Cretaceometra brasiliensis, Nel & Popov, 2000

Nel, A. & Popov, Y. A., 2000, The oldest known fossil Hydrometridae from the Lower Cretaceous of Brazil (Heteroptera: Gerromorpha), Journal of Natural History 34 (12), pp. 2315-2322 : 2316-2321

Cretaceometra brasiliensis sp. nov.

Material. HOLOTYPE specimen i 9556, Museo Civico di Storia Naturale , Milano, Italy . PARATYPES: one specimen in Axerold coll., American Museum of Natural History , New York, USA and specimen MNHN-LP-R.55206, Borschukewitz coll., Laboratoire de PaleÂontologie , MuseÂum National d’ Histoire Naturelle, Paris, France .

Stratum typicum. Lower Cretaceous, Upper Aptian, 110 million years ago, Crato FormationÐNova Olinda Member (sensu Martill et al., 1993; 5 Santana FormationÐCrato Member auct.).

Locus typicus. Chapada do Araripe, vicinity of Nova Olinda, State of CearaÂ, N.E. Brazil ( Maisey, 1990).

Etymology. Named after Brasil, the latin name for Brazil.

Presentation. These bugs are limonite (iron oxide) mummies. On the type, only the dorsal part of the body and part of the lateral side of the head and thorax are visible. Legs and antennae are well-preserved.

Description. the proposed description is based on the study of all the specimens. Some of the states of the characters of this fossil taxon can be polarized after the phylogenetic analyses of Andersen (1977, 1982a,b).

1. Apterous insect.

2. Body very long and slender, nearly ten times longer than broad [apomorphic]. Length of the body, 11.3 mm (i 9556) and 12.0 mm ( R.55206); width, 1.1 mm (i 9556) and 1.4 mm ( R.55206).

3. Head very long and slender [apomorphic]. Length, 3.1 mm (i 9556) and 3.4 mm ( R.55206); minimal width, 0.26 mm (i 9556) and 0.3 mm ( R.55206); maximal width, 0.57 mm (i 9556) and 0.6 mm ( R.55206); median width, 0.41 mm (i 9556) and 0.45 mm ( R.55206); width near the head base, 0.52 mm (i 9556) and 0.55 mm ( R.55206).

4. Largest part of the head near its apex.

5. Narrower part of the head in its median part.

6. Head subcylindrical behind the eyes [plesiomorphic].

7. Eyes inserted in the posterior third of the head. Distance between the level of center of eyes and the apex of head, 2.25 mm (i 9556) and 2.5 mm ( R.55206); distance between eyes and base of the head, 0.85 mm (i 9556) and 0.9 mm ( R.55206).

8. Eyes elliptical, prominent, broader than the distance between them [plesiomorphic]. Eye smaller diameter, 0.3 mm, distance between the eyes, 0.2 mm (i 9556).

9. No visible transverse ridge or groove between eyes [plesiomorphic].

10. Dorsal median longitudinal groove of the head indistinct, only visible between the eyes [plesiomorphic].

11. No visible ocelli [apomorphic].

12. Anteclypeus clearly visible, triangular, 0.1 mm long (i 9556).

13. Left ventral lobe of the head visible, as long as the anteclypeus.

14. No pair of prominent elevations in the posterior part of the head that would be the insertions of the posterior pair of trichobothriae [plesiomorphic].

15. No visible trichobothria on the head.

16. Antenna long (length, 6.4 mm in specimen i 9556).

17. Antenna four-jointed.

18. First antennal joint a little shorter than the second [apomorphic]. Length of the ®rst antennal segment, 1.4 mm, of the second, 1.7 mm (i 9556).

19. First antennal joint surpassing the apex of the head with more than half of its own length.

20. Articulation between the ®rst and the second antennal joint apical [plesiomorphic].

21. Third antennal joint longer than the second (length, about 2.4 mm in specimen i 9556).

22. Basal part of the fourth antennal joint simple, without any lateral projection (it is apically broken on the type, length of its preserved part, 0.9 mm in specimen i 9556).

23. No visible subdivision of the fourth antennal joint [plesiomorphic].

24. Thorax long and slender, with its greatest width nearly less than half the median length [apomorphic]. Thorax 3.0 mm long and 1.1 mm wide (i 9556) and 3.2 mm long and 1.4 mm wide ( R.55206).

25. Pronotum longer than the anteocular part of the head [plesiomorphic]. Length of pronotum, 1.9 mm; width, 1.0 mm in i 9556).

26. Distance (d.p±m) between prothoracic coxa and mesothoracic coxa is nearly the same as distance (d.m±m) between mesothoracic coxa and metathoracic coxa [plesiomorphic]. d.p±m, 1.2 mm (i 9556) and 1.4 mm ( R.55206); d.m±m, 1.3 mm (i 9556) and 1.5 mm ( R.55206).

27. Pronotal sides parallel.

28. No elevation on the posterior part of the pronotum.

29. Head much shorter than the abdomen and thorax taken together [plesiomorphic].

30. Head longer than the thorax alone [apomorphic].

31. Prothoracic femur longer than the head [apomorphic]. Length of prothoraci c femur, 4.3 mm, of prothoracic tibia, 4.5 mm, of tarsus, 0.8 mm (i 9556). The segmentation of the tarsus is not preserved in i 9556 but it is three-segmented in R.55206.

32. Length of the mesothoracic femur, 4.4 mm, of the mesothoracic tibia, 7.7 mm, of the tarsus, 1.0 mm (i 9556).

33. Mesothoracic tarsus three-segmented.

34. First segment of the mesothoracic tarsus very short (0.1 mm long).

35. Second and third segment of the mesothoracic tarsus of equal length (0.4 mm in i 9556) [plesiomorphic].

36. Metathoraci c femur distinctly longer than abdomen. Length of metathoracic femur, 6.5 mm, of metathoraci c tibia, 6.7 mm, of tarsus, 1.4 mm (i 9556).

37. Metathoracic tarsus three-segmented.

38. Apical claws, aroliae and paraempodiae not preserved on the tarsi.

39. Length of the abdomen, 5.2 mm, width, 1.0 mm (i 9556).

40. No abdominal spiracle nor scent gland on the dorsal surface of the abdomen [more doubtful character, apomorphic].

41. Abdominal tergites and sternites quite distinct.

42. Seven abdominal tergites are visible.

43. Abdominal mediotergites longer than broad [apomorphic].

44. Last abdominal segment longer than the others, 1.2 mm long (i 9556).

45. Abdominal tergum without paired, longitudinal ridges [apomorphic].

46. No preserved pilosity on the body.

Discussion. The very long and slender body, the lack of ocelli, the very long head, the long and slender legs and the four-segmented antennae prove that this fossil belongs to the Hydrometridae .

After Andersen’s (1977, 1982b) phylogenetic tree, the characters 11, 27, 45 and 40 (with more doubt) show that Cretaceometra brasiliensis gen. nov., sp. nov. belongs to the group Limnobatodinae 1 Hydrometrinae [ Limnobatodes 1 { Eocenometra 1 (( Dolichocephalometra 1 Trichometra 5 Chaetometra )1 ( Protobacillometra 1 Baccilometra 1 Hydrometra ))}].

Cretaceometra brasiliensis is not related to the Heterocleptinae Villiers, 1948 ( Veliometra 1 Heterocleptes ) because its character 20 is in a plesiomorphic condition.

The lack of the tarsal claws renders more di cult the comparison with the Limnobatodinae (Limnobatodes) . After Andersen’s (1977) key of the recent genera, its states of character 19 (®rst antennal segment greatly surpassing the apex of the head) would make Cretaceometra fall near the genus Limnobatodes . Andersen indicated nothing concerning the polarity of this character but it is probably plesiomorphic because the same character state is also present in the Macroveliidae , sister group of Hydrometridae ( Andersen, 1982b) .

The state of character 18 in Cretaceometra , (i.e. ®rst antennal segment shorter than the second), shows that it is related to the Hydrometrinae . Its plesiomorphic state of character 25 (pronotum longer than the anteocular part of the head) shows that it is rather at the base of the Hydrometrinae , probably as sister-group of this subfamily. The comparison with the fossil genus Eocenometra is di cult because the state of character 18 in Cretaceometra is more apomorphic than in Eocenometra but the state of character 25 is unknown for Eocenometra .

The state of characters 43 (abdominal mediotergites longer than broad) and 24 (thorax very long and slender) in Cretaceometra are considered by Andersen as synapomorphies of the group Bacillometra 1 Hydrometra . (1 Protobacillometra ) Those characters are not visible on Eocenometra .

If we only use the known characters, Cretaceometra is more closely related to the Hydrometrinae than is Eocenometra .

The genus-group ( Dolichocephalometra 1 Trichometra Chaetometra ) is characterized by very small eyes. Dolichocephalometra presents a very long head, longer than the rest of the body and Chaetometra presents a long erect pubescence. Those striking apomorphies are clearly absent on Cretaceometra .

With the present state of knowledge, Cretaceometra belongs to the Hydrometrinae or to the sister-group of this subfamily but establishing its exact position relative to this subfamily and to Eocenometra relies on discoveries of new material.

The great antiquity of this fossil taxon and its clear a nities with the`most specialized’ hydrometrid subfamily show that the evolution of the Hydrometridae and other gerromorphan families occurred very early, probably during the Upper Jurassic (154±135 million years ago), perhaps earlier.

Recent Hydrometridae live in humid terrestrial, marginal aquatic, plant-covered water surface or free stagnant water surface habitats ( Andersen, 1979). The presence of this morphologically similar fossil species shows that those types of habitats probably occured around the insect paleolake of the Santana formation.