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Evolution of the Crocodilia , and on the Stagonolepis Robertsoni On Downloaded from http://jgslegacy.lyellcollection.org/ at University of Virginia on July 10, 2012 Quarterly Journal of the Geological Society On Stagonolepis Robertsoni, and on the Evolution of the Crocodilia Thomas H. Huxley Quarterly Journal of the Geological Society 1875, v.31; p423-438. doi: 10.1144/GSL.JGS.1875.031.01-04.29 Email alerting click here to receive free service e-mail alerts when new articles cite this article Permission click here to seek permission request to re-use all or part of this article Subscribe click here to subscribe to Quarterly Journal of the Geological Society or the Lyell Collection Notes © The Geological Society of London 2012 Downloaded from http://jgslegacy.lyellcollection.org/ at University of Virginia on July 10, 2012 PROF. T. H. HU~LEY ON 8TtkG01~OLEPIS ROBERTSONI. 4~0~ 27. On Srxao~oL~.Pzs ROBERTSO~Z, and o~ the Evo~vTmZ~ of the CR0COD~IA. By Prof. TKo~.~s H. HUXLey, LL.D., Sec. R.S., F.G.S. (Read April 28, 1875.) [PLATEXIX.] Nv.xa~r.y seventeen years ago I had the honour of laying before the Geological Society ~ an account of such remains of a remarkable reptile (Stagonolepis Robertsoni) as, up to that time, had been found in the sandstones of the neighbourhood of Elan, and the conclu- sion at which I had arrived, "that ~tagonoleTis is, in the main, a Croeodilian reptile." These remains, however, like all the other fossils from the same district which have come under my notice, were not in a condition very favourable to their interpretation. With the exception of a few dermal scutes, I do not think that a single entire bone, or cast of a bone, has come into my hands; and the most instructive specimens have not been the bones themselves, the osseous matter being always soft, friable, and injured, but their casts in the sand- s~one. The evidence afforded by the remains of vertebrm and scutes was sufficiently decisive to warrant my conclusion as to the general nature of the animal; but, in respect of the other parts of the skeleton, the surmises which I made in 1858 needed confirmation, or the reverse, by the study of additional materials. Such materials have from time to time been obtained by the ex- ertions of my friend the Rev. Dr. Gordon, of Birnie, near ]~lgin, who, aided by a grant from the Donation Fund of the Royal Society, has undertaken the exploration of the fossiliferous beds whenever the operations of the quarrymen laid them bare, and has from time to time sent me consignments of valuable and instructive specimens. From these and others, for which I am indebted to Mr. Grant of Lossiemouth, I have been enabled to make numerous important addi- tions to my knowledge of ,.~tagonoleTis; so that at present I am ac- quainted with the following parts of its skeleton :-- 1. The dermal scutes, which formed a dorsal and a ventral armour. 2. Yertebrm of the cervical, thoracic, lumbar, sacral, and caudal regions. 3. Ribs. 4. Parts of the skull and teeth. 5. The scapula, the coraeoid and the interclavicle. 6. The humerus and (probably) the radius. 7. The ilium, ischium, and pubis. 8. The femur and (probably) the tibia. 9. Two metacarpal or metatarsal bones. * "On the StagonoleTis Rober~soni (Agassiz) of the Elgin Sandstones." --Quart. Journ. Geol. ~oc. 1859 Downloaded from http://jgslegacy.lyellcollection.org/ at University of Virginia on July 10, 2012 4~ PROF. T. H. ~ ON 8TAGONOLEPI8 BOBERTSONI~ Under these circumstances, it is possible to form a distinct and tolerably complete conception of the nature of Stagonolepis, and to compare it with other reptiles, so as to arrive at a just notion of its afllnities. So far as the vertebrm, ribs, scapula, and dermal armour are con- cerned, I have nothing to alter in the views which I took of the nature of the bones and their systematic significance in 1858. The bone which, in the body of my paper, I interpreted as a coracoid, turns out to have been correctly identified; while that referred to in the note at p. 459, and which led me to doubt whether I was right in this interpretation, has been shown by better specimens to have been an ilium seen from the inner side. The distal moiety of a limb-bone, which is regarded as a femur at p. 452, is shown, by further evidence, to be a humerus ; and, finally, the mandible with long curved teeth, which I supposed might belong to s certainly appertains to some other animal. It is a very remarkable circumstance that, up to the present date, the fossiliferous sandstones of Elgin have yielded remains of Stago- no/ep/8 (several individuals, some of which must have attained a length of 12 or 14 feet), of ttyperodapedon (one almost complete specimen, half another, and fragments of others, the largest pro- bably 6 feet long), of Teler~eton (two nearly entire specimens about a foot long), and of the large animal to which the mandible with long curved teeth belonged, and absolutely no~.hlng else. Not a trace of other vertebrate or invertebrate ~n~mals, or of plants, has yet been detected; and the only ether indication of life is the well-known series of foot-prints, which, so far as I can ascertain, do not occur in the same beds with the reptilian remains. As ~$agonohT/$, at any rate, was a carnivorous animal, and must have needed a consider- able supply of aliment, the absence of any trace of the animals on which it fed (unless, as is not very likely, it devoured Lizards) is a curious illustration of the value of negative evidence. From the evidence which has now been collected, and which con- sists entirely of specimens associated with the characteristic scutes of ~lgono/ep/s, it is demonstrable that, in outward form, this reptile mnst have resembled one of the Caimans or Jacares of the present fauna of intertropical hmerica, that it possessed strong limbs, of which the anterior were at least as large, in proportion to the pos- terior, as in the modern Urocodilia, but that StagonolelMs differed from the Caimans in possessing a long and narrow skull, more like that of a Gaviah As in the existing Caimans and Jacares, the twmk and tail were protected by a strong armour, composed of a dorsal and a ventral set of thick bony dermal scutes, which, in the trunk, were so arranged as to constitute separate dorsal and ventral shields, while in the tail they formed a continuous girdle. In contradistinction to existing Crocodilia, the dorsal shield was made up of not more than two longitudinal series of seutes, and the ventral shield of not more than eight series in any part. Downloaded from http://jgslegacy.lyellcollection.org/ at University of Virginia on July 10, 2012 AND ON TH~ ~VQ~UTION 0P THE OROOODIZIA, 4~5 The dorsal scutes are angulated and longitudinally keeled on their free surfaces; the ventral seutes are fiat, and formed of a single ossification. The free surfaces of the scutes have a deeply pitted or grooved sculpture. The vertebr~ (except doubtless the atlas and axis) are amphicoBlons, the anterior and the posterior surfaces of their centres being alike slightly concave. The transverse processes resemble those of Crocodiles ; and, as in some recent Gro~dil~ (e. g. G. nilo- ti~s) and in Belodon, those of the anterior thoracic vertebr~ are inclined upwards. The transverse processes of the lumbar vertebra, of which there were not fewer than two, are long, broad, and directed horizontally, those of the last lumbar vertebra being wider at their outer than their inner ends. The sacrum consists of i~ro unankylosed, amphico~lous ver~ebr~; and the ends of the sacral ribs are remarkably wide---more so in proportion than in any Crocodile known ~ me. The eentrum of the first caudal vertebra is amphie~lous. The skull is produced into a slender rostrum ; and the rami of the man- dible are united in a long symphysis. The posterior nares are situ- ated far forward, as in Lizards; and neither the palatine nor the pterygoid bones unite to prolong the nasal passage backwards and give rise to secondary posterior nares, as in existing Crocodiles. In the mode of formation of the proper posterior nares, however, ~go- noleTis conforms ~o the Crocedilian type. All the teeth which I have reason to refer to S~gonolel~ have short, swollen, obtusely pointed crowns, like the back teeth of some existing Gro~odilia~ and they sometimes exhibit signs of wear by mutual attrition. In the pectoral arch, the scapula resembles tha~ of recent Croco- diles ; but the eoraeoid is short and rounded, like that of the Orni- thoscelida, and of some existing Lizards, such as Hatter~. As in existing Crocodiles, there is an interclavicle2 but no clavicles. The humerus is more Lacer~ian than that of existing Crocodiles in the expansion of its ends, and the presence of a ridge and groove on the radial side of its distal end. The ilium differs from that of existing Crocodiles and is more Lacertian, in the large size of the ala, especially in front, and in the forward prolongation of its anterior dorsal angle; further, in the shape of the ventral margin of the acetabular portion of the bone, and in the absence of any notch or excavation in that margin. The acetabular end of the ischium resembles that of a Lizard, and not that of a Crocodile ; and the rest of the bone is shorter dorso- ventrally, and longer antero-posteriorly, than in recent Crocodiles, in both which respects it closely resembles Belodon.
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