Paleosuchus undetermined
Creators: name: Clarac, Francois
name: Campos, Zilca
name: Marquis, Olivier
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Crocodylia
Eusuchia
Alligatoridae
Paleosuchus
Paleosuchus undetermined

description: RESULTS
THE DIFFERENTIAL EXPRESSION OF BONE ORNAMENTATION ON THE OSTEODERM SHIELD
The crocodylian osteoderm ornamentation is composed of a pattern of repetitive excavated pits that are separated by ridges (de Buffrénil 1982; Clarac 2021). Here we can observe that these pits are systematically deep on the dorsal part of both the trunk and the neck (Fig. 1; Table 1). Among the osteoderms which come from the flanks, the tail, the belly and the limbs; only 3.7% (n = 39) are deeply pitted, 15.1% (n = 161) show shallow pits and 81.1 % (n = 861) are deprived of ornamentation (Fig. 1; Table 1).
MICROANATOMICAL COMPARATIVE ANALYSES
Within our cross-section subsample that is composed of 12 osteoderms, the osteoderm porosity varies between 0.04 and 0.16 with a mean value of 0.071 and a median value of 0.06 (Table 2; Figs 2; 3). Within the dorsal osteoderms, which compose half of the cross-section subsample (Cat. 1; n = 6), the porosity varies between 0.06 and 0.16 with a mean value of 0.09 and a median value of 0.085 (Table 2; Figs 2A; 3A). Within the non-dorsal osteoderms, which compose the second half of the cross-section subsample (Cat. 2; n = 6), the porosity varies between 0.08 and 0.054 with a mean value of 0.053 and a median value of 0.05 (Table 2; Figs 2B; 3A). The Mann-Whitney test shows a significant difference between the median porosity of the dorsal osteoderms (Cat. 1) and the median porosity of the non-dorsal osteoderms (Cat. 2; Table 3) which plots a lower median value (median Cat. 2 = 0.05 <median Cat. 1 = 0.085).
We have compared the full dataset (Cat. 1 and 2; n = 12) with a previous dataset that is composed of an interspecific sample which includes both extant and extinct pseudosuchian species that lived during the Triassic and later periods (Clarac et al. 2020). Within this previous study, the sample was split in two sub-samples: 1) the terrestrial taxa which lived during the Mesozoic; and 2) the semi-aquatic taxa that appeared at the lower-Jurassic and who present some descendants that are still present in the extant nature (i.e., Crocodylia; Benton & Clark 1988). Here we have added a new dataset as a third sub-sample (Table 2; n = 12) in order to perform statistical comparisons via two-sampled non-parametric tests (i.e., Mann-Whitney). This test revealed that the median porosity is significantly different between P. palpebrosus and the other semi-aquatic forms whereas it is not with the terrestrial forms (Table 4; Fig. 3B). The test also revealed a significant difference of the median porosity between the semi-aquatic and the terrestrial forms (Table 4; Fig. 3B). The median value is indeed lower in both the terrestrial forms (Median = 0.05) and in P. palpebrosus (Median = 0.06) than in the semi-aquatic interspecific sample (Med = 0.175). The second and the third percentile show a narrower range in P. palpebrosus than either in the terrestrial forms or in the semi-aquatic interspecific group (Fig. 3B).
description: Published as part of Clarac, Francois, Campos, Zilca & Marquis, Olivier, 2024, The extended osteoderm shield in Paleosuchus sp.: a dwarf crocodylian adaptation to the equatorial forest ecosystem?, pp. 161-170 in Comptes Rendus Palevol 23 (12) on pages 164-166, DOI: 10.5852/cr-palevol2024v23a12, http://zenodo.org/record/10813965