Structure of the Tail of a Phytosaur (Reptilia, Archosauria) from the Norian (Late Triassic) of Lombardy (Northern Italy)

Home , Aetosaurus, Calcare di Zorzino, Megalancosaurus, Mystriosuchus

Rivista Italiana di Paleontologia e Stratigrafia volume I u) numero 1 tavole 1 naoinc I ì5-1 4a Aprile 1999

NOTA BREVE . SHORT NOTE

STRUCTURE OF THE TAIL OF A PHYTOSAUR (REPTILIA, ARCHOSAURIA) FROM THE NORIAN (LATE TRIASSIC) OF LOMBARDY (NORTHERN ITALY)

SIVIO RENESTOX & CRISTINA LOMBARDO*

Receiped Ntnentber 2, 1998; accepted December 3, 1998

Key"uords: Reptilia, Archosauria, Phytosauridae, Norian (Late sent endemic or poorly known taxa. Despite the deposi- Triassic), Lombardy (Nonhern Italy), new specimen, caudal verre- tional environment (marine basins amid carbonate brae, functional morphology. a platform; Jadoul, 1986; Jadoul et aI., 1992), rerresrrial Riassunto. In questa nota viene descritta la morfologia della reptiles are more common than aquatic ones, suggesting porzione caudale della colonna venebrale di uno scheletro completo the presence of land nearby, possibly ephemeral islands di Fitosauro (Reptilia, Diapsida, Phytosauria) rinvenuto nel Calcare di with freshwater reservoirs in which insecrs (Vhaiiey, Zorzino, di età Norica (Triassico Superiore), nella località fossilifera di Endenna (Zogno, Bergamo). Lo stato di avanzamento del lavoro di 1986) and endemic reptiles lived. Marine repriles are rep- preparazione consente una descrizione precisa della morfologia delle resented by the placodont Psephoderma (Pinna & Nosot- vertebre caudali, e del loro numero complessivo. La struttura del cra- ti, 1989; Renesto & Tintori, 1995) and the thalattosaur nio, non ancora completamente preparato, fa supporre affinità con il Endennasaurars (Renesto, 1984, 1992). Among non-mari- genere Mystriosuchus, m l'attribuzione è per ora ipotetica. La presen- za di un' adattamento alla locomozione in acqua più spinto che in ne reptiles, the oldest pterosaurs so far known have altri Fitosauri è testimonìato dalla morfologia delle emapofisi e delle been collected $fild, 1978, 1984; Renesto, 1993), along spine neurali, finora non figurata in letteratura per i fitosauri. Può with odd diapsids hke Drepanosaurus (Piîîa 1980; Rene- darsi che il fitosauro completo di Endenna apparrenga ad una nuova sto, 1994a) and Megalancosaurus (Calzavara 1980; specie, particolarmente adattata all'ambiente marino. et ai., Renesto, 1.994b) both scansorial reptiles with arboreal Abstrdct. The structure of the caudal porrion of a venebral habits. The peculiar small prolacertiform, Langobardi- column belonging to a complete ph1'tosaur skeleton is described. The saurus (Freîesto, 1994c) is unknown from lher localiti- skeleton has been collected from the Calcare di Zorztno (Zorztno es, while the sphenodoîr.íd Diplrydontosam.,s (Renesro, Limestone) of Norian (Late Triassic) age, in the small quarry of En- denna (Bergamo, Lombardy, Northern ltaly). The specimen is curren- I995b) is reponed also from the Late Triassic fissure fil- tly being prepared, and only a detailed description of the tail is possi- lings of England (Vhiteside, 1986). Remains of aetosaurs ble. The exposed portion of the skull, which shows, among other and phytosaurs have been found and referred to genera characters, à nàrroq flattened snout, suggests possible relatìonships well known from the coeval Srubensandstein Formation with the genus Mystrioswchus, btt preparation of the skull must be finished prior to attempting any classification. The morphology of (Late Triassic of Germany) . Aetosaurus ferratus is repre- the tail venebrae has never been figured for phytosaurs; however, the sented by some fragments of the dorsal armour (\fild, structure of the tail vertebrae of this specimen reflects a great degree 1991), while phytosaurs were so far known only from of adaptation toward aquatic life, justifying its description prior to an isolated skuli without lower jaw; placed the genus cornpiete preprrrtion. [f rhis specìmen represenrs r new species, ir in should have been highly specialised toward marine life than most ot- Mystriosuchus (Renesto Er Paganoni, 1998). her phytosaurs in which the postcranial skeleton is known. In November 1.995, a large, complere, and articulated reptile skeleton was found (Tintori et al., 1.996). \íhen it vzas still covered by matrix, it was tentatively Introduction. considered a large thalattosaur, owing to the very long The Norian (Late Triassic) Calcare di Zorzino tail and the rather short limbs. Initial prepararion, how- (Zorzino Limestone) formation yielded an interesting ever, revealed that it was a nearly four meter long, nar- vertebrate fauna (Renesfo, 7995a; Tintori, 1995). Finds row snouted phytosaur mainly consist of fishes; however, reptiles, wrth more Phytosaurs were carnivorous, crocodilelike archo- than LO genera of greàt importance and often repre- saur reptiles well known from several Late Triassic loca- ^re

'r Dipartimento di Scienze della Terra, Università degli Studi di Milano, via Mangiagalli 34,I-20133 Milano, ftely; e-mail : [email protected]. it. 1.36 S. Renesto & C. Lombardo

Fig. 1 - Shetch of the disposition of the larger stone slabs in which Specimen MCSNB 10.087 js pre'erued. The rl- ready prepared ponions o{ the skeleton are shown in black.

Hungerbùhler, pers. comm.). In addition the structure of the ceudul vertebrae oI this speci- me. i..""rrlir. f^..1.-^ r.lytosaurs. .rnd Lhe tail has never been [igu- red so far. The structure of the tail, especially the haemapophyses and neural spines, reveals a strong adlptation toward aquatic life, suggesting more marine life habits for this narrow-snouted, gavialJike phytosaur.

lities mainly in the Northern Hemisphere (McGregor, Systematic palaeontology 1906; Gregory, 1962; Chatterjee, 1978; Buffetaut et al., 1988; Ballew, 1989; Hunt 6t Lucas, 1989; Buffetaut, 1993; Doyle & Sues, 1995) and Madagascar (Chatterjee, Class Reptilia re78). Superdivision N e o d i a p s i d a Benton, 1985 Phytosaurs are usually associated to freshwater en- Division A rc h o s a u r i a Cope 1869 vironments and it was assumed (Renesto, 1995a) that P s 1861 also the isolated Mystriosuchus skull found in the Enden- Family h y t o au r i d a e Meyer na locaiity belonged to a specimen that did not live on Genus ? MystrtoswchusFraas, 1,896 the islands close to the basins in which 'the Zorzino (Plate 1; Fig. 2-3 Limestone was deposited, but on more distant continen- ) tal land, this latter sharing its fauna with the European Material. continent. The new find of the complete and articulated A neariy complete, articulated phytosaur skeleton, about metres long, exposed dorsal view. specimen leads us to reconsider this point of vieq sug- 4 in gesting instead that the phytosaurs found in the Calcare Apart some smali fragments, the skeleton is preserved di Zorzino may well have lived ciose to the basins, both on four large slabs and a smaller one (Fig. 1). Only two in freshwater and marine environment, as already sugge- of the slabs have been prepared so far, revealing the sted by Buffetaut (1,993) for the Mystrioswclrazs specimens middle and distal portion of the tail and, in part, the found in the Norian Dachsteinkalk (Austria), which was skull and some cervicai vertebrae. The specimen has deposited in a shallow marine environment. been catalogued as MCSNB 10.087 (MCSNB being the "E. Preparation is still in progress, but the tail has acronym of the Museo Civico di Scienze Naturali been exposed almost entirely (oniy some of the most Caffi" di Bergamo, Lombardy, Northern Italy, where proximal caudal vertebraé are still covered by matrix), the specimen will be stored after preparation). along with part of the skull, cerwical vertebrae and ribs. The skull has a narrow, flamened snout, and it may be Remarks. Mystriosucbus is well known from many tentatively referred to the genus Mystriosucbus, already beauti{u1 isolated skulls and severai fragmentary remains known at this locality from an isolated skull (Renesto & of the postcranial skeieton from the German Stuben- Paganoni, 1998). Any attempt of a definitive taxonomic sandstein (Fraas, 1896; Mc Gregor, 1906; Westphai, assignment of the specimen, however, must await a 1.976). The structure of the skull is well documented more complete preparation. The description of the tail and useful for classification, in contrast with less known prior to complete preparation of the entire skeleton is postcranial material. The already prepared portion of justified, because the caudal veftebrae, especially the the skull of specimen MCSNB 10.087 (Fig 2) reveals more distal ones, are unknown or poorly known in the presence of an uncrested, rather long and narrow many phytosaur genera, particularly from Europe (A. snout; external nares close to the orbits and lying presu- The tail of a Late Triassic pbytosaur

Fig.2 - Specimen MCSNB 10.087. skull after preliminary preparxtion, scale ber equals 1O cm

mably above the antorbiral fenestrae; frontals and nasals The tail. deeply sculptured, and a compressed, inverred U-shaped parietal-supraoccipital complex, along with a truncated Description. The cleaned porrion of the tail (Fig. posterior processes of the squamosals. Flunt & Lucas 3) is about 1.44 cm long and 64 caudal verrebrae have (1989) have cited all these characters as diagnostic for been exposed. The more proximal portion of the tail, Mystriosuchus. The postorbital bar, however, is nor so (lying on another siab) is still embedded in the matrix, wide as it could be expected in this genus (Hunt & Lu- for a length of approximately 45-50 cm, whiie anorher cas, 1989) and the snout is proporrionally less elongated small part is missing; thus the total length should be than usually occurs ìn Mystriosucbus (Fraas, 1896, Mc about two metres. By comparison with the length of Gregor, 1906; Gregory, 1962; SR, pers. obs.). The appa- the most proximal centra already prepared, it can be rently different width of the postorbital bar may be due estimated that at least 10-12 caudai vertebrae are still to preservation (the skul1 is dorsoventrally flattened; the embedded in the matrix, giving a count of ca.7A-75 cav top of the skull seems to have collapsed during fossiliza- dal vertebrae. This number is rather high, since Mc Gre- tion and some lateral bones are broken or distorted). On gor (1906) figured only approximately 34 caudal verte- the other hand, the skull length/rosrrum length ratio brae in his combined reconstruction of a phytosaur (My- for Mystriosuchus should range from 65 to 72o/o, accor- striosuchus skull with Rutiodon postcranial skeleton). \X/estphal ding to Vestphal (1976). Specimen MBSN 10.087 with a (1976) quoted an average of 50 and Romer skuil length of ca. 55 cm (approximately half the length (1956) an average of 40 caudal vertebrae. The long tail of of the larger Mysuiosuchus skulls) and a rosrrum iength specimen MCSNB 10.082 might reflect the high num- of about 35 cm has a skull length,/rostrum length ratio ber of caudal vertebrae typical of primitive archosaurs of about 63%, clóse to with that for Mystriosuchus. Ot- (Romer, 1956), but much more probably a derived con- her characters are required prior to assessing definitely dition, suggesting a greater degree of adaptation for the taxonomic status of the specimen, but, at present, swimming, as detailed in the following section. there seem to be good reasons to include the specimen The caudal vertebrae are amphicoelous and the tentatively in the genus Mystriosuchus. No specific as- ventral outline of the centra is slightly concave; in rhe signment is atternpted however, even if the peculiar proximal exposed portion of the tail both pre-and po- morphology of the tail and the possibly different body stzygapophyses are stout with nearly horizontal articu- proportions may suggest that specimen MCSNB 10.087 lar facets. Indeed, the structure of the caudal vertebrae belongs to a new species. changes distinctly aiong the series. The more proximal 138 S. Renesto & C. Lombardo

Fio I Specimen 14CSNB 10.087, the rnain slab with the tail, during preprration. .crle brr equals 10 cm.

central in position and have stout, enlarged articular facets. Their distal ends are expanded anteroposteriorly into a "foot"; ,r-^ ..^-,-.r ..foor" rrr4tó1r1-^-^:- ur^r,his L shows some fluting. At the ?20 t h clud"rl vertebra, the neur.rl 1,i, ...,,..ii iiqj1" spines start'to slant posteriorly * (Fig. 6). The following c.rud.rl vertebrae are exposed in dorsai view, and the associated neural !-1,:i" ".r spines are frequentiy broken or *;'"Ì ;M poorl;' preser-ved, but a gradual l,lrllit incre.ise ,::'liii oI the sllnting is cle;rly deteeLable. In Lhis region the r rJnsve rse processes h.ive ne.rrly disappeared, and the centra seem to be mediolateraily compressed. 'I'he more distal portion of the tai1, from caudal vertebra ?40 to the rery end of the r,ril, is expo- scd again on its left side (Pl. 1. fig. 1l). The size of the centra decreases progressiveiy, and the centra themselves are spool-sha- pcJ up to the last vertebr.r. which is triangular. The pre- and postzygapophyses become reduced. The most unusual fea- tures are the structure of the neural spines and the haemal arches (Fig. 7 A-B). The neural arches become rather low, whiie the neural spines are still very 1ong, narrow and strongly slanting posteriorly, overhanging Lhe following centrum and at least half of the further succeeding one. The spines are preserved in natural position and are not bro- caudal vertebrae (approximately caudal vertebrae 15-20,; ken; their pronounced backward slant represents indeed Fig a-5) are exposed in lateral (eft) view. They bear high the original condition, as it is testified by the continuity neural arches and spines and very short but stout tran- of marks and pores on the bone surface. The haemal sverse processes. The neural spines are somewhat expan- arches become short, and the haemal spines are antero- ded at their bases, then show a slightly concave anterior posteriorly expanded at their ventral margin, forming a and posterior outiine ending with a flattened top. They sort of expanded "foot " very similar to rhrt of pa- are extremely thin, in contrast with their height. The chypleurosaurids as figured by Carroll Ec Gaskill (1985). haemal spines also are deep and robust, nearly as long This pattern persists until the very end of the tlil, ex- as, but narrower than, the neural spines. They are inter- cludine the last two or three vertebrae. The tail of a Late Triassic phyrosaur 1,39

Functional morphology. Phytosaurs have generally been considered crocodilelike in habits, with some genera more adapted to amphibious or aquatic li{e than others. According to Vestphal (1976), Mystriosu- chus is possibly the most "aqu;ì- tic" phytosrur, brsed on its gavial- like snout and the high and laterally compressed tail (Westph.rl, 1976). However, even greater adaptation towards aquatic locomotion is suggested for specimen MCSNB 10.082 by both the general shape of the tail and the morphology of its vertebrae. While the lateral compression of the tail ("Rud- derschwanz", Westphal, 1976) o{ .l4ystriosuchus was aiready known, the distal expansion of the haemal spines along with the b.rckward sl.rnting of rhe neurai spines of the middle and distal caudal vertebrae have never been reported or figured (the same applies to the great F;. l Specimen MCSNB 10.087, proximal caudal venebrae (?12-18), scale bar equals 10 cm lensth^- "br^^ oI r he teill ln his de-

)*.,. í... - "."... i.'r,'. 'i:ì;r.',:- . -' r \''. r'.- , \'\, :' .

Fig' 6 Specimen MCSNB 10.087, )20th caudal vertebra, startrng F;, C Specimen MCSNB 10.087, proximal crudal venebrae (ap- point of the posterior slanting of the neurai spines, scale proximately 15-18th). Scale bar equals 4 cm. bar eouals 4 cm. 1,44 S. Renesto & C. Lombardo

Fig. 7 - Specimen MCSNB 10.087, two series of distal caudal vertebrae (A: ?50-55; B: ?57- o2) in shrch rhe posrerior slanting of the neural spines and the anteroposteriorly ex- p.rnded hremrl spines rre 'i- sible, scale bars equal 4 crn.

the same category of undulatory swimmers, which are charac- terised by "Trunk stocky, limbs lirrle modified, t,ril larerally compressed, but not elongate" (Carroll, 1985, p. 142). Speci- men MCSNB 10.087 (and possibly other Mystrioswchus specl- mens?) does not fit many of these characters: the trunk seems more slender than in A non-marine crocodiles and in other phytosaurs, the limbs ap- peàr to be somewhat reduced fitLdging from the .rlre.idy prep.r- red portion of a knee jornt) and finally the tail is elongate. All these characters point to another of Carroil' s (1985) categorì' es of swimmers, which includes some nothosaurs, along with other aquatic diapsids, such as FIo- 'uAsaurus and C/audiosaurus, B more specialized toward aquatic 1ife. They show "Neck modera- scription oî Mystrioswcbus Mc Gregor (1906) did not de- tely elongate, trunk not elongate but iaterally compres- scribe the caudal vertebrae and restored those of Rutio- sed, limbs somewhat reduced and slightly modified as don with long but narro'w "non-footed" haemal spines paddles, tail long and laterally compressed" (Carroll, aiong with "normal", vertical neural spines. Westphal 1985, ibid.). FIowever, specimen MCSNB 10.087 does (1976) also reported elongated neural spines and che- not show any particular elongation of the neck nor are vrons for Mystriosuchus, but did not mention any distal the limbs modified as paddies, rendering its classifica- expansion or slanting. tion in Carroll's scheme rather difficult. It is clear that The very long and compressed tail (along with specimen MCSNB 10.082 represents a step further to- the possible presence of rather short and slender limbs) ward a more aquatic adaptation, compared to other points undoubtedly to axial swimming sensu Braun & known phytosaurs. It was probably a rather efficient Reif (1985), possibly some sort of undulation (caudai swimmer, and the tail was the main source of propul- subundulatory mode sensu Braun & Reif, 1985). In his sion. The "footed" haemapophyses are present in many survey of aquatic locomotion in diapsid reptiles, Carroll aquatic reptiles; in some Neusticosaurws (Paclrypleurosaw- (1985) put the phytosaurs together with non-marine cro- rws) species (Carroll & Gaskill, 1985; Sander, 1989), they codiles, choristoderans and non-armoured placodonts in are very similar to the more distai ones of specimen

PLATE 1 Fig. 1 - Specimen MCSNB 10.087, distal caudal venebrae (?51-55), scale bar equals 5 cm Fig.2 - Specimen MCSNB 10.087, distal caudal vertebrae?57-64. Scale bar equals 5 cm. Fig. 3 - Specimen MCSNB 10.087, distal end of the tail, scale bar equals 5 cm. The tail of a Late Triassic phytosaur r41 S. Renesto & C. Lombardo

MCSNB 10.087. Flaemal spines, that are laterally flatte- duced allowing good mobility). It may be hypothesised ned and anteroposteriorly expanded can easily be explai- that some stiffness of the distal portion of the tail may ned as adaptation for undulatory swimming, since they have improved thrust (Hildebrand, 1978). In any case) offer a greater surface for the insertion of axial muscula- the posterior slant of the neural spines rendered the dor- ture. On the other hand, the peculiar backward slanting sal outline of the tail rather low, despite to their length. of the neural spines of the mid- and dorsal portion of A low tail is present in some aquatic diapsids, which the tail is rather unusual and requires an explanation. swim by undulation of both the trunk and the tail in a The great elongation of the neural spines may be related sort of anguilliform swimming pattern (pleurosaurs, to the need of increasing the surface for thrust and to some aigialosaurs, and thalattosaurs, Carroll, 1985). Ac- the development of a strong epaxial muscuiature ro im- cording to Carroll (1985), this latter kind of locomotion prove iateral undulation, as suggested for Hupehsuchws is more frequent in reptiles and fishes that lived among (Carroli & Dong, 1991). The posterior slant of the neu- rocks or muddy bottoms. Their swimming was rather ral spines, which increases toward the end of rhe tail, slovz and involved neither speed, nor r:ipid bursts of ac- represents a problem, because it probably rendered the celeration (Carroll, 1985), that are required in a gavial- region rather stiff. In some Jurassic marine crocodilians like fish eater. This pattern of locomotion was hindered (Romer, 1956) a similar pattern is due to the presence of by the morphology of the neural spines. Caudal undula- an inverted heterocercal tail fin, in which the stiff distai tion associated to a rigid trunk allows perhaps better portion of the tail supports the ventral lobe. In these propulsion in reptiles, but must be associated with a la- crocodilians, however, the neural spines of the distal terally compressed tail in order ro obtain effective portion of the tail slant backward only up to the begin- thrust. It may be hypothesised that the posterior por- ning of the tail lobe, where the direction of slanting be- tion of the tail of specimen MCSNB 10.082 might have comes inverted (anterior). Due to the deep ventral ben- borne some kind of fin-like expansion in order to in- ding of the tail, they project vertically, giving probably crease the efficiency of the whole srrucrure. In conclu- support to the dorsal lobe of the fin. In addition, a sion, specimen MCSNB 10.087 represenrs a phyrosaur "fan" shape is reported for the haemapophyses, which (possibly a new species of Mysrriosucbw) highly speciali- prevented any possibility of undulation. In specimen zed toward aquatic life, which inhabited seashore and MCSNB 10.087, the slanting of the neural spines does shallow marine environmenrs, feeding upon fishes and not change its direction, and neither is there a tail bend, possibly other smaller reptiles hke Endennasaurus, rep- resenting nor the ventral ends of the haemapophyses are so close one of the top predators in its environment. to each other. Thus a lobed caudal fin like that of marine crocodiles is not plausible. Perhaps the slanting is a way to counterbalance the extreme thinness of the neural spines and, toward the end of the tail, of the entire caudal vertebrae. The whole skeleton seems rather lightiy built, but this do not contrast with aquatic habits if the animal had not to reach the bottom, but swum and fed at, or near to, the surface of the water (Hildebrand, 1978). As detailed in the description, the caudai vertebrae become very slender and their thickness is greatly reduced posteriorly. This may be an unusual feature for Achnozaledgements. an aquatic animai, uniess light caudal vertebrae are re- Ve wish to thank Prof. A. Tintori. Milano. who found the quired to save weight, in order to balance a very long fossil and worked (very hardl) to dig it out, along with other members of the team that recovered fossil: M. tail with respect to a rather short trunk, to avoid pit- the G. Manarolla, Manenti, M. Vendico. Milano. Our sincere thanks also to the tearn ching "head up". Such a thin tail may have been not which is currently preparing the specimen jointly with one of the very efficient for swimming, unless the posterior slan- authors (CL): B. Marazzi and G. Manarolla, both of Milano. Thanks ting neural spines increased the strength of the structure are due to Prof. H. D. Sues, Toronto, who reviewed the mrnuscript and revised also the English language. Finally we wish to thank the overhanging each a consequence centra by other. As the people and institutions who give financial support to the prepantion were linked together in some way and also yawing was of the specimen: the Association Amici del Museo e dell'Ono reduced, because lateral torsion was hindered by the se- Botanico di Bergamo, The bank Credito Bergamasco, The Bergamo Municipality, Assessorato alla Cultura and to the curator, Dr. A. quence of overhanging neural spines. The influence of Paganoni, and the staff of the Museo Civico di Scienze Naturali "E. these elongated neural spines on caudal undulation Caffi", Bergamo, in which this exceptional fossil will be stored when should be investigated (the zygapophyses are greatly re- preoared. Tbe tail of a Late Triassic phytosaur 1-43

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