are missing. Here the nasal appears to rim the upper orbit, a very strange organization. Compare this image to Fig. 2 and the nasals look like they really are the prefrontals tipped by frontal palpebrals.  But then, I’m interpreting a drawing, which is always fraught with danger. Send a jpeg of this fossil if you have a decent one and we’ll solve this problem together. Also see Fig. 4, where the bones rimming the orbit are indeed the prefrontals. 

Perhaps the actual fossil skull of Simolestes can clear the air (Fig. 4). It appears to have all the skull roofing bones in their standard positions. But, then, this is a lateral view, not a dorsal view as above (Fig. 3).

Figure 6. Simolestes fossil skull with a few more roofing bones present. Everything appears to be in the right place. Perhaps some sort of fusion is present between the nasal the prefrontal.

Figure 4. Simolestes fossil skull with a few more roofing bones present. Everything appears to be in the right place. Perhaps some sort of fusion is present between the nasal the prefrontal.

Then there’s Dolichorhynchops (Fig. 5). O’Keefe does not identify the nasal, but fuses the frontal and nasal and his prefrontal is smaller than in sister taxa. He gives the palpebral process to the frontal. In my interpretation all bones are in their standard positions and sizes, including the previous unidentified postfrontal.

Figure x. Dolichorhynchops skull (above), interpreted here (color) and interpreted by O'Keefe (drawing).

Figure 5. Dolichorhynchops skull (above), interpreted here (color) and interpreted by O’Keefe (drawing). O’Keefe does not identify the nasal but fuses the frontal and nasal and his prefrontal is smaller than in sister taxa. In my interpretation all bones are in their standard positions and sizes.

Carpenter’s take on the Dolichorhynchops skull is similar in most respects to that of other workers, but different in a few details (Fig. 6).

Figure x. Dolichorhynchops UCM 35059 colorized to show standard placement of bones.

Figure 6. Dolichorhynchops UCM 35059 by Ken Carpenter (1996), colorized to show standard placement of bones based on sister taxa. Here the premaxilla does indeed tentatively contact the parietal, a trait very few tetrapods, other than germanodactylid pterosaurs share. Carpenter’s SPO is his supraorbital, otherwise referred to as a postfrontal in previous figures. Carpenter gives the palpebral process partly to the prefrontal (PF), but labels the portion anterior to the orbit the lacrimal, different than all other workers do and did. No nasal is identified (colored pink here).

So, there’s some work to do here.

References
Andrews CW 1913. A descriptive catalogue of the Marine Reptiles of the Oxford Clay, Part II. BM(NH), London.
Benson RBJ, Evans M, Smith AS, Sassoon J, Moore-Faye S, Ketchum HF and Forrest RF 2013. A Giant Pliosaurid Skull from the Late Jurassic of England. PLOSOne online here.
Carpenter K. 1996. A Review of short-necked plesiosaurs from the Cretaceous of the western interior, North America”. Neues Jahrbuch für Geologie und Paläeontologie Abhandlungen (Stuttgart) 201 (2): 259–287.
McHenry CR 2009. ‘Devourer of Gods’ – The palaeoecology of the Cretaceous pliosaur Kronosaurus queenslandicus. Ph.D. dissertation, University of Newcastle, 616 pp. online and download here.
O’Keefe FR 2004. Cranial anatomy and taxonomy of Dolichorhynchops bonneri new combination, a polycotylid (Sauropterygia: Plesiosauria) from the Pierre Shale of Wyoming and South Dakota. Marshall University. Marshall Digital Scholar 1-1-2008, 26 pp. online here.
Smith AS and Dyke GJ 2008. The skull of the giant predatory pliosaur Rhomaleosaurus cramptoni: implications for plesiosaur phylogenetics. Naturwissentschaften 95:975-980.
Williston SW 1903. North American Plesiosaurs (Part 1). Field Columbian Museum, Publ. 73, Geological Series 2(1):1-79.

Did the frontal migrate to the nasal position in pliosaurs – or not? – part 1

A recent online paper
by Benson et al. (2013) had me scratching my head. What looked like nasals were identified as frontals (Fig. 1, green circle). And the prefrontals contacted the parietals, which were extended anteriorly beyond mid orbit. The nasals were absent, according to Benson et al. (2013) and they’re not the only ones. Benson et al. were following tradition. Knowing that this could really screw up – or clarify – phylogenetic analysis, I dived into pliosaurs, a subject I barely knew. Here are the results of my studies. (And yes, I sent these to Dr. Benson, but he stood by his interpretation).

Figure 1. Are the frontals mislabeled or overlooked? Here are several views and interpretations of Pliosaurus kevani together with two other plesiosaur skulls, both of which have fairly standard nasals and frontals.

Figure 1. Are the frontals mislabeled or overlooked? Here are several views and interpretations of Pliosaurus kevani together with two other plesiosaur skulls, both of which have fairly standard nasals (in magenta) and frontals (in white). The bright blue bones are a tooth and an unidentified crescentic fragment. Note that Benson et al. identify the bone over the naris as a frontal (fr). There might be a suture between the frontal and parietal but there’s also a small crack there, but that’s not important.  The frontals may be fused to the parietals but not to each other. They have not migrated. In the revised figures (in color) the frontal contacts the orbit, as in the compared taxa.

Benson et al. (2013) identified the bone over the naris in Pliosaurus kevani as a frontal, rather than a nasal, contra the identification in related forms like Simosaurus and Plesiosaurus (Fig. 1). Such identifications are not novel to Benson et al. In fact, they go back about a century (Williston 1903, Fig. 2) who didn’t realize the frontals had fused to the parietals but not to each other. It’s really hard to get rid of the frontals. But it’s easy to get rid of frontals if they are fused to the parietals and the resulting bones are called the parietals.

Figure 2. Brachauchenius showing the fusion of the parietal and frontal and the resulting confusion over the nasal.

Figure 2. Brachauchenius from Williston 1903, showing the fusion of the parietal and frontal and the resulting confusion over the nasal. Fusion and abrasion have both contributed to this confusion.

Evidently each parietal fused to each frontal
without fusing medially, and that was not realized. So Williston didn’t know whether the nasal was the nasal or the frontal. A century later, the problem has not gone away.

This goes back to a very old problem in palaeontology.
Often when two bones fuse, the resulting bone is given one name. So the other bone becomes absent, when in reality it is present, but incorporated or fused (Fig. 2).

For the nasals to become the frontals
there has to be a transitional taxon that shows this. But their are no such fossil taxa. If the nasals and frontals fuse, the nasals are still there. If the parietals and frontals fuse, the frontals are still there. We don’t have an inborn bias against nasals, so why did they get sent to the list of absent bones?

Is it possible that the frontals fused to the parietals?
Or was the frontal/parietal suture overlooked?
Either way the nasal can remain over the naris, as it is in related taxa. Otherwise we have to accept that the frontals migrated to take the place and shape of the nasals, without creating vestigial nasals in the process of moving out.

In all other aspects, the Benson et al. paper is well done and well presented.

Final note:
Whether you agree or disagree with the above assessment, this is Science at its best, repeating the observation or experiment and confirming or refuting the original observation or experiment. If there’s a disagreement, third and fourth parties are encouraged to repeat the observation and report. That’s what they call consensus, which is currently in the Benson et al. camp among pliosaur aficionados.

Tomorrow, a look at more evidence from more pliosaur frontals.

References
Benson RBJ, Evans M, Smith AS, Sassoon J, Moore-Faye S, Ketchum HF and Forrest RF 2013. A Giant Pliosaurid Skull from the Late Jurassic of England. PLOSOne online here.
Williston SW 1903. North American Plesiosaurs (Part 1). Field Columbian Museum, Publ. 73, Geological Series 2(1):1-79.

An new look for Kronosaurus

The Harvard mount of the giant pliosaur, Kronosaurus, alas, is mostly plaster. The skeleton was created at a time when just a few bits and pieces were known. Today, in 2014, we know of a dozen specimens. Thanks to a dissertation by McHenry (2009) and some recent discoveries, we can finally put the giant marine reptile back together again, the right way.

For decades we’ve had this powerful torpedo-like image of Kronosaurus (Fig. 1). Sadly, it’s not quite right.

Figure 1. The Yale Peabody Museum sculpture of Kronosaurus. Impressive, but a little too tubular.

Figure 1. Click to enlarge. The Harvard Museum of Comparative Zoology sculpture of Kronosaurus. Impressive, but a little too tubular, as subsequent discoveries have revealed.

Since then a nearly complete specimen has been found for K. boyacensis (Fig. 2) in Columbia, far from the resting point of many other specimens in Australia.

Figure 2. Kronosaurus boyacensis (Hampe and Leimkuhler 1996) in situ.

Figure 2. Kronosaurus boyacensis (Hampe 1992, Hampe and Leimkuhler 1996) in situ, from Columbia.

Kronosaurus (Longman 1924) is chiefly known from bits and pieces, but a few big skeletons are also known (Fig. 2). McHenry (2009) put the bits and pieces of the skull together, producing excellent restorations and reconstructions. These were used to create a new look for Kronosaurus (Fig. 3).

From the McHenry abstract: The cranial anatomy of Kronosaurus queenslandicus is here summarised for the first time, and outstanding questions concerning the taxonomy of the relevant material are addressed as fully as possible given available data. Three-dimensional geometry is critical data for the functional analyses that can form the basis for reconstruction of palaeoecology, in particular, approaches based in computational biomechanics that make use of high resolution Finite Element Modeling. These techniques have been used successfully to infer diet and feeding behaviour in various species of extinct carnivore, and are here applied to a species of large pliosaur for the first time.” 

Figure 3. Click to enlarge. Kronosaurus in several views. The ribcage is much wider than previously envisioned. The pectoral girdle may be larger, but if so, it is not exposed. The skull is traced from McHenry 2009. Note the rise in the mandible posterior to the jaw joint. This would have prevented overextension of the mandible as it opened, flooding with seawater pushing it even further open. The wide, round torso is more like that of slower-moving plesiosaurs, despite the attractiveness of the prior torpedo-like shape.

Figure 3. Click to enlarge. Kronosaurus in several views. The ribcage is much wider than previously envisioned. The pectoral girdle may be larger, but if so, it is not exposed. The skull is traced from McHenry 2009. Note the rise in the mandible posterior to the jaw joint. This would have prevented overextension of the mandible as it opened, flooding with seawater pushing it even further open. The wide, round torso is more like that of slower-moving plesiosaurs, despite the attractiveness of the prior torpedo-like shape.

The new, wider torso and longer neck of Kronosaurus is more like that of other plesiosaurs and pliosaurs, and not so torpedo-like, as in the Harvard mount.

McHenry’s description of the discovery and naming of the holotype:
“In 1899 – about the time that Williston was first coming to grips with the Kansas Brachauchenius – a small fossil was sent to the Queensland Museum in Brisbane by a Mr Andrew Crombie in 1899, and was received by Charles deVis, who was at that time director of the museum. The specimen represented a fragment of mandibular symphysis, and deVis assigned it to the Enaliosauria, the group which at that time included both the Ichthyosaurs and the Plesiosaurs, but his mention in the letter of the English translation of Ichthyosaur, ‘fish lizard’, suggests that he believed the specimen to an example of Ichthyosaurus australis. He did, however, make note of the large thecodont dentition, unusual for an ichthyosaur. No locality information exists for that specimen, but it was described by Heber Longman, the next director of the Museum, who mentioned that Mr Crombie came from Hughenden, a small farming town in the Rolling Downs of Central Western Queensland, and presumably the fossil was found near the town. Longman astutely recognised that the fragment of symphysis belonged to a large pliosaur, which he christened Kronosaurus queenslandicus (Longman 1924). This specimen, the designated holotype, holds the Queensland Museum collection number QM F1609.”

Very few images of Kronosaurus on Google Search reflect the new, more accurate look. But I was able to find this wonderfully accurate sculpture from a small town (ca. 550 citizens) in Australia with its own, life-size Kronosaurus (Fig. 4).

Figure 4. Life size sculpture of Kronosaurus in the small outback town of Richmond, Australia.

Figure 4. Life size sculpture of Kronosaurus in the small outback town of Richmond, Australia. They got it right!

A few last notes from the McHenry 2009 summary.

“Based upon the analysis in this thesis, the fossilised remains of large pliosaurs from the Early Cretaceous marine sequence of the Great Artesian Basin represent a single genus of brachaucheniid pliosaur, Kronosaurus. Specimens from the Doncaster Formation and the Toolebuc Formation indicate the presence of this taxon in the Late Aptian and Late Albian epeiric seas respectively: some isolated teeth from the Griman Creek Formation may be referable to Kronosaurus and thus record its presence in the Early Albian Sea. Available evidence is consistent with the presence of a single species in the Late Albian, Kronosaurus queenslandicus Longman, 1924. The Late Aptian material is consistent with Kronosaurus queenslandicus, pending further study of the Colombian species Kronosaurus boyacensis Hampe 1992.

Analysis of 11 specimens from the Late Aptian and Late Albian of Queensland indicates a size range from 4 to 10 metres in Total Length, and 1–10 tonnes in body mass. By the criterion of the degree of fusion of cranial elements in the rostrum and circum-orbital region, smaller individuals are interpreted as immature sub-adult animals.

The dentition is markedly anisodont, with the largest teeth in the anterior part of the tooth row. Maximum basal skull length is 2.2 m, with a mandible length of 2.7 m. 35 pre Of large pliosaur taxa described to date, only Kronosaurus queenslandicus has four pairs of premaxillary teeth.
The post-cranial skeleton is of a compact, fusiform body shape with a short (but flexible) neck and a short tail. Presacral vertebral count is 35, including 13 cervicals and 3 pectorals. The centra of the posterior pectorals/ anterior dorsal vertebrae have the largest diameter, with height exceeding width. Transverse processes are robust, suggesting robust ribs in the thoracic region. The femuri are longer and more robust than the humeri, and the pectoral limbs appear to have been of a lesser diameter than the pelvic. The distal limbs are hydrofoils with a high aspect ratio. Maximum total length is 10.5 metres, with a hind limb span of 5 metres and a body mass of ~11,000 kg.
 
Comparative biomechanical analysis suggests that bite force was large: 15–22 kN for an anterior bite, and 27–38 kN for a posterior bite, depending on the modelling approach used. For its skull volume and its body size, bite force magnitude is comparable to that of modern crocodilians. Finite element analysis indicates that, compared with a 3.1 m small adult saltwater crocodile Crocodylus porosus, the rostrum of Kronosaurus was subject to higher strains during normal bites. Similarly, when subjected to torsional and laterally directed loads that simulate the twisting and shaking behaviours used by large extant Crocodylus to kill and process large prey, the skull of Kronosaurus carried more strain than that of C. porosus. Based on this result, maximum prey size, relative to body size, is considered to have been smaller in Kronosaurus than for a 3.1 m C. porosus, although the actual magnitude of this limit is unknown due to insufficient data on diet in C. porosus. The apparent discrepancy between the bite force result, which suggest comparable sized prey, and the finite element analysis may be due to hydrodyamic factors involved with rapid adduction of a >2 m mandible.
Data from stomach contents confirms that Kronosaurus fed upon other reptiles and was able to process large animals into smaller pieces suitable for swallowing. Confirmed prey includes a small turtle, a small elasmosaur, a large elasmosaur, with a possible instance of a large shark. Biomechanical and functional considerations suggest that twist feeding may not have been employed to process large prey, but that the pronounced underbite in the rear half of the tooth row, coupled with large bite forces, may have allowed Kronosaurus to process prey through straightforward biting. There is also evidence of intra-specific aggression directed at a sub-adult, possibly by a larger animal.
Non-biomechanical comparison with the functional morphology of various species of crocodilian and odontocete suggests that the elongate rostrum and flexible neck might have allowed Kronosaurus to take relatively smaller prey than can Crocodylus porosus. General patterns in the ecology of large marine amniotes suggest that a broad prey base was likely, perhaps ranging from a lower limit of 1 kg an upper limit of 3,000 kg. Potential prey were probably nektonic and demersal, and may have included teleosts, cephalopods, sharks, and reptiles. Ontogenetic shifts in diet most likely involved an increasing proportion in relatively large prey with age. Kronosaurus is therefore characterised as a dietary generalist, capable of taking large reptilian prey due to its own large size and robust dentition, but with much smaller reptiles, sharks, teleosts and cephalopods comprising most of its diet.
A broad overview of the functional morphology of aquatic marine predators suggests that they operate under a pair of conflicting constraints of (1) selection for a skull morphology that allows efficient capture of small agile prey, which is predicted to be a longirostrine form, and (2) selection for a skull shape that resists the bending loads caused by biting large prey, which is predicted to be a high vaulted, brevirostral shape. A skull morphology that lies close to either one of these opposing ends of this morphological spectrum is interpreted as specialisation on small and large prey respectively. The playtrostral, mesorostral skull of extant carnivorous odontocetes and crocodilians is interpreted as a biological trade-off between these conflicting requirements. In Kronosaurus, a different pattern of trade-off is achieved involving (1) an elongate mesorostral to longirostral skull, (2) an array of caniniform teeth placed relatively far forward in the jaw, (3) a robust dorsal median ridge on the rostrum that acts as a dorsal compression member, and (4) a high bite force. This functional complex requires complex patterns of growth in the orbital and rostral regions of the skull that result in an osteology exhibiting pronounced ontogenetic variation.
Maximum body size of Kronosaurus is estimated at 10.5 metres total length and approximately 11,000 kg mass. This size class is consistent with the maximum size of apex marine predators in neritic environments from the Middle Triassic to the Recent. Estimates of body size that are significantly greater than this class may indicate a qualitatively different niche, as with modern mysticete whales and the sperm whale Physeter.”
Well done, Dr. McHenry!

References
McHenry CR 2009. ‘Devourer of Gods’ – The palaeoecology of the Cretaceous pliosaur Kronosaurus queenslandicus. Ph.D. dissertation, University of Newcastle, 616 pp. online and download here.
Hampe O 1992. Ein grosswuchsiger Pliosauridae (Reptilia: Plesiosauria) aus der Unterkreide (oberes Aptium) von Kolumbien Courier Forsch.-Inst. Senckenberg 145:1-32.
Hampe O and  Leimkuhler C 1996. Die Anwendung der Photogrammetrie in der Wirbeltierpalaontologie am Beispiel eines Kronosaurus-Fundes in Kolumbien. Mainzer geowissenschaftliche Mitteilungen 25:55-78.
Longman HA 1924. A new gigantic marine reptile from the Queensland Cretaceous. Memoirs of the Queensland Museum 8:26-28.