60 
(1994), with Baryonyx replacing Spinosauridae as an O.T.U., is to 
confirm the systematic position of Baryonyx as a ‘basal tetanuran’, 
and, at the same time, to cast serious doubts upon any particularly 
close connexion with Torvosaurus and/or Afrovenator. 
Another cladistic analysis of the Theropoda that deserves brief 
consideration is that of Russell & Dong (1993: 2122-2125). Many 
of the O.T.U.s (mostly at family level, but including also Baryonyx) 
were novel, as were many of the synapomorphies proposed, and this 
resulted in a cladogram that was unusual in several respects. One 
group, including Baryonyx, Yangchuanosaurus, Allosaurus, 
dromaeosaurids and tyrannosaurids appeared to be defined ‘by the 
acquisition of horn-like tuberosities along the dorsolateral edge of 
the skull and relatively large teeth which are few in number (Russell 
& Dong, 1993: 2121). In fact, all that appears to pertain to Baryonyx 
in the former connexion is one small tuberosity on the lacrimal. Its 
teeth (in the lower jaw at any rate) are more numerous than in any 
other theropod except Troodon (Osmolska & Barsbold 1990) and 
Pelecanimimus (Pérez-Moreno et al. 1994), both of which are 
systematically remote from Baryonyx. Russell & Dong’s analysis 
does not seem to shed any additional light upon the systematic 
position of the latter. 
Finally, Holtz (1995) published a new phylogeny of the Theropoda 
in which he proposed a weakly supported monophyletic 
Megalosauroidea comprising Afrovenator + (Megalosaurus + 
Baryonyx + Torvosaurus). 
Conclusions 
Our final conclusions on the systematic position of Baryonyx are 
that it should remain as the type-genus of the family Baryonychidae; 
that its nearest relatives (to be placed in the same superfamily 
Spinosauroidea) are the poorly known Spinosaurus, Angaturama 
and perhaps /rritator; that this group lies within the Tetanurae, close 
to the base of that taxon, with the Neotetanurae as its sister-group; 
and that Megalosaurus and Torvosaurus respectively are progres- 
sively more distant outgroups to the combined 
Spinosauroidea+Neotetanurae clade. 
This is the best that we can do in our present state of knowledge. 
Our conclusions are subject to the usual caveats: 
1. Lists of characters for the same group, drawn up by different 
authors, are often very different’ (Charig 1993) and are bound to 
be far from complete (Panchen 1982). 
2. The itemisation of the characters and the scoring of the character- 
states for the data-matrix require a great number of difficult 
subjective decisions. 
3. Small changes in selection of characters, itemisation and scoring 
can produce drastic changes in the results of the analysis. 
4. Our knowledge of those same character-states in Baryonyx 1s 
very incomplete, and in certain cases the scoring was likewise 
difficult. 
5. Other authors, generally using very different lists of characters 
and different O.T.U.s, have produced different cladograms for 
the Theropoda. 
6. The most parsimonious cladogram does not necessarily repre- 
sent the actual course of evolution (Charig 1982: 414). 
At the same time we must point out that, when two or more analyses 
based on very different lists of characters produce remarkably 
‘Holtz (1994a) used 126 characters in his analysis of the Theropoda; Sereno et al. 
(1994) used 80 (excluding the Ceratosauria). Even the most generous interpretation 
could find no more than 17 characters common to both, of which only 4 pertained to the 
skull and vertebral column. 
A.J. CHARIG AND A.C. MILNER 
similar cladograms, the fact that the shared topology is supported by 
different rafts of evidence greatly enhances our confidence in its 
correctness. 
PALAEOECOLOGY 
In Early Cretaceous times the Weald of Surrey, Sussex and Kent 
was partly occupied by the Wealden Lake, a large lake of fresh to’ 
brackish water that extended westwards into Hampshire. To the 
north lay dry land in the region of what is now the London conur- 
bation; to the south lay the Anglo-Paris Basin and the open sea. 
Two large rivers flowed down from the north and north-east to) 
discharge their waters into the lake through a common delta, with 7 
shallow creeks and oxbows. The climate was, in modern terms, 
sub-tropical. 
Ross & Cook (1995) have recently reported on the stratigraphy 
and sedimentology of the Smokejack’s locality in particular. The 
exposure at that site consists of 23 m of Upper Weald Clay, all of it 
of early Barremian age (estimate of absolute age approximately 130 
million years). The Baryonyx remains were in fine silty clays of non- 
marine origin, light olive-grey in colour and containing large irregular 
nodules of bioturbated sideritic siltstone. The sediments give indica- 
tions of shallow-water facies (e.g ripple-marks at the base of the 
dinosaur level) but show no signs of complete drying out (mud- 
cracks, erosion etc.), nor is there evidence of braided river deposition: 
they had obviously settled out of still water (a “low energy” environ- 
ment). This lithology, both at the Baryonyx horizon and in the bed: 
immediately below, has been interpreted by Ross & Cook as indicat- 
ing a fluvial and/or mudplain environment with areas of shallo 
water, lagoons and marsh. 
The fossil flora and fauna of the Smokejack’s locality as a 
whole give some idea of the environment in which Baryonyx live 
(Frontispiece), although it should be remembered that the flora, 
fauna and total environment all varied significantly at differen 
levels in the sequence. Common plant remains include the fer 
Weichselia reticulata (Stokes & Webb), concentrated locally in 
layers within the clay and in sideritic lenses, and an aquatic o1” 
marsh-dwelling herbaceous plant that grew in monotypic stands 
Bevhalstia pebja (Hill 1996). Also present were filicopsid ferns 
horsetails, club mosses and conifers. Of great importance to th 
environmental interpretation are the abundance and variety oj 
fossil insects at Smokejack’s, 10 orders of which were recorded by) 
Jarzembowski (1984). The exact stratigraphical positions of mam 
of the older finds are not known, but some insects have now bee: 
recovered in situ from sideritic siltstone lenses at a number 0 
horizons below Baryonyx (Ross & Cook 1995). Other elements 0 
the invertebrate fauna were ostracods, isopods, conchostracan! 
and bivalves. 
The vertebrate fauna includes sharks, bony fishes (notably 
Lepidotes mantelli Agassiz), crocodiles, pterosaurs, and dinosaurs 
Apart from Baryonyx walkeri, the only other dinosaur remaini 
yielded by this locality consist of a considerable quantity of materi 
referred to the relatively common ornithopod /guanodoi 
atherfieldensis Hooley, 1925, and a very few isolated bones of smal 
sauropods. In 1982 we excavated the hind portion of an articulat 
Iguanodon atherfieldensis skeleton at a distance of only about 1007 
from the Baryonyx site and at approximately the same stratigraphic 
level. Fragmentary remains of a large Iguanodon bernissartensi 
Boulenger, 1881, were collected in 1988 from a higher level in th 
sequence. 
—E 
